First-principles study on electronic structures and optical properties of double-peovskite halides Cs2AgFeX6(X=Cl,Br,I)
In recent years,silver halide double perovskites have been widely studied as potential environmentally friendly alternatives to lead-based hybrid halide perovskites.Recently,a novel lead-free double perovskite single crystal Cs2AgFeCl6 was synthesized experimentally.It is a semiconductor with cubic structure,and its ab-sorption spectrum can extend to 800 nm.In this work,the electronic structures and optical properties of Cs2Ag-FeX6(X=Cl,Rr,I)were investigated by using the first-principles method based on the density functional theory,and the inherent relevances between the two were discussed.Also,the influences of the change of X-site element on the properties of the materials were analyzed.The charge density calculation results show that from Cl to I,Fe-X bond gradually weakens,namely the binding capacity of atoms to charges weakens.On the other hand,the band gap widths of the three materials gradually decrease.Cs2AgFeCl6 and Cs2AgFeBr6 have band gaps of 1.40 eV and 0.91 eV,respectively,while Cs2AgFeI6 exhibits metallic nature.The spectral charac-teristic peaks of double perovskite Cs2AgFeX6 is obviously redshifted with the increase of X-site atomic num-ber,and the three materials all process remarkable light absorption in visible to infrared region.The absorption coefficient of Cs2AgFeCl6at 534 nm is 21.28 × 104 cm-1,and that of Cs2 AgFeBr6 at 712 nm is 20.54 × 104 cm-1.Cs2AgFeI6 has an extremely wide absorption peak in the infrared band over 1200 nm,and the absorption coefficient can reach up to 10 × 104cm-1.This paper provides theoretical guidance for the wide application of Cs2AgFeX6(X=Cl,Br,I)in the field of optoelectronic devices.
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