Crystalline TiO 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 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 shows a limiting current density of ~35.3 mA cm and durability of over 100 h at 10 mA cm in 1.0 M NaOH electrolyte, while none of photoelectrochemical behavior is observed in crystalline TiO 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.