Reversible Photo-Induced Phase Segregation and Origin of Long Carrier Lifetime in Mixed-Halide Perovskite Films

TL;DR

This study investigates reversible photo-induced phase segregation in mixed-halide perovskite films, revealing how halide ion migration affects optoelectronic properties and carrier lifetime, with implications for photovoltaic device stability.

Contribution

It uncovers the mechanism of photo-induced phase segregation and its reversibility, highlighting the role of exciton-phonon coupling and ion migration in mixed-halide perovskites.

Findings

Photo-excitation causes reversible phase segregation in perovskite films.

Charge carrier lifetime increases due to trapping in iodide-rich domains.

Phase segregation rate follows a power law with excitation power density.

Abstract

Mixed-halide based hybrid perovskite semiconductors have attracted tremendous attention as a promising candidate for high efficient photovoltaic and light-emitting devices. However, these advanced perovskite materials may undergo phase segregation under light illumination due to halide ion migration, affecting their optoelectronic properties. Here, we report photo-excitation induced phase segregation in triple-cation mixed-halide perovskite films that yields to red-shift in photoluminescence response. We demonstrate that photo-excitation induced halide ion migration leads to the formation of smaller-bandgap iodide-rich and larger-bandgap bromide-rich domains in the perovskite film, where the phase segregation rate is found to follow the excitation power-density as a power law. Results confirm that charge carrier lifetime increases with redshift in photoluminescence due to the trapping of photo-excited carriers in the segregated smaller-bandgap iodide-rich domains. Interestingly, we found that these photo-induced changes are fully reversible and thermally activated when the excitation power is turned off. A significant difference in activation energies for halide ion migration is observed during phase segregation and recovery process under darkness. Additionally, we have investigated the emission linewidth broadening as a function of temperature which is governed by the exciton-optical phonon coupling. The mechanism of photo-induced phase segregation is interpreted based on excitonphonon coupling strength in both mixed and demixed (segregated) states of perovskite film.