Exploring the A-Site Chemistry of A 2 LiTlCl 6 (A= K, Rb, and Cs) Double Perovskites: Structural Stability, Electronic Structure, and Transport Properties

Abstract

The electronic structure, optical, and thermoelectric properties of the halide perovskites A 2 LiTlCl 6 (A= K, Rb, and Cs) are systematically explored using first-principles calculations. The computational framework combining GGA-PBEsol and Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJ) is utilized for accurate band structure analysis. Phase and mechanical stability are confirmed through negative formation energies and elastic constants that fully satisfy Born's criteria. Electronic structure reveals direct band-gap nature with tunable values of 2.84, 2.77, and 2.66 eV for K 2 LiTlCl 6 , Rb 2 LiTlCl 6 , and Cs 2 LiTlCl 6 , respectively. The calculated optical responses, including complex dielectric constant, refractive index, optical conductivity, and absorption spectra, show strong absorption in the visible and ultraviolet region, highlighting their potential for optoelectronic and photovoltaic platforms. Thermoelectric transport analysis predicts promising ZT values of 0.74-0.76 at 300 K, indicating efficient heatto-electricity conversion. Altogether, the multifunctionality and significant potential of A 2 LiTlCl 6 highlight this family of lead-free halide perovskites as attractive candidates for cutting-edge thermoelectric and optoelectronic applications.