Mapping structural, electronic and optoelectronics features in Na2TlSbY6 (Y = Cl,Br): Implications for next-generation photovoltaics

Double perovskites represent a groundbreaking frontier in the advancement of renewable energy technologies, offering a unique combination of tunable properties that address the growing global demand for sustainable solutions. This study provides a comprehensive exploration of the optical, thermoelectric, thermodynamic, and mechanical properties of Na₂TlSbY₆ (Y = Cl,Br) using advanced Density Functional Theory (DFT) techniques. We rigorously assess the structural and thermodynamic stability of these materials through a detailed analysis of tolerance factors and formation energies, while their mechanical stability and ductility are validated via elastic constants and Pugh’s and Poisson’s criteria. Our findings reveal a notable band gap of 2.71 eV for Cs₂AgBiCl₆, which decreases to 1.76 eV upon the substitution of Cl with Br, driven by pronounced Pd-hybridization effects between anions and cations. A sophisticated investigation into the optical properties—encompassing dielectric constants, absorption spectra, refractive indices, and reflectivity—demonstrates strong absorption across the visible and ultraviolet regions, marking these materials as ideal candidates for high-efficiency solar cell applications.