Crystalline TiO 2 -passivated BiVO 4 ‖Ta 3 N 5 tandem photoanodes for efficient unassisted photoelectrochemical water splitting

Introducing an anatase TiO₂ passivation layer enhances carrier transport and suppresses recombination in BiVO₄. Coupling the optimized photoanode with a Ta₃N₅ back photoanode broadens light absorption, and subsequently integrating a Si solar cell enables unassisted PEC water splitting with a 3.1% STH efficiency.