Unassisted CsPbBr₃‐Cu₂O Tandem Devices for Solar‐Driven Overall Water Splitting

Abstract Generating sufficient photovoltage for solar‐driven overall water splitting is challenging for a single photoelectrode. Herein, a face‐to‐face type unbiased tandem solar overall water splitting device based on CsPbBr 3 ‐Cu 2 O dual‐photoelectrodes is reported. To realize the face‐to‐face configuration, the semitransparent CsPbBr 3 photoanode has been firstly prepared by integrating a transparent Ni‐based multifunctional layer on a perovskite light‐absorbing device, which achieves a low oxygen evolution reaction onset potential ( E on ) of 0.14 V versus RHE. Subsequently, the hydrogen evolution reaction (HER) E on and fill factor of the Cu 2 O photocathode have been improved by constructing buried heterojunctions, which positively shifts it's HER E on to 0.91 V versus RHE. The tandem device achieves a solar‐to‐hydrogen efficiency of 5.42%, a result of the matched E on between the semitransparent CsPbBr 3 photoanode and the Cu 2 O photocathode. This face‐to‐face tandem structure maximizes the utilization of solar energy and provides a viable strategy for the future development of solar water splitting systems based on perovskite‐based photoelectrodes.