Thermodynamic Studies of Bromide Incorporation into Cesium Lead Iodide (CsPbI₃)

Cesium lead iodide bromide (CsPbI₂Br) has attracted significant research attention as one of emerging inorganic halide perovskite materials for photovoltaic applications. However, thermodynamic properties that govern its intrinsic stability remain unclear. Using room temperature solution calorimetry in DMSO and differential scanning calorimetry, we herein report the formation enthalpy of orthorhombic CsPbI₂Br. We confirm that milder conditions, especially lower temperature, are needed for perovskite phase stabilization in CsPbI₂Br. The formation of solid CsPbI₂Br from CsPbI₃ and CsPbBr₃ is enthalpically neutral but is favored by entropy since the anions are probably randomly mixed, thus making the Gibbs free energy of mixing negative. This study sheds light on phase stabilization, materials stability, and anion mixing within halide perovskites and related systems.