Forster Resonance Energy Transfer in materials used in Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) or fluorescent concentrators are a cheap and efficient way to concentrate sun light into a photovoltaic cell. Solar cells can be made to perform better under high illumination conditions and LSCs can be employed to perform this task. Effective utilization of space is another added advantage of coupling LSCs with solar cells. They are made up of transparent materials like glass or poly-methyl methacrylate mixed with a dye. The dye molecule absorbs incident radiation and emits fluorescence. Total internal reflection of the emitted fluorescence, within the transparent material is guided to the edges. Concentrator ratio can be increased if we reduce the number of photons that can be lost. Two major loss mechanisms are dependent on the choice of fluorescent material: Non-unity quantum yield and reabsorption of the emitted fluorescence. Organic dyes have high quantum yields but suffer from reabsorption due to a large spectral overlap between the absorption and emission profiles. Semiconductor nanoparticles have little or no spectral overlap but suffer from low quantum yields. Organic donor-acceptor chromophores have been suggested to solve this problem. The donor part of the molecule absorbs the sun’s radiation and transfers it to the acceptor. The acceptor molecule is the emitting fluorophore which is shifted to lower energy reducing the chances of reabsorption. Covalently linked donating and accepting fluorophores will act as an energy down-converting system where absorbed energy is reduced. This sacrifice of energy is necessary to conserve the number of photons reaching the cell. This thesis provides a molecular level insight into the behaviour of Perylene-based chromophoric arrays. It involves a detailed spectroscopic analysis of these molecules using time resolved techniques. It identifies competing processes that can reduce the efficiency of energy transfer and suggests, on ways to design and improve these arrays.