An emerging aspirant for solar cell and non-conventional energy applications: Lead free fluoro-perovskites A2TlInF6 (A = K, Rb)

Abstract

In the present work; structural, electronic, optical, and thermoelectric properties of double perovskites A₂TlInF₆ (A = K, Rb) have been studied using the ab-initio method in conjunction with full potential Linear Augmented Plane Wave (FP-LAPW) method and PBE-GGA potential. Structural properties, cohesive energy, and formation enthalpy collectively confirmed the stability of the halide perovskites in a cubic structure with Fm3m symmetry. Electronic properties revealed the p-type semiconductor nature of both materials. The indirect band gap values for K₂TlInF₆ and Rb₂TlInF₆ were found to be 3.489 eV and 3.591 eV, respectively, with PBE. With PBE + SOC, the values dropped to 3.445 eV and 3.546 eV, respectively. Optical properties such as Dielectric function $\epsilon \left(\omega \right)$, Refractive Index $n\left(\omega \right)$, Extinction Coefficient $\kappa \left(\omega \right)$, Optical Conductivity $\sigma \left(\omega \right)$, Reflectivity $R\left(\omega \right)$, Electron Energy Loss Function $L\left(\omega \right)$, and Absorption Coefficient $\alpha \left(\omega \right)$ were determined using PBE-GGA potential. BoltzTraP code was used to determine thermoelectric properties, namely, Seebeck Coefficient (S), Electrical Conductivity ($\sigma )$, Thermal Conductivity (K), Power Factor (PF), and Figure of merit (ZT) which were studied in detail. The study suggests halide-based double perovskites may have the potential for solar energy utilization due to their high absorption coefficient, large values of refractive index, and optimal values of the figure of merit.