Michael F. Toney

State-of-the-art lithium (Li)-ion batteries are approaching their specific energy limits yet are challenged by the ever-increasing demand of today’s energy storage and power applications, especially for electric vehicles. Li metal is considered an ultimate anode material for future high-energy rechargeable batteries when combined with existing or emerging high-capacity cathode materials. However, much current research focuses on the battery materials level, and there have been very few accounts of cell design principles. Here we discuss crucial conditions needed to achieve a specific energy higher than 350 Wh kg−1, up to 500 Wh kg−1, for rechargeable Li metal batteries using high-nickel-content lithium nickel manganese cobalt oxides as cathode materials. We also provide an analysis of key factors such as cathode loading, electrolyte amount and Li foil thickness that impact the cell-level cycle life. Furthermore, we identify several important strategies to reduce electrolyte-Li reaction, protect Li surfaces and stabilize anode architectures for long-cycling high-specific-energy cells. Jun Liu and Battery500 Consortium colleagues contemplate the way forward towards high-energy and long-cycling practical batteries.

High K/sub u/, uniaxial magnetocrystalline anisotropy, materials are generally attractive for ultrahigh density magnetic recording applications as they allow smaller, thermally stable media grains. Prominent candidates are rare-earth transition metals (Co/sub 5/Sm,...), and tetragonal intermetallic compounds (L1/sub 0/ phases FePt, CoPtY,...), which have 20-40 times higher K/sub u/ than today's hexagonal Co-alloy based media. This allows for about 3 times smaller grain diameters, D, and a potential 10-fold areal density increase (/spl prop/1/D/sup 2/), well beyond the currently projected 40-100 Gbits/in/sup 2/ mark, Realization of such densities will depend on a large number of factors, not all related to solving media microstructure problems, In particular it is at present not known how to record into such media, which may require write fields in the order of 10-100 kOe. Despite this unsolved problem, there is considerable interest in high Ku alternative media, both for longitudinal and perpendicular recording. Activities in this area will be reviewed and data on sputtered and evaporated thin FePt films, with coercivities exceeding 10000 Oe will be presented.

Organic semiconductors with higher carrier mobility and better transparency have been actively pursued for numerous applications, such as flat-panel display backplane and sensor arrays. The carrier mobility is an important figure of merit and is sensitively influenced by the crystallinity and the molecular arrangement in a crystal lattice. Here we describe the growth of a highly aligned meta-stable structure of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) from a blended solution of C8-BTBT and polystyrene by using a novel off-centre spin-coating method. Combined with a vertical phase separation of the blend, the highly aligned, meta-stable C8-BTBT films provide a significantly increased thin film transistor hole mobility up to 43 cm(2) Vs(-1) (25 cm(2) Vs(-1) on average), which is the highest value reported to date for all organic molecules. The resulting transistors show high transparency of >90% over the visible spectrum, indicating their potential for transparent, high-performance organic electronics.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTQuantitative Determination of Organic Semiconductor Microstructure from the Molecular to Device ScaleJonathan Rivnay†, Stefan C. B. Mannsfeld‡, Chad E. Miller‡, Alberto Salleo*†, and Michael F. Toney*‡View Author Information† Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States‡ Stanford Synchrotron Radiation Lightsource (SSRL), SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States*E-mail: [email protected], [email protected]Cite this: Chem. Rev. 2012, 112, 10, 5488–5519Publication Date (Web):August 9, 2012Publication History Received14 March 2012Published online9 August 2012Published inissue 10 October 2012https://doi.org/10.1021/cr3001109Copyright © 2012 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views19802Altmetric-Citations931LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (17 MB) Get e-AlertsSUBJECTS:Organic semiconductors,Physical and chemical processes,Scattering,Thin films,X-rays Get e-Alerts

A polymer is described that is conductive and stretchable, which can lead to electronics that can conform to the human body.

Morphological characterization has been used to explain the previously observed strong correlation between charge carrier mobility measured with thin-film transistors and the number-average molecular weight (MW) of the conjugated polymer regioregular poly(3-hexylthiophene). Atomic force microscopy and X-ray diffraction show that the low-mobility, low-MW films have a highly ordered structure composed of nanorods and the high-mobility, high-MW films have a less ordered, isotropic nodule structure. Modifying the morphology for a constant MW by changing the casting conditions or annealing the samples strongly affects the charge transport and morphology in the low-mobility, low-MW films, but has little effect on the high-MW films. In-plane grazing incidence X-ray scattering shows the in-plane π-stacking peak increases when the mobility increases for a constant MW. When the MW is changed, this correlation breaks down, confirming that in-plane π-stacking does not cause the mobility−MW relationship. We believe a combination of disordered domain boundaries and inherent effects of chain length on the electronic structure cause the mobility−MW relationship.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMetal Oxide Surfaces and Their Interactions with Aqueous Solutions and Microbial OrganismsGordon E. Brown, Victor E. Henrich, William H. Casey, David L. Clark, Carrick Eggleston, Andrew Felmy, D. Wayne Goodman, Michael Grätzel, Gary Maciel, Maureen I. McCarthy, Kenneth H. Nealson, Dimitri A. Sverjensky, Michael F. Toney, and John M. ZacharaView Author Information Surface and Aqueous Geochemistry Group, Department of Geological & Environmental Sciences, Stanford University, Stanford, California 94305-2115 Surface Science Laboratory, Department of Applied Physics, Yale University, New Haven, Connecticut 06520 Department of Land, Air, and Water Resources, University of California, Davis, Davis, California 95616 G.T. Seaborg Institute for Transactinium Science, Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071-3006 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255 Institute of Chemical Physics, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland Department of Chemistry, Colorado State University, Ft. Collins, Colorado 80523 Theory, Modeling and Simulation Group, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352 Jet Propulsion Laboratory-183-301, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109-8099 Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, Maryland 21218 IBM Almaden Research Center, San Jose, California 95120 Environmental Molecular Sciences, Laboratory Pacific Northwest National Laboratory, Richland, Washington 99352 Cite this: Chem. Rev. 1999, 99, 1, 77–174Publication Date (Web):December 24, 1998Publication History Received27 February 1998Revised9 November 1998Published online24 December 1998Published inissue 13 January 1999https://doi.org/10.1021/cr980011zCopyright © 1999 American Chemical SocietyRequest reuse permissionsArticle Views9647Altmetric-Citations880LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (2 MB) Get e-AlertscloseSUBJECTS:Adsorption,Interfaces,Ions,Metals,Oxides Get e-Alerts

Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π-π stacking distance) greatly influences electron orbital overlap and therefore mobility. Using our method to incrementally introduce lattice strain, we alter the π-π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33 Å to 3.08 Å. We believe that 3.08 Å is the shortest π-π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π-π distance of 3.04 Å has been achieved through intramolecular bonding). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from 0.8 cm(2) V(-1) s(-1) for unstrained films to a high mobility of 4.6 cm(2) V(-1) s(-1) for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.

We introduce a novel siloxane-terminated solubilizing group and demonstrate its effectiveness as a side chain in an isoindigo-based conjugated polymer. An average hole mobility of 2.00 cm(2) V(-1) s(-1) (with a maximum mobility of 2.48 cm(2) V(-1) s(-1)), was obtained from solution-processed thin-film transistors, one of the highest mobilities reported to date. In contrast, the reference polymer with a branched alkyl side chain gave an average hole mobility of 0.30 cm(2) V(-1) s(-1) and a maximum mobility of 0.57 cm(2) V(-1) s(-1). This is largely explained by the polymer packing: our new polymer exhibited a π-π stacking distance of 3.58 Å, while the reference polymer showed a distance of 3.76 Å.

Li2S is a high-capacity cathode material for lithium metal-free rechargeable batteries. It has a theoretical capacity of 1166 mAh/g, which is nearly 1 order of magnitude higher than traditional metal oxides/phosphates cathodes. However, Li2S is usually considered to be electrochemically inactive due to its high electronic resistivity and low lithium-ion diffusivity. In this paper, we discover that a large potential barrier (∼1 V) exists at the beginning of charging for Li2S. By applying a higher voltage cutoff, this barrier can be overcome and Li2S becomes active. Moreover, this barrier does not appear again in the following cycling. Subsequent cycling shows that the material behaves similar to common sulfur cathodes with high energy efficiency. The initial discharge capacity is greater than 800 mAh/g for even 10 μm Li2S particles. Moreover, after 10 cycles, the capacity is stabilized around 500–550 mAh/g with a capacity decay rate of only ∼0.25% per cycle. The origin of the initial barrier is found to be the phase nucleation of polysulfides, but the amplitude of barrier is mainly due to two factors: (a) charge transfer directly between Li2S and electrolyte without polysulfide and (b) lithium-ion diffusion in Li2S. These results demonstrate a simple and scalable approach to utilizing Li2S as the cathode material for rechargeable lithium-ion batteries with high specific energy.

Abstract Developing a better understanding of the evolution of morphology in plastic solar cells is the key to designing new materials and structures that achieve photoconversion efficiencies greater than 10%. In the most extensively characterized system, the poly(3‐hexyl thiophene) (P3HT):[6,6]‐phenyl‐C 61 ‐butyric‐acid‐methyl‐ester (PCBM) bulk heterojunction, the origins and evolution of the blend morphology during processes such as thermal annealing are not well understood. In this work, we use a model system, a bilayer of P3HT and PCBM, to develop a more complete understanding of the miscibility and diffusion of PCBM within P3HT during thermal annealing. We find that PCBM aggregates and/or molecular species are miscible and mobile in disordered P3HT, without disrupting the ordered lamellar stacking of P3HT chains. The fast diffusion of PCBM into the amorphous regions of P3HT suggests the favorability of mixing in this system, opposing the belief that phase‐pure domains form in BHJs due to immiscibility of these two components.

Tin and lead iodide perovskite semiconductors of the composition AMX3, where M is a metal and X is a halide, are leading candidates for high efficiency low cost tandem photovoltaics, in part because they have band gaps that can be tuned over a wide range by compositional substitution. We experimentally identify two competing mechanisms through which the A-site cation influences the band gap of 3D metal halide perovskites. Using a smaller A-site cation can distort the perovskite lattice in two distinct ways: by tilting the MX6 octahedra or by simply contracting the lattice isotropically. The former effect tends to raise the band gap, while the latter tends to decrease it. Lead iodide perovskites show an increase in band gap upon partial substitution of the larger formamidinium with the smaller cesium, due to octahedral tilting. Perovskites based on tin, which is slightly smaller than lead, show the opposite trend: they show no octahedral tilting upon Cs-substitution but only a contraction of the lattice, leading to progressive reduction of the band gap. We outline a strategy to systematically tune the band gap and valence and conduction band positions of metal halide perovskites through control of the cation composition. Using this strategy, we demonstrate solar cells that harvest light in the infrared up to 1040 nm, reaching a stabilized power conversion efficiency of 17.8%, showing promise for improvements of the bottom cell of all-perovskite tandem solar cells. The mechanisms of cation-based band gap tuning we describe are broadly applicable to 3D metal halide perovskites and will be useful in further development of perovskite semiconductors for optoelectronic applications.

Abstract Grazing incidence X‐ray scattering (GIXS) is used to characterize the morphology of poly(3‐hexylthiophene) (P3HT)–phenyl‐C61‐butyric acid methyl ester (PCBM) thin film bulk heterojunction (BHJ) blends as a function of thermal annealing temperature, from room temperature to 220 °C. A custom‐built heating chamber for in situ GIXS studies allows for the morphological characterization of thin films at elevated temperatures. Films annealed with a thermal gradient allow for the rapid investigation of the morphology over a range of temperatures that corroborate the results of the in situ experiments. Using these techniques the following are observed: the melting points of each component; an increase in the P3HT coherence length with annealing below the P3HT melting temperature; the formation of well‐oriented P3HT crystallites with the (100) plane parallel to the substrate, when cooled from the melt; and the cold crystallization of PCBM associated with the PCBM glass transition temperature. The incorporation of these materials into BHJ blends affects the nature of these transitions as a function of blend ratio. These results provide a deeper understanding of the physics of how thermal annealing affects the morphology of polymer–fullerene BHJ blends and provides tools to manipulate the blend morphology in order to develop high‐performance organic solar cell devices.

Crystalline self-assembled monolayers (SAMs) of organosilane compounds such as octadecyltrimethoxysilane (OTMS) and octadecyltrichlorosilane (OTCS) were deposited by a simple, spin-casting technique onto Si/SiO2 substrates. Fabrication of the OTMS SAMs and characterization using ellipsometry, contact angle, atomic force microscopy (AFM), grazing angle attenuated total reflectance Fourier transform infrared (GATR-FTIR) spectroscopy and grazing incidence X-ray diffraction (GIXD) are described. The characterization confirms that these monolayers exhibit a well-packed crystalline phase and a remarkably high degree of smoothness. Semiconductors deposited by vapor deposition onto the crystalline OTS SAM grow in a favorable two-dimensional layered growth manner which is generally preferred morphologically for high charge carrier transport. On the OTMS SAM treated dielectric, pentacene OFETs showed hole mobilities as high as 3.0 cm2/V·s, while electron mobilities as high as 5.3 cm2/V·s were demonstrated for C60.

Abstract Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li 1.17– x Ni 0.21 Co 0.08 Mn 0.54 O 2 , these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.

Rechargeable lithium-sulfur (Li-S) batteries hold great potential for high-performance energy storage systems because they have a high theoretical specific energy, low cost, and are eco-friendly. However, the structural and morphological changes during electrochemical reactions are still not well understood. In this Article, these changes in Li-S batteries are studied in operando by X-ray diffraction and transmission X-ray microscopy. We show recrystallization of sulfur by the end of the charge cycle is dependent on the preparation technique of the sulfur cathode. On the other hand, it was found that crystalline Li(2)S does not form at the end of discharge for all sulfur cathodes studied. Furthermore, during cycling the bulk of soluble polysulfides remains trapped within the cathode matrix. Our results differ from previous ex situ results. This highlights the importance of in operando studies and suggests possible strategies to improve cycle life.

The solution-processability of conjugated polymers in organic solvents has classically been achieved by modulating the size and branching of alkyl substituents appended to the backbone. However, these substituents impact structural order and charge transport properties in thin-film devices. As a result, a trade-off must be found between material solubility and insulating alkyl content. It was recently shown that the substitution of furan for thiophene in the backbone of the polymer PDPP2FT significantly improves polymer solubility, allowing for the use of shorter branched side chains while maintaining high device efficiency. In this report, we use PDPP2FT to demonstrate that linear alkyl side chains can be used to promote thin-film nanostructural order. In particular, linear side chains are shown to shorten π–π stacking distances between backbones and increase the correlation lengths of both π–π stacking and lamellar spacing, leading to a substantial increase in the efficiency of bulk heterojunction solar cells.

New types of energy storage are needed in conjunction with the deployment of renewable energy sources and their integration with the electrical grid. We have recently introduced a family of cathodes involving the reversible insertion of cations into materials with the Prussian Blue open-framework crystal structure. Here we report a newly developed manganese hexacyanomanganate open-framework anode that has the same crystal structure. By combining it with the previously reported copper hexacyanoferrate cathode we demonstrate a safe, fast, inexpensive, long-cycle life aqueous electrolyte battery, which involves the insertion of sodium ions. This high rate, high efficiency cell shows a 96.7% round trip energy efficiency when cycled at a 5C rate and an 84.2% energy efficiency at a 50C rate. There is no measurable capacity loss after 1,000 deep-discharge cycles. Bulk quantities of the electrode materials can be produced by a room temperature chemical synthesis from earth-abundant precursors.

Abstract Laser powder bed fusion additive manufacturing is an emerging 3D printing technique for the fabrication of advanced metal components. Widespread adoption of it and similar additive technologies is hampered by poor understanding of laser-metal interactions under such extreme thermal regimes. Here, we elucidate the mechanism of pore formation and liquid-solid interface dynamics during typical laser powder bed fusion conditions using in situ X-ray imaging and multi-physics simulations. Pores are revealed to form during changes in laser scan velocity due to the rapid formation then collapse of deep keyhole depressions in the surface which traps inert shielding gas in the solidifying metal. We develop a universal mitigation strategy which eliminates this pore formation process and improves the geometric quality of melt tracks. Our results provide insight into the physics of laser-metal interaction and demonstrate the potential for science-based approaches to improve confidence in components produced by laser powder bed fusion.

Abstract Most optimized donor‐acceptor (D‐A) polymer bulk heterojunction (BHJ) solar cells have active layers too thin to absorb greater than ∼80% of incident photons with energies above the polymer's band gap. If the thickness of these devices could be increased without sacrificing internal quantum efficiency, the device power conversion efficiency (PCE) could be significantly enhanced. We examine the device characteristics of BHJ solar cells based on poly(di(2‐ethylhexyloxy)benzo[1,2‐ b :4,5‐ b ′]dithiophene‐ co ‐octylthieno[3,4‐ c ]pyrrole‐4,6‐dione) (PBDTTPD) and [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM) with 7.3% PCE and find that bimolecular recombination limits the active layer thickness of these devices. Thermal annealing does not mitigate these bimolecular recombination losses and drastically decreases the PCE of PBDTTPD BHJ solar cells. We characterize the morphology of these BHJs before and after thermal annealing and determine that thermal annealing drastically reduces the concentration of PCBM in the mixed regions, which consist of PCBM dispersed in the amorphous portions of PBDTTPD. Decreasing the concentration of PCBM may reduce the number of percolating electron transport pathways within these mixed regions and create morphological electron traps that enhance charge‐carrier recombination and limit device quantum efficiency. These findings suggest that (i) the concentration of PCBM in the mixed regions of polymer BHJs must be above the PCBM percolation threshold in order to attain high solar cell internal quantum efficiency, and (ii) novel processing techniques, which improve polymer hole mobility while maintaining PCBM percolation within the mixed regions, should be developed in order to limit bimolecular recombination losses in optically thick devices and maximize the PCE of polymer BHJ solar cells.

Grazing incidence X-ray diffraction reveals that a pentacene monolayer, grown on an amorphous SiO2 substrate that is commonly used as a dielectric layer in organic thin film transistors (OTFTs), is crystalline. A preliminary energy-minimized model of the monolayer, based on the GIXD data, reveals that the pentacene molecules adopt a herringbone arrangement with their long axes tilted slightly from the substrate normal. Although this arrangement resembles the general packing features of the (001) layer in single crystals of bulk pentacene, the monolayer lattice parameters and crystal structure differ from those of the bulk. Because carrier transport in pentacene OTFTs is presumed to occur in the semiconductor layers near the dielectric interface, the discovery of a crystalline monolayer structure on amorphous SiO2 has important implications for transport in OTFTs.

A comparison of three samples of poly(3-hexylthiophene) having regioregularities of 86, 90, and 96% is used to elucidate the effect of regioregularity on polymer-fullerene-composite solar cell performance. It is observed that polymer samples with lower regioregularity are capable of generating fullerene composites that exhibit superior thermal stability. The enhanced thermal stability of the composites is attributed to a lower driving force for polymer crystallization in the less regioregular polymer samples, which is supported with two-dimensional grazing incidence X-ray scattering and differential scanning calorimetry measurements. Furthermore, it is demonstrated that all three polymer samples are capable of generating solar cells with equivalent peak efficiencies of approximately 4% in blends with [6,6]-phenyl-C61-butyric acid methyl ester. While it may be non-intuitive that polymers with lower regioregularity can exhibit higher efficiencies, it is observed that the charge-carrier mobility of the three polymers is on the same order of magnitude (10(-4) cm2 V(-1) s(-1)) when measured from the space-charge-limited current, suggesting that highly regioregular and crystalline polythiophenes are not required in order to effectively transport charges in polymer solar cells. Overall, these results suggest a design principle for semicrystalline conjugated polymers in fullerene-composite solar cells in which crystallization-driven phase separation can be dramatically suppressed via the introduction of a controlled amount of disorder into the polymer backbone.

Abstract The performance of polymer:fullerene bulk heterojunction solar cells is heavily influenced by the interpenetrating nanostructure formed by the two semiconductors because the size of the phases, the nature of the interface, and molecular packing affect exciton dissociation, recombination, and charge transport. Here, X‐ray diffraction is used to demonstrate the formation of stable, well‐ordered bimolecular crystals of fullerene intercalated between the side‐chains of the semiconducting polymer poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐ b ]thiophene. It is shown that fullerene intercalation is general and is likely to occur in blends with both amorphous and semicrystalline polymers when there is enough free volume between the side‐chains to accommodate the fullerene molecule. These findings offer explanations for why luminescence is completely quenched in crystals much larger than exciton diffusion lengths, how the hole mobility of poly(2‐methoxy‐5‐(3′,7′‐dimethyloxy)‐p‐phylene vinylene) increases by over 2 orders of magnitude when blended with fullerene derivatives, and why large‐scale phase separation occurs in some polymer:fullerene blend ratios while thermodynamically stable mixing on the molecular scale occurs for others. Furthermore, it is shown that intercalation of fullerenes between side chains mostly determines the optimum polymer:fullerene blending ratios. These discoveries suggest a method of intentionally designing bimolecular crystals and tuning their properties to create novel materials for photovoltaic and other applications.

The conclusions reached by a diverse group of scientists who attended an intense 2-day workshop on hybrid organic-inorganic perovskites are presented, including their thoughts on the most burning fundamental and practical questions regarding this unique class of materials, and their suggestions on various approaches to resolve these issues.

We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm(2) V(-1) s(-1), with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases. Thermal annealing generally reduces both the face-on population and the misoriented edge-on domains. The highest hole mobilities of this series were obtained from edge-on molecular packing and in-plane liquid-crystalline texture, but films with a bimodal orientation distribution and no discernible in-plane texture exhibited surprisingly comparable mobilities. The high hole mobility may therefore arise from the molecular packing feature common to the entire polymer series: backbones that are strictly oriented parallel to the substrate plane and coplanar with other backbones in the same layer.

Sodium-ion batteries (SIBs) for grid-scale applications need active materials that combine a high energy density with sustainability. Given the high theoretical specific capacity 501 mAh g−1, and Earth abundance of disodium rhodizonate (Na2C6O6), it is one of the most promising cathodes for SIBs. However, substantially lower reversible capacities have been obtained compared with the theoretical value and the understanding of this discrepancy has been limited. Here, we reveal that irreversible phase transformation of Na2C6O6 during cycling is the origin of the deteriorating redox activity of Na2C6O6. The active-particle size and electrolyte conditions were identified as key factors to decrease the activation barrier of the phase transformation during desodiation. On the basis of this understanding, we achieved four-sodium storage in a Na2C6O6 electrode with a reversible capacity of 484 mAh g−1, an energy density of 726 Wh kg−1 cathode, an energy efficiency above 87% and a good cycle retention. Sodium-ion batteries are a cost-effective alternative to lithium-ion for large-scale energy storage. Here Bao et al. develop a cathode based on biomass-derived ionic crystals that enables a four-sodium ion storage mechanism leading to exceptionally high specific capacity and energy density.

As one of the most remarkable oxygen evolution reaction (OER) electrocatalysts, metal chalcogenides have been intensively reported during the past few decades because of their high OER activities. It has been reported that electron-chemical conversion of metal chalcogenides into oxides/hydroxides would take place after the OER. However, the transition mechanism of such unstable structures, as well as the real active sites and catalytic activity during the OER for these electrocatalysts, has not been understood yet; therefore a direct observation for the electrocatalytic water oxidation process, especially at nano or even angstrom scale, is urgently needed. In this research, by employing advanced Cs-corrected transmission electron microscopy (TEM), a step by step oxidational evolution of amorphous electrocatalyst CoS x into crystallized CoOOH in the OER has been in situ captured: irreversible conversion of CoS x to crystallized CoOOH is initiated on the surface of the electrocatalysts with a morphology change via Co(OH)2 intermediate during the OER measurement, where CoOOH is confirmed as the real active species. Besides, this transition process has also been confirmed by multiple applications of X-ray photoelectron spectroscopy (XPS), in situ Fourier-transform infrared spectroscopy (FTIR), and other ex situ technologies. Moreover, on the basis of this discovery, a high-efficiency electrocatalyst of a nitrogen-doped graphene foam (NGF) coated by CoS x has been explored through a thorough structure transformation of CoOOH. We believe this in situ and in-depth observation of structural evolution in the OER measurement can provide insights into the fundamental understanding of the mechanism for the OER catalysts, thus enabling the more rational design of low-cost and high-efficient electrocatalysts for water splitting.

Reduced-dimensional metal halide perovskites (RDPs) have attracted significant attention in recent years due to their promising light harvesting and emissive properties. We sought to increase the systematic understanding of how RDPs are formed. Here we report that layered intermediate complexes formed with the solvent provide a scaffold that facilitates the nucleation and growth of RDPs during annealing, as observed via in situ X-ray scattering. Transient absorption spectroscopy of RDP single crystals and films enables the identification of the distribution of quantum well thicknesses. These insights allow us to develop a kinetic model of RDP formation that accounts for the experimentally observed size distribution of wells. RDPs exhibit a thickness distribution (with sizes that extend above n = 5) determined largely by the stoichiometric proportion between the intercalating cation and solvent complexes. The results indicate a means to control the distribution, composition and orientation of RDPs via the selection of the intercalating cation, the solvent and the deposition technique.

The recent development of efficient binary tin- and lead-based metal halide perovskite solar cells has enabled the development of all-perovskite tandem solar cells, which offer a unique opportunity to deliver high performance at low cost. Tin halide perovskites, however, are prone to oxidation, where the Sn2+ cations oxidize to Sn4+ upon air exposure. Here, we identify reaction products and elucidate the oxidation mechanism of both ASnI3 and ASn0.5Pb0.5I3 (where A can be made of methylammonium, formamidinium, cesium, or a combination of these) perovskites and find that substituting lead onto the B site fundamentally changes the oxidation mechanism of tin-based metal halide perovskites to make them more stable than would be expected by simply considering the decrease in tin content. This work provides guidelines for developing stable small band gap materials that could be used in all-perovskite tandems.

Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT, is a semiconducting polymer that forms thin film transistors (TFTs) with high field effect mobility on silicon dioxide dielectrics that are treated with alkyltrichlorosilanes ( approximately 0.2 to 0.5 cm2/V s) but forms TFTs with poor mobility on bare silicon dioxide (<0.005 cm2/V s). The microstructure of spin-coated thin films of PBTTT on these surfaces was studied using synchrotron X-ray diffraction and atomic force microscopy. PBTTT crystallizes with lamellae of pi-stacked polymer chains on both surfaces. The crystalline domains are well-oriented relative to the substrate in the as-spun state and become highly oriented and more ordered with thermal annealing in the liquid crystalline mesophase. Although the X-ray scattering from PBTTT is nearly identical on both surfaces, atomic force microscopy showed that the domain size of the crystalline regions depends on the substrate surface. These results suggest that electrical transport in PBTTT films is strongly affected by the domain size of the crystalline regions and the disordered regions between them.

Organic photovoltaics (OPV) have the advantage of possible fabrication by energy-efficient and cost-effective deposition methods, such as solution processing. Solvent additives can provide fine control of the active layer morphology of OPVs by influencing film formation during solution processing. As such, solvent additives form a versatile method of experimental control for improving organic solar cell device performance. This review provides a brief history of solution-processed bulk heterojunction OPVs and the advent of solvent additives, putting them into context with other methods available for morphology control. It presents the current understanding of how solvent additives impact various mechanisms of phase separation, enabled by recent advances in in situ morphology characterization. Indeed, understanding solvent additives' effects on film formation has allowed them to be applied and combined effectively and synergistically to boost OPV performance. Their success as a morphology control strategy has also prompted the use of solvent additives in related organic semiconductor technologies. Finally, the role of solvent additives in the development of next-generation OPV active layers is discussed. Despite concerns over their environmental toxicity and role in device instability, solvent additives remain relevant morphological directing agents as research interests evolve toward nonfullerene acceptors, ternary blends, and environmentally sustainable solvents.

Substantial in-plane crystallinity and dominant face-on stacking are observed in thin films of a high-mobility n-type rylene-thiophene copolymer. Spun films of the polymer, previously thought to have little or no order are found to exhibit an ordered microstructure at both interfaces, and in the bulk. The implications of this type of packing and crystalline morphology are discussed as they relate to thin-film transistors.

Abstract The electronic devices that play a vital role in our daily life are primarily based on silicon and are thus rigid, opaque, and relatively heavy. However, new electronics relying on polymer semiconductors are opening up new application spaces like stretchable and self-healing sensors and devices, and these can facilitate the integration of such devices into our homes, our clothing, and even our bodies. While there has been tremendous interest in such technologies, the widespread adoption of these organic electronics requires low-cost manufacturing techniques. Fortunately, the realization of organic electronics can take inspiration from a technology developed since the beginning of the Common Era: printing. This review addresses the critical issues and considerations in the printing methods for organic electronics, outlines the fundamental fluid mechanics, polymer physics, and deposition parameters involved in the fabrication process, and provides future research directions for the next generation of printed polymer electronics.

High performance, solution processable semiconductors are critical to the realization of low cost, large area electronics. We show that a signature molecular packing motifside-chain interdigitationcorrelates to high performance for a large and important class of organic semiconductors. The side chains of recently developed high performance copolymers of poly(alkylthiophenes) can and do interdigitate substantially, whereas they do not in the most common form of the extensively studied, lower performance poly(alkythiophenes). Side-chain interdigitation provides a mechanism for three-dimensional ordering; without it, poly(alkylthiophenes) are limited to small domains and poor performance. We propose the synthetic design rule that three-dimensional ordering is promoted by side-chain attachment densities sufficiently low to permit interdigitation.

Advanced MaterialsVolume 21, Issue 16 p. 1568-1572 Communication Charge-Transport Anisotropy Due to Grain Boundaries in Directionally Crystallized Thin Films of Regioregular Poly(3-hexylthiophene) Leslie H. Jimison, Leslie H. Jimison [email protected] 476 Lomita Mall, 213 McCullough Building Stanford, CA 94305 (USA)Search for more papers by this authorMichael F. Toney, Michael F. Toney [email protected] 2575 Sand Hill Road, Mailstop 0069 Menlo Park, CA 94025 (USA)Search for more papers by this authorIain McCulloch, Iain McCulloch [email protected] Department of Chemistry Imperial College of London South Kensington Campus London SW7 2AZ (UK)Search for more papers by this authorMartin Heeney, Martin Heeney [email protected] Queen Mary University of London Mile End Road, Eng. 224 London E14NS (UK)Search for more papers by this authorAlberto Salleo, Corresponding Author Alberto Salleo [email protected] 476 Lomita Mall, 239 McCullough Building Stanford, CA 94305 (USA)476 Lomita Mall, 239 McCullough Building Stanford, CA 94305 (USA).Search for more papers by this author Leslie H. Jimison, Leslie H. Jimison [email protected] 476 Lomita Mall, 213 McCullough Building Stanford, CA 94305 (USA)Search for more papers by this authorMichael F. Toney, Michael F. Toney [email protected] 2575 Sand Hill Road, Mailstop 0069 Menlo Park, CA 94025 (USA)Search for more papers by this authorIain McCulloch, Iain McCulloch [email protected] Department of Chemistry Imperial College of London South Kensington Campus London SW7 2AZ (UK)Search for more papers by this authorMartin Heeney, Martin Heeney [email protected] Queen Mary University of London Mile End Road, Eng. 224 London E14NS (UK)Search for more papers by this authorAlberto Salleo, Corresponding Author Alberto Salleo [email protected] 476 Lomita Mall, 239 McCullough Building Stanford, CA 94305 (USA)476 Lomita Mall, 239 McCullough Building Stanford, CA 94305 (USA).Search for more papers by this author First published: 21 April 2009 https://doi.org/10.1002/adma.200802722Citations: 291AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Graphical Abstract P3HT films that are highly anisotropic in-plane are produced using a directional crystallization technique, and the charge-transport properties of grain bourdaries between different orientations of crystallites are studied. Boundaries along the fiber provide a small barrier to charge transport when compared to fiber-to-fiber grain boundaries. The films allow a correlation to be drawn between the grain-boundary type and charge-transport behavior in P3HT. References 1 M. L. Chabinyc, A. Salleo, Chem. Mater. 2004, 16, 4509. 2 P. E. Burrows, G. Gu, V. Bulovic, Z. Shen, S. R. Forrest, M. E. Thompson, IEEE Trans. Electron. Dev. 1997, 44, 1188. 3 K. Coakley, M. D. McGehee, Chem. Mater. 2004, 16, 3533. 4 H. Sirringhaus, R. J. Wilson, R. H. Friend, M. Inbasekaran, W. Wu, E. P. Woo, M. Grell, D. D. C. Bradley, Appl. Phys. Lett. 2000, 77, 406. 5 A. B. Chwang, C. D. Frisbie, J. Appl. Phys. 2001, 90, 1342. 6 T. W. Kelley, C. D. Frisbie, J. Phys. Chem. B 2001, 105, 4538. 7 B. Grévin, P. Rannou, R. Payerne, A. Pron, J. Travers, Adv. Mater. 2003, 15, 881. 8 R. J. Kline, M. D. McGehee, E. N. Kadnikova, J. S. Liu, J. M. J. Frechet, M. F. Toney, Macromolecules 2005, 38, 3312. 9 R. Street, J. Northrup, A. Salleo, Phys. Rev. B 2005, 71, 13. 10 K. R. Amundson, B. J. Sapjeta, A. J. Lovinger, Z. N. Bao, Thin Solid Films 2002, 414, 143. 11 S. Nagamatsu, W. Takashima, K. Kaneto, Y. Yoshida, N. Tanigaki, K. Yase, Macromolecules 2003, 36, 5252. 12 S. Li, C. Newsome, D. Russell, T. Kugler, M. Ishida, T. Shimoda, Appl. Phys. Lett. 2005, 87, 062101. 13 C. Yang, C. Soci, D. Moses, A. Heeger, Synth. Met. 2005, 155, 639. 14 M. Brinkmann, J. Wittmann, Adv. Mater. 2006, 18, 860. 15 C. De Rosa, C. Park, E. L. Thomas, B. Lotz, Nature 2000, 405, 433. 16 B. Wunderlich, Macromolecular Physics, Vol. 1, Academic Press, New York 1973. 17 B. Ong, Y. Wu, P. Liu, S. Gardner, Adv. Mater. 2005, 17, 1141. 18 G. Horowitz, M. E. Hajlaoui, R. Hajlaoui, J. Appl. Phys. 2000, 87, 4456. 19 D. Beljonne, G. Pourtois, C. Silva, E. Hennebicq, L. M. Herz, R. H. Friend, G. D. Scholes, S. Setayesh, K. Mullen, J. L. Bredas, Proc. Natl. Acad. Sci. USA 2002, 99, 10982. 20 H. Sirringhaus, P. J. Brown, R. H. Friend, M. M. Nielsen, K. Bechgaard, B. M. W. Langeveld-Voss, A. J. H. Spiering, R. A. J. Janssen, E. W. Meijer, P. Herwig, D. M. de Leeuw, Nature 1999, 401, 685. 21 D. M. DeLongchamp, B. Vogel, Y. Jung, M. C. Gurau, C. A. Ritcher, O. A. Kirillov, J. Obrzut, D. A. Fischer, S. Sambasivan, L. J. Ritcher, E. K. Lin, Macromolecules 2005, 17, 5610. 22 A. Salleo, R. Street, Phys. Rev. B 2004, 70, 8. Citing Literature Volume21, Issue16April 27, 2009Pages 1568-1572 ReferencesRelatedInformation

As thin films become increasingly popular (for solar cells, LEDs, microelectronics, batteries), quantitative morphological and crystallographic information is needed to predict and optimize the film’s electrical, optical, and mechanical properties. This quantification can be obtained quickly and easily with X-ray diffraction using an area detector in two sample geometries. In this paper, we describe a methodology for constructing complete pole figures for thin films with fiber texture (isotropic in-plane orientation). We demonstrate this technique on semicrystalline polymer films, self-assembled nanoparticle semiconductor films, and randomly packed metallic nanoparticle films. This method can be immediately implemented to help understand the relationship between film processing and microstructure, enabling the development of better and less expensive electronic and optoelectronic devices.

Abstract A novel method of strain‐aligning polymer films is introduced and applied to regioregular poly(3‐hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge‐mobility anisotropy, where the in‐plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two‐dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane‐on and edge‐on packing configurations, as the strain alignment is found to induce a significant face‐on orientation of the originally highly edge‐on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge‐mobility anisotropy of 9, providing a simple and effective method to investigate charge‐transport mechanisms in polymer semiconductors.

Exploratory synthesis in new chemical spaces is the essence of solid-state chemistry. However, uncharted chemical spaces can be difficult to navigate, especially when materials synthesis is challenging. Nitrides represent one such space, where stringent synthesis constraints have limited the exploration of this important class of functional materials. Here, we employ a suite of computational materials discovery and informatics tools to construct a large stability map of the inorganic ternary metal nitrides. Our map clusters the ternary nitrides into chemical families with distinct stability and metastability, and highlights hundreds of promising new ternary nitride spaces for experimental investigation-from which we experimentally realized seven new Zn- and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity and covalency of solid-state bonding from the density functional theory (DFT)-computed electron density, we reveal the complex interplay between chemistry, composition and electronic structure in governing large-scale stability trends in ternary nitride materials.

Abstract An overlooked factor affecting stability: the residual stresses in perovskite films, which are tensile and can exceed 50 MPa in magnitude, a value high enough to deform copper, is reported. These stresses provide a significant driving force for fracture. Films are shown to be more unstable under tensile stress—and conversely more stable under compressive stress—when exposed to heat or humidity. Increasing the formation temperature of perovskite films directly correlates with larger residual stresses, a result of the high thermal expansion coefficient of perovskites. Specifically, this tensile stress forms upon cooling to room temperature, as the substrate constrains the perovskite from shrinking. No evidence of stress relaxation is observed, with the purely elastic film stress attributed to the thermal expansion mismatch between the perovskite and substrate. Additionally, the authors demonstrate that using a bath conversion method to form the perovskite film at room temperature leads to low stress values that are unaffected by further annealing, indicating complete perovskite formation prior to annealing. It is concluded that reducing the film stress is a novel method for improving perovskite stability, which can be accomplished by lower formation temperatures, flexible substrates with high thermal expansion coefficients, and externally applied compressive stress after fabrication.

Reversible high-voltage redox chemistry is an essential component of many electrochemical technologies, from (electro)catalysts to lithium-ion batteries. Oxygen-anion redox has garnered intense interest for such applications, particularly lithium-ion batteries, as it offers substantial redox capacity at more than 4 V versus Li/Li+ in a variety of oxide materials. However, oxidation of oxygen is almost universally correlated with irreversible local structural transformations, voltage hysteresis and voltage fade, which currently preclude its widespread use. By comprehensively studying the Li2−xIr1−ySnyO3 model system, which exhibits tunable oxidation state and structural evolution with y upon cycling, we reveal that this structure–redox coupling arises from the local stabilization of short approximately 1.8 Å metal–oxygen π bonds and approximately 1.4 Å O–O dimers during oxygen redox, which occurs in Li2−xIr1−ySnyO3 through ligand-to-metal charge transfer. Crucially, formation of these oxidized oxygen species necessitates the decoordination of oxygen to a single covalent bonding partner through formation of vacancies at neighbouring cation sites, driving cation disorder. These insights establish a point-defect explanation for why anion redox often occurs alongside local structural disordering and voltage hysteresis during cycling. Our findings offer an explanation for the unique electrochemical properties of lithium-rich layered oxides, with implications generally for the design of materials employing oxygen redox chemistry. Reversible high-voltage redox is a key component for electrochemical technologies from electrocatalysts to lithium-ion batteries. A point defect explanation for why anion redox occurs with local structural disordering and voltage hysteresis is proposed.

Halide double perovskites have recently been developed as less toxic analogs of the lead perovskite solar-cell absorbers APbX3 (A = monovalent cation; X = Br or I). However, all known halide double perovskites have large bandgaps that afford weak visible-light absorption. The first halide double perovskite evaluated as an absorber, Cs2AgBiBr6 (1), has a bandgap of 1.95 eV. Here, we show that dilute alloying decreases 1's bandgap by ca. 0.5 eV. Importantly, time-resolved photoconductivity measurements reveal long-lived carriers with microsecond lifetimes in the alloyed material, which is very promising for photovoltaic applications. The alloyed perovskite described herein is the first double perovskite to show comparable bandgap energy and carrier lifetime to those of (CH3NH3)PbI3. By describing how energy- and symmetry-matched impurity orbitals, at low concentrations, dramatically alter 1's band edges, we open a potential pathway for the large and diverse family of halide double perovskites to compete with APbX3 absorbers.

Control of crystallographic texture from mostly face-on to edge-on is observed for the film morphology of the n-type semicrystalline polymer {[N,N-9-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)}, P(NDI2OD-T2), when annealing the film to the polymer melting point followed by slow cooling to ambient temperature. A variety of X-ray diffraction analyses, including pole figure construction and Fourier transform peak shape deconvolution, are employed to quantify the texture change, relative degree of crystallinity and lattice order. We find that annealing the polymer film to the melt leads to a shift from 77.5% face-on to 94.6% edge-on lamellar texture as well as to a 2-fold increase in crystallinity and a 40% decrease in intracrystallite cumulative disorder. The texture change results in a significant drop in the electron-only diode current density through the film thickness upon melt annealing, while little change is observed in the in-plane transport of bottom gated thin film transistors. This suggests that the texture change is prevalent in the film interior and that either the (bottom) surface structure is different from the interior structure or the intracrystalline order and texture play a secondary role in transistor transport for this material.

The crystallite size and cumulative lattice disorder of three prototypical, high-performing organic semiconducting materials are investigated using a Fourier-transform peak shape analysis routine based on the method of Warren and Averbach (WA). A thorough incorporation of error propagation throughout the multistep analysis and a weighted fitting of Fourier-transformed data to the WA model allows for more accurate results than typically obtained and for determination of confidence bounds. We compare results obtained when assuming two types of column-length distributions, and discuss the benefits of each model in terms of simplicity and accuracy. For strongly disordered materials, the determination of a crystallite size is greatly hindered because disorder dominates the coherence length, not finite size. A simple analysis based on trends of peak widths and Lorentzian components of pseudo-Voigt line shapes as a function of diffraction order is also discussed as an approach to more easily and qualitatively assess the amount and type of disorder present in a sample. While applied directly to organic systems, this methodology is general for the accurate deconvolution of crystalline size and lattice disorder for any material investigated with diffraction techniques.

We report quantitative measurements of ordering, molecular orientation, and nanoscale morphology in the active layer of bulk heterojunction (BHJ) organic photovoltaic cells based on a thieno[3,4-b]thiophene-alt-benzodithiophene copolymer (PTB7), which has been shown to yield very high power conversion efficiency when blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). A surprisingly low degree of order was found in the polymer—far lower in the bulk heterojunction than in pure PTB7. X-ray diffraction data yielded a nearly full orientation distribution for the polymer π-stacking direction within well-ordered regions, revealing a moderate preference for π-stacking in the vertical direction (“face-on”). By combining molecular orientation information from polarizing absorption spectroscopies with the orientation distribution of ordered material from diffraction, we propose a model describing the PTB7 molecular orientation distribution (ordered and disordered), with the fraction of ordered polymer as a model parameter. This model shows that only a small fraction (≈20%) of the polymer in the PTB7/PC71BM blend is ordered. Energy-filtered transmission electron microscopy shows that the morphology of PTB7/PC71BM is composed of nanoscale fullerene-rich aggregates separated by polymer-rich regions. The addition of diiodooctane (DIO) to the casting solvent, as a processing additive, results in smaller domains and a more finely interpenetrating BHJ morphology, relative to blend films cast without DIO.

We investigate the chemical and structural properties of solution-processed thin films of P3HT blended with p-type dopant F4TCNQ. The maximum in-plane electrical conductivity of doped films is observed at a molar doping fraction of 0.17, in agreement with the binding mechanism of F4TCNQ:P3HT complexes. Through the use of X-ray diffraction, a previously unreported crystalline phase is observed for P3HT films doped above a critical threshold concentration. This crystalline phase involves the incorporation of F4TCNQ molecules into ordered polymer regions and ultimately improves charge dissociation, leading to higher carrier density in thin film. Finally, optical absorption and X-ray diffraction reveal that the chemical state of P3HT in solution has a dramatic impact on the electrical and structural properties of the blended films.

Organo-metal halide perovskites are an intriguing class of materials that have recently been explored for their potential in solar energy conversion. Within a very short period of intensive research, highly efficient solar cell devices have been demonstrated. One of the heavily debated questions in this new field of research concerns the role of chlorine in solution-processed samples utilizing lead chloride and 3 equiv of methylammonium iodide to prepare the perovskite samples. We utilized a combination of X-ray photoelectron spectroscopy, X-ray fluorescence, and X-ray diffraction to probe the amount of chlorine in samples before and during annealing. As-deposited samples, before annealing, consist of a crystalline precursor phase containing excess methylammonium and halide. We used in situ techniques to study the crystallization of MAPbI3 from this crystalline precursor phase. Excess methylammonium and chloride evaporate during annealing, forming highly crystalline MAPbI3. However, even after prolonged annealing times, chlorine can be detected in the films in X-ray fluorescence measurements.

Advanced MaterialsVolume 23, Issue 20 p. 2284-2288 Communication Structural Order in Bulk Heterojunction Films Prepared with Solvent Additives James T. Rogers, James T. Rogers Departments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USASearch for more papers by this authorKristin Schmidt, Kristin Schmidt Departments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USASearch for more papers by this authorMichael F. Toney, Michael F. Toney Stanford Synchrotron Radiation Lightsource, Menlo Park, CA, USASearch for more papers by this authorEdward J. Kramer, Corresponding Author Edward J. Kramer [email protected] Departments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USADepartments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USA.Search for more papers by this authorGuillermo C. Bazan, Corresponding Author Guillermo C. Bazan [email protected] Departments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USADepartments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USA.Search for more papers by this author James T. Rogers, James T. Rogers Departments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USASearch for more papers by this authorKristin Schmidt, Kristin Schmidt Departments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USASearch for more papers by this authorMichael F. Toney, Michael F. Toney Stanford Synchrotron Radiation Lightsource, Menlo Park, CA, USASearch for more papers by this authorEdward J. Kramer, Corresponding Author Edward J. Kramer [email protected] Departments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USADepartments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USA.Search for more papers by this authorGuillermo C. Bazan, Corresponding Author Guillermo C. Bazan [email protected] Departments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USADepartments of Chemistry & Biochemistry, Department of Materials, Center for Polymers and Organic Solids, University of California, Santa Barbara, CA 93106, USA.Search for more papers by this author First published: 18 January 2011 https://doi.org/10.1002/adma.201003690Citations: 239Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Graphical Abstract Solvent additives are shown to drastically affect internal ordering of the polymeric component of bulk heterojunction solar cells. Grazing incidence wide angle x-ray scattering measurements reveal that additives affect polymeric crystallite type, perfection, orientation, and population within the film. Improvements in device performance that result from additive processing are well correlated with increases in the population of crystallites within the film of the type capable of π–π stacking. Citing Literature Supporting Information Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Filename Description adma_201003690_sm_suppl.pdf344.9 KB suppl Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. Volume23, Issue20Special Issue: Special Issue: Materials Research at the University of California, Santa BarbaraMay 24, 2011Pages 2284-2288 RelatedInformation

Significance Many applications, including solar cells and touch screens, require coatings that are both optically transparent and electrically conductive. Most device structures use indium tin oxide to serve as this transparent conductor (TC), even though it accounts for a disproportionally large amount of device cost. Alternatives, such as polymer-based materials, may not only provide additional cost benefits, but may also allow for added functionality, such as flexibility. In this paper, we examine conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) deposited by solution shearing as a TC film. Morphological and chemical changes caused by solution shearing deposition lead to record-high conductivities and overall excellent TC performance.

Electrochemical CO2 reduction to formate provides an avenue to reduce globally accelerating CO2 emissions and produce value-added products. Unfortunately, high selectivity in formate electrosynthesis has thus far only been achieved at highly cathodic potentials. Here we use density functional theory to investigate the effect of alloying Cu and Sn on the activity and selectivity towards formate. A theoretical thermodynamic analysis of the reaction energetics suggests that the incorporation of copper into tin could suppress hydrogen evolution and CO production, thus favouring formate generation. Consistent with theoretical trends, the designed CuSn3 catalysts by co-electrodeposition exhibit a Faradaic efficiency of 95% towards formate generation at −0.5 V versus RHE. Furthermore, the catalysts show no degradation over 50 h of operation. In situ Sn L3-edge and Cu K-edge X-ray absorption spectroscopy indicate electron donation from Sn to Cu, which indicates positive oxidation states of Sn in CuSn3 under operating conditions. The electroreduction of carbon dioxide to formate represents a desirable strategy for the production of fuels and commodity chemicals. Now, guided by density functional theory, Cui and colleagues report CuSn3 alloys that exhibit high activity and selectivity for formate production from CO2 electroreduction at potentials as low as −0.5 V versus RHE.

Abstract Single-crystal cathode materials for lithium-ion batteries have attracted increasing interest in providing greater capacity retention than their polycrystalline counterparts. However, after being cycled at high voltages, these single-crystal materials exhibit severe structural instability and capacity fade. Understanding how the surface structural changes determine the performance degradation over cycling is crucial, but remains elusive. Here, we investigate the correlation of the surface structure, internal strain, and capacity deterioration by using operando X-ray spectroscopy imaging and nano-tomography. We directly observe a close correlation between surface chemistry and phase distribution from homogeneity to heterogeneity, which induces heterogeneous internal strain within the particle and the resulting structural/performance degradation during cycling. We also discover that surface chemistry can significantly enhance the cyclic performance. Our modified process effectively regulates the performance fade issue of single-crystal cathode and provides new insights for improved design of high-capacity battery materials.

We demonstrate that intercalation of fullerene derivatives between the side chains of conjugated polymers can be controlled by adjusting the fullerene size and compare the properties of intercalated and nonintercalated poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene (pBTTT):fullerene blends. The intercalated blends, which exhibit optimal solar-cell performance at 1:4 polymer:fullerene by weight, have better photoluminescence quenching and lower absorption than the nonintercalated blends, which optimize at 1:1. Understanding how intercalation affects performance will enable more effective design of polymer:fullerene solar cells.

The self-assembly of nanocrystals enables new classes of materials whose properties are controlled by the periodicities of the assembly, as well as by the size, shape, and composition of the nanocrystals. While self-assembly of spherical nanoparticles has advanced significantly in the past decade, assembly of rod-shaped nanocrystals has seen limited progress due to the requirement of orientational order. Here, the parameters relevant to self-assembly are systematically quantified using a combination of diffraction and theoretical modeling; these highlight the importance of kinetics on orientational order. Through drying-mediated self-assembly, we achieve unprecedented control over orientational order (up to 96% vertically oriented rods on 1 cm(2) areas) on a wide range of substrates (ITO, PEDOT:PSS, Si(3)N(4)). This opens new avenues for nanocrystal-based devices competitive with thin film devices, as problems of granularity can be tackled through crystallographic orientational control over macroscopic areas.

Morphology control of solution coated solar cell materials presents a key challenge limiting their device performance and commercial viability. Here we present a new concept for controlling phase separation during solution printing using an all-polymer bulk heterojunction solar cell as a model system. The key aspect of our method lies in the design of fluid flow using a microstructured printing blade, on the basis of the hypothesis of flow-induced polymer crystallization. Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes. The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation. We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

Abstract Organic electronics have emerged as a viable competitor to amorphous silicon for the active layer in low‐cost electronics. The critical performance of organic electronic materials is closely related to their morphology and molecular packing. Unlike their inorganic counterparts, polymers combine complex repeat unit structure and crystalline disorder. This combination prevents any single technique from being able to uniquely solve the packing arrangement of the molecules. Here, a general methodology for combining multiple, complementary techniques that provide accurate unit cell dimensions and molecular orientation is described. The combination of measurements results in a nearly complete picture of the organic film morphology.

Solution-processed lead halide perovskite thin-film solar cells have achieved power conversion efficiencies comparable to those obtained with several commercial photovoltaic technologies in a remarkably short period of time. This rapid rise in device efficiency is largely the result of the development of fabrication protocols capable of producing continuous, smooth perovskite films with micrometer-sized grains. Further developments in film fabrication and morphological control are necessary, however, in order for perovskite solar cells to reliably and reproducibly approach their thermodynamic efficiency limit. This Perspective discusses the fabrication of lead halide perovskite thin films, while highlighting the processing-property-performance relationships that have emerged from the literature, and from this knowledge, suggests future research directions.

Structural fluctuations between two equilibrium phases are observed in copper sulfide nanoparticles.

The challenge of continuous printing in high‐efficiency large‐area organic solar cells is a key limiting factor for their widespread adoption. A materials design concept for achieving large‐area, solution‐coated all‐polymer bulk heterojunction solar cells with stable phase separation morphology between the donor and acceptor is presented. The key concept lies in inhibiting strong crystallization of donor and acceptor polymers, thus forming intermixed, low crystallinity, and mostly amorphous blends. Based on experiments using donors and acceptors with different degree of crystallinity, the results show that microphase separated donor and acceptor domain sizes are inversely proportional to the crystallinity of the conjugated polymers. This methodology of using low crystallinity donors and acceptors has the added benefit of forming a consistent and robust morphology that is insensitive to different processing conditions, allowing one to easily scale up the printing process from a small‐scale solution shearing coater to a large‐scale continuous roll‐to‐roll (R2R) printer. Large‐area all‐polymer solar cells are continuously roll‐to‐roll slot die printed with power conversion efficiencies of 5%, with combined cell area up to 10 cm 2 . This is among the highest efficiencies realized with R2R‐coated active layer organic materials on flexible substrate.

CsPbI3 nanocrystals with narrow size distributions were prepared to study the size-dependent properties. The nanocrystals adopt the perovskite (over the nonperovskite orthorhombic) structure with improved stability over thin-film materials. Among the perovskite phases (cubic α, tetragonal β, and orthorhombic γ), the samples are characterized by the γ phase, rather than α, but may have a size-dependent average tilting between adjacent octahedra. Size-dependent lattice constants systematically vary 3% across the size range, with unit cell volume increasing linearly with the inverse of size to 2.1% for the smallest size. We estimate the surface energy to be from −3.0 to −5.1 eV nm–2 for ligated CsPbI3 nanocrystals. Moreover, the size-dependent bandgap is best described using a nonparabolic intermediate confinement model. We experimentally determine the bulk bandgap, effective mass, and exciton binding energy, concluding with variations from the bulk α-phase values. This provides a robust route to understanding γ-phase properties of CsPbI3.

A long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics-however, the results have important implications on the operation of all optoelectronic devices with donor/acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting in larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation.Molecular orientation profoundly affects the performance of donor-acceptor heterojunctions, whilst it has remained challenging to investigate the detail. Using a controllable interface, Ran et al. show that the edge-on geometries improve charge generation at the cost of non-radiative recombination loss.

Efficient charge carrier transport in organic field-effect transistors (OFETs) often requires thin films that display long-range order and close π-π packing that is oriented in-plane with the substrate. Although some polymers have achieved high field-effect mobility with such solid-state properties, there are currently few general strategies for controlling the orientation of π-stacking within polymer films. In order to probe structural effects on polymer-packing alignment, furan-containing diketopyrrolopyrrole (DPP) polymers with similar optoelectronic properties were synthesized with either linear hexadecyl or branched 2-butyloctyl side chains. Differences in polymer solubility were observed and attributed to variation in side-chain shape and polymer backbone curvature. Averaged field-effect hole mobilities of the polymers range from 0.19 to 1.82 cm(2)/V·s, where PDPP3F-C16 is the least soluble polymer and provides the highest maximum mobility of 2.25 cm(2)/V·s. Analysis of the films by AFM and GIXD reveal that less soluble polymers with linear side chains exhibit larger crystalline domains, pack considerably more closely, and align with a greater preference for in-plane π-π packing. Characterization of the polymer solutions prior to spin-coating shows a correlation between early onset nanoscale aggregation and the formation of films with highly oriented in-plane π-stacking. This effect is further observed when nonsolvent is added to PDPP3F-BO solutions to induce aggregation, which results in films with increased nanostructural order, in-plane π-π orientation, and field-effect hole mobilities. Since nearly all π-conjugated materials may be coaxed to aggregate, this strategy for enhancing solid-state properties and OFET performance has applicability to a wide variety of organic electronic materials.

The bulk heterojunction (BHJ) solar cell performance of many polymers depends on the polymer molecular weight ( M n ) and the solvent additive(s) used for solution processing. However, the mechanism that causes these dependencies is not well understood. This work determines how M n and solvent additives affect the performance of BHJ solar cells made with the polymer poly(di(2‐ethylhexyloxy)benzo[1,2‐ b :4,5‐ b ′]dithiophene‐ co ‐octylthieno[3,4‐ c ]pyrrole‐4,6‐dione) (PBDTTPD). Low M n PBDTTPD devices have exceedingly large fullerene‐rich domains, which cause extensive charge‐carrier recombination. Increasing the M n of PBDTTPD decreases the size of these domains and significantly improves device performance. PBDTTPD aggregation in solution affects the size of the fullerene‐rich domains and this effect is linked to the dependency of PBDTTPD solubility on M n . Due to its poor solubility high M n PBDTTPD quickly forms a fibrillar polymer network during spin‐casting and this network acts as a template that prevents large‐scale phase separation. Furthermore, processing low M n PBDTTPD devices with a solvent additive improves device performance by inducing polymer aggregation in solution and preventing large fullerene‐rich domains from forming. These findings highlight that polymer aggregation in solution plays a significant role in determining the morphology and performance of BHJ solar cells.

The reversible electrochemical insertion of multivalent ions into materials has promising applications in many fields, including batteries, seawater desalination, element purification, and wastewater treatment. However, finding materials that allow for the insertion of multivalent ions with fast kinetics and stable cycling has proven difficult because of strong electrostatic interactions between the highly charged insertion ions and atoms in the host framework. Here, an open framework nanomaterial, copper hexacyanoferrate, in the Prussian Blue family is presented that allows for the reversible insertion of a wide variety of monovalent, divalent, and trivalent ions (such as Rb + , Pb 2+ , Al 3+ , and Y 3+ ) in aqueous solution beyond that achieved in previous studies. Electrochemical measurements demonstrate the unprecedented kinetics of multivalent ion insertion associated with this material. Synchrotron X‐ray diffraction experiments point toward a novel vacancy‐mediated ion insertion mechanism that reduces electrostatic repulsion and helps to facilitate the observed rapid ion insertion. The results suggest a new approach to multi­valent ion insertion that may help to advance the understanding of this complex phenomenon.

In lithium-sulfur (Li-S) batteries, the insulating nature of sulfur and lithium sulfide (Li2S) results in large polarization and low sulfur utilization while the soluble polysulfides lead to internal shuttle upon cycling. Furthermore, the redox reaction via the dissolution-precipitation route destroys the electrode architecture by passivating the active interface responsible for the redox reaction, and thus the performance deteriorates with cycling. Here, we employ the redox chemistry of quinone to realize efficient, fast, and stable operation of Li-S batteries using Li2S microparticles. By adding a quinone derivative with tailored properties (e.g., oxidation potential, solubility, and electrochemical stability) to an electrolyte as a redox mediator (RM), initial charging of Li2S electrodes occurs below 2.5 V at 0.5C, and the subsequent discharge capacity is as high as 1,300 mAh gs−1. Moreover, deposition of dead Li2S, which was the primary cause of increasing polarization and decreasing capacity upon cycling, is effectively prevented with the RM.

<h2>Summary</h2> To shed light on the formation process and structure of the solid electrolyte interphase (SEI) layer on native oxide-terminated silicon wafer anodes from a carbonate-based electrolyte (LP30), we combined <i>in situ</i> synchrotron X-ray reflectivity, linear sweep voltammetry, <i>ex situ</i> X-ray photoelectron spectroscopy, and first principles calculations from the Materials Project. We present <i>in situ</i> sub-nanometer resolution structural insights and compositional information of the SEI, as well as predicted equilibrium phase stability. Combining these findings, we observe two well-defined inorganic SEI layers next to the Si anode—a bottom-SEI layer (adjacent to the electrode) formed via the lithiation of the native oxide, and a top-SEI layer mainly consisting of the electrolyte decomposition product LiF. Our study provides novel mechanistic insights into the SEI growth process on Si, and we discuss several important implications regarding ion and electron transport through the SEI layer.

Photoinduced halide segregation currently limits the perovskite chemistries available for use in high-bandgap semiconductors needed for tandem solar cells. Here, we study the impact of post-deposition surface modifications on photoinduced halide segregation in methylammonium lead mixed-halide perovskites. By coating a perovskite surface with the electron-donating ligand trioctylphosphine oxide (TOPO), we are able to both reduce nonradiative recombination and dramatically slow the onset of halide segregation in CH3NH3PbI2Br films. This result, coupled with the observation that the rate of halide segregation can be tuned by varying the selective contact, provides a direct link between surface modifications and photoinduced trap formation. On the basis of these observations, we discuss possible mechanisms for photoinduced halide segregation supported by drift-diffusion simulations. This work suggests that improved understanding and control of perovskite surfaces provides a pathway toward stable and high-performance wide-bandgap perovskites for the next generation of tandem solar cells.

Using atomic layer deposition of Al2O3 coating, improved high-voltage cycling stability has been demonstrated for the layered nickel–manganese–cobalt pseudoternary oxide, LiNi0.4Mn0.4Co0.2O2. To understand the effect of the Al2O3 coating, we have utilized electrochemical impedance spectroscopy, operando synchrotron-based X-ray diffraction, and operando X-ray absorption near edge fine structure spectroscopy to characterize the structure and chemistry evolution of the LiNi0.4Mn0.4Co0.2O2 cathode during cycling. Using this combination of techniques, we show that the Al2O3 coating successfully mitigates the strong side reactions of the active material with the electrolyte at higher voltages (>4.4 V), without restricting the uptake and release of Li ions. The impact of the Al2O3 coating is also revealed at beginning of lithium deintercalation, with an observed delay in the evolution of oxidation and coordination environment for the Co and Mn ions in the coated electrode due to protection of the surface. This protection prevents the competing side reactions of the electrolyte with the highly active Ni oxide sites, promoting charge compensation via the oxidation of Ni and enabling high-voltage cycling stability.

The interplay between electrochemical properties, crystal structure, and chemical bonding of Prussian Blue analogues determines their suitability for grid-scale aqueous batteries.

One-step deposition of perovskite films follows the downward crystallization from intermediate phases during thermal annealing.

Electrodeposited manganese oxide films are promising catalysts for promoting the oxygen evolution reaction (OER), especially in acidic solutions. The activity of these catalysts is known to be enhanced by the introduction of Mn3+ We present in situ electrochemical and X-ray absorption spectroscopic studies, which reveal that Mn3+ may be introduced into MnO2 by an electrochemically induced comproportionation reaction with Mn2+ and that Mn3+ persists in OER active films. Extended X-ray absorption fine structure (EXAFS) spectra of the Mn3+-activated films indicate a decrease in the Mn-O coordination number, and Raman microspectroscopy reveals the presence of distorted Mn-O environments. Computational studies show that Mn3+ is kinetically trapped in tetrahedral sites and in a fully oxidized structure, consistent with the reduction of coordination number observed in EXAFS. Although in a reduced state, computation shows that Mn3+ states are stabilized relative to those of oxygen and that the highest occupied molecular orbital (HOMO) is thus dominated by oxygen states. Furthermore, the Mn3+(Td) induces local strain on the oxide sublattice as observed in Raman spectra and results in a reduced gap between the HOMO and the lowest unoccupied molecular orbital (LUMO). The confluence of a reduced HOMO-LUMO gap and oxygen-based HOMO results in the facilitation of OER on the application of anodic potentials to the δ-MnO2 polymorph incorporating Mn3+ ions.

Identifying how small molecular acceptors pack with polymer donors in thin and thick (bulk) films is critical to understanding the nature of electrical doping by charge transfer. In this study, the packing structure of the molecular acceptor tetrafluorotetracyanoquinodimethane (F4TCNQ) with the semiconducting polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) is examined. A combination of solid-state NMR, synchrotron X-ray scattering, and optical spectroscopy was used to determine the packing motif for blends of PBTTT-C14 and F4TCNQ in thin and bulk films. These results indicate that F4TCNQ and PBTTT-C14 order in a cofacial arrangement where charge transfer is near 100% efficient in the solid state. These results provide crucial insights into the structures and compositions of ordered domains in doped semiconducting polymers and suggest a model for the microstructure where the location of the molecular acceptors are correlated rather than randomly dispersed.

We report the fabrication of monolithic all-perovskite tandem solar cells with a stabilized power conversion efficiency of 19.1% and demonstrate improved thermal, atmospheric, and operational stability of the tin–lead perovskite (FA_0.75Cs_0.25Sn_0.5Pb_0.5I₃) used as the low gap absorber.

Lead halide perovskites have emerged as successful optoelectronic materials with high photovoltaic power conversion efficiencies and low material cost. However, substantial challenges remain in the scalability, stability and fundamental understanding of the materials. Here we present the application of radiative thermal annealing, an easily scalable processing method for synthesizing formamidinium lead iodide (FAPbI3) perovskite solar absorbers. Devices fabricated from films formed via radiative thermal annealing have equivalent efficiencies to those annealed using a conventional hotplate. By coupling results from in situ X-ray diffraction using a radiative thermal annealing system with device performances, we mapped the processing phase space of FAPbI3 and corresponding device efficiencies. Our map of processing-structure-performance space suggests the commonly used FAPbI3 annealing time, 10 min at 170 °C, can be significantly reduced to 40 s at 170 °C without affecting the photovoltaic performance. The Johnson-Mehl-Avrami model was used to determine the activation energy for decomposition of FAPbI3 into PbI2.

Sodium-ion batteries have become a subject of increasing interest and are considered as an alternative to the ubiquitous lithium-ion battery. To compare the effect of two improvement strategies for metal oxide cathodes, specifically Co-doping and morphology optimization, four representatives of the prominent material class of layered NaxMO2 (M = transition metal) have been studied: hexagonal flakes and hollow spheres of P2–NaxMnO2 and P2–NaxCo0.1Mn0.9O2. The better electrochemical performance of the spheres over the flakes and of the Co-doped over the undoped materials are explained on the basis of structural features revealed by operando synchrotron X-ray diffraction. The higher cycling stability of the material doped with ∼10% Co is attributed to three effects: (i) the suppression of a Jahn–Teller-induced structural transition from the initial hexagonal to an orthorhombic phase that is observed in NaxMnO2; (ii) suppression of ordering processes of Na+; and (iii) enhanced Na+ kinetics as revealed by galvanostatic intermittent titration technique measurements and in situ electrochemical impedance measurements. Increased capacity and cycling stability of spheres over flakes may be related to smaller changes of the unit cell volume of spheres and thus to reduced structural stress. Co-doped spheres combine the advantages of both strategies and exhibit the best cycling stability.

Significant effort has focused on controlling the deposition of perovskite films to enable uniform films, enabling efficiencies to climb dramatically. However, little attention has been paid to the evolution of thin-film stresses during deposition and the consequent effect on film morphology. While a textured surface topology has potential benefits for light scattering, a smooth surface is desirable to enable the pinhole-free deposition of contact layers. We show that the highly textured morphology made by popular antisolvent conversion methods arises because of in-plane compressive stress experienced during the intermediate phase of film formation where the substrate constrains the film from expanding—leading to energy release in the form of wrinkling, resulting in trenches that can be hundreds of nanometers deep with periods of several micrometers. We demonstrate that the extent of wrinkling is correlated with the rate of film conversion and that ultrasmooth films are obtained by slowing the rate of film formation.

Polymer aggregation and crystallization behavior play a crucial role in the performance of all-polymer solar cells (all-PSCs). Gaining control over polymer self-assembly via molecular design to influence bulk-heterojunction active-layer morphology, however, remains challenging. Herein, we show a simple yet effective way to modulate the self-aggregation of the commonly used naphthalene diimide (NDI)-based acceptor polymer (N2200), by systematically replacing a certain amount of alkyl side-chains with compact bulky side-chains (CBS). Specifically, we have synthesized a series of random copolymer (PNDI-CBSx) with different molar fractions (x = 0-1) of the CBS units and have found that both solution-phase aggregation and solid-state crystallinity of these acceptor polymers are progressively suppressed with increasing x as evidenced by UV-vis absorption, photoluminescence (PL) spectroscopies, thermal analysis, and grazing incidence X-ray scattering (GIWAXS) techniques. Importantly, as compared to the highly self-aggregating N2200, photovoltaic results show that blending of more amorphous acceptor polymers with donor polymer (PBDB-T) can enable all-PSCs with significantly increased PCE (up to 8.5%). The higher short-circuit current density (Jsc) results from the smaller polymer phase-separation domain sizes as evidenced by PL quenching and resonant soft X-ray scattering (R-SoXS) analyses. Additionally, we show that the lower crystallinity of the active layer is less sensitive to the film deposition methods. Thus, the transition from spin-coating to solution coating can be easily achieved with no performance losses. On the other hand, decreasing aggregation and crystallinity of the acceptor polymer too much reduces the photovoltaic performance as the donor phase-separation domain sizes increases. The highly amorphous acceptor polymers appear to induce formation of larger donor polymer crystallites. These results highlight the importance of a balanced aggregation strength between the donor and acceptor polymers to achieve high-performance all-PSCs with optimal active layer film morphology.

In luminescent solar concentrator (LSC) systems, broadband solar energy is absorbed, down-converted and waveguided to the panel edges where peripheral photovoltaic cells convert the concentrated light to electricity. Achieving a low-loss LSC requires reducing the reabsorption of emitted light within the absorbing medium while maintaining high photoluminescence quantum yield (PLQY). Here we employ layered hybrid metal halide perovskites—ensembles of two-dimensional perovskite domains—to fabricate low-loss large-area LSCs that fulfil this requirement. We devised a facile synthetic route to obtain layered perovskite nanoplatelets (PNPLs) that possess a tunable number of layers within each platelet. Efficient ultrafast non-radiative exciton routing within each PNPL (0.1 ps−1) produces a large Stokes shift and a high PLQY simultaneously. Using this approach, we achieve an optical quantum efficiency of 26% and an internal concentration factor of 3.3 for LSCs with an area of 10 × 10 cm2, which represents a fourfold enhancement over the best previously reported perovskite LSCs. Luminescent solar concentrators are promising for semi-transparent, building-integrated photovoltaic systems. Here the authors minimize the absorption losses by relying on fast energy transfer in multiphase perovskite nanoplatelets to achieve optical quantum efficiency of 26% on 100 cm2 devices.

<h2>Summary</h2> Organic-inorganic metal-halide perovskite materials offer a promising route to reducing the dollars-per-watt cost of solar energy due to their good optoelectronic properties and facile, scalable processing. Compositional tuning allows for the preparation of absorbers with band gaps tailor-made for specific tandem and single-junction applications, but photoinduced phase segregation in mixed-halide materials leads to the formation of low-band-gap regions that reduce the voltage of devices. This work explores the structural origins of photoinduced phase segregation in FA_yCs_1−yPb(Br_xI_1−x)₃ perovskite alloys. We use synchrotron X-ray diffraction to map the solvus between the cubic and cubic-tetragonal mixed-phase region and time-dependent photoluminescence to assess stability under illumination. We show that the correlation between crystallographic phase and phase-segregation behavior is imperfect, so phase is not the sole determinant of optical stability. Instead, we consider several possible mechanisms that could underlie the dependence of optical stability on perovskite composition.

Abstract Whether attempting to eliminate parasitic Li metal plating on graphite (and other Li‐ion anodes) or enabling stable, uniform Li metal formation in ‘anode‐free’ Li battery configurations, the detection and characterization (morphology, microstructure, chemistry) of Li that cannot be reversibly cycled is essential to understand the behavior and degradation of rechargeable batteries. In this review, various approaches used to detect and characterize the formation of Li in batteries are discussed. Each technique has its unique set of advantages and limitations, and works towards solving only part of the full puzzle of battery degradation. Going forward, multimodal characterization holds the most promise towards addressing two pressing concerns in the implementation of the next generation of batteries in the transportation sector (viz. reducing recharging times and increasing the available capacity per recharge without sacrificing cycle life). Such characterizations involve combining several techniques (experimental‐ and/or modeling‐based) in order to exploit their respective advantages and allow a more comprehensive view of cell degradation and the role of Li metal formation in it. It is also discussed which individual techniques, or combinations thereof, can be implemented in real‐world battery management systems on‐board electric vehicles for early detection of potential battery degradation that would lead to failure.

Increasing the energy density of layered oxide battery electrodes is challenging as accessing high states of delithiation often triggers voltage degradation and oxygen release. Here we utilize transmission-based X-ray absorption spectromicroscopy and ptychography on mechanically cross-sectioned Li1.18–xNi0.21Mn0.53Co0.08O2–δ electrodes to quantitatively profile the oxygen deficiency over cycling at the nanoscale. The oxygen deficiency penetrates into the bulk of individual primary particles (~200 nm) and is well-described by oxygen vacancy diffusion. Using an array of characterization techniques, we demonstrate that, surprisingly, bulk oxygen vacancies that persist within the native layered phase are indeed responsible for the observed spectroscopic changes. We additionally show that the arrangement of primary particles within secondary particles (~5 μm) causes considerable heterogeneity in the extent of oxygen release between primary particles. Our work merges an ensemble of length-spanning characterization methods and informs promising approaches to mitigate the deleterious effects of oxygen release in lithium-ion battery electrodes. Oxygen release in Li-rich layered oxides is of both fundamental and practical interest in batteries, but a varied mechanistic understanding exists. Here the authors evaluate the extent of oxygen release over extended cycles and present a comprehensive picture of the phenomenon that unifies the current explanations.

Excitation localization involving dynamic nanoscale distortions is a central aspect of photocatalysis, quantum materials and molecular optoelectronics. Experimental characterization of such distortions requires techniques sensitive to the formation of point-defect-like local structural rearrangements in real time. Here, we visualize excitation-induced strain fields in a prototypical member of the lead halide perovskites via femtosecond resolution diffuse x-ray scattering measurements. This enables momentum-resolved phonon spectroscopy of the locally-distorted structure and reveals radially-expanding nanometer-scale elastic strain fields associated with the formation and relaxation of polarons in photoexcited perovskites. Quantitative estimates of the magnitude and the shape of this polaronic distortion are obtained, providing direct insights into the debated dynamic structural distortions in these materials. Optical pump-probe reflection spectroscopy corroborates these results and shows how these large polaronic distortions transiently modify the carrier effective mass, providing a unified picture of the coupled structural and electronic dynamics that underlie the unique optoelectronic functionality of the hybrid perovskites.

Layered oxides widely used as lithium-ion battery electrodes are designed to be cycled under conditions that avoid phase transitions. Although the desired single-phase composition ranges are well established near equilibrium, operando diffraction studies on many-particle porous electrodes have suggested phase separation during delithiation. Notably, the separation is not always observed, and never during lithiation. These anomalies have been attributed to irreversible processes during the first delithiation or reversible concentration-dependent diffusion. However, these explanations are not consistent with all experimental observations such as rate and path dependencies and particle-by-particle lithium concentration changes. Here, we show that the apparent phase separation is a dynamical artefact occurring in a many-particle system driven by autocatalytic electrochemical reactions, that is, an interfacial exchange current that increases with the extent of delithiation. We experimentally validate this population-dynamics model using the single-phase material Lix(Ni1/3Mn1/3Co1/3)O2 (0.5 < x < 1) and demonstrate generality with other transition-metal compositions. Operando diffraction and nanoscale oxidation-state mapping unambiguously prove that this fictitious phase separation is a repeatable non-equilibrium effect. We quantitatively confirm the theory with multiple-datastream-driven model extraction. More generally, our study experimentally demonstrates the control of ensemble stability by electro-autocatalysis, highlighting the importance of population dynamics in battery electrodes (even non-phase-separating ones). Although layered oxides electrodes in lithium-ion batteries are designed under conditions avoiding phase transitions, phase separation during delithiation has been observed. This apparent phase separation is shown to be a dynamical artefact occurring in a many-particle system driven by autocatalytic electrochemical reactions.

Electrochemical ion insertion involves coupled ion–electron transfer reactions, transport of guest species and redox of the host. The hosts are typically anisotropic solids with 2D conduction planes but can also be materials with 1D or isotropic transport pathways. These insertion compounds have traditionally been studied in the context of energy storage but also find extensive applications in electrocatalysis, optoelectronics and computing. Recent developments in operando, ultrafast and high-resolution characterization methods, as well as accurate theoretical simulation methods, have led to a renaissance in the understanding of ion-insertion compounds. In this Review, we present a unified framework for understanding insertion compounds across timescales and length scales ranging from atomic to device levels. Using graphite, transition metal dichalcogenides, layered oxides, oxyhydroxides and olivines as examples, we explore commonalities in these materials in terms of point defects, interfacial reactions and phase transformations. We illustrate similarities in the operating principles of various ion-insertion devices, ranging from batteries and electrocatalysts to electrochromics and thermal transistors, with the goal of unifying research across disciplinary boundaries. Electrochemical ion insertion is rapidly emerging as a powerful materials design strategy. This Review discusses how ion insertion enables reversible transformation and switching of physico-chemical properties, the role of defects and interfacial reactions, and opportunities for ultrafast ionic control.

Electrolytes are an essential component of all electrochemical storage and conversion devices, such as batteries. In the history of battery development, the complex nature of electrolytes has often been a bottleneck. Fundamental knowledge of electrolyte systems encompasses elucidation of structure–property relationships of the solution species. Recently, nanometric aggregates have been observed in several classes of electrolytes, including super-concentrated, redox-flow, multivalent, polymer, and ionic liquid-based electrolytes. Compared with the well-studied local solvation structures such as contact ion pairs and solvent-separated ions, these aggregates impose unique effects on the ion distribution and transport both within bulk electrolytes and at electrode/electrolyte interfaces. This Perspective highlights the discovery of the aggregates in various battery electrolytes and their impact on electrolyte properties. We also present an outlook for future studies of this emerging field of nanometric aggregates and the need for the development of new experimental and computational tools to study their properties.

The performance and stability of metal halide perovskite solar cells strongly depend on precursor materials and deposition methods adopted during the perovskite layer preparation. There are often a number of different formation pathways available when preparing perovskite films. Since the precise pathway and intermediary mechanisms affect the resulting properties of the cells, in situ studies have been conducted to unravel the mechanisms involved in the formation and evolution of perovskite phases. These studies contributed to the development of procedures to improve the structural, morphological, and optoelectronic properties of the films and to move beyond spin-coating, with the use of scalable techniques. To explore the performance and degradation of devices, operando studies have been conducted on solar cells subjected to normal operating conditions, or stressed with humidity, high temperatures, and light radiation. This review presents an update of studies conducted in situ using a wide range of structural, imaging, and spectroscopic techniques, involving the formation/degradation of halide perovskites. Operando studies are also addressed, emphasizing the latest degradation results for perovskite solar cells. These works demonstrate the importance of in situ and operando studies to achieve the level of stability required for scale-up and consequent commercial deployment of these cells.

By using coordinating anions such as acetate, a water-in-salt-like coordination environment of Zn ions is achieved in relatively dilute conditions, leading to prolonged and efficient cycling of zinc metal anodes.

The magnetic domain structure and magnetization curves of chemically ordered epitaxial FePt (001) films with perpendicular magnetic anisotropy are discussed. Films were dc magnetron sputtered from a Fe50Pt50 alloy target onto Pt seeded MgO (001) at substrate temperatures of 550 °C. The thickness of the FePt layers was varied between 18 and 170 nm. Specular and grazing incidence x-ray diffraction measurements confirm the presence of the anisotropic, face centered tetragonal (L10) crystal structure. Long range chemical order parameters of up to 0.95 and small mosaic spread, similar to results reported for FePt (001) films grown by molecular beam epitaxy. For film thicknesses ⩾50 nm in-plane and out-of-plane hysteresis measurements indicate large perpendicular magnetic anisotropies and at the same time low (about 10%) perpendicular remanence. Magnetic force microscopy reveals highly interconnected perpendicular stripe domain patterns. From their characteristic widths, which are strongly dependent on the film thickness, a value of the dipolar length D0∼50±5 nm is derived. Assuming an exchange constant of 10−6 erg/cm, this value is consistent with an anisotropy constant K1∼1×108 erg/cc.

Growth of epitaxial films of the L10 phase of FePt, with the tetragonal c axis along either the film normal or in-plane, is described. Films were grown by coevaporation of Fe and Pt, under ultrahigh vacuum conditions, onto a seed film of Pt grown on MgO or SrTiO3 substrates. The perpendicular or in-plane orientation of the c axis was controlled by selecting the (001) or (110) substrate plane, respectively. Nearly complete chemical ordering was achieved for growth at 500 °C for both orientations. Magnetic and magneto-optical characterization of these films confirmed the huge magnetic anisotropy expected for this phase. In the most highly ordered films, anisotropy fields in excess of 120 kOe were measured.

Magnetic media using materials with high uniaxial magneto-crystalline anisotropy, KU, combined with a thermal assist to overcome write field limitations have been proposed as one of the potential technologies to extend the areal density of magnetic disk recording beyond the limitations of current technology. Here we present an investigation on structural and temperature dependent magnetic properties of chemically ordered epitaxial Fe55−xNixPt45 thin films. Increasing Ni additions result in a steady reduction of magneto-crystalline anisotropy, saturation magnetization, and Curie temperature. The ability to control thermomagnetic properties over a wide range makes Fe55−xNixPt45 and similar FePt-based pseudo-binary alloys attractive base materials for media applications in thermally assisted magnetic recording.

In situ surface X‐ray diffraction was used to identify the detailed structure of the passive film that forms on (000)− and (110)‐oriented iron single crystals in a borate buffer solution at +0.4 V vs. mercurous sulfate reference electrode, a high passive potential. The passive film is a new phase: a spinel with a fully occupied oxygen lattice, octahedral site occupancy of 80 ± 10%, tetrahedral site occupancy of 66 ± 10%, and an octahedral interstitial site occupancy of 12 ± 4%. The passive film forms with an epitaxial relationship to the substrate iron; for growth on Fe(001), film(001)||Fe(001) and , while for growth on Fe(110), film(111)||Fe(110) and . The in‐plane lattice parameter for the passive film (the LAMM phase) is 8.39 ± 0.01 Å for growth on both faces, and the out‐of‐plane lattice parameter is 8.25 ± 0.1 Å [Fe(001)] and 8.42 ± 0.1 Å [Fe(110)]. The passive film forms a nanocrystalline microstructure with numerous defects. Specifically, the grain size is 50–80 Å in‐plane and about 30 Å out‐of‐plane. There is a small mosaic spread of 2.5 to 4.1° and a high density of antiphase boundaries and stacking faults. The structure of the film determined in situ was found to be identical to that found for an emersed sample, indicating that the high potential film studied here is stable on removal from the electrolyte. Some of the implications of the film structure on passivity are discussed. © 2000 The Electrochemical Society. All rights reserved.

Abstract In organic thin film transistors (OTFTs), charge transport occurs in the first few monolayers of the semiconductor near the semiconductor/dielectric interface. Previous work has investigated the roles of dielectric surface energy, roughness, and chemical functionality on performance. However, large discrepancies in performance, even with apparently identical surface treatments, indicate that additional surface parameters must be identified and controlled in order to optimize OTFTs. Here, a crystalline, dense octadecylsilane (OTS) surface modification layer is found that promotes two‐dimensional semiconductor growth. Higher mobility is consistently achieved for films deposited on crystalline OTS compared to on disordered OTS, with mobilities as high as 5.3 and 2.3 cm 2 V −1 s −1 for C 60 and pentacene, respectively. This is a significant step toward morphological control of organic semiconductors which is directly linked to their thin film charge carrier transport.

Dielectric insulator materials containing nanometer-scale closed-cell pores with low dielectric constants (k < 2.2), good mechanical properties, and high dielectric breakdown strengths are required for future semiconductor devices. In this paper we present a novel method for preparing nanoporous polyorganosilicate films, which promise to satisfy the key requirements, via inorganic/organic polymer hybrid templating. The nanometer-scale inorganic/organic polymer hybrids are generated in situ upon heating mixtures of methylsilsesquioxane (MSSQ) prepolymer with star-shaped hydroxy-terminated poly(ε-caprolactone) (PCL) to ∼250 °C, causing chain extension and cross-linking of MSSQ. Subsequent heating to 430 °C results in the thermal decomposition and volatilization of PCL components from the vitrified poly(methylsilsesquioxane) (PMSSQ) matrix, leaving behind porous PMSSQ films with pores with the size and shape of the original hybrid morphology. A dielectric constant as low as 2.1 has been achieved for closed-cell nanoporous PMSSQ films with hydrophobic surfaces and excellent breakdown strengths close to that of SiO2. Moreover, conductance measurements on inorganic/organic polymer hybrids offer insight into the development of interconnected PCL domains as the PCL content is increased above ∼25%.

The structure of electrochemically deposited submonolayer Cu on Au(111) in sulfuric acid has been extensively investigated but is still poorly known. We report an x-ray scattering determination of this structure that explains existing data. The Cu adatoms form a honeycomb lattice and are adsorbed on threefold hollow sites, while sulfate anions occupy the honeycomb centers. Three oxygens of each sulfate bond to Cu atoms. This stabilizes the structure and illustrates that anion effects can be important in electrodeposited structures. Our results indicate that previous scanning tunneling and atomic force microscopy measurements imaged the sulfate molecules not the Cu atoms.