Origin of Pressure-Induced Structural Instability in CsPbX$_3$ Photovoltaic Perovskites

TL;DR

This study investigates the atomic-level origins of pressure-induced structural instability in CsPbBr3 perovskites, revealing how pressure affects free energy and bond dynamics, and suggests strategies for enhancing stability through compositional tuning.

Contribution

It provides a detailed atomic and thermodynamic analysis of pressure-induced phase transition mechanisms in halide perovskites, highlighting the role of volume and entropy in stability.

Findings

Pressure causes a first-order phase transition at 1.3 GPa in CsPbBr3.

Pressure influences Gibbs free energy mainly through the pressure-volume term.

Doping strategies can promote continuous structural changes and improve mechanical resilience.

Abstract

Under external stimuli, lead halide perovskites exhibit large atomic fluctuations, impacting optical and electron transport properties that affect device performance in operational settings. However, a thorough understanding of the atomic basis for the underlying structural instability is still absent. Focusing on the model material CsPbBr$_3$, the inherent lattice softness of halide perovskites is elucidated at the atomic level through in-situ single-crystal X-ray diffraction measurements under pressure complemented by atomic level simulations. We identify and explore the nature of the first-order phase transition to a distorted P21/c phase at 1.3 GPa, induced by the sudden Cs-Br bonds breaking. Unlike classical transition metal oxide perovskites, where the internal energy term dominates, we show explicitly that pressure primarily influences the Gibbs free energy for halide perovskites through the pressure-volume term. As such, strategically mitigating bond strains from volume shrinkage is the key to suppressing the first-order behavior for maintaining the coordinates of PbX$_6$ polyhedral upon external perturbation. Our thermodynamic calculation reveals the demand for high entropy in the -T*del-S term, which can be achieved by exploring a broader spectrum of doped A site and B sites in ABX$_3$ systems, enabling continuous structural changes that facilitate recovery from mechanical damage in practical applications.