Author Description

Perovskites are a class of materials that find tremendous applications in various areas, one of them being photovoltaics. As the power conversion efficiency of perovskite based solar cells surged in the past decades, a pressing issue that concerns both the solid state chemistry and materials communities is whether perovskite materials having desirable functional properties possess stabilities necessary for the proposed applications. Thermodynamic studies of perovskite materials play a pivotal role in understanding their structures, properties, and proposed applications, evaluating thermodynamic stability and material compatibility, predicting possible material behavior, and providing guidance for developing new materials for better performance in applications. The aim of my Ph.D. research, is to use a combination of calorimetry and other methods to study the thermodynamics of three dimensional cesium lead halide (CsPbX3, X = I, Br and Cl), and two dimensional Ruddlesden-Popper and Dion-Jacobson perovskites, and to investigate structure-property correlations within these materials. Chapter 1 is a brief introduction that delineates general concepts of perovskites and the motivation that drives my research endeavors. Chapter 2 studies the energetics, structures and phase transitions of two cesium lead iodide (CsPbI3) polymorphs, orthorhombic ([delta]) and cubic ([alpha]) CsPbI3. Both polymorphs are stable with regard to their binary iodides, CsI and PbI2. The metastability of cubic ([alpha]) CsPbI3 with respect to orthorhombic ([delta]) CsPbI3, under ambient conditions, is confirmed, indicating that the solar active cubic ([alpha]) CsPbI3 phase may encounter problems for long term applications. Chapter 3 presents the thermodynamic and structural effects of bromide incorporation into cesium lead iodide (CsPbI3). Such incorporation leads to milder conditions for perovskite phase stabilization. The formation of solid CsPbI2Br from CsPbI3 and CsPbBr3 is energetically neutr