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Issue 6, 2011
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Energy versus electron transfer in organic solar cells: a comparison of the photophysics of two indenofluorene: fullerene blend films

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Abstract

In this paper, we compare the photophysics and photovoltaic device performance of two indenofluorene based polymers: poly[2,8-(6,6,12,12-tetraoctylindenofluorene)-co-4,7-(2,1,3-benzothiodiazole] (IF8BT) and poly[2,8-(6,6,12,12-tetraoctylindenofluorene)-co-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiodiazole] (IF8TBTT) blended with [6,6]-phenyl C61 butyric acid methyl ester (PCBM). Photovoltaic devices made with IF8TBTT exhibit greatly superior photocurrent generation and photovoltaic efficiency compared to those made with IF8BT. The poor device efficiency of IF8BT/PCBM devices is shown to result from efficient, ultrafast singlet Förster energy transfer from IF8BT to PCBM, with the resultant PCBM singlet exciton lacking sufficient energy to drive charge photogeneration. The higher photocurrent generation observed for IF8TBTT/PCBM devices is shown to result from IF8TBTT's relatively weak, red-shifted photoluminescence characteristics, which switches off the polymer to fullerene singlet energy transfer pathway. As a consequence, IF8TBTT singlet excitons are able to drive charge separation at the polymer/fullerene interface, resulting in efficient photocurrent generation. These results are discussed in terms of the impact of donor/acceptor energy transfer upon photophysics and energetics of charge photogeneration in organic photovoltaic devices. The relevance of these results to the design of polymers for organic photovoltaic applications is also discussed, particularly with regard to explaining why highly luminescent polymers developed for organic light emitting diode applications often give relatively poor performance in organic photovoltaic devices.

Graphical abstract: Energy versus electron transfer in organic solar cells: a comparison of the photophysics of two indenofluorene: fullerene blend films

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Publication details

The article was received on 02 Dec 2010, accepted on 21 Feb 2011 and first published on 18 Mar 2011


Article type: Edge Article
DOI: 10.1039/C0SC00606H
Citation: Chem. Sci., 2011,2, 1111-1120
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    Energy versus electron transfer in organic solar cells: a comparison of the photophysics of two indenofluorene: fullerene blend films

    Y. W. Soon, T. M. Clarke, W. Zhang, T. Agostinelli, J. Kirkpatrick, C. Dyer-Smith, I. McCulloch, J. Nelson and J. R. Durrant, Chem. Sci., 2011, 2, 1111
    DOI: 10.1039/C0SC00606H

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