Efficient and Stable Perovskite‐Based Photocathode for Photoelectrochemical Hydrogen Production

Abstract Although organometal halide perovskites (OHPs) have desirable photovoltaic properties, their photoelectrochemical (PEC) water‐splitting application for hydrogen production is limited by the instability originating from their intrinsic ionic defects and hygroscopic vulnerability. Herein, a highly efficient and stable OHP‐based photocathode achieved by a new zwitterion (L‐proline) passivation and a eutectic gallium indium alloy (EGaIn) encapsulation method is described. The zwitterion, which has both cations and anions, can simultaneously passivate both positively and negatively charged defects in OHPs. The resulting OHP photovoltaic cells with passivated shows an over 20% power conversion efficiency with an open‐circuit voltage of 1.13 V and a short‐circuit current of 22.13 mA cm −2 . The EGaIn‐incorporated Ti foil provides complete encapsulation from the external environment while maintaining good transport of photogenerated charges from OHPs. Thus, these photocathodes exhibit a remarkable average photocurrent density of 21.2 mA cm −2 which has less than 5% current loss between PV cells and PEC cells. More admirably, the photocathode has the highest stability over 54 hours under continuous full sunlight illumination in a sulfuric acid electrolyte.