In-depth understanding the temperature-dependent reversible phase transition in CsPbI3−xBrx perovskites and its associated photophysical properties

Abstract

Although all-inorganic CsPbI_3−xBr_x (0 ≤ x ≤ 3) perovskites largely display potential for photoelectric applications, an in-depth understanding of the origin of the phase transition and its associated photophysical properties is still lacking. Herein, we develop an in situ characterization technique that allows us to synchronously observe the crystallographic microstructure information in reciprocal space and the temperature-dependent phase transition process (α → β → γ → δ) on an atomic scale. A temperature–composition phase diagram for CsPbI_3−xBr_x perovskite is elaborately established with a curve T = −72.2x + 322.3 (0 ≤ x ≤ 2.5). Likewise, the phase-transition-associated octahedral tilting in CsPbI_3−xBr_x is theoretically proved to be closely related to the strong noncovalent interaction between two adjacent halide Br/I atoms in CsPbI_3−xBr_x perovskites through density functional theory (DFT) calculations. While the temperature-dependent phase transition occurs, we find that the diversification of carrier mobility and L_D (carrier diffusion length) are significantly influenced by both the carrier–phonon coupling and the efficient transport of excitons. This study has its roots in a completely new crystallographic domain that could further advance our knowledge of perovskite phase transition and thereby provide an innovative foundation for closely related applications, including solar cells and other optoelectronic devices.