Light trapping in fluorescent solar collectors

Abstract

A fluorescent solar collector (FSC) is an optoelectronic waveguide device that can concentrate both diffuse and direct sunlight onto a solar cell which is then converted to electricity. Fluorescent collectors offer the potential to reduce the cost of crystalline silicon (c-Si) solar cells, but so far their effectiveness has been demonstrated only theoretically.

The major problems in the device obtaining high practical efficiency are photon transport losses and material instability. This aim of this research is to increase the fundamental understanding of photon transport losses in fluorescent collectors, and to explore the method in overcoming the losses in fluorescent solar collectors. This thesis presents the theoretical and experimental results obtained during the development and characterisation of fluorescent collectors, a thin film c-Si solar cell used to detect photons from the fluorescent solar collector.

A method for preparing fluorescent collector plates was by spin-coating dye-doped PMMA (Polymethylmethacrylate) on glass slides (BK7 glass). An optical characterisation technique for determining reabsorption loss of the fluorescent collectors was developed and used to evaluate the performance of the fluorescent collector base on laser dyes. The validity of this approach was verified by comparing the results with theoretical solutions, derived using a model adapted from the Weber and Lambe, and the modified Weber and Lambe, theories.

Different losses in the FSC are studied in this work and we investigate the effect of surface scattering in a realistic FSC. To characterise the photon transport inside the collector, we monitor the angular distribution of a collimated light beam, which enters the collector from the edge, after propagation and total internal reflection. We find that the surface scattering process is described well by Fraunhofer diffraction at surface inhomogeneities of a size, roughly 11 ?m.

The major losses in FSC are found to be caused by the surface roughness, which increases the probability of the escape cone losses in FSC from the top surface. This loss can be suppressed to less than 2% using an index matching planarisation layer. The influence of the bulk and surface scattering on the performance of the FSC are presented in this work, which were compared with the experiment and theory.

The angular dependence of the edge fluorescence was studied in this work, and it showed the edge fluorescence decreases by increasing the detection angle, and the value of reabsorption also decreases by increasing the detection angle, up to 20°, before increasing again. It was shown, also, that that the quasi blackbody function agrees well with angular dependence of the edge fluorescence spectral, divided by the cos(detection angle) region where the absorption and fluorescence band of the dye overlap. Also, the modified Weber and Lambe theory for the angular dependence of the fluorescence agreed well with the experimental results.

More information

Identifiers

ORCID for B. Ganapathisubramani: orcid.org/0000-0001-9817-0486

Catalogue record

Export record