The electronic structure of the TiO2/dye/electrolyte interface determined by synchrotron photoelectron spectroscopy on well-defined frozen adsorption models

Wolfram Jaegermann^a, Konrad Schwanitz^a, Thomas Mayer^a

^aTechnical University of Darmstadt, Jovanka-Bontschits-Straße, 2, Darmstadt, Germany

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Thomas Mayer, 001
Publication date: 5th February 2015

At BESSY we run the experimental station SoLIAS dedicated to Solid-Liquid Interface Analysis. SoLIAS allows for adsorption from solution and coadsorption of volatile solvent and redox active species onto liquid nitrogen cooled electrodes. Nano-porous anatase TiO₂ electrodes were stained with the standard Ru(N3)-dye from ethanol solution under clean N₂ atmosphere in an UHV-integrated electrochemical cell (EC) and acetonitrile was coadsorbed in UHV [1], [2]. Now the electrolyte has been completed by adsorbing iodide using Iodolyte molten salt dissolved in acetonitrile. Based on the experimental data the alignment of electronic states at the TiO₂/dye/electrolyte interface has been deduced. Comparing dye solvent and Iodide solvent coadsorbates we find a barrier of 1.3 eV for dye re-reduction ((2) in the figure). In contact of dye, iodide, and solvent, a new state X appears, tentatively assigned to an interacting state between dye-HOMO and Iodide-5p orbital, that promotes dye photo hole transfer to the iodide/triiodide redox couple ((1) in the figure). In the talk, we will show step by step the built up of the electronic structure at the TiO₂/dye/electrolyte interface by stepwise increasing complexity from singly adsorbed dye, acetonitrile, or iodide to coadsorbates of two of these components to finally all three of them.
EElectronic structure at TiO2/Ru(N3)-dye/acetonitrile/iodide interfacelectronic structure at TiO2/
1. K. Schwanitz, U. Weiler, R. Hunger, T. Mayer, and W. Jaegermann, Synchrotron-i,nduced photoelectron spectroscopy of the dye-sensitized nanocrystalline TiO2/electrolyte interface: Band gap states and their interaction with dye and solvent molecules. Journal of Physical Chemistry C, 2007. 111(2): p. 849-854. 2. K. Schwanitz, E. Mankel, R. Hunger, T. Mayer, and W. Jaegermann, Photoelectron spectroscopy at the solid-liquid interface of dye-sensitized solar cells: Unique experiments with the solid-liquid interface analysis system SoLiAS at BESSY. Chimia, 2007. 61(12): p. 796-800.

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