A systemic study on Thallium based 3D halide perovskite with enhanced figure of merit

Abstract

First principles calculations are carried out to explore structural, elastic, electronic, charge density and thermoelectric properties of TlZnX3 (X = F, Cl, Br and I) 3D halide cubic perovskites within the Generalized Gradient Approximation (GGA) through Quantum Espresso code. The elastic coefficients (C11, C12 and C44) and elastic modulii such as Young’s modulus, bulk modulus, shear modulus reveals that stiffness is higher in TlZnF3. Additionally using Pugh’s ratio and Cauchy’s pressure TlZnF3 is classified as ductile whereas TlZnX3 (X = Cl, Br and I) are classified as brittle materials. Phonon dispersion curve proves the dynamic stability of TlZnF3. The band structures of TlZnX3 (X = F, Cl and Br) and TlZnI3 shows semiconducting and metallic nature respectively. Due to replacement of halide ion the indirect band gap of TlZnX3 (X = F, Cl and Br) decreases from 3.82 eV, 1.39 eV and 0.37 eV as the size of the anion increases. Using the Boltztrap code, thermoelectric parameters are analysed at temperatures of 400 K, 600 K and 800 K and chemical potential provides insight about optimal dopant. Large Seebeck Coefficient combined with ultra low thermal conductivity results in a high figure of merit for TlZnF3 that satisfies industry standards (ZT ≈ 1). Together, these outcomes highlights that these Thallium based halide perovskite are reliable materials for high temperature thermoelectric devices.