High charge-separation efficiency combined with the reduced fabrication costs associated with solution processing and the potential for implementation on flexible substrates make ‘plastic’ solar cells a compelling option for tomorrow’s photovoltaics1. Attempts to control the donor/acceptor morphology in bulk heterojunction materials as required for achieving high power-conversion efficiency have, however, met with limited success2,3,4. By incorporating a few volume per cent of alkanedithiols in the solution used to spin-cast films comprising a low-bandgap polymer and a fullerene derivative, the power-conversion efficiency of photovoltaic cells (air-mass 1.5 global conditions) is increased from 2.8% to 5.5% through altering the bulk heterojunction morphology5. This discovery can potentially enable morphological control in bulk heterojunction materials where thermal annealing is either undesirable or ineffective.
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The research was financially supported by grants from the Department of Energy (DE-FC26-04NT42277) (G.C.B.), the Office of Naval Research (N0014-0411) (G.C.B.), the Department of Energy (DE-FG02-06ER46324)(A.J.H.), Konarka Technologies (A.J.H.) and by the Ministry of Science & Technology of Korea under the International Cooperation Research Program Global Research Laboratory Program. J.P. thanks the NDSEG fellowship for support. The authors thank J. Yuen for thin-film transistor substrate preparation and Tom Mates for assistance with XPS measurement and analysis. We thank C. J. Brabec, Z. Zou, D. Waller and R. Gaudiana at Konarka Technologies for making the PCPDTBT available for our use. We thank C. Waldauf for important discussions.
A. J. Heeger is a member of the board of directors of Konarka Technologies, and serves as chief scientist. The work reported here was carried out at UCSB; the University of California is seeking intellectual property rights on this discovery.
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Peet, J., Kim, J., Coates, N. et al. Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols. Nature Mater 6, 497–500 (2007). https://doi.org/10.1038/nmat1928
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