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

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 8(w), Refractive Index n(w), Extinction Coefficient kappa(w), Optical Conductivity sigma(w), Reflectivity R(w), Electron Energy Loss Function L(omega), and Absorption Coefficient alpha(w) 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.