title: Visualizing excitations at buried heterojunctions in organic semiconductor blends.
abstract: Interfaces play a crucial role in semiconductor devices, but in many device architectures they are nanostructured, disordered and buried away from the surface of the sample. Conventional optical, X-ray and photoelectron probes often fail to provide interface-specific information in such systems. Here we develop an all-optical time-resolved method to probe the local energetic landscape and electronic dynamics at such interfaces, based on the Stark effect caused by electron-hole pairs photo-generated across the interface. Using this method, we found that the electronically active sites at the polymer/fullerene interfaces in model bulk-heterojunction blends fall within the low-energy tail of the absorption spectrum. This suggests that these sites are highly ordered compared with the bulk of the polymer film, leading to large wavefunction delocalization and low site energies. We also detected a 100 fs migration of holes from higher- to lower-energy sites, consistent with these charges moving ballistically into more ordered polymer regions. This ultrafast charge motion may be key to separating electron-hole pairs into free charges against the Coulomb interaction.
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Jakowetz
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Marcus L
authors.initials: ML
authors.lastname: Böhm
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Aditya
authors.initials: A
authors.lastname: Sadhanala
authors.affiliation: Fakultät für Biologie, Chemie und Geowissenschaften, University Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Huettner
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Akshay
authors.identifier: 0000-0003-0320-2962
authors.initials: A
authors.lastname: Rao
authors.affiliation: Cavendish Laboratory, Department of Physics, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK.
authors.forename: Richard H
authors.initials: RH
authors.lastname: Friend
mesh_terms: D037741:Fullerenes / Q000737:chemistry*; D055095:Optics and Photonics / Q000295:instrumentation / Q000379:methods*; D012666:Semiconductors
chemical_list: D037741:Fullerenes