School of Chemistry - Theses

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End date: 2023 × Start date: 2020 × Subject: Cross-linker × Subject: Nanoparticles ×

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    Energy Transfer Systems for Light Harvesting
    Pervin, Rehana ( 2023-03)
    Luminescent solar concentrators (LSCs) are solar harvesting devices that employ luminescent materials embedded within a waveguide to collect solar energy. The waveguide is typically made of a low-cost material such as glass or plastic and is designed to capture sunlight and redirect it towards solar cells. The luminescent materials, also known as luminophores, absorb the sunlight and re-emit it at a longer wavelength, allowing it to be trapped within the waveguide and guided towards the edges, where solar cells can convert the light into electricity. However, their performance is associated with several drawbacks, including reabsorption, which refers to the primary emission of the luminophore in the waveguide being reabsorbed by other luminophores in the waveguide. To overcome this, various strategies have been explored such as using different types of luminophores, optimizing the concentration of luminophores, and improving the design of the waveguide. Foster energy transfer (FRET), which reduces luminophore reabsorption, is a crucial aspect for improving energy conversion and device efficiency in LSCs. FRET works on separating the absorption and emission spectra of the luminophores by controlling the intermolecular spacing between donor and emitter molecules. Implementing these strategies can significantly enhance the performance of LSCs and accelerate their practical applications for solar energy harvesting. This thesis aims to advance the understanding of different energy transfer strategies for light harvesting applications. To implement an effective FRET approach, the concentration of luminophores is a crucial factor. The donor luminophore concentration should be higher than that of the emitter to allow energy migration through several donors to reach the emitter. However, increasing the dye concentration often leads to dye aggregation, which can quench the dye's fluorescence properties. To mitigate dye aggregation, molecular insulation in the luminophores can be an effective approach. In this thesis, the molecular insulation strategy is applied to both the donor and emitter luminophores to suppress dye aggregation at high concentrations. Several sterically hindered groups have been employed for both the donor and emitter through the imide position of the luminophore, and their photophysical properties have been observed at various concentrations. The results demonstrate that these sterically hindered groups effectively reduce dye aggregation at high dye concentrations. Furthermore, incorporating luminophores in a polymer backbone enables efficient energy transfer from the donor to the emitter by controlling the distance between the luminophores. The polymer chain acts as a spacer between the luminophores, reducing dye aggregation and suppressing the reabsorption issue. To investigate this approach, a variety of linear polymers with incorporated luminophores were employed in this study, where the luminophores were covalently linked to the polymer chain. Optical properties were analysed in both solid and solution states, and it was determined that this strategy did not adversely affect the luminophore's optical characteristics. Moreover, it was discovered that the more sterically hindered donor efficiently transferred its energy to the emitter, effectively suppressing aggregation-caused quenching (ACQ) in comparison to the less sterically hindered donor molecule. The success of the FRET energy transfer technique in polymer chains has inspired the use of crosslinked luminophore embedded nanoparticles for light harvesting. This approach involves embedding the dye within the polymer particles, resulting in a high dye concentration in a small area and promoting efficient energy transfer. In this study, a series of donor-emitter luminophore embedded crosslinked nanoparticles were synthesized using various luminophore concentrations, and their photophysical properties were studied to examine FRET efficiency. The cross-linked polymer particles effectively reduced luminophore aggregation and reabsorption. These polymer nanoparticles were used to fabricate bulk LSC films, which also demonstrated effective energy transfer. The photophysical observations were subsequently utilized in Monte-Carlo simulations of a large-scale bulk LSC device. The simulation results indicated that the incorporation of cross-linked polymer particles had a significant effect in mitigating the reabsorption process of luminophores in the bulk LSC waveguide.