Energy versus electron transfer in organic solar cells: A comparison of the photophysics of two indenofluorene: Fullerene blend films

Ying W. Soon, Tracey M. Clarke, Weimin Zhang, Tiziano Agostinelli, James Kirkpatrick, Clare Dyer-Smith, Iain Mcculloch, Jenny Nelson, James R. Durrant

Research output: Contribution to journalArticlepeer-review

42 Scopus citations

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-(40,70-di-2-thienyl-20,10,30-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.

Original languageEnglish (US)
Pages (from-to)1111-1120
Number of pages10
JournalChemical Science
Volume2
Issue number6
DOIs
StatePublished - Jun 1 2011

ASJC Scopus subject areas

  • Chemistry(all)

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