Optical Properties of Mixed-Halide Double Perovskites Cs2AgBi(Br1-xIx)6: First-Principle Study

Lead-free halide double perovskite Cs2AgBiBr6 is a nontoxic promising material for optoelectronic applications. However, halide mixing in Cs2AgBiBr6 is expected to be a valuable process that may result in favorable optical properties. Here, we studied the optical properties along with band structures of mixed halide Cs2AgBi(Br1-xIx)6 for different iodine (I) concentrations using density functional theory (DFT). The indirect bandgap is confirmed from the energy band structures having nonlinearly decreasing energy gaps with the increment of I-content. The I-content-dependent different optical properties like refractive index, absorption coefficient, extinction coefficient, reflectivity, optical conductivity, and energy loss are studied. Two absorption windows in the visible and ultraviolet regions are noticed having a redshift in the absorption spectra with increasing I-content. The peak absorption is recorded to be in the order of 10⁵ cm^-1 to 10⁶ cm^-1 having I-content dependence. Other optical properties also show promising characteristics both in the visible and ultraviolet regions demonstrating its potential applications in next-generation optoelectronic devices.