Formamidinium lead iodide perovskite (FAPI) holds promise to be used in high–efficiency solar cells. A comprehensive understanding of the immediate surface properties of this material can provide insights into its interaction with other materials and guide future engineering of its interface with other constituents of the solar cell. In this thesis, the orientations of the formamidinium cations on flat FAI and PbI2 terminated (001) surfaces of the of α–FAPI were studied with classical and ab initio molecular dynamics simulations at a temperature of 300 K. The cations on the FAI terminated surface displayed a preference to lie flat on the surface, while the cations near the PbI2 terminated surface displayed a preference to be oriented in such a way that the molecular planes were perpendicular to the surface. Average near edge X–ray fine structure (NEXAFS) spectra at the carbon and nitrogen K–edges were simulated from the trajectories of the FAI terminated structure and compared with existing experimental spectra obtained from a clean FAPI surface under ultrahigh vacuum. By comparing the experimental and calculated NEXAFS spectra it was observed that the distribution of formamidinium orientations which contribute to the experimental NEXAFS spectra is different from the one seen in the outermost FAI layer from the molecular dynamics simulation. This observation can be explained by the finite probing depth of the X–ray or the fact that the surface is not perfectly FAI terminated in the experiment. The more uniform distribution of formamidinium orientations one layer below the surface resulted in simulated NEXAFS spectra which were more similar to the experimental ones.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:su-224042 |
| Date | January 2023 |
| Creators | Geirsson, Torsten |
| Publisher | Stockholms universitet, Fysikum |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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