Cerium-based lead-free vacancy ordered double perovskites A2CeX6(A = Cs, K and X = Cl, Br) for sustainable energy applications

Abstract

Double perovskites (DP) continue to be a primary area of research, and scientists continuously explore various combinations of cations to discover new materials with unique properties. In this study, we investigated the structural, mechanical, electronic, and optical properties of Cerium-based DPs (A₂CeX₆, where A $=$ Cs or K and X $=$ Cl or Br) for applications in renewable energy. Using density functional theory (DFT), we showed the non-magnetic behaviour of these compounds through ground-state energy analysis. Structural and mechanical stability was confirmed through formation energy and elastic constant evaluation. The elastic constants revealed that these materials possess mechanical anisotropy and a brittle nature. Debye temperature (${\theta }_D$) was found to range between 140 and 199 K for these compounds. Electronic structure analysis revealed direct bandgaps ranging from 1.23 to 1.76 eV, suitable for effective light absorption in the visible spectrum. The calculated hole effective masses are larger than the free electron mass, and depict the anisotropic hole conductivity. Optical property evaluation revealed significant light absorption ( $10^{5}c{m}^{-1}$) and low reflectivity below 15 % in the visible energy range. Thickness-dependent calculations of Spectroscopic Limited Maximum Efficiency (SLME) suggest that these materials could achieve a theoretical efficiency of 30 % at a thickness of $10\mu m$. These findings highlight the potential of these compounds for applications in solar cells and optoelectronic devices.