The Role of Surfaces, Interfaces and Oxides in Antimony Selenide Photovoltaics



Fleck, Nicole
(2021) The Role of Surfaces, Interfaces and Oxides in Antimony Selenide Photovoltaics. PhD thesis, University of Liverpool.

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Abstract

This thesis investigates antimony selenide (Sb2Se3) as an absorber layer for photovoltaic cells. Literature focus thus far has centred around orientation and device optimisation. Fundamental material bulk, surface and interface properties are explored here as well as integration of Sb2Se3 layers into solar cell devices. The phonon modes of Sb2Se3 are investigated by standard, and angle-resolved polarised Raman spectroscopy to resolve inconsistencies in the Raman literature of the material. Oriented bulk crystals of Sb2Se3 are used and a stringent peak-fitting procedure employed to deconvolute individual vibrational modes in the spectra. Group theory calculations predicted the intensity variation of Raman peaks with rotation of the samples and these are fitted to the experimentally observed variations to assign vibrational symmetries to each mode. The results are corroborated by density functional theory calculations and previous literature reports. 14 of the 30 predicted phonon modes are experimentally observed and assigned vibrational symmetries. An x-ray photoelectron spectroscopy study of Sb2Se3 samples directly after fabrication, stored under atmospheric conditions or in vacuum is reported in order to understand spontaneous device improvements shortly after fabrication. Highly surface localised oxidation of the films stored in air as well as the formation of a more selenium-rich back surface is shown to improve the back contact, possibly by decreasing recombination at the interface and resulting in a 10% increase in efficiency of the cells over time. These results are experimentally verified by the deposition of thin layers of selenium and/or Sb2O3 at the back contact. Finally, a device study is presented with molybdenum-doped indium oxide (IMO) trialled as a partner layer for Sb2Se3 solar cells. The properties of sputtered IMO films are found to depend on the history of the sputtering target which is very sensitive to oxygen exposure. The IMO-Sb2Se3 interface is also found to be non-ideal for carrier collection but further studies may be able to overcome this challenge. Alternative deposition methods are suggested for future work but promising initial efficiencies of 0.57% were achieved.

Item Type: Thesis (PhD)
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Symplectic Admin
Date Deposited: 29 Mar 2022 13:52
Last Modified: 31 Mar 2022 00:11
DOI: 10.17638/03149384
Supervisors:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3149384