Promising Double Perovskites Rb 2 CeCuX 6 (X = Cl, Br, I) for Low Cost Energy Applications: First‐Principles DFT Study
Mehmood Elahi, Fahim Ahmed, Yasir Altaf, Naimat Ullah KhanABSTRACT
Density functional theory with the GGA‐PBE functional and HSE06 is used to analyze physical properties of Rb 2 CeCuX 6 (X = Cl, Br, and I). As the size of halogen increases from Cl to I, band gaps decrease to 2.02 from 2.02 eV. Structural stability was confirmed by using tolerance factor, octahedral factor, and formation energy calculations. All three compounds were found to be stable, with no indications of dynamical stability problems. On the thermoelectric side, Rb 2 CeCuBr 6 performs the best by far, with a figure of merit (ZT) of 1.50, as compared to 1.13 for the Rb 2 CeCuCl 6 and only 0.11 for the Rb 2 CeCuI 6 . Thus, the choice of halogen is crucial in this situation. These materials absorb light very well because of their large optical absorption, which is around 2.05 × 10 6 cm − 1 for Rb 2 CeCuCl 6 , 1.796 × 10 6 cm − 1 for Rb 2 CeCuBr 6 , and 1.659 × 10 6 cm − 1 for Rb 2 CeCuI 6 . All these findings indicate that Rb 2 CeCuX 6 may be beneficial for thermoelectric waste‐heat recovery and solar energy conversion completely without the lead‐toxicity issues associated like many other perovskite systems.