A Close Look at Charge Generation in Polymer:Fullerene Blends with Microstructure Control

Abstract
© 2015 American Chemical Society. We reveal some of the key mechanisms during charge generation in polymer:fullerene blends exploiting our well-defined understanding of the microstructures obtained in pBTTT:PCBM systems via processing with fatty acid methyl ester additives. Based on ultrafast transient absorption, electro-absorption, and fluorescence up-conversion spectroscopy, we find that exciton diffusion through relatively phase-pure polymer or fullerene domains limits the rate of electron and hole transfer, while prompt charge separation occurs in regions where the polymer and fullerene are molecularly intermixed (such as the co-crystal phase where fullerenes intercalate between polymer chains in pBTTT:PCBM). We moreover confirm the importance of neat domains, which are essential to prevent geminate recombination of bound electron-hole pairs. Most interestingly, using an electro-absorption (Stark effect) signature, we directly visualize the migration of holes from intermixed to neat regions, which occurs on the subpicosecond time scale. This ultrafast transport is likely sustained by high local mobility (possibly along chains extending from the co-crystal phase to neat regions) and by an energy cascade driving the holes toward the neat domains.

Citation
Scarongella M, De Jonghe-Risse J, Buchaca-Domingo E, Causa’ M, Fei Z, et al. (2015) A Close Look at Charge Generation in Polymer:Fullerene Blends with Microstructure Control. Journal of the American Chemical Society 137: 2908–2918. Available: http://dx.doi.org/10.1021/ja510032x.

Acknowledgements
M.S., M.C. and N.B. are funded by the Swiss National Science Foundation, through the Ambizione Fellowship (PZ00P2_136853) and the Stipend Professorship (PP00P2_150536). N.B. and M.C. are also supported by the

Publisher
American Chemical Society (ACS)

Journal
Journal of the American Chemical Society

DOI
10.1021/ja510032x

PubMed ID
25650696

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