Iodide Expulsion at Photoirradiated Mixed Halide Perovskite Interface

Abstract

Visible light irradiation of a mixed halide perovskite (with bromide and iodide in the X-site) in contact with a solvent like dichloromethane (DCM) leads to selective expulsion of iodide from the film. This causes a concurrent blue-shift in band edge. We find that addition of Cs to A-site reduces the mobility of iodide ions under photoirradiation. In the absence of a solvent, these mixed halide perovskites undergo phase segregation, the rate of which decreases with the addition of Cs. Interestingly, the iodide expulsion rate in DCM is strongly dependent on the rate of photoinduced segregation. At Cs atomic concentrations greater than 50%, the films become stable as the iodide expulsion is largely suppressed. The role of the A-site cation in dictating the mobility of halide ions will be discussed in the talk.