Exploring the Structural, Electronic, and Optical Properties of Cs 2 TeX 6 (X = Cl, Br) Double Perovskites for Next‐Generation Solar Cells

ABSTRACT In this study, the crystal structure, mechanical, electronic, and optical properties of cubic double perovskites Cs 2 TeX 6 (X = Cl, Br) were systematically investigated using density functional theory (DFT) with generalized gradient approximation (GGA), GGA–modified Becke–Johnson (mBJ) functionals. The structural analysis reveals that the shorter Cs–Cl bond lengths, particularly in Cs 2 TeCl 6 , strengthen the metal–chlorine interactions, enhancing the chemical stability of the compounds. The negative formation energy confirms their thermodynamic stability. The electronic structure analysis demonstrates that both materials are indirect bandgap semiconductors with relatively flat conduction and valence bands, characteristic of p‐type charge carriers. The bandgap arises from electronic transitions between Cl‐p orbitals and hybridized (Se‐p, Sn‐p, Te‐p, and Ti‐d) states, which ensures efficient charge transport. The optical properties reveal strong ultraviolet absorption and a high static refractive index, making these compounds promising for optoelectronic and photovoltaic applications. The prominent peak in the real part of the dielectric function within the ultraviolet region minimizes charge carrier recombination, thereby boosting photovoltaic efficiency. Overall, the exceptional stability, favorable semiconducting nature, and robust optical performance of Cs 2 TeX 6 (X = Cl, Br) make these double perovskites strong candidates for next‐generation optoelectronic and solar cell technologies.