AVS 57th International Symposium & Exhibition
    Energy Frontiers Topical Conference Thursday Sessions
       Session EN+AS-ThM

Paper EN+AS-ThM3
Anchoring of N3, N719 and Z907 Dye Molecules on TiO2(110) Surface

Thursday, October 21, 2010, 8:40 am, Room Pecos

Session: Surface and Interface Analysis of Materials for Energy
Presenter: P. Nachimuthu, Pacific Northwest National Laboratory
Authors: P. Nachimuthu, Pacific Northwest National Laboratory
A. Pandey, Pacific Northwest National Laboratory
Z.Q. Yu, Pacific Northwest National Laboratory
Z.H. Zhu, Pacific Northwest National Laboratory
K.M. Beck, Pacific Northwest National Laboratory
S. Thevuthasan, Pacific Northwest National Laboratory
M.A. Henderson, Pacific Northwest National Laboratory
D.R. Baer, Pacific Northwest National Laboratory
Correspondent: Click to Email
In dye-sensitized solar cells, the alignment of the energy levels for the dye and TiO2 resulting from the electronic coupling between these states determines the photoinduced electron transfer across the dye-TiO2 interface. The electronic coupling which in turn is strongly modified by the mode of binding of the dye molecules onto TiO2 surface, its relative orientations and geometrical structures. In order to understand the mode of binding of the dye molecules on TiO2(110) surface, the N3, N719 and Z907 dye molecules in the powder form and adsorbed on TiO2(110) surface using 0.25-1.0 mg/ml in ethanol were investigated using high-resolution x-ray photoelectron spectroscopy. The S 2p XPS data from N3 dye molecules adsorbed onto TiO2 surface show two S components in addition to SOx suggesting that the S atoms in the –NCS functional groups exist in two different chemical environments with a binding energy difference of ~1 eV and the intensity ratio of ~1 indicating that in each intact N3 molecule on TiO2, one –NCS group is bound to TiO2(110) surface and the other is projected away from TiO2 surface. The O 1s XPS data show components at 531.2 eV and 533.1 eV which are arising from C=O / COO- and C-OH bonds from carboxylic acid groups in N3 molecule, respectively, in addition to a peak at 529.7eV from TiO2. The relative intensity ratio of the O 1s XPS components at 533.1 eV to 531.2 eV signifies the presence of protonated carboxylic acid groups in N3 molecule and is found to be 0.388 suggesting that only one carboxylic acid group in each N3 molecule is deprotonated and it is most likely bound to TiO2 surface. In contrast, both the -NCS groups in the N719 and Z907 dye molecules were projected away from the TiO2 surface and are not involved in binding with TiO2 surface. One of the carboxylic acid groups in Z907 is deprotonated and it is most likely bound to TiO2 surface. Furthermore, with decreasing the dye concentration in ethanol results in a gradual dissociation of –NCS groups from Ru in these dye molecules.