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Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/PC71BM devices.

Zhang, Yiwei and Parnell, Andrew J. and Pontecchiani, Fabio and Cooper, Joshaniel F. K. and Thompson, Richard L. and Jones, Richard A. L. and King, Stephen M. and Lidzey, David G. and Bernardo, Gabriel (2017) 'Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/PC71BM devices.', Scientific reports., 7 . p. 44269.


We demonstrate that the inclusion of a small amount of the co-solvent 1,8-diiodooctane in the preparation of a bulk-heterojunction photovoltaic device increases its power conversion efficiency by 20%, through a mechanism of transient plasticisation. We follow the removal of 1,8-diiodooctane directly after spin-coating using ellipsometry and ion beam analysis, while using small angle neutron scattering to characterise the morphological nanostructure evolution of the film. In PffBT4T-2OD/PC71BM devices, the power conversion efficiency increases from 7.2% to above 8.7% as a result of the coarsening of the phase domains. This coarsening process is assisted by thermal annealing and the slow evaporation of 1,8-diiodooctane, which we suggest, acts as a plasticiser to promote molecular mobility. Our results show that 1,8-diiodooctane can be completely removed from the film by a thermal annealing process at temperatures ≤100 °C and that there is an interplay between the evaporation rate of 1,8-diiodooctane and the rate of domain coarsening in the plasticized film which helps elucidate the mechanism by which additives improve device efficiency.

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Publisher statement:This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit © The Author(s) 2017.
Date accepted:07 February 2017
Date deposited:21 March 2017
Date of first online publication:13 March 2017
Date first made open access:No date available

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