Ionization energy as a stability criterion for halide perovskites

Instability of hybrid organic-inorganic halide perovskites hinders their development for photovoltaic applications. First-principle calculations are used for evaluation of a decomposition reaction enthalpy of hybrid halide perovskites, which is linked to experimentally observed degradation of device characteristics. However, simple criteria for predicting stability of halide perovskites are lacking since Goldschmidt's tolerance and octahedral geometrical factors do not fully capture formability of those perovskites. In this paper, we extend the Born-Haber cycle to partition the reaction enthalpy of various perovskite structures into lattice, ionization, and molecularization energy components. The analysis of various contributions to the reaction enthalpy points to an ionization energy of a molecule and a cage as an additional criterion for predicting chemical trends in stability of hybrid halide perovskites. Prospects of finding new perovskite structures with improved chemical stability aimed for photovoltaic applications are discussed.