Thermodynamics of cesium lead halide (CsPbX₃, x= I, Br, Cl) perovskites

Inorganic cesium lead halide (CsPbX₃, X = I, Br, Cl) perovskites have sparked broad interest for photovoltaic applications, which, however, may be plagued by chemical and thermodynamic instabilities. This work reports calorimetric studies on the formation enthalpies of CsPbX₃ perovskites, confirming decreasing thermodynamic stability in the order CsPbCl₃, CsPbBr₃ and CsPbI₃. Cesium lead iodide (CsPbI₃), one of the most studied inorganic lead halide perovskites, is shown to be only barely stable from a thermodynamic perspective. This order of increasing instability is consistent with the variation of Goldschmidt tolerance factor. The perovskites are high temperature entropy-stabilized phases with respect to low temperature polymorphs, with the thermodynamics of phase transitions reflecting the above thermodynamic trends.