Unassisted solar water splitting by dual Cu2O–based tandem device with complementary wavelength–dependent quantum efficiency and antipodal conductivity

Unprecedented standalone tandem cell consisted of dual Cu2O, of which the complementary wavelength–dependent quantum efficiency is in favor of the full utilization of the broadband sunlight with the photon energy above their characteristic band gap and the striking difference in the Fermi level as a result of their distinct p–type and n–type conductivities turns into a strong photovoltage, is developed in the present contribution to carry out unassisted photoelectrochemical water splitting using energy exclusively from the sun. Further deposition of the n–type TiOx overlayer on p–type Cu2O engineered into a wire–like nanostructure, forming the core–shell p–n heterojunction to provide additional photovoltage to accelerate the hydrogen evolution reaction, and the circumvention of the severe charge accumulation at the Schottky Cu/n–Cu2O back contact well relax the associated kinetic overpotentials. The synergistic effect renders the solar–to–hydrogen efficiency of the tandem n–TiOx/p–Cu2O//n–Cu2O device amounting to 0.32%, which is among the highest performance reported to date for the Cu2O–based tandem PEC//PEC cells in the literature.