School of Chemistry - Theses
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ItemUnderstanding cadmium telluride nanocrystal solar cells( 2016)Solution-processed solar cells use cheaper manufacturing methods that could potentially bring down the cost of solar energy to be cost-competitive with fossil fuels. However, solution processed solar cells still have many issues that keep them from being commercially viable. While several solution processed techniques have resulted in efficiencies comparable to solar cells available on the market, there are many issues with long-term performance and stability. The work presented here is focused on one of the major candidates for commercial development of solution-processed solar cells. Nanocrystal (NC) cadmium telluride (CdTe) solar cells have reached power conversion efficiencies of over 12 % which is comparable to commercially available CdTe solar cells that use high cost vacuum depositions. However, these efficiencies are reached with a biasing treatment and degrade over time. We refer to the improvement in PCE through biasing treatments as “the biasing effect”. The work presented in this thesis will give a comprehensive analysis of NC CdTe solar cells by understanding the role of processing steps on chemical and electronic properties of CdTe films. Following this, we will show the major cause of degradation of NC CdTe films and devices. We will give comprehensive understanding and show the cause of the biasing effect. Finally we will show some possibilities for stabilizing and improving the current nanocrystal CdTe device which is an integral part of commercializing this technology. This thesis will answer the following questions: 1. What is the purpose of the cadmium chloride treatment and temperature annealing in NC CdTe films? 2. What is the cause of degradation and the biasing effect? 3. Can we stabilize and improve the device?
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ItemSynthesis and optical properties of CdSe core and core/shell nanocrystals( 2008)The synthesis of nanocrystals is unique compared to the formation of larger micron-sizesspecies as the final crystal sizes are not much larger than the primary nuclei. As a consequencethe final outcome of a nanocrystal synthesis i.e mean crystal size, concentrationand standard deviation is almost solely determined by the end of the nucleation phase. Directingthe growth of crystals beginning from aggregates of only tens of atoms into maturemonodisperse nanocrystals requires that the governing kinetics are strictly controlled at everymoment of the reaction. To effect this task various different ligands need to be employed,each performing a particular function during both nucleation and growth. (For complete abstract open document)