Exploring double perovskites Cs2AgSbX6 (X = Cl, Br, and I) as promising optoelectronic and thermoelectric materials: a first-principles study†

Perovskite compounds have been well explored, and they are suitable for solar energy as well as thermoelectric applications. Herein, we present the structural, electronic, optical, thermoelectric, and elastic properties of Cs₂AgSbX₆ (X = Cl, Br, and I) perovskites with the help of density functional theory (DFT). The Wu-Cohen generalized gradient approximation (WC-GGA) and Perdew–Burke–Ernzerhof GGA (PBE-GGA) were used to calculate the structural parameters. According to the cohesive energy, phonon spectrum, and AIMD simulation results, Cs₂AgSbX₆ demonstrated good thermodynamic, dynamical, and thermal stabilities. The compounds exhibited an indirect band gap according to the band structure results obtained via the PBE and Heyd–Scuseria–Ernzerhof (HSE06) functionals. The band gap were 2.28, 1.63, and 0.99 eV for Cs₂AgSbCl₆, Cs₂AgSbBr₆, and Cs₂AgSbI₆, respectively. Optical absorption (6.05 × 10⁵ cm⁻¹) and spectroscopic limited maximum efficiency (SLME > 30%) calculations revealed that Cs₂AgSbI₆ worked effectively in the visible range. The figure of merit (ZT) calculations showed an increasing trend with increasing temperature. The maximum values were ∼0.77 (500 K), 0.76 (700 K), and 0.76 (750 K) for Cs₂AgSbCl₆, Cs₂AgSbBr₆ and Cs₂AgSbI₆, respectively. The elastic stability for the selected compounds was confirmed via “Born stability criteria” and found well consistent with the values for cubic materials. Further, Cauchy's pressure (C₁₂ − C₄₄) and Pugh's ratio (B/G) indicated the ductile nature of these compounds. The appropriate band gap, optimum ZT, and thermal and mechanical stabilities suggest the suitability of these compounds for use in optoelectronic and thermoelectric applications.