Lead-Free Semiconductors with High Absorption: Insight into the Optical Properties of K2GeSnBr6 and K2GeSnI6 Halide Double Perovskites

Structural, electronic and optical properties for halide double perovskites compounds K2GeSnBr6 and K2GeSnI6 are studied in this work. Based on the (FP-LAPW) method, the previous properties are treated within the (GGA-PBE) and the (mBJ-GGA) approximations. The results show that these compounds are stable in the non-magnetic phase (NM). Electronic properties indicate that these compounds have a semiconductor behavior with a direct band gap. The calculated formation energy and cohesive energy indicate that these alloys have good chemical stability. High absorption coefficient and high reflectivity prove that these materials are appropriates for optoelectronic applications, including solar and photovoltaic cells.