Thermodynamic modeling and electronic properties of CsPb1−xSnxI3 as a polymorphic alloy

Abstract

We performed first-principles calculations combined with a statistical approach based on the generalized quasichemical approximation (GQCA) to study the polymorphic features of CsPb1−xSnxI3 alloy. Our analysis explored the impact of these polymorphic features on electronic properties, statistical attributes, and thermodynamic stability. Our findings indicate that a0a0a0 (Pm3¯m) polymorph makes only a minor contribution to alloy, while a−a+a− pattern has the highest probabilities at room temperature. Encompassing multiple polymorphic degrees within the same generalized ensemble, we found an increase in composition range where phase segregation becomes thermodynamically favored, albeit with a relatively low critical temperature (28.8 K). Despite this, our GQCA-PCE results obtained from the Spectroscopic Limited Maximum Efficiency (SLME) model reveal that the efficiency of alloy-based solar cells could be a little smaller than that of CsSnI3 pure metal halide perovskite (MHP), in range 26.6 % → 30.7 % for CsPbI3 → CsSnI3 at 300 K, which would be compensated by the presence of Pb reducing the tendency of Sn-based MHPs to oxidize in air, favoring the fabrication of photovoltaic devices with enhanced long-term stability.