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Title: Organometallic precursors for the production of printable photovoltaic materials
Author: Allinson, Matthew Robert
ISNI:       0000 0004 7427 6624
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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This thesis studies the synthesis of nanocrystaline inorganic electron transporting materials for printable electronic applications. The main requirements of such a synthesis method is that it takes place below 200 °C and all components are soluble in organic solvents. Firstly, the synthesis of zinc oxide in-situ in thin films of poly 3 hexylthiophene (P3HT) is developed. By dissolving P3HT and diphenylzinc together and producing thin films of the polymer- precursor blend, a ZnO:P3HT bulk heterojunction (BHJ) can be produced by annealing the film at 150 °C in an anaerobic, H2O saturated atmosphere. The BHJ morphology is characterised by scanning electron microscopy (SEM) and shown to be suitable for charge separation. Photovoltaic devices are made with a ZnO:P3HT BHJ active layer, and the J-V characteristics are studied. The peak photoconversion efficiency was 0.38%, which is 10 times higher than the control device made following a literature synthesis. This synthesis route was modified in order to attempt to make ZnS:P3HT BHJs, by producing thin films of polymer-precursor blends and exposing them to an atmosphere of H2S. This is carried out first in solution to demonstrate the feasibility of the reaction, and then on thin films both polymer-precursor blends and films of just the precursor. Films are characterised using SEM, UV-Vis and TAS. No method that annealed the films under 200 °C produced a thin film of zinc sulphide. Finally, a synthesis for producing gallium doped zinc oxide nanoparticles was developed. Diethylzinc and trimethylgallium are mixed in solution with a capping ligand, and the doped oxide is produced by the addition of H2O. The resulting nanoparticles are characterised by Transmission electron microscopy and X-ray diffraction spectroscopy and confirmed to be gallium doped zinc oxide nanoparticles 5 nm in diameter. These can be spin coated at room temperature to form thin films, which are characterised by SEM. Sheet resistances were unexpectedly high (>108 Ω/□), and methods for improving the nanoparticles for conductive applications are discussed.
Supervisor: Williams, Charlotte ; Shaffer, Milo ; Nelson, Jenny Sponsor: Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral