In this thesis, cadmium selenide (CdSe) quantum dots (QDs) are synthesized and characterized for patterning applications as well as for photovoltaic devices. The QDs were patterned and embedded into various polymers to form fluorescent composites. Their photophysical properties were investigated in detail. Through template assisted deposition the QDs-polymer composites were patterned into fluorescent nanorods. CdSe QDs were combined with multi-wall carbon nanotubes (CNTs) using a synthesized organic perylene derivative dye (N,N'-di(ethanethiol)-perylene-3,4,9,10-tetracarboxyl diimide) (ETPTCDI) as a link between QDs and CNTs. Upon testing, the QDs-ETPTCDI-CNTs nanocomposite displayed photoactive properties. Photophysical quenching studies of QD-ETPTCDI-CNTs provided better understanding of the electron-hole transfer of each component in the nanocomposite. The nanocomposite material was patterned onto microelectrode devices for photocurrent measurements under an AM1.5 solar simulated light source. These nanocomposites can be used as photovoltaic devices. The preliminary characterization studies of the device show excellent photoresponse under AM1.5 solar simulated light. The band gap alignment of each component of the nanocomposite and the charge transfer kinetics are the key to efficient electron-hole transfer. Optimization of the semiconducting material's interface can potentially make these nanocomposites a system for photovoltaic-based devices.

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This thesis presents the transport, material characterization, and device applications of photovoltaic polymers used in bulk heterojunction solar cells. These three areas were found to be well correlated. Materials properties affect charge transport behaviors. Charge transport behaviors affect organic photovoltaic (OPV) cell performances. Two typical PV polymers were selected for investigation. They were poly(3-hexylthiophene) (P3HT) and poly[N-9-hepta- decanyl-2,7- carbazole-alt-5,5-(4’,7’-di-2- thienyl-2’,1’,3’- benzothiadiazole)] (PCDTBT). Different charge transport measurement techniques were employed to study how charge carriers move in OPV materials including space-charge-limited current (SCLC) measurement, dark-injection space-charge-limited current (DI-SCLC) measurement, and admittance spectroscopy (AS). For hole transport measurement on P3HT, electron leakages were found in a presumed hole-only device structure resulting in ill-defined DI-SCLC and AS signals. After inserting a thin electron blocking and trapping (EBT) layer between the active layer and the Au cathode, the electron leakages can be significantly suppressed leading to well-defined transport measurement signals. Applying the EBT layer to the polymer:fullerene bulk heterojunction (BHJ) blends, the transport properties can also be studied. Charge transport measurements were carried out at different temperatures for Gaussian Disorder Model (GDM) analysis to extract energetic disorders σ and high-temperature limit mobilities μ_∞. For P3HT BHJ films, σ were found to be much smaller than PCDTBT BHJ films. Within the same polymer system, similar σ were extracted. σ can be correlated to the device parameters such as open-circuit voltage V_OC and fill factor FF. Large σ was found to limit both V_OC and FF. With the experience of transport measurement for PV materials gained, we focused on a common problem of batch-to-batch variations in device performance. Five batches of amorphous polymers PCDTBT were purchased from two vendors. From gel permeation chromatography, bimodal distributions of molecular weight were observed in all five batches of PCDTBT with different fraction of small molecular weight component. The corresponding charge carrier mobilities and device performances drop significantly with the small molecular weight component. From GDM, all five batches of polymers have similar σ. However, μ_∞ for each batch of PCDTBT appear to have significant differences. The differences originate from the variation of charge carrier hopping distances caused by different amounts of the small molecular weight component of PCDTBT. At last, ZnO prepared by low temperature annealing sol gel method was used as functional layers for OPV cells and charge transport measurements. Structural, elemental, energetic, optical, and electrical characterizations were performed to examine the ZnO. The results suggested that the ZnO should be suitable for organic device applications. The applications of the ZnO on inverted OPV cells and charge transport measurements were demonstrated.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2017. / The development of solar roads to convert insolation on vast stretches of land to electrical energy, otherwise dedicated solely for transportation, is in its nascent stage. A great potential is seen for PV application with the maturing of solar road technology. Apart from increasing the versatility by smart utilization of land resources, widening the cover of renewable energy generation will lead to a sustainable, secure energy future. A stand-alone solar pathway for public park lighting or area lighting system, completely independent of the power grid, was designed and operated. Public lighting for 65 m stretch of walkway located next to the Electrical, Electronic and Computer Engineering Department building, was chosen as a case study in this study. The case study presented simplified method for sizing, performance evaluation and simulation of a stand-alone solar pathway to power public lighting on the Bellville Campus of the Cape Peninsula University of Technology. Depending on the requirements of the electrical, the quantity and quality of lighting, as well as the required duration of the lighting were calculated. Battery storage capacity, based on the desired autonomy period, and maximum and average daily depth of discharge, were sized. PV array size, based on the type and specifications of PV module, the time of year with the highest average daily lighting load and minimum solar radiation, were selected and measured. Control strategies for battery protection and lighting control conditions were determined, and the control set points were specified. The operating efficiency of solar pathway was evaluated and showed excellent performance compared to the expected with annual average value of the monthly performance ratio and system efficiency. A stand-alone solar pathway system was programmed using MATLAB, in order to size a PV system to the supply public lighting for the walkway. The computer program used, can be applied to any site with different weather conditions.

abstract: ABSTRACT As the use of photovoltaic (PV) modules in large power plants continues to increase globally, more studies on degradation, reliability, failure modes, and mechanisms of field aged modules are needed to predict module life expectancy based on accelerated lifetime testing of PV modules. In this work, a 26+ year old PV power plant in Phoenix, Arizona has been evaluated for performance, reliability, and durability. The PV power plant, called Solar One, is owned and operated by John F. Long's homeowners association. It is a 200 kWdc, standard test conditions (STC) rated power plant comprised of 4000 PV modules or frameless laminates, in 100 panel groups (rated at 175 kWac). The power plant is made of two center-tapped bipolar arrays, the north array and the south array. Due to a limited time frame to execute this large project, this work was performed by two masters students (Jonathan Belmont and Kolapo Olakonu) and the test results are presented in two masters theses. This thesis presents the results obtained on the south array and the other thesis presents the results obtained on the north array. Each of these two arrays is made of four sub arrays, the east sub arrays (positive and negative polarities) and the west sub arrays (positive and negative polarities), making up eight sub arrays. The evaluation and analyses of the power plant included in this thesis consists of: visual inspection, electrical performance measurements, and infrared thermography. A possible presence of potential induced degradation (PID) due to potential difference between ground and strings was also investigated. Some installation practices were also studied and found to contribute to the power loss observed in this investigation. The power output measured in 2011 for all eight sub arrays at STC is approximately 76 kWdc and represents a power loss of 62% (from 200 kW to 76 kW) over 26+ years. The 2011 measured power output for the four south sub arrays at STC is 39 kWdc and represents a power loss of 61% (from 100 kW to 39 kW) over 26+ years. Encapsulation browning and non-cell interconnect ribbon breakages were determined to be the primary causes for the power loss. / Dissertation/Thesis / M.S.Tech Technology 2012

The naturally occurring mineral of Cu2ZnSnS4 (CZTS) is a promising alternative absorber layer for thin film based photovoltaic devices. It has the remarkable advantage that it consists of abundant, inexpensive and non-toxic elements compared to its crystallographically related and highly successful counterparts: the Cu(In,Ga)(S,Se)2 (CIGSSe) and CuIn(S, Se)2 (CISSe) material systems. Therefore, there is real commercial potential for reduced material costs and improved device efficiencies. A two-stage high throughput combinatorial process for the fabrication of Cu-Zn-Sn-S thin film libraries is presented, which consists of either sequentially stacking or co-depositing Cu,Sn and Zn precursor layers by DC magnetron sputtering followed by a sulphurisation process. Sputtering conditions and target-substrate geometry are developed to give compositionally graded Cu-Zn-Sn precursor layers spanning a wide spatial region around the point of stoichiometry. Conversion into Cu-Zn-Sn-S libraries is achieved by thermally evaporating a uniform layer of sulphur directly onto the metal alloy and annealing the sample at 500 °C in a furnace. Effects of the precursor composition on the structural properties of the films prior to the incorporation of sulphur are investigated. The sulphurised libraries are then studied by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy as a function of composition, to assess the effects on morphology and phase formation. Observations of changes in lattice parameters and crystallinity are clear. The opto-electronic and electrical properties of the CZTS film libraries are measured using photoconductivity and hot point probe techniques, respectively. Changes in the band gap and conductivity type are studied as a function of atomic ratios. Based on high performing compositions, devices have been fabricated with the highest achieving cell at 1.26 %. The observations are discussed in the context of the particular compositions and synthesis conditions, and recommendations are made for further work.

This thesis investigates statistical techniques that can be used to improve estimates and methods in feasibility assessments of photovoltaic (PV) systems. The use of these techniques are illustrated for a case study of a 1MW PV system proposed for the Nelson Mandela Metropolitan University South Campus in Port Elizabeth, South Africa. The results from the study provide strong support for the use of multivariate profile analysis and interval estimate plots for the assessment of solar resource data. A unique view to manufacturing process control in the generation of energy from a PV system is identified. This link between PV energy generation and process control is lacking in the literature and exploited in this study. Variance component models are used to model power output and energy yield estimates of the proposed PV system. The variance components are simulated using Bayesian simulation techniques. Bayesian tolerance intervals are derived from the variance components and are used to determine what percentage of future power output and energy yield values fall within an interval with a certain probability. The results from the estimated tolerance intervals were informative and provided expected power outputs and energy yields for a given month and specific season. The methods improve on current techniques used to assess the energy output of a system.

M.Sc. / I-III-VI2 compound semiconductors are important photovoltaic (PV) materials with optical and electrical properties that can be tuned for optimum device performance. Recent studies indicated that the efficiencies (1) > 18%) of CuInSe2/CdS/ZnO thin film devices are in good agreement with that of standard silicon cells. In this study, CuInSe 2 absorber films with excellent material properties were produced by relatively simple and reproducible two-stage growth techniques. In these approaches, metallic precursors (Cu/InSe, InSe/Cu, Cu/InSe/Cu and InSe/Cu/InSe) were deposited by thermal evaporation from specially designed graphite heaters at temperatures around 200°C. In the second stage of the process, the alloys were exposed to elemental Se vapour or H2Se/Ar gas. A systematic study was conducted in order to determine optimum growth parameters for the different deposition processes. Optimum material properties (homogeneous and dense films with a high degree of compositional uniformity) were obtained when InSe/Cu/InSe precursors were selenized in elemental Se vapour or H2Se/Ar gas. Comparative studies also indicated that the reaction kinetics is enhanced when H2Se/Ar is used as chalcogen source. Fully selenized films were obtained at temperatures as low as 450°C in a H2Se/Ar atmosphere, compared to temperatures of 600°C in the case of Se vapour. The optical and electrical properties of the absorber layers were accurately controlled by small variations in the bulk composition of the films. A standard CdS/ZnO window layer technology was also developed in our laboratories and preliminary solar cell devices were fabricated and evaluated.

M.Eng. / The need and problem was originated from the trends of the earths dwindling energy resource. As time progresses humans are becoming more aware of need to use so called “alternative energy sources” to alleviate the main energy converters i.e. power stations. The student was tasked with investigating the thermal performance of a solar powered refrigeration cycle (prototype) that could: produce enough refrigeration effect that it replaces the standard home vapour compression unit, used for cooling or freezing of foods, heats up a geyser sufficiently to have hot water for a common house hold, has excess energy to heat or cool liquid or air based environments and has the potential to lower the electrical bill of a house. The introductory step was to obtain the thermo fluid properties of aqua ammonia solutions. A setback came about when determining the aqua ammonia properties. There were too many conflicting properties being yielded by six different authors. In an attempt to gain confidence in only one author a comparison table was prepared. The table compared the six authors to each other. By looking at all the values compared it brought great clarity to the problem. When continuing the research into the fundamental law approach of solving for the cycle new findings were made. Initially very little comprehensive studies were done which explained in fundamental laws to solve for the absorption cycle. After extensive reviewing of a detailed study on how to solve for absorption refrigeration cycles, then it was able to begin improving on the thermo – fluid design of the cycle. As cycle and component design began to progress the train of thought began to steer in a direction. Each component needed to be detail designed. The advantage of having each component specifically catered for in the cycle design was that it would increase the cycle efficiency. In this way it would ensure that during the concept generation phase the functioning of each component was clear, thereby enabling a clear understanding of how components would compliment each other in a cycle. A mode of solving for the cycle was to endeavour that all parameters could be calculated unambiguously, with the aid of computerisation. Testing was carried out on a real life commercial thermal siphoning machine in order to realistically understand how absorption refrigeration works and gain experience. At the end of the study the most important result is that the dissertation research shows strong evidence that it will be possible to create a device which can fulfil the four tasks listed above. Another result is a program which is a refined cycle design of the pump absorption type refrigeration. The program solves for points along the cycle. Lastly it was found that even though EES was the simpler program to use for aqua ammonia solution properties it was the only program which catered for sub cooling and super heating.

Ph.D. / One of the solutions to the high cost of solar modules is the development of thin film solar cell technologies, which enable material saving, few processing steps, good stability in outdoor testing, high conversion efficiency and flexibility for large area coatings. Polycrystalline CuInSe2 (CIS) thin films and related quaternary and pentenary compounds such as Cu(In,Ga)Se2 (CIGS) and Cu(In,Ga)(Se,S)2 (CIGSS) are the most promising thin film candidates to fulfil the requirements of economically viable solar modules. Presently CIS, CIGS and CIGSS thin film solar cells are prepared mostly by two – stage deposition processes, where Cu-In-Ga alloys are deposited, followed by selenization and/or sulfurization using H2Se/Ar and/or H2S/Ar gases, Se and/or S vapours. Key problems related to this approach are (1) the widely reported compositional change and loss of material during the annealing and selenization stages, and (2) the formation of a graded film structure with most of the Ga residing at the back of the film, due to the difference in the reaction rates between the binary selenides. The present study aims to develop CIGS quaternary and CIGSS pentenary thin film absorbers which are substantially homogeneous and single phase. In order to achieve this aim different deposition processes were developed. This included thermal evaporation of pulverized compound materials from a single crucible with and without subsequent reaction of the precursors in Se vapour or H2Se/Ar atmosphere. Alternatively, controlled partial selenization/sulfurization of the Cu-In-Ga magnetron sputtered precursor films under controlled conditions of reaction time, temperature and gas phase concentration were applied to produce CIGSS films. The latter approach allowed homogeneous incorporation of Ga and S species into CIS compound material, and with that a corresponding increase of band gap of the material in the active region of the solar cell. CIGS quaternary and CIGSS pentenary based solar cells were completed by depositing a CdS buffer layer of around 50 nm thickness, high resistivity ZnO and low resistivity Al – doped ZnO with thicknesses of about 50 nm and 0.5 μm respectively. I-V measurements on fabricated solar cells, under standard A.M. 1.5 conditions, demonstrated good solar cell device quality with efficiencies of about 10 % and 15% respectively.