title: Ultrafast Recombination Dynamics in Dye-Sensitized SnO2/TiO2Core/Shell Films.
abstract: Interfacial dynamics are investigated in SnO2/TiO2core/shell films derivatized with a Ru(II)-polypyridyl chromophore ([RuII(bpy)2(4,4'-(PO3H2)2bpy)]2+, RuP) using transient absorption methods. Electron injection from the chromophore into the TiO2shell occurs within a few picoseconds after photoexcitation. Loss of the oxidized dye through recombination occurs across time scales spanning 10 orders of magnitude. The majority (60%) of charge recombination events occur shortly after injection (τ = 220 ps), while a small fraction (≤20%) of the oxidized chromophores persists for milliseconds. The lifetime of long-lived charge-separated states (CSS) depends exponentially on shell thickness, suggesting that the injected electrons reside in the SnO2core and must tunnel through the TiO2shell to recombine with oxidized dyes. While the core/shell architecture extends the lifetime in a small fraction of the CSS, making water oxidation possible, the subnanosecond recombination process has profound implications for the overall efficiencies of dye-sensitized photoelectrosynthesis cells (DSPECs).
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Melissa K
authors.initials: MK
authors.lastname: Gish
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Lapides
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: M Kyle
authors.initials: MK
authors.lastname: Brennaman
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Templeton
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Meyer
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599, United States.
authors.forename: John M
authors.identifier: http://orcid.org/0000-0002-0902-6990
authors.initials: JM
authors.lastname: Papanikolas