First-principles study of physical properties of Na2ZnIM6 (M = Br, Cl, Se) double perovskites

In this article, the physical properties of the double perovskites based on Na2ZnIM6 (M = Br, Cl, Se) are explored using the first-principles techniques. Investigations of the elastic properties in terms of elastic constants, bulk and shear moduli, anisotropy, Poisson's ratio, and Young's modulus reveal that these compounds are covalent and brittle. Furthermore, calculations of the electronic structures indicated them as semiconductors with wide and direct bandgaps. In optical properties, the dielectric constants (real and imaginary parts) were plotted against the frequency, and the trends in absorption, refraction, loss functions, and optical conductivities and their essential electronic and optical implications have been analyzed and discussed. Meanwhile, the studied compounds with strong absorptions, low reflections, and direct band gaps can be employed as photoelectric absorption layers in solar cells.