How chloride suppresses photoinduced phase segregation in mixed halide perovskites

Halide ion mobility in metal halide perovskites plays an important role in dictating the overall device performance and long-term stability of perovskite solar cells. Alloying with chloride (Cl), which is known to stabilize the perovskite solar cells, has now been found to suppress the photoinduced halide ion segregation in mixed halide (Br/I) perovskites. By varying the chloride concentration of 1–10% (as part of the halide composition), we have probed both photoinduced segregation and dark recovery kinetics at different temperatures. When we increased the concentration of Cl from 0 to 5%, we observed a decrease in the rate constant of segregation by a factor of ∼5 and a decrease in the fraction of halide segregation from 45 to 20%. The activation energy for photoinduced halide segregation increases (∼4 kJ/mol) upon the introduction of chloride into the mixed halide film, reflecting an increased energetic barrier for halide ion migration.