DFT+U study of TlXBr3 (X = Sn, Ge) perovskites as next-generation materials for optoelectronics applications

The lead-free perovskite has gained increasing importance in optoelectronic device applications. In this study, we investigate the structural, electronic, optical, mechanical, thermodynamic, and thermoelectric properties of cubic phase TlSnBr3 and TlGeBr3 using the plane wave pseudopotential method based on density functional theory (DFT). To overcome constraints of the GGA-PBE technique, we implemented the LDA+U technique to solve on-site self-interaction errors. The Hubbard parameter 'U' was identified as a suitable solution for considering on-site self-interactions and calculating better electronic energy band gaps. The obtained lattice parameters are consistent with previous published results. Our findings indicate that both materials have a direct energy band gap, with values of 1.75 eV and 1.94 eV for TlSnBr3 and TlGeBr3, respectively. We also observe the existence of covalent and ionic bonding. The optical properties of these materials demonstrate high absorption coefficients and conductivity in the visible region. The mechanical properties are derived using the Voigt-Reuss-Hill approximation and suggest strong evidence of ductile behavior. Finally, the thermoelectric properties are evaluated by analyzing thermal to electrical conductivity, Seebeck coefficient, and Figure of merit criteria. Our comparative study of TlXBr3 (X = Sn, Ge) suggests that these compounds are promising candidate materials for photovoltaic and optoelectronic devices.