A thesis submitted to the Faculty of Science, University of the Witwatersrand in partial
fulfilment of the requirement for the degree Doctor of Philosophy (PhD) in Chemistry. Johannesburg, June 2017. / Due to a high global demand for energy, research groups have been focusing a lot of energy
into finding alternative and cleaner energy sources. Solar power has all the attributes to be the
energy of the future. Solar power is abundantly available and is a cleaner form of energy as
compared to the market-leading fossil fuels.
In this thesis, we consider new materials that can be used in hybrid solar cells. These new
materials combine the properties of inorganic nanomaterials and polymers. The nanomaterials
possess unique properties that can be exploited and the polymers allow for the thin films to
potentially be light weight and flexible.
Copper selenide was synthesized and characterized to produce particles with different sizes as
a function of time. These size variations are shown to emit a spectrum of different colours. In
addition the particles synthesized at various temperatures are reported. Temperature had an
effect on the size of the particles with bigger sizes obtained as the temperature was increased.
Also shown in the results is that Cu2Se nanocrystals were quite resistant to changes with the
sizes marginally increasing with increasing time and temperature. A hybrid material using a
conductive polymer polyvinylcarbazole (PVK) and copper selenide was synthesized and used
as the active layer via a spin coating technique to fabricate a solar cell. Varying amounts (10%
- 50%) of Cu2Se nanocrystals were used in the polymer nanocomposites. The 10% weight
loading resulted in the highest efficiency of 0.74% whilst successive addition of the
nanocrystals affected the polymeric structure of PVK thus resulting in solar cells with even
lower efficiencies.
Niobium selenide was synthesized via the colloidal method using TOP/HDA combination for
the first time. The effect of time on the particles synthesized using a 1:1 mole ratio of Nb:Se
was negligible with particles showing similar properties. The XRD of the samples revealed that
they were amorphous thus making it difficult to conclusively say that niobium selenide was
synthesized successfully. The samples were then annealed however only small improvements
were observed. The concentration of the selenium was then increased in order to form the more
common NbSe2 and NbSe3. The XRD showed the formation of NbSe2 and NbSe3 for 1:2 and
1:3 Nb:Se ratios respectively. In addition, the particles resembled 2D nanostructures readily
observed in layered materials such as NbSe2 and NbSe3. However, some impurities in the form
of oxides were still observed. Hybrid solar cells prepared from the amorphous 1:1, 1:2 and 1:3
Nb:Se samples were fabricated. The NbSe3 composite had the best performing solar cell with
the power conversion efficiency of 3.234% with the amorphous particles generating no current. / LG2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/23559 |
| Date | January 2017 |
| Creators | Govindraju, Stefan Joel |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (154 leaves), application/pdf |
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