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Correlating photovoltaic properties of PTB7-Th:PC71BM blend to photophysics and microstructure as a function of thermal annealing

Abstract

Selective optimisation of light harvesting materials and interface properties has brought breakthroughs in power conversion efficiency (11-12 %) of organic photovoltaics (OPVs). However to translate this promising efficiency to economically viable applications, long term stability is a fundamental requirement. A number of degradation pathways, both extrinsic and intrinsic, reduce the long term stability of OPVs. Here, the photovoltaic properties of a highly efficient bulk heterojunction PTB7-Th:PC71BM blend were investigated as a function of thermal annealing. The changes in charge generation, separation, and transport due to thermal annealing were measured and related to changes in the microstructure and photovoltaic performance. A 30 % drop in power conversion efficiency of PTB7-Th:PC71BM blends upon thermal annealing at 150 oC was identified as mainly due to morphological instability induced by strong phase separation of donor and acceptor molecules of the blend films. Based on the insight gained from these investigations, enhanced thermal stability was demonstrated by replacing the PC71BM fullerene acceptor with the non-fullerene acceptor ITIC, for which power conversion efficiency dropped only by 9 % upon thermal annealing at 150 oC.

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Publication details

The article was received on 11 Apr 2017, accepted on 04 Jun 2017 and first published on 08 Jun 2017


Article type: Paper
DOI: 10.1039/C7TA03144K
Citation: J. Mater. Chem. A, 2017, Accepted Manuscript
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    Correlating photovoltaic properties of PTB7-Th:PC71BM blend to photophysics and microstructure as a function of thermal annealing

    L. K. Jagadamma, M. T. Sajjad, V. Savikhin, M. F. Toney and I. D. W. Samuel, J. Mater. Chem. A, 2017, Accepted Manuscript , DOI: 10.1039/C7TA03144K

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