Fundamental First-Principles Basis for Stability and Optoelectronic Characteristics in Lead-Free Mg ₃ PCl ₃ Perovskite

In this study, a comprehensive first-principles investigation based on density functional theory (DFT) is performed to explore the structural, electronic, mechanical, vibrational, and optical properties of the lead-free perovskite Mg 3 PCl 3 . The optimized lattice parameter (a = 5.24 Å) shows good agreement with previously reported data. The calculated elastic constants satisfy the Born stability criteria, confirming the mechanical stability of the material, while phonon dispersion analysis reveals the absence of imaginary frequencies, indicating dynamical stability. Electronic band structure analysis demonstrates that Mg 3 PCl 3 is a direct bandgap semiconductor with a bandgap of 2.28 eV at the Γ-point. Charge density analysis suggests predominantly ionic bonding characteristics. Furthermore, carrier transport analysis indicates relatively low effective masses and favorable electron mobility, which facilitate efficient charge transport and reduced recombination losses. Optical properties reveal a moderate static dielectric constant (ε1 (0) = 5) along with strong optical absorption in the visible region, highlighting its suitability for photovoltaic applications. Overall, these findings suggest that Mg 3 PCl 3 is a promising candidate for next-generation lead-free solar cells and optoelectronic devices.