Probing the opto-electronic, thermoelectric, thermodynamic and elastic responses of lead-free double perovskite Li2ATlCl6 (A = Na and K) for potential photovoltaic and high- energy applications: A DFT study

The physical properties of double halide perovskite Li2ATlCl6 (A = Na and K) were examined through a first- principles study and semi-classical Boltzmann theory using the WEIN2k package, focusing on renewable energy generation and solar cell applications. Research on halides is growing within the optoelectronics and thermoelectric field and is anticipated to meet energy shortage demands. The volume-energy diagram confirms their structural stability, while the Pugh and Poisson ratios suggest ductility based on their elastic properties. The electronic properties were analyzed, and bandgaps were calculated using modified Becke-Johnson (mBJ) potentials, yielding bandgaps of 3.51 eV and 2.97 eV for Li2ATlCl6 (A = Na and K) respectively. The optical properties, evaluated using complex dielectric functions, indicated optimal light absorption in the infrared (IR) regions. Additionally, the thermoelectric (TE) properties of Li2ATlCl6 (A = Na and K) were analyzed using semi classical Boltzmann theory with a constant relaxation time approximation. At 1200 K, the calculated figures of merit (ZT) values were 0.75 and 0.69, respectively, indicating their potential for thermoelectric applications. Also, the thermodynamic properties are computed under pressure (0-15 GPa) and temperature (0-1200 K). These investigations offer a profound comprehension of these materials for their further employment. These results highlight their potential for optoelectronic device applications and are expected to encourage further experimental research on the feasibility of Li2ATlCl6 (A = Na and K) for optical devices.