title: Nanoscale transport of charge-transfer states in organic donor-acceptor blends.
abstract: 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.
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: P B
authors.initials: PB
authors.lastname: Deotare
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: W
authors.initials: W
authors.lastname: Chang
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: E
authors.initials: E
authors.lastname: Hontz
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: D N
authors.initials: DN
authors.lastname: Congreve
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: L
authors.initials: L
authors.lastname: Shi
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: P D
authors.initials: PD
authors.lastname: Reusswig
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: B
authors.initials: B
authors.lastname: Modtland
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Bahlke
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: C K
authors.initials: CK
authors.lastname: Lee
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: A P
authors.initials: AP
authors.lastname: Willard
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: V
authors.initials: V
authors.lastname: Bulović
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: T
authors.initials: T
authors.lastname: Van Voorhis
authors.affiliation: Center for Excitonics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Baldo