Multilayer oxide-based protection layer with multiple carrier-tunnelling paths for efficient and durable Si-based photocathode

Constructing a low-resistance oxide protection layer is challenging but highly beneficial for realizing a practical photoelectrochemical (PEC) device. The thickness of oxide layer strongly influences its behaviors of carrier transport and corrosion resistance, generally leading to a trade-off between efficiency and durability. Different from the previous methods, here we propose and demonstrate a universal approach to decouple the trade-off of oxide layer by multiple carrier-tunnelling paths. This approach with oxide/metal architecture ((O/M)_n, n is the number of nano-scale repeating unit) enables low-resistance carrier transport as required for high efficiency, while allowing the layer to be sufficiently thick, which reinforces durability. This approach can be applied to various oxide-based layers, such as (TiO₂/Fe)_n, (CeO₂/Fe)_n and (TiO₂/Pd)_n. In addition, a good correlation between carrier dynamics and (O/M)_n is established by employing systematic PEC-electrical measurements and simulation models. These findings have important contributions for further development of practical photoelectrodes in PEC devices and provide the possibility for controlling the carrier transport behaviors in complex multilayer structure.