Effect of Light Illumination on Mixed Halide Lead Perovskites: Reversible or Irreversible Transformation

One intriguing aspect of mixed halide lead perovskites (e.g., CH3NH3PbBrxI3–x) is halide ion segregation when subjected to visible illumination, but this aspect gives rise to the concerns regarding the influence of halide ion movement on the long–term stability and applications. Here, the impact of light illumination on mixed halide hybrid perovskite films was investigated by exposing such films to continuous wavelength laser (25 mW/cm2). It turns out that under illumination the segregated iodide-rich perovskite species further decompose and ultimately form metallic lead (Pb0). The chemical changes in decomposed films were found to cause an irreversible shift of the absorption band edge and a significant change in film morphology, while no decomposition of MAPbI3 and MAPbBr3 films was observed after exposure to the same illumination condition. Our results unambiguously demonstrate the deleterious effect of phase segregation on material stability for mixed halide perovskites.