Application of Fluorescent and Photonic Concentrators to Solar cells

Abstract

Fluorescent solar collectors are cheap plates made generally of glass or plastic that is doped with fluorescent molecules. Fluorescence can be used to trap incident solar radiation in order to concentrate light and also to shift the radiation to wavelengths converted at higher efficiencies. This project investigates both these aspects. Solar concentration using fluorescent solar collectors is examined for different combinations of solar cells and mirrors coupled to different surfaces of fluorescent solar collectors. The effects of the fabrication method i.e. spin coating or moulding is also studied. Modelling of the fluorescence re-absorption is the key to obtain the efficiency of such systems and these models will be shown to be useful in the optimisation of certain configurations of fluorescent collectors that behave like ideal models. On comparison with experimental results these models can also be used to quantify and identify losses in configurations that suffer additional losses. Devices tested in the lab are estimated to have the potential to achieve power conversion efficiencies close to 4% while results of optimisation results indicate possible further improvements. Angular resolved measurements of the fluorescence exiting the fluorescent solar collector edge is also used to study the photon transport of light within these devices. The combination of solar concentration and wavelength shifting (to wavelengths with superior solar cell performance) has been exploited for application to cadmium telluride solar cells for the first time. The theory of operation of these devices is used to model the current output measured experimentally. Novel photonic-based structures that incorporate fluorescent molecules within one-dimensional photonic crystals has also been fabricated and characterised. It will be shown that these devices have the potential to reduce fundamental loss mechanisms found in conventional fluorescent solar collectors by suppressing and reducing emission within loss cones and tuning emission reaching the solar cells to certain wavelengths. The theory of operation of these devices will used to describe the propagation of light within the structure and explain the experimentally measured emission characteristics. The maximum theoretical efficiencies of photonic-based fluorescent solar collectors have also been derived and adapted from previous work to show the potential of such devices.

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