First-principles study of double perovskites Cs2Sn(Br1−xIx)6 for the design of high-efficiency thin-film photovoltaics

Abstract

This paper studied how the chemical content of halogen atom impacts the structural, electrical, optical and photovoltaic characteristics of double perovskite Cs2Sn(Br1−xIx)6. When the iodide (I) content of x was increased, the lattice constant went up with a slight deviation from Vegard's linear law. Upon enhancing I concentration, the energy bandgap (Eg) fades. In fact, by rising the I content x from 0.00 to 1.00 in 0.25 increments, the Eg obtained values using the Perdew-Burke-Ernzerhof Generalized-Gradient Approximation (PBE-GGA) functional decrease from 1.413 to 0.210 eV, and those determined using the modified Becke Johnson generalized gradient approximation (mBJ-GGA) decrease from 2.497 to 0.934 eV. Calculated dielectric functions, refractive index, and absorption coefficient show a red shift at higher I content. Spectroscopic limited maximum efficiency (SLME) is 33.015%, which corresponds to the I content x = 0.557, closely approaching the Shockley-Queisser limit (33.16%).