An intriguing aspect that influences the solar cell performance is the mobility of halide ions within the perovskite film. Whereas entropy of mixing explains the thermally activated mixing of halide ions to yield mixed halide perovskite, an opposite trend is observed when the mixed halide film is subjected to photoirradiation. This process commonly referred to as <i>photoinduced phase segregation</i> or <i>halide segregation, </i>yields Br-rich and I-rich perovskite domains. As the mixed halide perovskite phase segregates, the I-rich domains act as recombination sites for the photogenerated charge carriers. The formation of these recombination sites has been shown to limit the performance of halide perovskite-based solar cells. The interesting aspect of halide segregation is its reversibility. We see a total recovery when the film is left in the dark as thermal activation drives the segregated domains back to the original homogenized composition. The obvious question is how photoexcitation overcomes entropy of mixing and serve as the driving force for photosegregation. In order to obtain insight into these two processes we have now undertaken temperature-dependent studies of segregation and dark recovery kinetics. The kinetic and thermodynamic arguments that explain the photoinduced halide segregation and dark recovery in methyl ammonium lead halide perovskite films will be discussed.

Understanding halide ion mobility in mixed halide perovskites: How photoexcitation overcomes entropy of mixing

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.