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Photovoltaics: Upconversion Configurations versus Tandem Cells
Published online by Cambridge University Press: 10 July 2017
Abstract
For a wide range of bandgaps of solar cell materials, the potential contribution of upconversion materials was calculated and related to various configurations of the solar cell and upconversion layers. Moreover, by comparing these various strategies with the potential of a dual junction tandem cell configuration, a compelling case is made for upconverters.
At idealized 100% conversion efficiency, the upconverter with a single junction cell is more efficient than a dual junction tandem cell. It was also found that a single junction cell with an upconverter that is ‘only’ 80% efficient has a similar efficiency as an ideal dual junction cell. This result shows that upconverters are certainly a route worthwhile to pursue, especially because the single junction cells plus upconverters could have more cost reduction potential than dual junction cell configurations.
Additionally, it was investigated if an upconverter that uses two different photon energies would create a large surplus in efficiency. For a cell band gap of 1.55 eV a theoretical maximum efficiency (here defined as Voc*Isc) of 54.5% was calculated. Although there is a further increase in efficiency compared to converters with a single conversion energy, very careful bandgap tuning with a tolerance < 0.02 eV is required, which makes this system rather sensitive for material and solar spectrum fluctuations and it is suggested that a simple upconverter material is a more favorable strategy.
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