Enhanced PEC performance of nanoporous Si photoelectrodes by covering HfO₂ and TiO₂ passivation layers

Nanostructured Si as the high efficiency photoelectrode material is hard to keep stable in aqueous for water splitting. Capping a passivation layer on the surface of Si is an effective way of protecting from oxidation. However, it is still not clear in the different mechanisms and effects between insulating oxide materials and oxide semiconductor materials as passivation layers. Here, we compare the passivation effects, the photoelectrochemical (PEC) properties, and the corresponding mechanisms between the HfO₂/nanoporous-Si and the TiO₂/nanoporous-Si by I-V curves, Motte-schottky (MS) curves, and electrochemical impedance spectroscopy (EIS). Although the saturated photocurrent densities of the TiO₂/nanoporous Si are lower than that of the HfO₂/nanoporous Si, the former is more stable than the later.