Partial Phase Remixing of Segregated Mixed Halide Perovskite Nanocrystals Induced by an Instant Change in an External Electric Field

The bandgap energy of semiconductor lead mixed halide perovskite can be flexibly tuned by changing the bromide to iodide ratio, which is beneficial for the fabrication of tandem solar cells to efficiently capture light power across the visible spectral range. Unfortunately, the phase segregation effect would be induced in mixed halide perovskite upon continuous light illumination, with the bandgap energy deviating from the desired value due to unexpected formations of bromide- and iodide-rich domains. Here we have induced phase segregation in a solid film of mixed halide perovskite CsPbBr 1.2 I 1.8 nanocrystals (NCs) by laser excitation and demonstrated that the original mixed phase can be partially recovered right after the application or removal of an external electric field. We propose that the iodide ions created after phase segregation can be instantly enriched at the opposite direction of the external electric field, thus enhancing the entropic driving force for them to reoccupy the internal vacancies of some segregated CsPbBr 1.2 I 1.8 NCs. This electric-field-induced partial phase remixing can also be applied to segregated CsPbBr 1.5 I 1.5 and CsPbBr 1.2 I 1.8 NCs, signifying the universal role played by the spatial distribution of iodide ions in the deep understanding and effective control of phase segregation in mixed halide perovskite NCs.