Correlating photovoltaic properties of PTB7-Th:PC71BM blend to photophysics and microstructure as a function of thermal annealing
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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.
Krishnan Jagadamma , L , Sajjad , M T , Savikhin , V , Toney , M & Samuel , I D W 2017 , ' Correlating photovoltaic properties of PTB7-Th:PC71BM blend to photophysics and microstructure as a function of thermal annealing ' , Journal of Materials Chemistry A , vol. 5 , no. 28 , pp. 14646-14657 . https://doi.org/10.1039/C7TA03144K
Journal of Materials Chemistry A
© 2017, Royal Society of Chemistry. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at pubs.rsc.org / https://doi.org/10.1039/C7TA03144K
DescriptionWe acknowledge support from EPSRC (grant number EP/L012294/1) and the European Research Council (grant number 321305). I.D.W.S. also acknowledges a Royal Society Wolfson Research Merit Award. VS acknowledges support from the Office of Naval Research NDSEG fellowship. Research data supporting this paper is available at doi http://dx.doi.org/10.17630/eadf56f3-8c70-47da-ac6d-67f2d78b3f74
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