Conjugated Polythiophene Frameworks as a Hole-Selective Layer on Ta₃N₅ Photoanode for High-Performance Solar Water Oxidation

Discovering a competent charge transport layer promoting charge separation in photoelectrodes is a perpetual pursuit in photoelectrochemical (PEC) water splitting to achieve high solar-to-hydrogen (STH) conversion efficiency. Here, a conjugated polythiophene framework (CPF-TTB) on Ta3N5 is elaborately electropolymerized, substantiating the hole transport behavior in their heterojunction. Tailored band structures of the CPF-TTB/Ta3N5 reinforce the separation of photogenerated carriers, elevating a fill factor of the photoanode modified with a cocatalyst. The enhanced hole extraction enables the NiFeOx/CPF-TTB/Ta3N5/TiN photoanode to generate a remarkable water oxidation photocurrent density of 9.12 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode. A tandem device combining the photoanode with a perovskite/Si solar cell implements an unbiased solar water splitting with a STH conversion efficiency of 6.26% under parallel illumination mode. This study provides novel strategies in interface engineering for metal nitride-based photoelectrodes, suggesting a promise of the organic-inorganic hybrid photoelectrode for high-efficiency PEC water splitting.