Electronic and Molecular Surface Structure of Ru(tcterpy)(NCS)₃ and Ru(dcbpy)₂(NCS)₂ Adsorbed from Solution onto Nanostructured TiO₂:  A Photoelectron Spectroscopy Study

Abstract

The element specificity of photoelectron spectroscopy (PES) has been used to compare the electronic and molecular structure of the dyes Ru(tcterpy)(NCS)3 (BD) and Ru(dcbpy)2(NCS)2 adsorbed from solution onto nanostructured TiO2. Ru(dcbpy)2(NCS)2 was investigated in its acid (N3) and in its 2-fold deprotonated form (N719) having tetrabutylammonium (TBA+) as counterions. A comparison of the O1s spectra for the dyes indicates that the interactions through the carboxylate groups with the TiO2 surface are very similar for the dyes. However, we observe that some of the dye molecules also interact through the NCS groups when adsorbed at the TiO2 surface. Comparing the N719 and the N3 molecule, the fraction of NCS groups interacting through the sulfur atoms is smaller for N719 than for N3. We also note that the counterion TBA+ is coadsorbed with the N719 and BD molecules although the amount was smaller than expected from the molecular formulas. Comparing the valence levels for the dyes adsorbed on TiO2, the position of the highest occupied electronic energy level is similar for N3 and N719, while that for BD is lower by 0.25 eV relative to that of the other complexes.

Solid-state carbon-13 NMR and computational characterization of the N719 ruthenium sensitizer adsorbed on TiO2 nanoparticles

“…14 We report here the characterization by MAS-NMR of carbon-13 resonances of the common DSC sensitizing dye N719 adsorbed on TiO 2 . Attempts have been made to characterize the TiO 2 -N719 interface using vibrational, [15][16][17][18][19] X-ray absorption (XAFS and XANES) 20 and photoelectron spectroscopy 21 techniques. These investigations indicate that the dye binds to the TiO 2 surface through carboxylate groups, but their number is still a matter of debate.…”

Investigation of the influence of coadsorbent dye upon the interfacial structure of dye-sensitized solar cells

“…[9][10][11][12][13][14][15][16] However, it is unclear whether the behavior of dye molecules on a single crystal surface is faithfully reproduced by molecules on nanocrystalline TiO 2 , which is the material used for photovoltaic cell electrodes. Direct observations are very difficult because of the complex structure of nanocrystalline TiO 2 , so a high-resolution method with high specificity is required for observing the microscopic structure of the surface morphology of these porous materials.…”

In-Situ Probing of H2O Effects on a Ru-Complex Adsorbed on TiO2 Using Ambient Pressure Photoelectron Spectroscopy

“…6. The broad feature between 8 and 2 eV is dominated by the valence band of the TiO 2 and the small feature at the lowest binding energy is the HOMO level of the dye [9,43]. The HOMO level is known to be a mixture of molecular orbitals from the NCS-ligand and Ru [44].…”

“…The measurement spot on the sample was frequently changed to minimize the effects of radiation damage on the spectra collected. The binding energies of all spectra were calibrated versus the substrate Ti 2p 3/2 peak binding energy (458.56 eV) according to previous measurements [9].…”

“…PES studies of DSCs have typically been performed on dry electrodes under ultra-high vacuum conditions, including attempts to understand the interaction with solvent molecules [9][10][11][12][13]. In addition, complementary studies conducted on iodide electrolytes using a liquid jet system have been made [14,15].…”