title: Heterojunction topology versus fill factor correlations in novel hybrid small-molecular/polymeric solar cells.
abstract: The authors present organic photovoltaic (OPV) devices comprising a small molecule electron acceptor based on 2-vinyl-4,5-dicyanoimidazole (Vinazene) and a soluble poly(p-phenylenevinylene) derivative as the electron donor. A strong dependence of the fill factor (FF) and the external quantum efficiency [incident photons converted to electrons (IPCE)] on the heterojunction topology is observed. As-prepared blends provided relatively low FF and IPCE values of 26% and 4.5%, respectively, which are attributed to significant recombination of geminate pairs and free carriers in a highly intermixed blend morphology. Going to an all-solution processed bilayer device, the FF and IPCE dramatically increased to 43% and 27%, respectively. The FF increases further to 57% in devices comprising thermally deposited Vinazene layers where there is virtually no interpenetration at the donor/acceptor interface. This very high FF is comparable to values reported for OPV using fullerenes as the electron acceptor. Furthermore, the rather low electron affinity of Vinazene compound near 3.5 eV enabled a technologically important open circuit voltage (V(oc)) of 1.0 V.
authors.affiliation: Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany.
authors.forename: Marcel
authors.initials: M
authors.lastname: Schubert
authors.forename: Chunhong
authors.initials: C
authors.lastname: Yin
authors.forename: Mauro
authors.initials: M
authors.lastname: Castellani
authors.forename: Sebastian
authors.initials: S
authors.lastname: Bange
authors.forename: Teck Lip
authors.initials: TL
authors.lastname: Tam
authors.forename: Alan
authors.initials: A
authors.lastname: Sellinger
authors.forename: Hans-Heinrich
authors.initials: HH
authors.lastname: Hörhold
authors.forename: Thomas
authors.initials: T
authors.lastname: Kietzke
authors.forename: Dieter
authors.initials: D
authors.lastname: Neher