Three-Dimensional High-Density Hierarchical Nanowire Architecture for High-Performance Photoelectrochemical Electrodes

Three-dimensional (3D) nanowire (NW) networks are promising for designing high-performance photoelectrochemical (PEC) electrodes owing to their long optical path for efficient light absorption, high-quality one-dimensional conducting channels for rapid electron–hole separation and charge transportation, as well as high surface areas for fast interfacial charge transfer and electrochemical reactions. By growing titanium dioxide (TiO2) nanorods (NRs) uniformly on dense Si NW array backbones, we demonstrated a novel three-dimensional high-density heterogeneous NW architecture that could enhance photoelectrochemical efficiency. A 3D NW architecture consisting of 20 μm long wet-etched Si NWs and dense TiO2 NRs yielded a photoelectrochemical efficiency of 2.1%, which is three times higher than that of TiO2 film-Si NWs having a core–shell structure. This result suggests that the 3D NW architecture is superior to straight NW arrays for PEC electrode design. The efficiency could be further improved by optimizing the number of overcoating cycles and the length/density of NW backbones. By implementing these 3D NW networks into electrode design, one may be able to advantageously impact PEC and photovoltaic device performance.