title: Direct Observation of Entropy-Driven Electron-Hole Pair Separation at an Organic Semiconductor Interface.
abstract: How an electron-hole pair escapes the Coulomb potential at a donor-acceptor interface has been a key issue in organic photovoltaic research. Recent evidence suggests that long-distance charge separation can occur on ultrafast time scales, yet the underlying mechanism remains unclear. Here we use charge transfer excitons (CTEs) across an organic semiconductor-vacuum interface as a model and show that nascent hot CTEs can spontaneously climb up the Coulomb potential within 100 fs. This process is driven by entropic gain due to the rapid rise in density of states with increasing electron-hole separation. In contrast, the lowest CTE cannot delocalize, but undergoes self-trapping and recombination.
authors.affiliation: Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Monahan
authors.affiliation: Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
authors.forename: Kristopher W
authors.initials: KW
authors.lastname: Williams
authors.affiliation: Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
authors.forename: Bharat
authors.initials: B
authors.lastname: Kumar
authors.affiliation: Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
authors.forename: Colin
authors.initials: C
authors.lastname: Nuckolls
authors.affiliation: Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
authors.forename: X-Y
authors.initials: XY
authors.lastname: Zhu