First principles study on the structural stability, mechanical stability and optoelectronic properties of alkali-based single halide perovskite compounds XMgI3 (X = Li/Na): DFT insight

Metal-halide perovskites are recognized as cutting-edge solar energy technology, boasting remarkable absorption capabilities, minimal environmental impact, and cost-effectiveness. This study delves into the structural stability, mechanical stability, and optoelectronic properties of lead-free halide perovskites, specifically XMgI₃ (X = Li/Na), by utilizing the CASTEP and WIEN2k software along with the GGA-PBE and Tran–Blaha modified Becke–Johnson (TB-mBJ) exchange–correlation functions to compare their electronic properties. The structural and mechanical stabilities were confirmed by assessing their tolerance factor and formation energy and by evaluating their elastic constants, respectively. Using the TB-mBJ exchange–correlation potential function, the calculated indirect band gap values for LiMgI₃ and NaMgI₃ were 2.474 and 2.556 eV, respectively. These band gaps are suitable for solar energy harvesting due to their broad optical absorption ranging from infrared to visible light. The partial density of states and the total density of states were determined to investigate the contribution of individual atoms. Consequently, this study can guide researchers focusing on the experimental synthesis of these materials at the laboratory scale for in-depth exploration, particularly in applications such as photovoltaics and various optoelectronic devices.