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Bulk heterojunction solar cells with internal quantum efficiency approaching 100%

Abstract

We report the fabrication and measurement of solar cells with 6% power conversion efficiency using the alternating co-polymer, poly[N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT) in bulk heterojunction composites with the fullerene derivative [6,6]-phenyl C70-butyric acid methyl ester (PC70BM). The PCDTBT/PC70BM solar cells exhibit the best performance of any bulk heterojunction system studied to date, with JSC = 10.6 mA cm−2, VOC = 0.88 V, FF = 0.66 and ηe = 6.1% under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW cm−2. The internal quantum efficiency is close to 100%, implying that essentially every absorbed photon results in a separated pair of charge carriers and that all photogenerated carriers are collected at the electrodes.

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Figure 1: Device structure and energy level diagram of the components.
Figure 2: The effects of TiOx layer as an optical spacer on device performance.
Figure 3: The effects of CF, CB and DCB solvents on film morphology and device performance.
Figure 4: The effect of blending ratio on film morphology and device performance.
Figure 5: Internal quantum efficiency (IQE) of PCDTBT:PC70BM solar cells.
Figure 6: Power conversion efficiency of PCDTBT:PC70BM solar cells.

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Acknowledgements

The research leading to the results reported here was supported by the Air Force Office of Scientific Research, the Department of Energy and by a grant from the US Army CERDC. The TiOx development work was carried out at the Heeger Center for Advanced Materials (Gwangju Institute of Science and Technology (GIST) and UCSB) with support from under the Global Research Laboratory (GRL) Program sponsored by the Korean Government. The authors thank C. Brabec and R. Gaudiana for advice and encouragement, and for supplying the PC70BM. The measurements at NREL were carried out by P. Ciszek and K. Emery. We thank them for their help and cooperation.

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Correspondence to Kwanghee Lee or Alan J. Heeger.

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Alan J. Heeger is on the Board of Directors at Konarka Technologies Inc. He also serves as chief scientist for Konarka.

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Park, S., Roy, A., Beaupré, S. et al. Bulk heterojunction solar cells with internal quantum efficiency approaching 100%. Nature Photon 3, 297–302 (2009). https://doi.org/10.1038/nphoton.2009.69

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