Mixed halide lead perovskites (CH3NH3PbBrxI3-x and Cs PbBrxI3-x ) have been the focus of recent photovoltaic research because of their ability to tune the bandgap through halide composition. They offer interesting opportunity to develop single junction and multijunction tandem solar cells. The ease of halide ion mobility across different perovskite layers poses a challeng to design a tandem structure of perovskite layers of different compositions. In order to keep the lead halide perovskite nanocrystals intact without undergoing exchange of halide ions and retain the original band structure one needs to suppress the halide ion migration across the nanocrystals. One strategy to overcome this problem involves introduction of a barrier with PbSO4. For example, in the case of CsPbBr3 and CsPbI3 nanocrystals we can introduce a capping with PbSO4-Oleate and suppress halide ion exchange between the two. The temperature and light effects exhibit unusual behavior of halide ion mobility. Whereas at higher temperature (80-120 °C) gradient films homogenize, they undergo phase segregation in light. Fundamental understanding of these processes can enable strategies to employ these mixed halide perovskites.

Intricacies of halide ion mobility in metal halide perovskites

2019 Fall National Meeting

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