Halide perovskites received significant attention in the photovoltaic community owing to its higher power conversion efficiency, high absorption coefficient, and bandgap tunability. However, their stability in aqueous medium is poor making them unsuitable to employ for direct water splitting. Various protective layers coupled with halide perovskite were utilized to prevent the exposure of the absorber to aqueous medium. However, these protective layers are susceptible to failure with prolonged operation. So, employing a water stable absorber material is found to be the key for successful photoelectrochemical (PEC) water splitting.
Vacancy ordered double perovskites with the formula A2BX6 are a promising alternative to conventional ABX3 perovskites due to excellent stability, comparable absorption coefficient and bandgap tunability. This class of materials have their alternate octahedra being vacant enabling a wider range of B-site elements due to rotational freedom. Here, we have reported the most stable vacancy ordered halide perovskite Cs2PtX6 (X= I, Br, Cl) which showed extraordinary stability in air and even in extreme acidic and basic mediums. Furthermore, these materials exhibit absorption properties that encompass a substantial portion of visible light. These materials were successfully employed as photoanode for PEC water oxidation which displayed good photocurrent density at 1.23 V vs. RHE and long-term operational stability