Lead halide perovskites (CH3NH3PbX3 and CsPbX3 exhibit halide ion composition dependent photochemistry and enable bandgap tuning for selective visible light response. By varying the ratio of Br:I ratio in the mixed halide perovskite (CH3NH3PbBrxI3−x ), it is possible to tune the bandgap between 1.55 -2.43 eV. When subjected to visible light irradiation such mixed halide perovskites exhibit migration of halide ions to create iodide-rich and bromide-rich regions. This intriguing aspect of halide ion movement in mixed halide films is now probed through emission and transient absorption spectroscopy. The spectroscopy measurements have allowed us to establish the time scale with which such segregation occurs under laser (405 nm, 25 mW/cm2-1.7 W/cm2) irradiation as well as dark recovery. While the phase segregation occurs with a rate constant of 0.1-0.3 s-1, the recovery occurs over a time period of several minutes-hour. The kinetics of the photoinduced segregation and dark recovery becomes slower in halide deficient films suggesting the involvement of halide defects in the phase segregation. Implications of such phase segregation in solar cell performance will be discussed.

Halide ion exchange and migration in mixed halide lead perovskites

254th National Meeting (2017)

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