Journal
SCIENTIFIC REPORTS
Volume 7, Issue -, Pages -Publisher
NATURE PORTFOLIO
DOI: 10.1038/srep44269
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Funding
- EPSRC [EP/I028641/1, EP/J017361/1, EP/M025020/1]
- European Commission [658391]
- NSF [DMR-0520547]
- STFC/RCUK
- University of Sheffield
- Engineering and Physical Sciences Research Council [1434445, EP/M028437/1] Funding Source: researchfish
- EPSRC [EP/M028437/1] Funding Source: UKRI
- Marie Curie Actions (MSCA) [658391] Funding Source: Marie Curie Actions (MSCA)
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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 degrees 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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