Theoretical investigation of Ruddlesden Popper phase La₂XO₄(X = Zn, Ca, Mg, and Be) compounds with multifunctional properties for flexible photovoltaic applications

In this work, Ruddlesden popper phase (RPP) family member with formula La₂XO₄ has been explored by using theoretical quantum computational method CASTEP code to analyze its electronic, optical, and mechanical properties. Moreover, density functional perturbation theory has been employed to calculate the thermodynamic properties of the compounds. Results revel that these compounds have zero-point energy ranging from 0.8648 to 1.0875 eV which is important for solar applications since it affects electron-phonon coupling, bandgap, and material stability. Heat capacity clearly rises with temperature, approaching to Dulong–Petit limit at approximately 600 K. Electronic structure analysis revels that the compounds are semiconductor in nature with direct bandgaps for La₂ZnO₄ (1.62 eV) and La₂CaO₄ (2.09 eV) while La₂MgO₄ (3.40 eV) and La₂BeO₄ (3.56 eV) demonstrate indirect bandgaps. Optical features of the compounds are also analyzed including dielectric function, optical conductivity, absorption coefficient, extinction coefficient, reflectivity, refractive index, and loss function for photovoltaic applications. Notably, high values of absorption coefficient (10⁵ cm^{− 1}₎, dielectric function (10), optical conductivity (8 fs^{− 1}), refractive index ranging from 3 to 4 lie in the visible and near UV range. Additionally, elastic properties confirm the ductile nature of these materials, supporting their suitability for flexible photovoltaic and optoelectronic applications.