Abstract
It is an effective method to use SnF2 and SnF4 molecules to assist in enhancing the performance of FASnI3 perovskite. However, the mechanism in this case is not clear as it lacks a certain explanation to specify the phenomenon. Through first-principles calculations, this paper constructed several modes of SnF2 and SnF4 adsorbed on the surfaces of FASnI3 and explored adsorption energies, band structures, photoelectric properties, absorption spectra, and dielectric functions. The SnF2 molecule adsorbed at the I5 position on the FAI-T surface has the lowest adsorption energy for the F atom, which is 0.5376 eV. The Sn–I bond and Sn–F bond mainly affect the photoelectric properties of FASnI3 perovskite solar cells, and the SnF2 adsorption on the FAI-T surface can effectively strengthen the bond energies, which shortens the bond lengths of the Sn–I and Sn–F bond, and eliminate surface unsaturated bonds to passivate the surface defects. Furthermore, the probability of energy transfer was lower between the SnF2 molecule and the ion around it than between SnF4 and its ion. Especially, in the aspect of optical properties, we found that the intensity of the absorption peak of SnF2 adsorption increase was larger than that of SnF4 adsorption. Additionally, the static dielectric constants of SnF4 adsorption on the two surfaces, denoted SnF4, made the perovskite respond more slowly to the external electric field. Based on this work, we found that SnF2 had a greater positive effect on the optical property of perovskite than SnF4. We consider that our results can help to deeply understand the essence of SnF2 assistance in the performance of FASnI3 and help researchers strive for lead-free perovskite solar cells.
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