Enthalpy of formation of CsSn(Cl_x(Br,I)_1-x)₃ and CsPb(Cl_x(Br,I)_1-x)₃

Abstract

Organic-inorganic hybrid halide perovskites, e.g., MAPbI3, have revolutionized the field of solution-processable photovoltaic applications. However, due to organic cation, they are found to be unstable under external environment such as moisture and high temperature. Moreover, the toxicity of lead (Pb) in their structure is harmful for human health and hurdle for commercialization. These inspire us to pursue for families of perovskites structure with the formula CsSn(Clx(Br,I)1-x)3 with x = 1/3, 2/3, 1, which are nontoxic and could have better structural stability under ambient conditions. We have investigated the enthalpy of formation of CsSn(Clx(Br,I)1-x )3 and in based on the density functional theory (DFT) with the generalized gradient approximation (GGA). The main objective is to seek for structural stability with respect to the composition x's. We found that the structural stability increases linearly with composition x's of halide atom from I to Br to Cl. We also calculate enthalpy of formation of CsPb(Cix(Br,I)1-x)3 perovskites for comparative purpose, and found that the structural stability of CsSn(Clx(Br,I)1-x)3 is slightly lower than its Pb-counterpart. Thus CsSn(Clx(Br,I)1-x)3 is still the promise candidate for photovoltaics. These studies could serve as a guidance to compromise the stability, by varying composition of halide atoms, with the optimal band gap or other solar-cell-desired properties.