Zhang, Lina;
(2024)
Synthesis and Characterisation of Defect Perovskite Materials (A₂BX₆ and A₃Bi₂X₉).
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Lead-free halides with perovskite-related structures such as defect-ordered perovskites in the form of Cs3Bi2X9 and A2BX6 are of interest for photovoltaic applications. The main content is about the characterisations of mixed halide A2BX6 vacancy double perovskites and the characterisations of doping mixed valences Sn2+ and Sn4+ into defect-ordered triple perovskite Cs3Bi2X9(X=Cl- or Br-). Substitutional doping was used to produce mixed halides in A2BX6 vacancy double perovskites via solution-phased synthesis and high temperature solid-state synthesis. The products of solution synthesis are series Cs2SnBr6-6xCl6x and Cs2SnI6-6xBr6x (where x= 0 to 1 in increments of 0.1, and x= 0 represents nominal Br%=0). A distortion of pure cubic Cs2SnX6(X=Cl, Br or I) structures was caused by changing the spacing of the BX6 octahedra related to the size of A-site to maintain the overall symmetry. Optical band gap was varied by the ratio of mixed halides in composition from 4.53 eV in Cs2SnCl6 to 1.38 eV in Cs2SnI6 and showed a highly non-linear correlation with changes of mixed halide ratio in the composition. The high temperature solid-state approach to mix halides in the compounds was unsuccessful. Moreover, addition of SnX2 into Cs3Bi2X9(X=Cl or Br) resulted mixed valences (Sn2+ and Sn4+) in the Cs3Bi2X9 with no change of the general phase structures, using solution-phased synthesis (SpS) and solid-state grinding (SsG). The mixed-valence compounds showed intense absorption in the visible and near infrared region due to the intervalence charge transfer. The double substitution complex enhanced the stability of Sn2+ in the compounds. The similar approaches doping Sn into Cs3Sb2Cl9 or Rb3Bi2Br9 are unsuccessful.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Synthesis and Characterisation of Defect Perovskite Materials (A₂BX₆ and A₃Bi₂X₉) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2024. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10200095 |
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