Study of promising lithium-based lead-free double perovskites Li₂AuBiX₆ (X = Cl, Br, and I) for optoelectronic and other renewable energy applications

The current study effort primarily focuses on the computational investigation of the physical properties of Li₂AuBiX₆ (X = Cl, Br, and I) double perovskites (DPs) utilizing the Density Functional Theory (DFT) framework. The structural and elastic characteristics have been evaluated to reveal phase and mechanical stability. The assessed formation energy and elasticity constants calculations validate that the examined DPs possess cubic phase, exhibit stability, and demonstrate ductility. The band structure analysis has been accomplished with a modified Becke-Johnson (mBJ) potential. The band structure simulations reveal that Li₂AuBiCl₆, Li₂AuBiBr₆, and Li₂AuBiI₆ possess an indirect energy gap, with values of 1.12 eV, 0.77 eV, and 0.084 eV, respectively. We further examined the optical parameters in the spectrum of incoming photons from 0 to 4 eV. Considerable absorbance in the visible spectrum has been observed for Li₂AuBiX₆ (X = Cl, Br, and I), suggesting that these DPs are compatible with photovoltaics. Finally, we have computed thermoelectric (TE) characteristics in relation to temperatures within the range of 100 to 600 K. The investigated DPs might be suitable for thermoelectric systems, as indicated by the moderate values of the figure of merit, which needs to be improved. The obtained absorption and figure of merit values surpass similar perovskites Rb₂AuBiX₆. Hence, the current work might be advantageous for developing novel photovoltaic and TE systems.