Mesoporous TiO2 microbead electrodes for solid state dye-sensitized solar cells

Mesoporous TiO₂ microbead films have been investigated as working electrode for solid state dye sensitized solar cells and 3.5% efficiency was achieved. Low trap density of microbead film leads to high voltage and fast electron transport.

Frontier electronic structures of Ru(tcterpy)(NCS)3 and Ru(dcbpy)2(NCS)2: A photoelectron spectroscopy study

The frontier electronic structures of Ru(tcterpy)(NCS)3 [black dye (BD)] and Ru(dcbpy)2(NCS)(2) (N719) have been investigated by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS) and resonant photoelectron spectroscopy (RPES). N1s XAS has been used to probe the nitrogen contribution in the unoccupied density of states, and PES, together with RPES over the N1s edge, has been used to delineate the character of the occupied density of states. The experimental findings of the frontier electron structure are compared to calculations of the partial density of states for the nitrogens in the different ligands (NCS and terpyridine/bipyridine) and for Ru4d. The result indicates large similarities between the two complexes. Specifically, the valence level spectra show two well separated structures at low binding energy. The experimental results indicate that the outermost structure in the valence region largely has a Ru4d character but with a substantial character also from the NCS ligand. Interestingly, the second lowest structure also has a significant Ru4d character mixed into the structure otherwise dominated by NCS. Comparing the two complexes the BD valence structures lowest in binding energy contains a large contribution from the NCS ligands but almost no contribution from the terpyridine ligands, while for N719 also some contribution from the bipyridine ligands is mixed into the energy levels.

Heparin coating durability on artificial heart valves studied by XPS and antithrombin binding capacity

The durability and functionality of a heparin coating on artificial heart valve leaflets were evaluated with X-ray photoelectron spectroscopy (XPS) and by the coatings' capacity to bind antithrombin. Current methods for accelerated life-time testing are based on exposing leaflets to water solutions. In this paper a method is explored, in which heart valve leaflets were exposed to a continuous high shear rate (4 L/min) of human citrated plasma. It was found that the heparin coating was stable and wear resistant enough to still be present after 3 weeks and to have about the same antithrombin uptake as coatings not exposed to circulating plasma. It was, however, partly destroyed by the test as found using XPS. We suggest that heparin chains from the upper layer of heparin have been torn off from the carrier chain, in combination with loss of heparin conjugate and plasma deposition in patches. This study showed that XPS provides additional information to biological measurements such as antithrombin uptake. XPS is therefore a valuable technique not only to characterize biomaterials but also to evaluate the effect of a performance test.

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

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.

Interfacial properties of the nanostructured dye-sensitized solid heterojunction TiO2/RuL2(NCS)2/CuI

The interfaces of the nanostructured dye-sensitized solid heterojunction TiO(2)/Ru-dye/CuI have been studied using photoelectron spectroscopy of core and valence levels, x-ray absorption spectroscopy and atomic force microscopy. A nanostructured anatase TiO(2) film sensitized with RuL(2)(NCS)(2) [cis-bis(4,4(')-dicarboxy-2,2(')-bipyridine)-bis(isothio-cyanato)-ruthenium(II)] was prepared in a controlled way using a novel combined in-situ and ex-situ (Ar atmosphere) method. Onto this film CuI was deposited in-situ. The formation of the dye-CuI interface and the changes brought upon the dye-TiO(2) interface could be monitored in a stepwise fashion. A direct interaction between the dye NCS groups and the CuI is evident in the core level photoelectron spectra. Concerning the energy matching of the valence electronic levels, the photoelectron spectra indicate that the dye HOMO overlaps in energy with the Cu 3d-I 5p hydrid states. The CuI grow in the form of particles, which at the initial stages displace the dye molecules causing dye-TiO(2) bond breaking. Consequently, the very efficient charge injection channel provided by the dye-TiO(2) carboxylic bonding is directly affected for a substantial part of the dye molecules. This may be of importance for the functional properties of such a heterojunction.

Characterization of heparin surfaces using photoelectron spectroscopy and quartz crystal microbalance

In order to gain insight into the molecular structure of a new heparin surface (Corline heparin surface, CHS), quartz crystal microbalance dissipation (QCM-D) and photoelectron spectroscopy (PES) were used. Two surfaces, with different surface thickness and surface concentration of heparin, were compared. QCM-D measurements provided information on the thickness of the two different heparin surfaces and confirmed that the process of formation of the two layers were virtually identical. PES showed that the thicker coating resulted in complete coverage of the substrate, whereas with the thinner coating Fe signals originating from the stainless steel substrate could be detected. Information of the molecular surface structure of the heparin coatings could be derived from the ratios at different photon energies between S2p signals from sulfonate groups in heparin and disulfide groups originating from a cross-linking unit in the heparin conjugate.