Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.762819
Title: Copper and silver bismuth iodide semiconductors as potential solar cell absorber materials
Author: Sansom, Harry
ISNI:       0000 0004 7658 9843
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2018
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Abstract:
The work presented in this thesis concentrates on the synthesis of ternary and quaternary materials containing Cu, Ag, Bi and I as powders, crystals and thin films. They are characterised towards their use as solar absorbers in thin film photovoltaics. In Chapter 3, the sealed-tube solid state synthetic procedures used to prepare pure AgBiI4 and CuBiI4 powder phases are discussed, as well as the crystal growths of AgBiI4 and Cu2BiI5 via chemical vapour transport (CVT). The exploration of the CuI-AgI-BiI3 phase field is presented, explaining the optimised synthetic procedures for the synthesis of two new pure CuAgBiI5 and Cu2AgBiI6 powder phases and their crystal growths. The structures of the phases synthesised are discussed in Chapter 4. Although the structures of AgBiI4 and CuBiI4 material had been previously reported to crystallise in a 3D Bi-I network in the form of a defect-spinel, it was found that a metrically cubic CdCl2 2D layered structure could also be a solution to the powder X-ray diffraction (PXRD) and single crystal X-ray diffraction (SXRD) data (although not a statistical mix of both structure types). Additionally, an AgBiI4 crystal which had a metrically rhombohedral CdCl2 structure was isolated. The Cu2BiI5 structure is solved from SXRD for the first time, crystallising in the i-CdCl2 structure. By using combined PXRD and neutron powder diffraction (NPD), and SXRD data, the CuAgBiI5 was found to crystallise in a defect-spinel structure. The Cu2AgBiI6 structure was solved via SXRD to have the i-CdCl2 structure. In Chapter 5 the properties, stabilities and solution processability of the phases are discussed. The AgBiI4 powder has a band gap measured as 1.63(1) eV indirect with band edge states similar to those of BiI3; Ag 4d states are lower in the valence band. The top of the valence band is mainly I 5p states, while the bottom of the conduction band is a mixture of Bi 6p and I 5p states. The band gap of CuBiI4 was measured as 1.03(1) eV indirect, but was not studied further as it was a metastable phase and decomposed to CuI and BiI3 at room temperature. The band gaps of CuAgBiI5 and Cu2AgBiI6 powders were measured as 1.33(1) eV indirect and 1.31(1) eV indirect, respectively. It is shown that AgBiI4 and Cu2AgBiI6 powders are stable towards light in inert atmospheres, whereas CuAgBiI5 undergoes a colour change from black to yellow. Furthermore AgBiI4 is stable in light with wavelengths larger than 600 nm and in heat within the temperature range reached in the operating/testing of solar cells. The AgBiI4, CuAgBiI5, and Cu2AgBiI6 phases are importantly shown to be solution processable from DMSO solutions in to thin films.
Supervisor: Rosseinsky, Matthew ; Claridge, John Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.762819  DOI:
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