Crystalline TiO2 protective layer with graded oxygen defects for efficient and stable silicon-based photocathode

The trade-offs between photoelectrode efficiency and stability significantly hinder the practical application of silicon-based photoelectrochemical devices. Here, we report a facile approach to decouple the trade-offs of silicon-based photocathodes by employing crystalline TiO 2 with graded oxygen defects as protection layer. The crystalline protection layer provides high-density structure and enhances stability, and at the same time oxygen defects allow the carrier transport with low resistance as required for high efficiency. The silicon-based photocathode with black TiO 2 shows a limiting current density of ~35.3 mA cm −2 and durability of over 100 h at 10 mA cm −2 in 1.0 M NaOH electrolyte, while none of photoelectrochemical behavior is observed in crystalline TiO 2 protection layer. These findings have significant suggestions for further development of silicon-based, III–V compounds and other photoelectrodes and offer the possibility for achieving highly efficient and durable photoelectrochemical devices. While silicon-based materials can convert sunlight directly to fuel and electricity, balancing their stability and efficiency constrains usage. Here, authors protect silicon photocathodes with crystalline titanium dioxide layers with graded oxygen defects to improve both durability and efficiency.