Abstract
Two-dimensional (2D) halide perovskites have drawn attention for their unique optoelectronic properties. Interestingly, Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium and Dion-Jacobson 2D mixed-halide perovskite films with 1,4-phenylenedimethanammonium undergo halide segregation under irradiation. Anions become mobile under steady state irradiation to form I-rich and Br-rich domains. Upon ceasing illumination, film reverts to their original, mixed-halide compositions, establishing the reversibility of the phase segregation phenomenon. However, if films are in contact with dichloromethane, light irradiation causes the sequential expulsion of iodide and bromide and introduces irreversible changes to 2D films. The sequential disappearance of I- and Br- from pristine films (BA2Pb2Br4, and BA2Pb2I4) under photoirradiation, as observed from variances in expulsion rates, reflect differences in halide ion mobilities in these films. The impact of anion migration, leading to I- and Br- expulsion into solvents, within the context of 2D perovskite photostability will be discussed.
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