Spectrum splitting photovoltaics: light trapping filtered concentrator for ultrahigh photovoltaic efficiency

Emily D. Kosten; Emily C. Warmann; John Lloyd; Harry A. Atwater

doi:10.1117/12.2024275

7 October 2013 Spectrum splitting photovoltaics: light trapping filtered concentrator for ultrahigh photovoltaic efficiency

Emily D. Kosten, Emily C. Warmann, John Lloyd, Harry A. Atwater

Author Affiliations +

Proceedings Volume 8821, High and Low Concentrator Systems for Solar Electric Applications VIII; 882109 (2013) https://doi.org/10.1117/12.2024275
Event: SPIE Solar Energy + Technology, 2013, San Diego, California, United States

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.

Citation Download Citation

Emily D. Kosten, Emily C. Warmann, John Lloyd, and Harry A. Atwater "Spectrum splitting photovoltaics: light trapping filtered concentrator for ultrahigh photovoltaic efficiency", Proc. SPIE 8821, High and Low Concentrator Systems for Solar Electric Applications VIII, 882109 (7 October 2013); https://doi.org/10.1117/12.2024275

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