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Broadband Up-Conversion at Subsolar Irradiance: Triplet Triplet Annihilation Boosted by Fluorescent Semiconductor Nanocrystals

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Monguzzi A., Braga D., Gandini M., Holmberg V. C., Kim D. K., Sahu A., Norris D. J., Meinardi F.,
Project Electronic Impurity Doping of Semiconductor Nanocrystals
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Original article (peer-reviewed)

Volume (Issue) 14(11)
Page(s) 6644 - 6650
Title of proceedings NANO LETTERS
DOI 10.1021/nl503322a


Conventional solar cells exhibit limited efficiencies in part due to their inability to absorb the entire solar spectrum. Sub-band-gap photons are typically lost but could be captured if a material that performs up-conversion, which shifts photon energies higher, is coupled to the device. Recently, molecular chromophores that undergo triplet−triplet annihilation (TTA) have shown promise for efficient up-conversion at low irradiance, suitable for some types of solar cells. However, the molecular systems that have shown the highest upconversion efficiency to date are ill suited to broadband light harvesting, reducing their applicability. Here we overcome this limitation by combining an organic TTA system with highly fluorescent CdSe semiconductor nanocrystals. Because of their broadband absorption and spectrally narrow, size-tunable fluorescence, the nanocrystals absorb the radiation lost by the TTA chromophores, returning this energy to the up-converter. The resulting nanocrystal-boosted system shows a doubled lightharvesting ability, which allows a green-to-blue conversion efficiency of ∼12.5% under 0.5 suns of incoherent excitation. This record efficiency at subsolar irradiance demonstrates that boosting the TTA by light-emitting nanocrystals can potentially provide a general route for up-conversion for different photovoltaic and photocatalytic applications.