Deposition and Characterization of Wide Band Gap P-Type Metal Oxides for Photovoltaic Applications

Umar, Medina. Deposition and Characterization of Wide Band Gap P-Type Metal Oxides for Photovoltaic Applications. 2020, Doctoral Thesis, University of Basel, Faculty of Science.


Official URL: https://edoc.unibas.ch/88175/

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Daily, the population in the world is increasing, along with the quantity of needed energy. However, the fossils are running out and climate change is a global concern now, thus, the demand for alternative energies is growing. Solar energy comes free by the sun light and, if well harvested, it could be a valuable and readily available alternative source of energy for humanity. In this work, we perform deposition and characterization of thin films of copper oxides to be used in photovoltaic devices.
Thin films of copper oxide were grown by radio frequency-magnetron sputtering in an oxygen-argon environment onto silicon and FTO-coated substrates at two different oxygen partial pressures (15% and 23%). Control over the oxygen flow during deposition is of paramount importance and quite difficult, making reproducible growth challenging. Post deposition annealing in vacuum environment was conducted on the films at different temperatures (between 250°C and 550°C), as an alternative pathway towards the creation of the desired phase and stoichiometry of copper oxide films in a reproducible manner.
We investigated the surface morphology of the thin films by Scanning Electron Microscopy, Energy Dispersive X-ray, Atomic Force Microscopy and Kelvin Probe Force Microscopy. These studies show that the pristine films are made up of densely packed grains that are homogeneously distributed. In the annealed thin films, the size of the grains evolves greatly with the annealing temperature increase: besides the change in the morphology of the grains, which become bigger and less homogeneous, the films become nano porous in the annealed samples. The contact potential difference measurements show the presence of some islands in samples annealed at temperature higher than 450°C, only above this temperature, that the regions with higher and lower CPD values correlated with higher and lower work functions, respectively. Suspecting that these areas represent the co-existence of CuO and Cu2O crystals.
The structural properties of the thin films were studied via spectroscopy and X-ray diffraction and Raman, which reveal that two oxide phases (i.e. CuO and Cu2O) co-exist in the films deposited with high oxygen ratio. In particular, high oxygen pressure during deposition favours CuO and annealing in vacuum converts CuO to Cu2O. Instead, low oxygen pressure
directly promotes the formation of Cu2O thin films. In the thin films deposited on glass, we also performed transmission measurements and found that the transmittance of films is higher in the near IR region while absorption is higher at the ultraviolet to visible region of the spectra.
Finally, we uncovered a novel parasitic crystallite growth as a result of aging on the pristine and low-temperature annealed samples, and we found out that high temperature annealing prevents this kind of aging. This aging effect is completely absent in the thin films deposited onto the FTO substrates.
Our results demonstrate the impact of the annealing mediation route in the reproducibility of Cu2O thin films, which should be explored towards the standardization of copper oxides formation technique. The produced thin films are good substrates for the deposition of Ga2O3 for dye sensitized solar cells.
Advisors:Glatzel, Thilo and Zardo, Ilaria and Postorino, Paolo
Faculties and Departments:05 Faculty of Science > Departement Biozentrum > Growth & Development > Biochemistry (Spiess)
UniBasel Contributors:Glatzel, Thilo and Zardo, Ilaria
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:14670
Thesis status:Complete
Number of Pages:III, 117
Identification Number:
  • urn: urn:nbn:ch:bel-bau-diss146700
edoc DOI:
Last Modified:15 Apr 2022 04:30
Deposited On:14 Apr 2022 10:48

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