Large crystalline domains and enhanced exciton diffusion length enable efficient organic solar cells
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We studied crystallinity and exciton harvesting in bulk heterojunctions of a semiconducting polymer PffBT4T-2OD and electron acceptor PC71BM which are used to make highly efficient organic solar cells. Grazing incidence wide-angle X-ray scattering (GIWAXS) shows that the size of crystalline domains of PffBT4T-2OD increases to ~18 nm in photovoltaic blends upon thermal annealing at 100 °C for 5 minutes. These domains are larger than the typical exciton diffusion lengths in conjugated polymers. Time-resolved fluorescence measurements show that exciton diffusion length in PffBT4T-2OD increases from ~14 to ~24 nm upon thermal annealing, which enables efficient charge generation in blends with large domains. Solar cells prepared using thermally annealed blends show higher photocurrent, open circuit voltage and fill factor compared to as spin-coated blends which indicates reduced recombination losses. Our results demonstrate the advantages of large crystalline domains in organic photovoltaics, providing exciton diffusion is sufficient.
Zhang , Y , Sajjad , M T , Blaszczyk , O , Parnell , A J , Ruseckas , A , Serrano , L A , Cooke , G & Samuel , I D W 2019 , ' Large crystalline domains and enhanced exciton diffusion length enable efficient organic solar cells ' , Chemistry of Materials , vol. 31 , no. 17 , pp. 6548-6557 . https://doi.org/10.1021/acs.chemmater.8b05293
Chemistry of Materials
© 2019, American Chemical Society. 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 as such may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1021/acs.chemmater.8b05293
DescriptionThe authors thank the European Research Council for financial support (EXCITON Grant 321305).
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