title: Electron transport in acceptor-sensitized polymer-oxide solar cells: the importance of surface dipoles and electron cascade effects.
abstract: Fullerene and acenequinone compounds have been examined as electron mediators between a p-type semiconductive polymer and two n-type oxide semiconductors. Composite interlayer materials and photovoltaic test cells were assembled and studied for their fluorescence quenching, current-voltage, and quantum efficiency behavior to characterize the efficacy of the acceptor-sensitizers as electron-selective interlayers. The sensitizers are generally more effective with titanium dioxide than with zinc oxide, due to the difference in magnitude of dipole-induced vacuum level shifts at the respective oxide interfaces. In titanium dioxide-based solar cells, where dipole effects are weak, photovoltage and fill factor increase in a trend that matches the increase in the first reduction potential of the acceptor-sensitizers. Photosensitization of the oxide semiconductor by the acceptor-sensitizers is observed to operate either in parallel with the polymer as an alternate photosensitizer or in series with the polymer in a two-photon process, according to an acceptor-sensitizer's first reduction potential. In zinc oxide-based solar cells, where dipole effects are stronger, the acceptor-sensitizers impaired most devices, which is attributed to an upward shift of the oxide's conduction band edge caused by dipole-induced vacuum level shifts. These results have broad implications for designing electron-selective interlayers and solid-state photocells using sensitized oxide semiconductors.
authors.affiliation: Department of Chemistry, University of North Texas , Denton, Texas 76203, United States.
authors.forename: Seare A
authors.initials: SA
authors.lastname: Berhe
authors.forename: Joy Y
authors.initials: JY
authors.lastname: Zhou
authors.forename: Keith M
authors.initials: KM
authors.lastname: Haynes
authors.forename: Marco T
authors.initials: MT
authors.lastname: Rodriguez
authors.forename: W Justin
authors.initials: WJ
authors.lastname: Youngblood
mesh_terms: D004579:Electron Transport; D004583:Electrons; D043942:Nanotubes / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D012666:Semiconductors; D012993:Solar Energy; D014025:Titanium / Q000737:chemistry; D015034:Zinc Oxide / Q000737:chemistry
chemical_list: D011108:Polymers; C009495:titanium dioxide; D014025:Titanium; D015034:Zinc Oxide