High-efficiency unbiased water splitting with photoanodes harnessing polycarbazole hole transport layers

Abstract

The construction of uniform heterojunctions for effective hole transport in a nanoporous BiVO₄ photoanode is highly challenging, despite its promise for unbiased photoelectrochemical (PEC) water splitting. Herein, we grew a nanoscale conjugated polycarbazole framework (CPF-TCB) on nanoporous Mo:BiVO₄ and exhaustively assessed its hole extraction capability. Type II band alignment in the CPF-TCB/Mo:BiVO₄ heterostructure enabled effective hole transport by suppressing charge recombination, enhancing both the fill factor and stability of the photoanode after loading a cocatalyst. The NiFeCoO_x/CPF-TCB/Mo:BiVO₄ photoanode generates a superlative water oxidation photocurrent density of 6.66 mA cm⁻² at 1.23 V versus the reversible hydrogen electrode. By combining the photoanode with a perovskite photocathode and a perovskite/Si solar cell, two types of PEC tandem devices exhibit solar-to-hydrogen conversion efficiencies of 6.75% and 9.02%, which are the topmost records under tandem illumination mode. This work provides a significant step for designing high-performance organic–inorganic hybrid photoelectrodes for solar hydrogen production.