Spectroscopy of luminescence materials for optimizing down-conversion efficiency
LE3 .A278 2014
van der Ende, Bryan
Bachelor of Science
This research project explores improving the current e ciencies of silicon photo- voltaic (PV) cells by using a spectral adaption technique to overcome the Shockley- Quessier limit of 30% e ciency. In theory, this approach minimizes the amount of energy lost primarily due to a mismatch between the solar emission spectrum and spectral response of crystalline silicon to achieve e ciency near 40%. The reduc- tion of these energy losses can be realized by the process of down-conversion (DC), which converts a single photon of relatively high-energy into two photons of lower en- ergy to increase the generation of electron-hole pairs in the semiconductor. Inorganic phosphorescent materials with intentional impurities can be administered to modify pre-existing silicon PV cells. This modi cation increases the absorption and emission of near-infrared photons. The luminescence compounds investigated were gadolinium, yttrium, and lan- thanum vanadate with varying dopant concentrations of ytterbium synthesized using a solid-state reaction procedure. By analyzing the powder x-ray di raction patterns, information is obtained regarding the crystal structure of the synthesized compounds for comparison to accepted values of the lattice parameters. Additionally, the e ect of replacement of the lanthanide ions in the crystal host lattice by dopant ions has been examined. Using spectroscopic techniques, the change in quantum cutting e ciencies as a function of dopant concentration can be observed. GdVO4 : 4 % Yb3+ yields the highest quantum e ciency (QE) at 198 %. Furthermore, these techniques provide information on the energetic positions of the optical transitions leading to emission of light and the energetic positions of absorption transitions.
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