Nanoscale transport of charge-transfer states in organic donor–acceptor blends

Charge-transfer (CT) states, bound combinations of an electron and a hole on separate molecules, play a crucial role in organic optoelectronic devices. We report direct nanoscale imaging of the transport of long-lived CT states in molecular organic donor–acceptor blends, which demonstrates that the...

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Bibliographic Details
Published in:	Nature materials Vol. 14; no. 11; pp. 1130 - 1134
Main Authors:	Deotare, P. B., Chang, W., Hontz, E., Congreve, D. N., Shi, L., Reusswig, P. D., Modtland, B., Bahlke, M. E., Lee, C. K., Willard, A. P., Bulović, V., Van Voorhis, T., Baldo, M. A.
Format:	Journal Article
Language:	English
Published:	London Nature Publishing Group UK 01-11-2015 Nature Publishing Group
Subjects:	639/301 639/301/1005 639/925/930/2735 Biomaterials Blends Condensed Matter Physics Diffusion Electrons Excitons Imaging Magnetic fields Materials Science Nanostructure Nanotechnology Optical and Electronic Materials Optoelectronic devices Photovoltaic cells Polymer blends Solar cells Transport
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Summary:	Charge-transfer (CT) states, bound combinations of an electron and a hole on separate molecules, play a crucial role in organic optoelectronic devices. We report direct nanoscale imaging of the transport of long-lived CT states in molecular organic donor–acceptor blends, which demonstrates that the bound electron–hole pairs that form the CT states move geminately over distances of 5–10 nm, driven by energetic disorder and diffusion to lower energy sites. Magnetic field dependence reveals a fluctuating exchange splitting, indicative of a variation in electron–hole spacing during diffusion. The results suggest that the electron–hole pair of the CT state undergoes a stretching transport mechanism analogous to an ‘inchworm’ motion, in contrast to conventional transport of Frenkel excitons. Given the short exciton lifetimes characteristic of bulk heterojunction organic solar cells, this work confirms the potential importance of CT state transport, suggesting that CT states are likely to diffuse farther than Frenkel excitons in many donor–acceptor blends. Direct visualization of the motion of long-lived charge-transfer states in an organic blend reveals that bound electron–hole pairs stretch and contract, and diffuse more than 10 nm before they dissociate or recombine.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1476-1122 1476-4660
DOI:	10.1038/nmat4424