First principle study of optoelectronic and mechanical properties of lead-free double perovskites Cs₂SeX₆ (X = Cl, Br, I)

The variant double perovskites are considered novel materials for solar cells and optoelectronic applications. Here, we explored electronic, mechanical, and optical characteristics of Cs₂SeX₆ (X = Cl, Br, I) by density functional theory (DFT) analysis. The tolerance factor between 0.97–1.0 signifies the structural stability of the investigated compounds while thermodynamic and mechanical stabilities were ensured by positive frequencies of phonon dispersion as well as elastic constants. Moreover, the Poisson and Pugh's ratios are explored for brittle and ductile behavior. The Debye and melting temperatures have also been reported through mechanical analysis. The tuning of the bandgap takes place from 3.10 to 2.64 eV and then 1.15 eV by substitution of Cl with Br and I, respectively. The optical spectra show a shift in absorption region from ultraviolet-to-visible. In addition, the low light reflection and optical energy loss range (0.0–3.0 eV) promises potential of the studied potential for solar cells and optoelectronics uses.