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Proceedings Paper

Spectrum splitting photovoltaics: light trapping filtered concentrator for ultrahigh photovoltaic efficiency
Author(s): Emily D. Kosten; Emily C. Warmann; John Lloyd; Harry A. Atwater
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Paper Abstract

While monolithic multijunction solar cell approaches have been quite successful, current and lattice matching requirements limit the maximum possible achievable efficiencies. Spectrum splitting, where light is optically distributed among subcells with differing bandgaps, avoids these constraints and offers a route to achieving higher efficiencies (<50%). We investigate a spectrum splitting approach where concentrated sunlight is trapped in a textured dielectric slab and then selectively coupled into underlying solar cells of different bandgaps through omnidirectional filters. We develop a multipass optical model to find regimes of high optical efficiency based on parameters such as slab refractive index, number of subcells, and angle restriction of light escape from the slab. Based on these results and filter design considerations, we describe a specific design featuring a textured slab of SiO2 coated with angle restricting incoupling elements based on compound parabolic concentrators and three underlying multijunction junction solar cells, for a total of eight junctions with bandgaps ranging from 2.2eV to 0.7. Using the multipass model in conjunction with modified detailed balance calculations, we find module efficiencies exceeding 50% are possible with an acceptance angle restricted to 20° or less and concentrations of a few hundred suns with ideal omnidirectional filters. Finally as proof of concept, we design a full set of omnidirectional filters for this design. Based on alternating layers of TiO2 and SiO2, we achieve angle averaged reflectivity greater than 90% within the reflection band and angle averaged transmission of approximately 90% within the transmission band for the long pass filter, for nearly 48% receiver efficiency.

Paper Details

Date Published: 7 October 2013
PDF: 3 pages
Proc. SPIE 8821, High and Low Concentrator Systems for Solar Electric Applications VIII, 882109 (7 October 2013); doi: 10.1117/12.2024275
Show Author Affiliations
Emily D. Kosten, California Institute of Technology (United States)
Emily C. Warmann, California Institute of Technology (United States)
John Lloyd, California Institute of Technology (United States)
Harry A. Atwater, California Institute of Technology (United States)

Published in SPIE Proceedings Vol. 8821:
High and Low Concentrator Systems for Solar Electric Applications VIII
Adam P. Plesniak, Editor(s)

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