LAUSR

A process accumulated record solar to hydrogen (STH) conversion efficiency of 8% is achieved on the Cu2ZnSnS4‐BiVO4 tandem cell by the synergistic coupling effect of solar thermal and photoelectrochemical (PEC) water splitting with the dynamic balance of solar energy storage and conversion of the greenhouse system. This is the first report of a Cu2ZnSnS4‐BiVO4 tandem cell with a high unbiased STH efficiency of over 8% for solar water splitting due to the greenhouse device system. The greenhouse acts as a solar thermal energy storage cell, which absorbs infrared solar light and storage as thermal energy with the solar light illumination time, while thermoelectric device (TD) converts thermal energy into electric power, electric power is also recycled and added onto Cu2ZnSnS4‐BiVO4 tandem cell for enhanced overall water splitting. Finally, the solar water splitting properties of the TD‐Cu2ZnSnS4‐BiVO4 integrated tandem cell in pure natural seawater are demonstrated, and a champion STH efficiency of 2.46% is presented, while a large area (25 cm2) TD‐Cu2ZnSnS4‐BiVO4 integrated tandem device with superior long‐term stability is investigated for 1 week, which provides new insight into photoelectrochemical solar water splitting devices.