Structural and multifunctional properties of elpasolite-type K2XInI6 (X = Li, Na, K and Cs) compounds for photovoltaic applications

Abstract

The present research work investigates the optoelectronic, elastic, structural, and mechanical properties of elpasolite-type family related K₂XInI₆ (X = Li, Na, K and Cs) compounds by using GGA (Generalized gradient approximation) and PBE (Perdew-Burke-Ernzerhof) approach. The estimated band gaps of all the compounds are indirect in GGA-PBE approach ranging 0.567–1.634 eV and the calculated band gaps in HSE06 approach are direct in energy ranging of 1.765–2.820 eV, which indicate that they are semiconductors and ideal for energy efficient applications. Thermodynamic properties of the compounds are explored by utilizing density functional perturbation theory (DFPT) approach and powder XRD analysis is performed by using reflex code, the XRD patterns exhibit distinct peaks of varying intensities between 2θ = 5° to 45°. The Debye temperature increases rapidly as the applied temperature (K) increases, entropy, enthalpy and free energy also vary with applied temperature while heat capacity (C_V) rises with temperature reaching the Dulong-Petit limit about 200 K. The optical features include refractive index (2–3), optical conductivity (5 fs⁻¹), absorption coefficient (10⁵cm⁻¹) and dielectric function (5–6) have all shown high values in visible and UV range. The mechanical characteristics support the ductile nature of compounds and indicate that they are ideal for flexible photovoltaic applications. This study gives critical information regarding the compounds, demonstrating that they are appropriate for next-generation solar technologies.