First principles investigation about interference effects of electronic and optical properties of inorganic and lead-free perovskite Cs3Bi2X9 (X=Cl, Br, I)

The electronic and optical properties of the Cs3Bi2X9 (X=Cl, Br, I) was emphatically explored theoretically by density functional theory methods based on first principles, and the influence of interference effect on the these three crystals is systematically elucidated. Our results reveal that the optical properties of the three materials are dominated by the valence electrons in p -orbitals of the Bi and halogen atoms. In the visible region, the absorption peaks have a red shift with increase of atomic number of halogen increases. The optical absorption is special and very sensitive to the interference structure on one - dimensional Cs3Bi2Cl9, but not to that of two - dimensional Cs3Bi2Br9 and zero -dimensional Cs3Bi2I9. The thickness of the Cs3Bi2Br9 film also influences the optical properties. While the zero -dimensional Cs3Bi2I9 is almost unaffected by crystal thickness and surface characteristic.