First-principles comparative study of perfect and defective CsPbX3 (X = Br, I) crystals

Abstract

First principles Density Functional Theory (DFT) hybrid functional PBESOL0 calculations of the atomic and electronic structure of perfect CsPbI₃, CsPbBr₃ and CsPbCl₃ crystals, as well as defective CsPbI₃ and CsPbBr₃ crystals are performed and discussed. For the perfect structure, decomposition energy into binary compounds (CsX and PbX₂) is calculated, and a stability trend of the form CsPbBr₃ > CsPbI₃ > CsPbCl₃ is found. In addition, calculations of the temperature-dependent heat capacity are performed and shown to be in good agreement with experimental data. As far as the defect structure is considered, it is shown that interstitial halide atoms in CsPbBr₃ do not tend to form di-halide dumbbells Br₂⁻ while such dimers are energetically favoured in CsPbI₃, analogous to the well-known H-centers in alkali halides. In the case of CsPbBr₃, a loose trimer configuration (Br₃²⁻) seems to be energetically preferred. The effects of crystalline symmetry and covalency are discussed, alongside the role of defects in recombination processes.