title: Thermodynamic Origin of Photoinstability in the CH3NH3Pb(I1-xBrx)3 Hybrid Halide Perovskite Alloy.
abstract: The formation of solid-solutions of iodide, bromide, and chloride provides the means to control the structure, band gap, and stability of hybrid halide perovskite semiconductors for photovoltaic applications. We report a computational investigation of the CH3NH3PbI3/CH3NH3PbBr3 alloy from density functional theory with a thermodynamic analysis performed within the generalized quasi-chemical approximation. We construct the phase diagram and identify a large miscibility gap, with a critical temperature of 343 K. The observed photoinstability in some mixed-halide solar cells is explained by the thermodynamics of alloy formation, where an initially homogeneous solution is subject to spinodal decomposition with I and Br-rich phases, which is further complicated by a wide metastable region defined by the binodal line.
authors.affiliation: Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, United Kingdom.
authors.forename: Federico
authors.initials: F
authors.lastname: Brivio
authors.affiliation: Universidade Federal da Fronteira Sul , Realeza Paraná 85770-000, Brazil.
authors.forename: Clovis
authors.initials: C
authors.lastname: Caetano
authors.affiliation: Centre for Sustainable Chemical Technologies and Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, United Kingdom.|Global E3 Institute and Department of Materials Science and Engineering, Yonsei University , Seoul 120-749, Korea.
authors.forename: Aron
authors.initials: A
authors.lastname: Walsh