title: Dissociation of Charge Transfer States and Carrier Separation in Bilayer Organic Solar Cells: A Time-Resolved Electroabsorption Spectroscopy Study.
abstract: Ultrafast optical probing of the electric field by means of Stark effect in planar heterojunction cyanine dye/fullerene organic solar cells enables one to directly monitor the dynamics of free electron formation during the dissociation of interfacial charge transfer (CT) states. Motions of electrons and holes is scrutinized separately by selectively probing the Stark shift dynamics at selected wavelengths. It is shown that only charge pairs with an effective electron-hole separation distance of less than 4 nm are created during the dissociation of Frenkel excitons. Dissociation of the coulombically bound charge pairs is identified as the major rate-limiting step for charge carriers' generation. Interfacial CT states split into free charges on the time-scale of tens to hundreds of picoseconds, mainly by electron escape from the Coulomb potential over a barrier that is lowered by the electric field. The motion of holes in the small molecule donor material during the charge separation time is found to be insignificant.
authors.affiliation: ∥Center for Physical Sciences and Technology, Savanoriu 231, LT-02300 Vilnius, Lithuania.
authors.forename: Andrius
authors.initials: A
authors.lastname: Devižis
authors.forename: Jelissa
authors.initials: J
authors.lastname: De Jonghe-Risse
authors.affiliation: §Laboratory for Functional Polymers, EMPA, Swiss Federal Laboratories for Materials Science and Technology, CH-8600, Dübendorf, Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: Hany
authors.affiliation: §Laboratory for Functional Polymers, EMPA, Swiss Federal Laboratories for Materials Science and Technology, CH-8600, Dübendorf, Switzerland.
authors.forename: Frank
authors.initials: F
authors.lastname: Nüesch
authors.affiliation: §Laboratory for Functional Polymers, EMPA, Swiss Federal Laboratories for Materials Science and Technology, CH-8600, Dübendorf, Switzerland.
authors.forename: Sandra
authors.initials: S
authors.lastname: Jenatsch
authors.affiliation: ∥Center for Physical Sciences and Technology, Savanoriu 231, LT-02300 Vilnius, Lithuania.
authors.forename: Vidmantas
authors.initials: V
authors.lastname: Gulbinas
authors.forename: Jacques-E
authors.initials: JE
authors.lastname: Moser