First-Principles Investigation of Na₂CuBiCl₆ as a Promising Material for High-Efficiency Optoelectronic Devices

This research employs first-principles calculations to explore Na₂CuBiCl₆, a double perovskite compound, as a promising material for high-efficiency optoelectronic devices. The structure of Na₂CuBiCl₆ is cubic double perovskite, with Cu⁺ and Bi³⁺ positioned at the B-sites, ensuring stable charge balance and lattice integrity. The Goldschmidt tolerance factor, calculated as 1.008, suggests geometric suitability, and the negative formation enthalpy (ΔH = −0.187 Ry) indicates thermodynamic stability. A Debye temperature of 223.23 K indicates strong lattice dynamics and thermal resilience. An indirect band gap of 1.3 eV is revealed by electronic structure analysis utilising the hybrid Heyd Scuseria Ernzerhof (HSE) functional. This value is consistent with values reported in the literature (1.294 eV), placing the material in the visible light range and making it suitable for optoelectronic applications. Density of states (DOS) analysis has identified orbital contributions indicative of a non-magnetic ground state, which is beneficial for minimizing electronic losses. The optical properties further underscore its potential, showing a strong dielectric function with transitions spanning the visible to ultraviolet regions. The absorption coefficient begins near 3 eV and increases at higher energies. In contrast, the elevated refractive index and extinction coefficient across the visible to near-infrared range suggest efficient light-matter interaction. Overall, Na₂CuBiCl₆ stands out as a structurally stable, thermally robust, and optically active semiconductor, indicating its significant potential for next-generation optoelectronic and thermoelectric applications.