Unveiling the physical properties of AlMgX₃ (X = Cl and I) for emerging energy applications

In this study, we employed first-principles density functional theory (DFT) to investigate the structural, elastic, optoelectronic, and thermoelectric properties of lead-free halide perovskites, AlMgX₃ (X = Cl and I), for renewable energy applications. AlMgX₃ exhibit an energetically favourable nature due to their lower formation energy (-4.17 eV per f.u.). Additionally, AlMgX₃ are mechanically favourable with high elastic constants. We found that AlMgI₃ exhibits higher ductility (B/G = 2.97) and anisotropy. Furthermore, AlMgX₃ remain stable at room temperature, as confirmed by AIMD simulations. Both AlMgX₃ exhibit a semiconducting nature. Interestingly, a direct band gap (3.60 eV) is observed for AlMgCl₃, which could be promising for optical devices. Moreover, AlMgI₃ demonstrates superior absorption in the visible spectrum, attributed to its reduced band gap, and exhibits a higher static dielectric constant, which could be beneficial for photovoltaic applications. Furthermore, AlMgI₃ achieves a higher figure of merit (ZT = 0.61 at 300 K) due to enhanced electrical conductivity and power factor, though its indirect gap limits its high-temperature performance compared to AlMgCl₃ (ZT = 0.70 at 800 K). Moreover, the suitable band edges make them promising for water splitting. These results underscore the suitability of AlMgX₃ for a wide range of applications such as solar cells, optoelectronics, thermoelectrics and photocatalysis.