Large crystalline domains and enhanced exciton diffusion length enable efficient organic solar cells

Zhang, Y. , Sajjad, M. T., Blaszczyk, O., Parnell, A. J., Ruseckas, A., Serrano, L. A., Cooke, G. and Samuel, I. D.W. (2019) Large crystalline domains and enhanced exciton diffusion length enable efficient organic solar cells. Chemistry of Materials, (doi:10.1021/acs.chemmater.8b05293) (Early Online Publication)

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Abstract

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.

Item Type:Articles
Additional Information:The authors thank the European Research Council for financial support (EXCITON grant 321305).
Status:Early Online Publication
Refereed:Yes
Glasgow Author(s) Enlighten ID:Cooke, Professor Graeme and Zhang, Dr Yiwei
Authors: Zhang, Y., Sajjad, M. T., Blaszczyk, O., Parnell, A. J., Ruseckas, A., Serrano, L. A., Cooke, G., and Samuel, I. D.W.
College/School:College of Science and Engineering > School of Chemistry
College of Science and Engineering > School of Physics and Astronomy
Journal Name:Chemistry of Materials
Publisher:American Chemical Society
ISSN:0897-4756
ISSN (Online):1520-5002
Published Online:01 April 2019
Copyright Holders:Copyright © 2019 American Chemical Society
First Published:First published in Chemistry of Materials 2019
Publisher Policy:Reproduced in accordance with the publisher copyright policy
Data DOI:10.17630/6fb583c8-92b9-45ab-9040-de8ee764c517

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