6 February 2013 Micro-optical design of photochemical upconverters for thin-film solar cells
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All presently available types of solar cells transmit light with energies below their band gaps, foregoing energy. An elegant way toward overcoming these subbandgap losses and using a larger fraction of the incident light is the re‐shaping of the solar spectrum by upconversion (UC) of photons. Recently, first results on solar cells augmented by either lanthanide-based UC or triplet-triplet-annihilation UC in organic chromophores were presented. Both of these UC strategies are characterized by a nonlinear response on the illumination density under conditions relevant to solar energy conversion, opening a route for increasing the UC yield by concentrating the light. While operation of the whole cell under concentrated sunlight is in most cases undesirable, application of micro-optical focusing of the transmitted light in the upconverting layer is a promising strategy. In the present work, a more than two-fold enhancement of the current gain by UC behind an amorphous silicon solar cell through optimization of the upconverter optical design is demonstrated, including employing a focusing microstructured back reflector. The experimental data is rationalized using a simple ray tracing modeling approach, highlighting a further enhancement potential of a microstructured UC unit.
© 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)
Tim F. Schulze, Yuen Yap Cheng, Tony H. Khoury, Maxwell Crossley, Bernd Stannowski, Klaus Lips, Timothy W. Schmidt, "Micro-optical design of photochemical upconverters for thin-film solar cells," Journal of Photonics for Energy 3(1), 034598 (6 February 2013). https://doi.org/10.1117/1.JPE.3.034598 . Submission:

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