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

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 NiFeCoOx/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. The conformal heterojunction of a competent hole transport layer onto the nanoporous BiVO4 photoanode is highly challenging, despite its promise for unbiased photoelectrochemical (PEC) water splitting.