Ultrafast Long-Range Charge Separation in Nonfullerene Organic Solar Cells

Abstract
Rapid, long-range charge separation in polymer-fullerene organic solar cells (OSCs) enables electrons and holes to move beyond their Coulomb capture radius and overcome geminate recombination. Understanding the nature of charge generation and recombination mechanisms in efficient, nonfullerene-acceptor-based OSCs are critical to further improve device performance. Here we report charge dynamics in an OSC using a perylene diimide (PDI) dimer acceptor. We use transient absorption spectroscopy to track the time evolution of electroabsorption caused by the dipolar electric field generated between electron-hole pairs as they separate after ionization at the donor-acceptor interface. We show that charges separate rapidly (<1 ps) and that free charge carriers are generated very efficiently (∼90% quantum yield). However, in the PDI-based OSC, external charge extraction is impaired by faster nongeminate decay to the ground state and to lower-lying triplet states.

Citation
Tamai, Y., Fan, Y., Kim, V. O., Ziabrev, K., Rao, A., Barlow, S., … Menke, S. M. (2017). Ultrafast Long-Range Charge Separation in Nonfullerene Organic Solar Cells. ACS Nano, 11(12), 12473–12481. doi:10.1021/acsnano.7b06575

Acknowledgements
The authors thank the Engineering and Physical Sciences Research Council (EPSRC) and the Winton Programme for the Physics of Sustainability. Y.T. was supported by JSPS Postdoctoral Fellowships for Research Abroad. Work at Georgia Tech was supported by the Department of the Navy, Office of Naval Research award no. N00014-14-1-0580 (CAOP MURI) and through a State-Sponsored Scholarship for Graduate Students to Y.F. from the China Scholarship Council. S.M.M. and R.H.F acknowledge support from the KAUST Competitive Research Grant Program.

Publisher
American Chemical Society (ACS)

Journal
ACS Nano

DOI
10.1021/acsnano.7b06575

Additional Links
https://pubs.acs.org/doi/10.1021/acsnano.7b06575

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