Low concentrator photovoltaic systems are capable of increasing the power produced by conventional silicon photovoltaic cells, thus effectively lowering the cost per kWh. However, power losses associated with resistance and temperature have limited the large scale implementation of this technology. In this study, the optical-,electrical- and thermal sub-systems of a low concentrator photovoltaic system are theoretically and experimentally evaluated with the aim of minimizing the power losses associated with series resistance and temperature. A 7-facet reflector system, with an effective concentration ratio of 4.7, is used to focus irradiance along a string of series connected poly-crystalline photovoltaic cells. I-V characteristics of 4-, 6- and 8-cell photovoltaic receivers are measured under 1-sun and 4.83-sun conditions. Under concentration, the 8-cell photovoltaic receiver produced 23 percent more power than the 4-cell photovoltaic receiver, which suggests that the effect of series resistance can be minimized if smaller, lower current photovoltaic cells are used. A thermal model, which may be used to predict operating temperatures of a low concentrator photovoltaic system, is experimentally evaluated within a thermally insulated enclosure. The temperatures predicted by the thermal model are generally within 5 percent of the experimental temperatures. The high operating temperatures associated with the low concentrator photovoltaic system are significantly reduced by the addition of aluminium heat sink. In addition, the results of a thermal stress test indicated that these high operating temperatures do not degrade the photovoltaic cells used in this study. The results of this study suggest that the power output of low concentrator photovoltaic systems can be maximized by decreasing the size of the photovoltaic cells and including an appropriate heat sink to aid convective cooling.

It is estimated that 1.6 billion people today live without access to electricity. Most of these people live in remote rural areas in developing countries. One economic solution to this problem is the deployment of small domestic photovoltaic (PV) systems called solar home systems (SHS). In order to improve the performance and reduce the life cycle cost of these systems, accurate monitoring data of real SHSs is required. To this end, two SHSs typical of those found in the field were designed and installed, one in a rural area of the Eastern Cape of South Africa and the other in the laboratory. Monitoring systems were designed to record energy ows in the system and important environmental parameters. A novel technique was developed to correct for measurement errors occurring during the utilization of pulse width modulation charge control techniques. These errors were found to be as large as 47.6 percent. Simulations show that correction techniques produce measurement errors that are up to 20 times smaller than uncorrected values, depending upon the operating conditions. As a tool to aid in the analysis of monitoring data, a PV performance model was developed. The model, used to predict the maximum power point (MPP) power of a PV array, was able to predict MPP energy production to within 0.2 percent over the course of three days. Monitoring data from the laboratory system shows that the largest sources of energy loss are charge control, module under performance relative to manufacturer specifications and operation of the PV array away from MPP. These accounted for losses of approximately 18-27 percent, 15 percent and 8-11 percent of rated PV energy under standard test conditions, respectively. Energy consumed by loads on the systems was less than 50 percent of rated PV energy for both the remote and laboratory systems. Performance ratios (PR) for the laboratory system ranged from 0.38 to 0.49 for the three monitoring periods. The remote system produced a PR of 0.46. In both systems the PV arrays appear to have been oversized. This was due to overestimation of the energy requirements of the loads on the systems. In the laboratory system, the loads consisting of three compact fluorescent lamps and one incandescent lamp, were used to simulate a typical SHS load pro le and collectively consumed only 85 percent of their rated power. The 8 predicted load profile for the remote system proved to be signi cantly overestimated. The results of the monitoring project demonstrate the importance of acquiring an accurate estimation of the energy demand from loads on the system. Overestimations result in over-sized arrays and energy lost to charge control while under-sized systems risk damaging system batteries and load shedding. Significant under-performance of the PV module used in the laboratory system, underlines the importance of measuring module IV curves and verifying manufacturer specifications before system deployment. It was also found that signi cant PV array performance gains could be obtained by the use of maximum power point tracking charge controllers. Increased PV array performance leads to smaller arrays and reduced system cost.

Bulk heterojunction (BHJ) organic photovoltaic (OPV) is one of the most promising techniques to generate electricity with advantages of flexibility, solution processing and capability for large area device fabrication. Although the power conversion efficiency (PCE) of BHJ solar cells has already achieved over 13%, there are still problems remain to be solved. This thesis presents the binary and ternary organic BHJ devices with alternative donor:acceptor (D:A) ratios, and the charge transport properties and electronic interactions in their BHJ films. In a high performance BHJ solar cell, the commonly optimized D:A weight ratio is about 1:x, where x is commonly in excess of 1.5, when PC71BM is used as the acceptor. We demonstrated how to achieve high PCEs of BHJ solar cells by enriching the D:A weight ratios. The PCEs of the re-optimized cells were improved for the PTB7:PC71BM, PCDTBT:PC71BM, PDTSTPD:PC71BM devices. Current-voltage (JV) and admittance spectroscopy (AS) measurements indicate enhanced hole mobilities for the polymer-rich BHJs based on PTB7, PCDTBT, and PDTSTPD. At the same time, although the relative weight ratio of PC71BM is reduced, the electron mobilities are maintained due to the dispersion of fullerene domains by increased DIO concentrations. The active layer thickness of most optimized BHJ solar cells is about 100nm. The thin active layer is unfavorable for optical absorption and film coating. We employed a ternary strategy to address this problem, and the thick-film BHJ devices can retain 90% PCEs of their optimized thin-film devices. Three model systems were studied, involving PTB7:PC71BM, PTB7-Th:PC71BM and P3HT:PCBM BHJs. Into these BHJs, a ternary component, p-DTS(fbtth2)2 (DTS) is introduced. With DTS, the corresponding thick film devices have significantly improved PCEs. The ternary component DTS improves hole mobility and reduces sub-bandgap trap states. Both observations are well correlated with improved FFs of the ternary BHJ cells. Photothermal deflection spectroscopy (PDS) and 1H nuclear magnetic resonance (1H NMR) results indicate that DTS behaves as conducting bridges in between two neighboring polymer segments. Most lab-based BHJ solar cells are optimized by their power conversion efficiencies (PCEs). We challenge this conventional view by showing that BHJ cells using fullerene acceptors should be optimized by their fill-factors (FFs). With the optimized-FF approach, BHJ cells tend to have higher fullerene content when compared to the BHJ cells that are optimized by PCEs. The FF-optimized BHJ cells have slightly reduced PCEs (due to smaller Jscs) compared to the PCE-optimized cells. Yet, FF-optimized cells enjoy a much better thermal stability. We demonstrate that these FF-optimized BHJs possess better-balanced electron-to-hole mobility ratios due to weakly field-dependent electron mobilities. The improved mobility ratio suppresses carrier recombination. Our results suggest that BHJ cells optimized by their PCEs should be meta-stable, and other D:A ratios should be considered for practical BHJ cell development.

Submitted to the Faculty of Science, School of Chemistry at University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 05 June 2017. / The colloidal method has extensively been used to synthesize ternary and quaternary copper sulfides and selenides. Although tellurides form part of the chalcogenides, little has been reported on them particularly the synthesis of these nanostructures. Achieving high-quality nanocrystals through colloidal synthesis requires thorough monitoring of parameters such as time, solvent, precursor as they affect nucleation and growth of the nanocrystals. Herein, we report on the colloidal synthesis of ternary CuInTe2 and quaternary CuIn1-xGaxTe2 nanostructured semiconductor materials. A typical synthesis of CuInTe2 entailed varying reaction temperature. At temperatures below 250 °C, no formation of CuInTe2 was seen. At 250 °C formation of CuInTe2 could be observed with the formation of binary impurities. A change in the sequence in which precursors were added at 250 °C yielded pure CuInTe2. Applying different surfactants aided in achieving differently structured morphologies of CuInTe2 nanocrystals. Morphology varied from rods, cubes, nanosheets etc. Different morphologies resulted in different optical properties with the high optical band gap of 1.22 eV measured for 1D rods. Different precursors were employed in the synthesis of quaternary CuIn1-xGaxTe2. Precursor 2 (entailed the use of Cu (acac)2, In (acac)3 and Ga(acac)3) yielded pure CuIn1-xGaxTe2 phase with no formation of impurities. Variation in reaction time influenced the optical properties of the quaternary CuIn1-xGaxTe2 with high band gap obtained at low reaction time (30 min). A change in Ga and In concentration resulted in reduced lattice parameters a and c with lowest values obtained with the highest Ga concentration. However, achieving the intended concentration proved challenging due to the loss of the material during synthesis. Increasing the Ga concentration resulted in a high optical band gap. Conducting the reaction with Hexadecylamine (HDA) resulted in a relatively high optical band though the formation of impurities was evident. The obtained band gap can be attributed to small sized particles as evident from TEM results. Heterojunction ZnO/CIT and ZnO/CIGT solar cell devices were fabricated through a simple solution approach. The performance of ZnO/CIGT device was superior to that of ZnO/CIT in which efficiency increased from 0.26-0.78%. In the ZnO/CIT device, high Voc of 880 mV was recorded while 573.66 mV was measured for ZnO/CIGT device. Chemical and thermal treatments were performed on the ZnO/CIGT devices. The efficiency increased from 0.78 1.25% when the device was chemically treated with a short-chain EDT ligand. A high conversion efficiency of 2.14% was recorded for devices annealed at 300 °C. High annealing temperatures resulted in poor device performance with the lowest efficiency of 0.089% obtained at annealing temperatures of 500 °C attributed to the leaching out of In and Ga into the ZnO layer. / LG2017

No description available.

The semiconducting sulphosalt Wittichenite has been identified as a possible absorber material for thin film photovoltaic devices. It has the chemical formula Cu3BiS3 and its component elements are those of low toxicity and high abundance making it a very attractive prospect for photovoltaic devices. The copper bismuth sulphur material system is not very well understood and information on it limited to a few small regions. To aid understanding of this system a pseudo-binary phase diagram along the CuS-Bi join of the Cu-Bi-S ternary phase diagram was constructed by making bulk samples of various compositions along the join and analysing them using X-ray diffraction and differential scanning calorimetry. This join was chosen because is crosses the point at which Cu3BiS3 would be expected to occur due to its stoichiometry. The CuS-Bi phase diagram shows Cu3BiS3 forms across a wide compositional range but is mixed with either bismuth metal or copper sulphides depending on composition. Films of Cu3BiS3 were made using sputtered copper and bismuth films annealed in a sulphur atmosphere and thermal co- evaporation of copper sulphide and bismuth.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

Solar energy has come to the forefront as a scalable and largely underutilized renewable energy resource. The current cost of solar electricity, namely from photovoltaics, along with other logistics factors, has prevented the widespread adaptation of the technology. A key determinant of efficiency and cost for a solar cell is the current collector grid. This work presents the Collimated Aerosol Beam Direct Write (CAB-DW) system as a non-contact printing method that can achieve current collector grid finger widths of less than 10 μm which are amenable to decreasing both resistive and optical losses. The ability to produce high aspect ratio grid fingers, and deposit optimized grid structures on high efficiency SHJ solar cells using silver nanoparticle inks is also demonstrated. A decrease in shadowing and via profile modification of the grid fingers is presented, along with a study of aging and degradation of electrical properties within silver nanoparticle inks.

Ma, Xuhang = 柔性襯底銅銦鎵硒太陽能電池製備工藝 / 馬續航. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 88-91). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Ma, Xuhang = Rou xing chen di tong yin jia xi tai yang neng dian chi zhi bei gong yi / Ma Xuhang.

在這個對可再生能源需求不斷增加的新時代,聚合物太陽能電池成為其中一個最熱門的研究題目。在過去十年,聚合物太陽能電池的研究大多集中在液體處理的塊材異質接面結構。與傳統的‘雙層’結構比較,塊材異質接面結構提供一個更大的給體-受體界面面積讓電荷分離及減少電荷重組,從而帶來更高的能量轉換效率。目前使用塊材異質接面結構的聚合物太陽能電池最高能量轉換效率約為8 %。最近在文獻中公佈的一篇文章中,聲稱‘雙層’器件也可以達到與塊材異質接面器件媲美的高效率。這類‘雙層’器件採用相連沉積的給體層P3HT 和以二氯甲烷作溶劑的受體層PCBM 製作。然而,也有報告指在熱退火處理下PCBM 會擴散進入P3HT 的非晶區從而堤高能量轉換效率。我的工作是研究這類所謂的‘雙層’系統。藉運用紫外-可見光光譜儀和掠角X 光繞射,對埰用不同處理手法的純P3HT 薄膜的聚集和結晶性能進行研究。結果發現P3HT 的聚集和結晶性能可能沒有直接的相關性。同時也發現通過縮短底層P3HT 溶劑的揮發時間,這類液體鑄型‘雙層’器件的能量轉換效率得以提高。通過加熱P3HT 薄膜來加快變乾的速度,可以造具較低聚集度和較高結晶密度的P3HT 層。比起常規P3HT 薄膜可以提高能量轉換效率大約15 %。同時也對重量比為1:1 的複合P3HT:PCBM 薄膜的聚集和結晶性能進行了研究。實驗結果進一步表明P3HT 的聚集和結晶性能可能沒有直接的相關性。雖然實驗未有充分運用所有其他可能的處理方法和物理参數對器件進行全面優化,但這項研究卻為液體鑄型雙層聚合物太陽能電池開闢一條新的優化路線。 / In this new age with increasing demand of renewable energy sources, organic solar cell (OSC) has become one of the most intense research topics. The major attention of research in OSC was given to the solution-processed bulk heterojunction (BHJ) architecture during the past ten years. Compared to traditional ‘bilayer’ architecture, the BHJ structure provides a greater donor-accepter interface area for charge separation and reduced recombination, which leads to a higher power conversion efficiency (PCE). The highest PCE reported using BHJ was about 8 %. In a recent article published in the literature, it was claimed that ‘bilayer’ devices can also achieve a high efficiency comparable to that for BHJ devices. Such ‘bilayer’ devices were fabricated by sequential deposition of the donor P3HT and acceptor PCBM layers using dichlormethane as the solvent of PCBM. However, it was also reported that the PCBM could diffuse into the amorphous regions of P3HT during thermal annealing to cause the efficiency enhancement. My work is to study such so-called ‘bilayer’ system. By using UV-Visible spectrophotometer and grazing incidence XRD, the aggregation and crystallization properties of the pure P3HT films fabricated using different processing methods were studied. It was found that the P3HT aggregation may not have direct correlations with crystallinity. It is also discovered that the PCE of such solution-cast bilayer devices are increased by shortening the evaporation time of the underlying P3HT layer from a solution. By heating the P3HT film to accelerate its drying, a less aggregated P3HT layer with a higher density of crystallites could be obtained. The PCE could be enhanced by about 15 % over that using a regular P3HT film. The aggregation and crystallization properties of the composite P3HT:PCBM films with a ratio of 1:1 by weight were also studied. The experimental results further indicate that the P3HT aggregation may not have direct correlations with crystallinity. Although the devices have not been fully optimized by exhausting all the other possible processing and physical parameters, this study opens up a new route to optimize solution-cast bilayer polymer solar cells. / Detailed summary in vernacular field only. / Wong, Man Kwong = 聚合物太陽能電池研究 / 王文廣. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Wong, Man Kwong = Ju he wu tai yang neng dian chi yan jiu / Wang Wenguang. / Abstract --- p.I / 摘要 --- p.III / Acknowledgement --- p.VI / Chapter Chapter 1 --- Introduction to Organic Solar Cells --- p.1 / Chapter 1-1 --- The history of the development of solar cells --- p.1 / Chapter 1-2 --- Motivation of developing polymer solar cells --- p.2 / Chapter 1-3 --- The materials used in polymer solar cells --- p.4 / Chapter 1-4 --- Basic working principles of the polymer solar cells --- p.6 / Chapter 1-5 --- Definition of some important parameters of solar cells --- p.8 / Chapter 1-5-1 --- Short circuit current density (J[subscript Ssubscript C]) --- p.8 / Chapter 1-5-2 --- Open circuit voltage (V[subscript Osubscript C]) --- p.9 / Chapter 1-5-3 --- Fill factor (FF) --- p.10 / Chapter 1-5-4 --- Power conversion efficiency (PCE) --- p.11 / Chapter 1-6 --- An outline of this thesis --- p.12 / Chapter Chapter 2 --- Experimental Procedures --- p.13 / Chapter 2-1 --- Common preparation procedures in all the experiments --- p.13 / Chapter 2-1-1 --- The cleaning of the glass and indium tin oxide (ITO) substrates --- p.13 / Chapter 2-1-2 --- The preparation of different donor and accepter solution --- p.13 / Chapter 2-1-3 --- The coating of PEDOT:PSS on the glass and ITO substrates --- p.14 / Chapter 2-1-4 --- The thermal vapor deposition of the cathode layer for solar cell devices --- p.14 / Chapter 2-2 --- The detailed experimental procedures of the active layers in different chapters --- p.15 / Chapter 2-2-1 --- Fabrication of the active layers in chapter 3 --- p.15 / Chapter 2-2-2 --- Fabrication of the active layers in chapter 4 --- p.17 / Chapter 2-2-3 --- Fabrication of the active layers in chapter 5 --- p.18 / Chapter 2-3 --- Measurement of the properties of the film samples and the performance of the solar cells --- p.19 / Chapter 2-4 --- Experimental errors --- p.20 / Chapter Chapter 3 --- A Survey on Polymer Solar Cells and Some Preliminary Works --- p.21 / Chapter 3-1 --- Traditional bilayer polymer solar cells --- p.21 / Chapter 3-2 --- Bulk heterojunction polymer solar cells --- p.22 / Chapter 3-3 --- Studies of thermal annealing effects --- p.26 / Chapter 3-4 --- Studies of solvent annealing effects --- p.28 / Chapter 3-5 --- Studies of the relationship between the thickness and the optical density of the films --- p.34 / Chapter 3-6 --- Solution-cast bilayer polymer solar cells --- p.35 / Chapter 3-7 --- Previous studies on solution-cast bilayer polymer solar cells --- p.39 / Chapter Chapter 4 --- Studies on Solution-Cast Bilayer Polymer Solar Cells --- p.42 / Chapter 4-1 --- Motivation and the basic ideas of my research work --- p.42 / Chapter 4-2 --- Higher PCE through the use of a low pressure environment of film formation --- p.43 / Chapter 4-3 --- Higher J[subscript Ssubscript C] through the use of chloroform as the P3HT solvent --- p.46 / Chapter 4-4 --- Higher PCE through the use of a pre-dried heating process --- p.52 / Chapter 4-5 --- Dependence of the device performances on the pre-dried heating temperature --- p.55 / Chapter 4-6 --- Effect of a small amount of PCBM in the underlying P3HT layer --- p.59 / Chapter 4-7 --- Short summaries --- p.62 / Chapter Chapter 5 --- Studies on P3HT:PCBM Blend Layers --- p.64 / Chapter 5-1 --- Motivation --- p.64 / Chapter 5-2 --- Effects on the P3HT aggregation and crystallization of the P3HT:PCBM blend layers due to different treatments --- p.64 / Chapter 5-3 --- Studies of the effects of the removal of PCBM on the P3HT aggregation and crystallization in P3HT:PCBM blend layers --- p.67 / Chapter 5-4 --- Short summaries --- p.70 / Chapter Chapter 6 --- Conclusion --- p.71 / Chapter 6-1 --- Summaries of the research work --- p.71 / Chapter 6-2 --- Ideas for future studies --- p.72 / Bibliography --- p.74