Prolonged Phase Segregation of Mixed-Halide Perovskite Nanocrystals in the Dark

TL;DR

This study reveals that mixed-halide perovskite nanocrystals undergo prolonged phase segregation in the dark, driven by local electric fields from trapped charges, which challenges the understanding of their stability.

Contribution

It demonstrates that phase segregation in mixed-halide perovskite nanocrystals can continue in the dark for minutes, driven by surface charge trapping, a process previously underexplored.

Findings

Prolonged phase segregation occurs in the dark for several minutes.

Local electric fields from trapped charges sustain phase segregation.

Dark remixing of phases is delayed due to slow charge dissipation.

Abstract

A critical issue hindering the potential applications of semiconductor mixed-halide perovskites is the phase segregation effect, wherein localized regions enriched with one type of halide anions would be formed upon continuous photogeneration of the excited-state charge carriers. These unexpected phases are capable of remixing again in the dark under the entropic driving force, the process of which are now being exclusively studied after mixed-halide perovskites have arrived at the final stage of complete phase segregation. Here we show that after the removal of laser excitation from a solid film of mixed-halide perovskite nanocrystals with partial phase segregation, the iodide- and bromide-rich regions can continuously grow in the dark for a prolonged time period of several minutes. We propose that this dark phase segregation is sustained by the local electric fields associated with the surface-trapped charge carriers, whose slow dissipation out of mixed-halide perovskite nanocrystals causes a delayed occurrence of the reversal phase remixing process.