First-principles investigations on the structural, optoelectronic, mechanical and transport properties of new stable lead-free double perovskites Cs2BB′I6 (B = Ag/Rb, B′ = Bi/Ga) halides

Abstract

Lead-free perovskite halides offer a promising alternative due to the successful replacement of lead-based perovskites in various applications. Density functional theory simulations have been utilized to ascertain the physical attributes of lead-free Cs2BB′I6 (B = Ag/Rb, B′=Bi/Ga) double perovskites in this work. The well-organized modified Becke-Johnson (mBJ) is employed to define exchange–correlation potential. The calculated negative formation energy values, structural optimization, along with evaluation of the tolerance factor support the stability of compounds. To judge the structural stability, several mechanical parameters are determined. For Cs2AgBiI6, a bandgap of 1.46 eV and 1.85 eV for Cs2RbGaI6 are achieved. The total and individual electronic states’ influence is also calculated. The optical absorption is prominent in the visible and UV regions for both perovskites depicting their potential use in optoelectronics. We also have an insight into the temperature-dependent transport characteristics of Cs2AgBiI6 and Cs2RbGaI6. The crucial ZT factor exhibits values of 0.78 and 0.75 for Cs2AgBiI6 and Cs2RbGaI6 at 800 K. The high Seebeck, ZT and electrical conductivity values also stand in the favor of their potential use in green technology.