A Thesis submitted to the Faculty of Science, School of Chemistry at University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015. / Photovoltaic cells offer a good alternative to the fossil fuels. Several approaches are being analysed in order to have solar cells that are capable to conquer the energy market all around the world. Quantum dots (QDs) have already proven features that can be taken into account to improve the properties of solar cells. Metal selenide nanoparticles (NPs) possess semiconducting behaviours that can vary with their structural and optical properties evolving from their synthesis. The reaction parameters such as the method, time, solvent and precursors can affect the growth and nucleation of particles and thus impose on the properties of the synthesized materials. The performance of solar cells made of the synthesized metal selenides will then be dependent upon the properties of the NPs used as active layer. Furthermore, the electrical current generation also depends on the structure of the deposited active layer and its interface with other films to be assembled for the device. The binary copper selenide, ternary copper indium selenide (CISe), quaternary copper indium gallium selenide (CIGSe) and quinary copper zinc tin sulphur selenide (CZTSSe) NPs were synthesized via conventional colloidal method (CCM) and microwave assisted method (MAM). The MAM has a particular interest as it is less time consuming and can easily be a large scale synthesis. Photovoltaic devices were fabricated from the synthesized materials as proof of concept for photovoltaic activities. The CCM was used to optimize various parameters for the synthesis of each type of the chalcogenide materials as this is easily controllable than the ones from the sealed vessel from MAM. The dependency of properties of all copper chalcogenide NPs on the time, precursor concentration, temperature and solvent of synthesis have been demonstrated via various characterization techniques including ultraviolet-visible-near infrared spectroscopy, photoluminescence spectroscopy, X-ray diffractometry and transmission electron microscopy. The binary copper selenide was first synthesized and considered as a template for evaluation of the use of copper chalcogenide materials in solar cells. Relatively smaller copper selenide NPs with average sizes of 4.5 and 6.0 nm were obtained from conventional colloidal and microwave assisted methods respectively. The sample yielded from the microwave assisted method possessed less polydispersed NPs. The later had better crystallinity in which prevailed a single cubic Cu2Se phase. To the best of our knowledge this is the first evidence of defined shapes and nearly single phase of small sized copper selenide NPs synthesized by mean of the MAM. The copper selenide particles synthesized via this method were used to fabricate a Schottky device. The conditions of copper selenide synthesis were optimized to 250 oC, 30 min of CCM synthesis using oleylamine (OLA) and a Cu/Se ratio of 1:1. Nearly hexagonal facets with blue-shifted absorption band edge of monodispersed NPs sizing 4-8 nm in diameter were obtained. The synthesized copper selenide showed better crystallinity with a single cubic Cu2Se phase. A Schottky device using MAM synthesized copper selenide NPs as the semiconducting layer was fabricated at room temperature. The diode effect was demonstrated with the electrical parameters such as the ideality factor, barrier height and the series resistances extracted from the experimental current-voltage data using the thermionic theory and Cheung’s modification. The thermionic theory resulted in the ideality factor of 4.35 and the barrier height of 0.895 eV whilst the Cheung’s method resulted in the ideality factor, barrier height and series resistance of 1.04, 2.59 10-3 eV and 0.870 Ω respectively. The ternary copper indium selenide NPs showed that the MAM allowed the formation of copper rich NPs alongside secondary products. The synthesis of the ternary sample via CCM was optimized using uncapped precursors (no TOP was added) in OLA at 220 oC for 30 min. The synthesized CuInSe2 NPs possessed a large blue-shift in their absorption band edges and emission peaks. The nearly stoichiometric CuInSe2 particles with diameter sizes of 5-9 nm were found in tetragonal crystalline orientation. The cyclic voltametry (CV) and the absorption spectra showed a large blue-shifted energy gap, about 0.95 eV, an increase from the bulk, proving the quantum confinement effects of synthesized copper indium selenide quantum dots. The CuInSe2 NPs were thus used as absorbing materials in the quantum dot sensitized solar cell devices (QDSSCs). The QDSSC devices were assembled via treatment of the titanium oxide, quantum dot layers and their interface. This was done by the treatment of copper indium selenide surface with mercapto-propionic acid (MPA) and ethanedithiol (EDT) during the deposition of the quantum dots onto TiO2 films. The MPA treatment did not reveal positive effects on copper indium selenide thin film and the assembled device under our optimized working conditions. However the use of EDT allowed the improvement of electron transport. The short circuit current (Jsc), open circuit voltage (Voc) and fill factor (FF) obtained from the current-voltage (J-V) curves reached the values of 324 μA cm-2, 487 mV and 43% respectively, indicating that the investigated quantum dots possess electrical properties. For the quaternary copper indium gallium selenide, relatively small sized NPs were synthesized via CCM and MAM. The CCM synthesized CIGSe NPs were less agglomerated with a shorter tailing in absorption than those from MAM. The stoichiometric CuIn0.75Ga0.25Se2 showed less agglomerated and highly crystalline particles with a large blueshifted absorption band edge and a smaller full width at halth maximum (FWHM) of the emission peak compared to CuIn0.5Ga0.5Se2 and CuIn0.25Ga0.75Se2. The use of OLA as solvent of synthesis improved the growth and dispersivity of copper indium gallium selenide NPs. The particles with a large blue-shifted absorption band edge, a lattice of tetragonal phase, more monodispersed CIGSe and possessing an average size of 6.5 nm were obtained from CCM synthesis using OLA. The OLA as-synthesized CIGSe NPs were used in thin film for the assembly of QDSSC. The device exhibited electrical properties with the Jsc, Voc and FF of 168 μA cm-2, 162 mV and 33% respectively. The overall device performance was poor but may further be improved for further photovoltaic application. The quinary CZTSSe NPs possessed large blue-shifted absorption band edges of 450-460 nm than the bulk material (827 nm). The emission peak at 532 nm and similar FWHM of less than 50 nm were observed in samples from both CCM and MAM. More monodispersed crystals were obtained with both methods whilst the average particle sizes of 10 and 9 nm were yielded from MAM and CCM respectively. The nanoparticles crystallized in tetragonal lattices between copper zinc tin sulphide and copper zinc tin selenide crystals. However, the MAM gave more crystalline phases. The CV and the absorption spectra showed a blue shifted energy gap, about 0.21 eV increase from the buk which is located at 1.51 eV. This is indicative of the quantum confinement effects of synthesized NPs. The evidence of electrical properties was also shown in the QDSSCs fabricated using the MAM synthesized quinary QDs. This was done following the same treatments as for copper indium selenide devices. The Jsc, Voc and FF were found at the maxima of 258 μA cm-2, 395 mV and 38% respectively. The MPA and EDT treatments did not improve the device performance under our working conditions. Nevertheless, the electrical properties observed in the assembled device were indicative of promising efficient solar cells from synthesized CZTSSe NPs.

Abstract not available

This project sets out a theory of how performance can contribute to the spread of ecological values as we, as a species, confront the challenges of the Anthropocene. In response to the theory that the roots of the contemporary ecological crisis lie in the agricultural revolution, the project examines an archive of performances that engage questions of agriculture, land use, and anthropogenic climate change. Chapter 1 looks at mainstream, Western dramas that depict ecodystopian futures; chapter 2 looks at teatros in the Chicano movements and their anti-agribusiness actos; chapter 3 looks at rural, community responsive theater on public lands threatened by fossil fuel development; and chapter 4 looks at anti-pipeline ritual performance in the Niobrara River Valley. These objects of analysis are united in their activist drive to dislodge the values that undergird industrial agriculture and replace them with ecological values. The project argues that an understanding of performance as “performance-assemblage” can help to explain its power to bring about this transvaluation by drawing on the posthuman characteristics of assemblages to “deterritorialize” and “reterritorialize”—that is, to shift elements from one assemblage to another, and to alter the meaning of those elements and assemblages in the process.

The Bush administration's decision to abandon the Kyoto Protocol can be explained by prospect theory. The change in federal climate policy between the Clinton and Bush administrations was due to the difference in domain that each president operated under. President Clinton operated under a domain of losses as he associated continued fossil fuel use with future socio-economic and environmental damages from climate change. This domain of losses increased President Clinton's risk tolerances and explains his pursuit of the Kyoto Protocol, an international agreement to limit greenhouse gas emissions. Conversely, President Bush operated under a domain of gains where he did not connect fossil fuel use with future damages, rather with continued economic growth. President Bush's domain of gains reduced his risk tolerance and resulted in his pursuit of fossil fuel intensive economic development policies. This paper defines the domain that Presidents Clinton and Bush operated under regarding climate change, the independent variable of this analysis. A total of 26 speeches on climate change by these presidents were coded to explicate domain according to two categories of beliefs. The single most salient variable is the decision makers beliefs about the perceived robustness of the current state of scientific knowledge on climate change. The second most important aspect of these decision makers beliefs revolve around the role of fossil fuels in economic growth. Once domain has been defined through the cognitive maps and each decision makers corresponding risk tolerance explicated, the dependent variable of policy preferences are analyzed. Two policy options are analyzed; the business as usual (BAU) option associated with the status quo, as well as a climate protection policy that is reflective of the emissions reductions associated with US compliance with Kyoto. These two policy options are evaluated in three case studies; the economy wide costs of compliance with Kyoto targets for greenhouse gas emissions, the public health impacts of greenhouse gas reductions, and finally against a component of the Kyoto Protocol that allows for international trading of permits to emit greenhouse gases.

This thesis estimates the impacts of rooftop photovoltaic (PV) capacity on electricity generation and CO2 emissions in America's Pacific Northwest. The region's demand for electricity is increasing at the same time that it is attempting to reduce its greenhouse gas emissions. The electricity generated by rooftop PV capacity is expected to displace electricity from fossil fueled electricity generators and reduce CO2 emissions, but when and how much? And how can this region maximize and focus the impacts of additional rooftop PV capacity on CO2 emissions? To answer these questions, an hourly urban rooftop PV generation profile for 2009 was created from estimates of regional rooftop PV capacity and solar resource data. That profile was compared with the region's hourly fossil fuel generation profile for 2009 to determine how much urban rooftop PV generation reduced annual fossil fuel electricity generation and CO2 emissions. Those reductions were then projected for a range of additional multiples of rooftop PV capacity. The conclusions indicate that additional rooftop PV capacity in the region primarily displaces electricity from natural gas generators, and shows that the timing of rooftop PV generation corresponds with the use of fossil fuel generators. Each additional Wp/ capita of rooftop PV capacity reduces CO2 emissions by 9,600 to 7,300 tons/ year. The final discussion proposes some methods to maximize and focus rooftop PV impacts on CO2 emissions, and also suggests some questions for further research.