Study on the stability of organic–inorganic perovskite solar cell materials based on first principle

Abstract

ABSTRACTIn order to better understand and elucidate the structural stability of perovskite materials, the lattice parameters and tolerance factors of three crystal structures of perovskite materials are calculated based on the first principle of density functional theory. We find that the perovskite crystal structures are relatively stable and is consistent with the experimental facts as the tolerance factor 0.81 < T < 1.11. The elastic modulus of three crystal structures of MAPbI3, FAPbI3 and the elastic modulus of FA0.75Cs0.25Sn0.5PB0.5I3 are studied. By Voigt-Reuss-Hill approximation, the elastic properties such as bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are obtained. From the elastic modulus Cij, we can find that the other six kinds of crystal structures are relatively stable except for the orthogonal structure of MAPbI3 (c). The ductility and brittle toughness of the material are also discussed by B/G and Poisson’s ratio. It is found that MAPbI3 (a) is the hardest and FAPBI3 (a) the weakest. Form the three-dimensional surface view of Young's modulus it is found that their dependence in three-dimensional direction is spherical for an isotropic system. The degree of deviation of the Young's modulus sphere reflects the anisotropy of crystal structures. The degree of elastic anisotropy of organic–inorganic perovskite materials follows the order of FAPbI3(c) > MAPbI3(a) > FA0.75 Cs0.25 Sn0.5Pb0.5I3 > FAPbI3(a) > MAPbI3(b) > MAPbI3(c) >FAPbI3(b). Furthermore, by the adsorption energies and density of states (DOS) of these seven crystals for water molecules, the reasons why perovskite materials are easily denatured in high humidity environment were explored. The results show that perovskite materials are easy to denaturate in high humidity environment.