A bias-free CuBi2O4–CuWO4 tandem cell for solar-driven water splitting

CuBi2O4 and CuWO4 films (2 × 2 cm) on an FTO substrate have been fabricated to construct an all-copper-based oxide tandem cell for solar-driven photoelectrochemical (PEC) water splitting. CuBi2O4 and CuWO4 films are of opposite semiconductivity, and exhibit a large difference in the onset potentials and matched light absorption, making them ideal for a tandem configuration for solar energy conversion. Under optimal conditions, the tandem cell (4 cm2) exhibits a water splitting photocurrent of 0.3 mA without an external bias under simulated solar insolation. The low cost, non-toxicity, good stability and easy manufacture of this copper-based oxide tandem cell warrant promising applications in the field of solar energy conversion.