Tailoring exciton diffusion and domain size in photovoltaic small molecules by processing
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Exciton diffusion is an important part of light harvesting in organic photovoltaics (OPVs) because it enables excitons to reach the interface betweeen donor and acceptor and contribute to the photocurrent. Here we used simple and cost-effective techniques of thermal annealing and solvent vapour annealing to increase the exciton diffusion coefficient and exciton diffusion length in two liquid crystalline electron donor materials BQR and BTR. We found that the three-dimensional exciton diffusion length increased to ~40 nm upon annealing in both materials. Grazing-incidence wide angle X-ray scattering (GIWAXS) measurements show an increase of crystallite size to ~37 nm in both materials after thermal annealing. We determined an average domain size of these materials in the blends with PC71BM using diffusion-limited fluorescence quenching and found that it increased to 31 nm in BTR PC71BM blends and to 60 nm in BQR PC71BM blends. Our results provide understanding of how annealing improves device efficiency.
Sajjad , M T , Zhang , Y , Geraghty , P B , Mitchell , V D , Ruseckas , A , Blaszczyk , O , Jones , D J & Samuel , I D W 2019 , ' Tailoring exciton diffusion and domain size in photovoltaic small molecules by processing ' , Journal of Materials Chemistry C , vol. In press . https://doi.org/10.1039/C9TC00951E
Journal of Materials Chemistry C
Copyright © 2019, the Author(s). 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/10.1039/C9TC00951E