Density functional theory investigation of the mechanical, electronic and optical properties of Pb-free vacancy-ordered double perovskites K <sub>2</sub> PdCl <sub>6</sub> and K <sub>2</sub> PdBr <sub>6</sub>
Xian‐Hao Zhao, Tianyu Tang, Quan Xie, Limin Lu, Yan-Lin Tang
Abstract
Abstract The current work has investigated the mechanical, electronic and optical properties of Pb-free vacancy-ordered double perovskites K 2 PdCl 6 and K 2 PdBr 6 by using first-principles calculations based on the framework of density functional theory (DFT). The calculated lattice constants of K 2 PdCl 6 and K 2 PdBr 6 are close to the experimental data. It is determined by calculating the Goldschmidt’s tolerance factors and elastic constants of K 2 PdCl 6 and K 2 PdBr 6 that they can be stabilized into 3D cubic crystal structures. The calculated Poisson and Pugh’s ratios indicate that K 2 PdCl 6 is a brittle material, while K 2 PdBr 6 exhibits ductile behavior. Both K 2 PdCl 6 and K 2 PdBr 6 are indirect band gap semiconductors, which show suitable band gaps of 2.151 eV and 1.368 eV for optoelectronic devices, respectively. In addition, the optical properties of K 2 PdCl 6 and K 2 PdBr 6 in the photon energy range of 0–6 eV further reveal the application potential of these compounds in single-junction and tandem solar cells as well as other optoelectronic devices.