Ionization Energy as a Stability Criterion for Halide Perovskites

Instability of hybrid organic–inorganic halide perovskites hinders their development for photovoltaic applications. First-principles 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 the intrinsic 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 an organic molecule and an inorganic complex ion as an additional criterion for predicting chemical trends in stability of hybrid halide perovskites. The ionization energy equal to or less than that for cesium and the size comparable to that of methylammonium define the design space for cations A + in the search for new perovskite structures APbI3 with improved chemical stability that are suitable for photovoltaic applications.