Multilayer oxide protection layer with multiple 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 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 oxide/metal architecture is established by employing systematic photoelectrochemical-electrical measurements and simulation models. Here we show important contributions for further developing the practical photoelectrodes in photoelectrochemical devices and controlling the carrier transport behaviors in complex multilayer structure.