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Bifacial n-type silicon solar cells for upconversion applications

: Rüdiger, M.; Fischer, S.; Frank, J.; Ivaturi, A.; Richards, B.S.; Krämer, K.W.; Hermle, M.; Goldschmidt, J.C.


Solar energy materials and solar cells 128 (2014), pp.57-68
ISSN: 0927-0248
Journal Article
Fraunhofer ISE ()
Solarzellen - Entwicklung und Charakterisierung; Silicium-Photovoltaik; Farbstoff; Organische und Neuartige Solarzellen; Herstellung von hocheffizienten Solarzellen; Photonenmanagement; Hochkonversion; Simulation; Solarzellen

Upconversion of sub-band-gap photons has the potential to increase the efficiency of solar cells significantly, but requires modification of the solar cells. In this paper, we present a calculation framework to assess the efficiency of a combined bifacial silicon solar cell upconverter device, which is then used to optimize the solar cell׳s front and rear side anti-reflection coatings. Our calculations show that an upconverter can increase the efficiency of an optimized solar cell by 3.0% relative. Subsequently, planar bifacial n-type silicon solar cells were fabricated with optimized anti-reflection coatings. An upconversion layer – containing the upconverter phosphor β-NaY0.8Er0.2F4 embedded in the polymer perfluorocyclobutyl – was attached to the rear side of the solar cells and an external quantum efficiency arising from the upconversion of sub-band-gap photons of 1.69% was measured under 1508 nm monochromatic excitation with an irradiance of 1091 W/m2. This corresponds to a value of 0.15 (W/cm2)−1 when normalized to the irradiance, constituting a five-fold increase compared to the previously best published normalized values that were achieved without optimized solar cells.