Mixed-Halide Perovskite Alloys CsPb(I<sub>1–<i>x</i></sub>Br<sub><i>x</i></sub>)<sub>3</sub> and CsPb(Br<sub>1–<i>x</i></sub>Cl<sub><i>x</i></sub>)<sub>3</sub>: New Insight of Configurational Entropy Effect from First-Principles and Phase Diagrams
Fang Pan, Junni Zhai, Jinyu Chen, Lin Yang, Hua Dong, Fang Yuan, Zhuangde Jiang, Wei Ren, Zuo‐Guang Ye, Guoxu Zhang, Jingrui Li
Abstract
Stability is one of the key issues in mixed-halide perovskite alloys that are promising in emergent optoelectronics. Previous density functional theory (DFT) and machine learning studies indicate that the formation-energy convex hulls of these materials are very shallow, and stable alloy compositions are rare. In this work, we revisit this problem using DFT, with a special focus on the effects of configurational and vibrational entropies. Allowed by the 20-atomic models for the C s P b ( I 1 − x B r x ) 3 and C s P b ( B r 1 − x C l x ) 3 series, the partition functions and therewith thermodynamic state functions are calculated by traversing all possible mixed-halide configurations. We can thus evaluate the temperature- and system-dependent configurational entropy, which largely corrects the conventional approach based on the ideal solution model. Finally, temperature–composition phase diagrams that include α, β, γ, and δ phases of both alloys are constructed based on the free energy data, for which the contribution of phonon vibrations is included.