There are several factors which conspire to limit the efficiency of solar cells. One of these is the fact that a solar cell is unable to absorb photons of energy less than the band gap of the semiconductor from which it is made; in the case of some high-band gap materials such as amorphous silicon – the model system used in this study – this can mean that as much as 50% of the solar spectrum is unusable. Upconversion phosphors – materials which can, by way of two or more successive photon absorptions, convert low energy (typically near infrared) light into high energy (typically visible) light – offer a potential solution to this problem as they can be used to convert light, which would otherwise be useless to the cell, into light which can be used for power generation. In this thesis we work towards the application of NaYF4-based upconverters to enhanced efficiency amorphous silicon (a-Si) photovoltaic power generation. We begin by synthesizing these upconverters at a range of temperatures and studying the crystallographic and spectroscopic properties of the resulting materials, elucidating heretofore undocumented trends in their luminescence and crystallography, including the effect of synthesis temperature on upconversion intensity, crystallite size, and lattice parameter. We also investigate the emission quantum yield of these materials, beginning with an in depth discussion and investigation of two methods for recording absolute quantum yields. We demonstrate that the quantum yields of the materials may vary by a factor of over 100, depending on the synthesis conditions. After we have fully characterized these properties we turn our attention to the application of these materials to amorphous silicon solar cells, for which we provide a proof of concept by demonstrating the effect of upconversion luminescence on the photoconductance of an a-Si film. We conclude by developing a roadmap for future improvements in the field.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/35065 |
| Date | 28 February 2013 |
| Creators | Faulkner, Daniel Owen |
| Contributors | Kherani, Nazir P., Ozin, Geoffrey Alan, Perovic, Doug |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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