A comparison of photovoltaic device performance between copper indium gallium diselenide thin film solar cells with indium tin oxide and indium molybdenum oxide top contacts
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2010-12
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University of Hawaii at Manoa
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The following work is a study involving two sets of copper indium gallium diselenide (CIGS) thin film solar cells (TFSC) with each set utilizing a different type of transparent conductive oxide (TCO) top contact. One of the sets utilized a conventional TCO such as Indium Tin Oxide (ITO) where the other used a more cutting-edge high mobility TCO (HMTCO) such as Indium Molybdenum Oxide (IMO). Based off reduced free-carrier absorption that has been observed in IMO thin films over the past decade, the CIGS TFSC sample set utilizing IMO as a top contact is expected to have larger photocurrents and thus higher efficiencies than ITO devices. Before exploring this application to solar cells, the optical and electrical properties of IMO thin films deposited on soda-lime glass (SLG) substrates were studied independently. A process was developed that optimized both optical transmission and electrical resistivity of IMO films. Optimized IMO films showed resistivities on the order of 10-3 Ω-cm, where as ITO films deposited on SLG substrates using the optimized Hawaii Natural Energy Institute (HNEI) process exhibited resistivities on the order of 10-4 Ω-cm. However, IMO films showed superior transmittance in the infrared compared to ITO films, which is attributed to the lower carrier concentrations and higher mobilities found in IMO films. More details on this can be found in chapter 4. Once an optimized process was discovered for fabricating IMO films, the comparison of device performance between the two previously mentioned CIGS TFSC sample sets was investigated. It was observed that, with use of an anti-reflective (AR) coating, both sample sets achieved the same average short-circuit current (Jsc). However, the average open-circuit voltage (Voc) of the IMO sample set was observed to be 60 mV lower, leading to a corresponding lower average efficiency than the ITO devices. More details on this can be found in chapter 6.
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Selenium cells, Photovoltaic cells--Materials
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Theses for the degree of Master of Science (University of Hawaii at Manoa). Electrical Engineering.
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