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Molecular weight dependent vertical composition profiles of PCDTBT:PC71BM blends for organic photovoltaics.

Kingsley, James W. and Marchisio, Pier Paolo and Yi, Hunan and Iraqi, Ahmed and Kinane, Christy J. and Langridge, Sean and Thompson, Richard L. and Cadby, Ashley J. and Pearson, Andrew J. and Lidzey, David G. and Jones, Richard A. L. and Parnell, Andrew J. (2014) 'Molecular weight dependent vertical composition profiles of PCDTBT:PC71BM blends for organic photovoltaics.', Scientific reports., 4 . p. 5286.


We have used Soxhlet solvent purification to fractionate a broad molecular weight distribution of the polycarbazole polymer PCDTBT into three lower polydispersity molecular weight fractions. Organic photovoltaic devices were made using a blend of the fullerene acceptor PC71BM with the molecular weight fractions. An average power conversion efficiency of 5.89% (peak efficiency of 6.15%) was measured for PCDTBT blend devices with a number average molecular weight of Mn = 25.5 kDa. There was significant variation between the molecular weight fractions with low (Mn = 15.0 kDa) and high (Mn = 34.9 kDa) fractions producing devices with average efficiencies of 5.02% and 3.70% respectively. Neutron reflectivity measurements on these polymer:PC71BM blend layers showed that larger molecular weights leads to an increase in the polymer enrichment layer thickness at the anode interface, this improves efficiency up to a limiting point where the polymer solubility causes a reduction of the PCDTBT concentration in the active layer.

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Date accepted:No date available
Date deposited:18 June 2014
Date of first online publication:June 2014
Date first made open access:No date available

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