Direct calorimetric verification of thermodynamic instability of lead halide hybrid perovskites

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 113; no. 28; pp. 7717 - 7721
• Main Authors: Nagabhushana, G. P., Shivaramaiah, Radha, Navrotsky, Alexandra
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 12.07.2016; Proceedings of the National Academy of Sciences
• Subjects: Energy efficiency; enthalpy of formation; hybrid halide perovskites; MATERIALS SCIENCE; Measurement; Perovskite; Physical Sciences; solar cells; thermodynamic instability; Thermodynamics; tolerance factor; enthalpy of formation; solar cells; tolerance factor; thermodynamic instability; hybrid halide perovskites
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1607850113

Hybrid perovskites, especially methylammonium lead iodide (MAPbI₃), exhibit excellent solar power conversion efficiencies. However, their application is plagued by poor chemical and structural stability. Using direct calorimetric measurement of heats of formation, MAPbI₃ is shown to be thermodynamically unstable with respect to decomposition to lead iodide and methylammonium iodide, even in the absence of ambient air or light or heat-induced defects, thus limiting its long-term use in devices. The formation enthalpy from binary halide components becomes less favorable in the order MAPbCl₃, MAPbBr₃, MAPbI₃, with only the chloride having a negative heat of formation. Optimizing the geometric match of constituents as measured by the Goldschmidt tolerance factor provides a potentially quantifiable thermodynamic guide for seeking chemical substitutions to enhance stability.