Enhanced stability of two-dimensional halide perovskites under an electric field for photocatalytic HI splitting

Halide perovskites (HPs) have been considered next-generation solar energy conversion materials since they have outstanding properties such as a long carrier lifetime and high light absorption coefficient. Nevertheless, the stability against humidity is a major obstacle to the application of HPs for solar energy conversion devices, for example, photocatalysts for HI splitting operating in an aqueous solution. Two-dimensional halide perovskites (2D HPs) have been suggested to overcome the vulnerable properties to humidity, in which large organic cations (i.e., spacer) bonded at their surface delay the penetration of H2O into the octahedron layer of 2D HPs. However, they still lack thermodynamic stability against humidity. In this work, we show by first-principles calculation that an external electric field causes a 2D HP stable to humidity in both thermodynamic and kinetic aspects since the energy of surface-adsorbed H2O is significantly lowered relative to intercalated H2O in addition to the progressive increase of the migration energy barrier of H2O with the external electric field. Further, the calculated band edge positions become suitable for photocatalytic HI splitting under the electric field. We suggest that 2D HPs exposed to an electric field are promising photocatalysts for HI splitting with humidity resistance as well as appropriate band edge position.