Exploring the A-site chemistry of A2LiTlCl6 (A = K, Rb, and Cs) double perovskites: structural stability, electronic structure, and transport properties

Abstract

The electronic, mechanical, optical, and thermoelectric properties of halide perovskites A₂LiTlCl₆ (A = K, Rb, and Cs) are systematically investigated using first-principles calculations. The computational framework combining the Tran–Blaha modified Becke–Johnson exchange potential (TB-mBJ) and the TB-mBJ-SOC potential is utilized for accurate band structure analysis. Stability analyses confirm their thermodynamic and mechanical stability, with negative formation energies and elastic constants that satisfy Born's criteria. The band structure, computed using the Tran–Blaha modified Becke–Johnson (TB-mBJ) and TB-mBJ-SOC potentials, reveals a direct band-gap nature with tunable values of 2.84 (2.81), 2.77 (2.76), and 2.66 (2.65) eV for K₂LiTlCl₆, Rb₂LiTlCl₆, and Cs₂LiTlCl₆, respectively. Optoelectronic properties, including complex dielectric constant, refractive index, optical conductivity, and absorption spectra calculated with the TB-mBJ potential, show strong absorption in the visible and ultraviolet spectral region, highlighting their potential for solar cell and other optoelectronic applications. The thermoelectric transport analysis predicts ZT values of 0.74–0.76 at 300 K, reflecting preliminary heat to electricity conversion. The multifunctionality and insights provided by A₂LiTlCl₆ make them promising candidates for cutting-edge thermoelectric and optoelectronic applications.