Thermodynamic, optical, and morphological studies of the Cs2AgBiX6 double perovskites (X = Cl, Br, and I): Insights from DFT study

In contrast to Pb-based perovskites, Cs ₂AgBiX ₆ (X = Cl, Br, I) double silver-bismuth perovskites have unveiled a promising future for the advancement of low-risk solar energy due to their high durability and non-toxicity of their constituents. Despite the focus on the optoelectronic properties of Cs ₂AgBiX ₆ double perovskites, research into their structural properties behavior has been limited. So in this paper, we investigated in depth the cubic structure of Cs ₂AgBiX ₆ double perovskites. The newly acquired cubic phase is more in line with current experimental results in optoelectronic characteristics, exhibiting higher optical properties useful for optoelectronic device design. All three halide compounds exhibit an indirect band gap character due to the highly dispersive nature of the valence band maximum and conduction band minimum, resulting in reduced effective mass values, as well as the disordering of the Ag ⁺ and Bi ³⁺ cations in their sublattices. The thermodynamic potentials of phonon modes include enthalpy (H), free energy (F), entropy (S), and heat capacity (C). The optical and thermodynamic properties of pure Cs ₂AgBiCl ₆ and Cs ₂AgBiBr ₆ samples imply that they have promising qualities for optoelectronic and photovoltaic applications.