Luminescent solar concentrators are largely dependent on concentration factor. The derived concentration factor values from previous research are always less than one; hence, various methods have been implemented in view of increasing the value of the concentration factor. The methods which rely on the application of large area luminescent solar collectors have also failed in producing solar factors greater than one. The cylindrical geometry of luminescent solar concentrators which offers greater potential compared with that of the planar geometry have also not almost been extensively studied before.
A new study led by professors Luís D. Carlos and Rute Ferreira from University of Aveiro in Portugal provided a new method for the fabrication of long-length fibre wave guiding luminescent solar concentrators with the use of an optical fibre manufacturing facility to obtain cylindrical large-area luminescent solar concentrators based on bulk-coated and hollow-core plastic optical fibres. The work was published in the journal, Progress in Photovoltaics: Research and Applications.
The authors fabricated in semi-industrial fibre manufacturing facility a length of approximately 2.5m bulk plastic optical fibres with di-ureasil, doped with either rhodamine 6G (RhdG) or Eu(tta)3.2H2O, coupled with another fabrication of PMMA-based hollow-core plastic optical fibres with di-ureasil [d-U(600)] or tripodal tri-ureasil [t-U(5000)] and doped with rhodamine or Eu(tta)3.2H2O. They further provided optical characterization of the surface and edges of the fibre waveguiding luminescent solar concentrators.
The authors showed similarities using emission spectra of fibre waveguiding luminescent solar concentrators collected at the fiber surface for the hollow-core and bulk-coated plastic optical fibres. Observations of the excitation spectrum at the optical active centers show a large ocerlap with that of AM1.5G within the region available for DS conversion. Also the luminescent solar concentrators with tripod tri-ureasil have high values of absolute emission quantum yield above 0.85.
A small value of refractive index contrast in the Eu(tta)3.2H2O -based fibre waveguiding luminescent solar concentrators resulted to a trapping efficiency of approximately 73% compared with that of the rhodamine-based which has a larger trapping efficiency of approximately 80%. The refractive index contrast was due to the difference between refractive index values of the PMMA and hybrid layer.
However, absorption losses were predominant in hollow-core geometry despite their higher trapping efficiency. After some further considerations, it was said that light propagation of the fibre waveguiding luminescent solar concentrators also depends on the absorption spectra of the hybrid and PMMA layers.
Low values of PMMA attenuation coefficient values for both Eu(tta)3.2H2O- and rhodamine-based fibre waveguiding luminescent solar concentrators indicated that light propagation may occur in total length of bulk-coated fibre waveguiding luminescent solar concentrators while light is expected to travel at a shorter length for hollow-core fibre waveguiding luminescent solar concentrators due to hybrids’ attenuation.
This study was able to achieve a high optical conversion efficiency of 72.4% and a concentration factor of 12.3 for the hollow-core fibre waveguiding luminescent solar concentrators. Maximum optical conversion efficiency and concentration factor for bulk-coated fibre waveguiding luminescent solar concentrators were 0.6% and 6.5 respectively.
The increased conversion efficiency and high value of concentration factor compared with previous reported ones verifies the approach used by the authors in developing lightweight and flexible high-performance waveguiding photovoltaics.
“This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID /CTM /50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement”
Correia, S.F.H.1,2, Lima, P.P.1, Pecoraro, E.3, Ribeiro, S.J.L.3, André, P.S.4, Ferreira, R.A.S.1, Carlos, L.D.1 Scale Up the Collection Area of Luminescent Solar Concentrators Towards Metre-Length Flexible Waveguiding Photovoltaics, Progress in Photovoltaics: Research and Applications 24 (2016) 1178-1193.