Photostable Solar Concentrator Based On Fluorescent Glass Films

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Solar Energy Materials and Solar Cells 33 (1994) 417-427

Photostable solar concentrators based on fluorescent glass films
R e n a t a R e i s f e l d a,., D i m i t r i S h a m r a k o v a, C h r i s t i a n J o r g e n s e n b
a Department oflnorganic Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, b Department de Chimie Minerale,Analytique et Appliquee, Universite de Geneve, CH 1211 Geneva 4, Switzerland

Received 7 May 1993; in revised form 10 September 1993

Abstract

Efficient luminescent solar concentrators (LSC) were prepared by deposition of organically modified sol-gel films doped by photostable perylimide dyes on plexiglas substrates. The absorption spectra of these dyes extends from 420 to 620 nm covering thevisible part of the solar spectrum and the emission is between 550 and 750 nm, close to the optimum response of silicon and gallium arsenide solar cells. The efficiency of this type of collector was calculated from the absorption coefficients, quantum efficiency of the fluorescence and the overlap between emission and absorption spectra by the method of Monte-Carlo and found to be close to 20%. Optimumconcentrations are shown to be strongly dependent on the extent of overlap between the absorption and the emission spectra, which also appears to be the limiting factor in respect to the efficiency of the concentrator.

I. I n t r o d u c t i o n

There is no doubt that solar energy, which is clean and non-hazardous, could contribute considerably to a solution of the energy problem ifappropriate methods were developed to collect, concentrate, store and convert solar radiation, which is diffuse and intrinsically intermittent [1]. At present, large-scale solar cell arrays are operating in inaccessible locations distant from conventional electricity plants. Previous estimates of price decreases to $ 1 / W - $ 2 / W which were obtained by making comparisons with the aluminium orelectronic computers industry, may be slightly optimistic as the difficulties of preparing inexpensive silicon with a high

* Corresponding author. 0927-0248/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0927-0248(94)00006-E

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R. Reisfeld et al. / Solar Energy Materials and Solar Cells 33 (1994) 417-427

photoelectric yield cannot be easily removed by increased production.One way of lowering the price of PV electricity is to concentrate the solar radiation, particularly that part which is most efficient in PV energy conversion, on high efficiency solar cells which are expensive, but their amount and cost can be considerably diminished by using concentrated solar light on their small areas. Recently, there has been a serious progress in technical development of solarceils [2]. Especially very high conversion efficiencies have been found in AIGaAs ceils [3]. Thus, the light emitted as fluorescence from the edges of the concentrator can be matched to more than 50% efficiency of solar cells. Fig. 1 presents the standard solar spectrum AM 1.5 (curve 1) and spectral sensitivity of monocrystaUine silicon cell (curve 2) and A1GaAs cell [3] (curve 3). The operationof an LSC is based on absorption of solar radiation in a collector containing a fluorescent species in which the emission bands have little or no overlap with the absorption bands [4]. The fluorescence emission is trapped by

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