First-Principle Study on Structural and Crystal Orientation-Dependent Electronic Properties of Cs₂InAg(C1₁₋ₓBrχ)₆ Mixed Halide

Lead-free perovskites have garnered significant attention in recent years owing to their notable chemical stability and the absence of toxicity. The substitution of the lead element in the perovskite structure adversely affects its overall performance. The double perovskite material does not make any compromises in this regard. Different properties of lead-free double perovskite CS2InAgBr6 were studied experimentally as well as theoretically in previous studies. Here, crystal orientation-dependent structural and electronic properties of CS2InAg(Ch-xBrx)6 are simulated using DFT under halide mixing conditions. The crystal structure and electronic band dispersion profiles are influenced by Br-content (x), leading to a change in the structural property and crystal orientation-dependent band structure which in turn changes electron concentrations and the electron's and hole's effective mass as well. The transformation from a face-centered cubic structure undergoes orthorhombic structures for the Br-contents in the range of x=0.167,0.5, and 0.833, and monoclinic structures for x=0.33 and 0.67. A gradual decrease in the energy bandgap is noted at critical points F, X, K, and L with increasing Br-content which demonstrates that mixed halide perovskites are suitable for tunable wavelength light sources. The crystal orientation-dependent electron- and hole-effective masses facilitate the fabrication of electronic devices with tunable transport properties under halide mixing conditions.