title: Polarization Energies at Organic-Organic Interfaces: Impact on the Charge Separation Barrier at Donor-Acceptor Interfaces in Organic Solar Cells.
abstract: We probe the energetic landscape at a model pentacene/fullerene (C60) interface to investigate the interactions between positive and negative charges, which are critical to the processes of charge separation and recombination in organic solar cells. Using a polarizable force field, we find that polarization energy, i.e., the stabilization a charge feels due to its environment, is larger at the interface than in the bulk for both a positive and a negative charge. The combination of the charge being more stabilized at the interface and the Coulomb attraction between the charges results in a barrier to charge separation at the pentacene/C60 interface that can be in excess of 0.7 eV for static configurations of the donor and acceptor locations. However, the impact of molecular motions, i.e., the dynamics, at the interface at room temperature results in a distribution of polarization energies and in charge separation barriers that can be significantly reduced. The dynamic nature of the interface is thus critical, with the polarization energy distributions indicating that sites along the interface shift in time between favorable and unfavorable configurations for charge separation.
authors.affiliation: Solar and Photovoltaics Engineering Research Center, King Abdullah University of Science and Technology , Thuwal 23599-6900, Kingdom of Saudi Arabia.|School of Chemistry and Biochemistry & Center for Organic Photonics and Electronics, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Ryno
authors.affiliation: School of Chemistry and Biochemistry & Center for Organic Photonics and Electronics, Georgia Institute of Technology , Atlanta, Georgia 30332-0400, United States.
authors.forename: Yao-Tsung
authors.initials: YT
authors.lastname: Fu
authors.affiliation: Department of Chemistry & Center for Applied Energy Research, University of Kentucky , Lexington, Kentucky 40506-0055, United States.
authors.forename: Chad
authors.initials: C
authors.lastname: Risko
authors.affiliation: Solar and Photovoltaics Engineering Research Center, King Abdullah University of Science and Technology , Thuwal 23599-6900, Kingdom of Saudi Arabia.
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Brédas
keywords: charge separation and recombination; energetic disorder; molecular dynamics; multiscale modeling; organic photovoltaics; organic−organic interfaces; polarization