Toward mixed-halide perovskites: Insight into photo-induced anion phase segregation

Tunable bandgap of the mixed-halide perovskites (MHPs) has made them very appropriate for the high-performance single-junction photovoltaics (PVs), as well as wide-bandgap components for multi-junction (tandem) structures. Whereas, the composition engineering of halide ions, an effective procedure to adjust MHPs’ bandgap for PVs, results in an irksome photoinstability for MHPs due to the photo-induced anion phase segregation (PIAPS) effect. Namely, the MHPs materials experience an inevitable phase transition from the homogeneous alloys to the conjugated lower/higher-bandgap phases, that is, iodide/bromide (I/Br) -rich domains, once exposed to light. Reasonably, the sub-bandgap trapping states could lead to the film inhomogeneity and performance deterioration of PVs. Meanwhile, it has been widely convinced that the PIAPS phenomenon, even reversible, may limit the commercial integration of MHPs into tandem applications because of their unstable output. Hence, in this review, we first study, analysis, and explore the “fashionable” PIAPS phenomenon systematically. Then, the feasible protocols to stabilize MHPs materials, especially for their inner mechanism correlation, are adequately exhibited to help researchers find out more suitable procedures. At last, we also provide some potential research points to study PIAPS phenomenon and stabilize MHPs for their future commercial applications.