T andem Dye-Sensitized Solar Cells devices (t-DSSCs) can theoretically overcome the well-known Shockley-Queisser limit due to their unique structure combining a n-type photoanode, a p-type photocathode and multiple dyes with complementary absorption characteristics. Nevertheless, nowadays, their further development suffers from the poor quality of the p-type material constituting the photocathode, i.e. NiO or Cu delafossites, and is therefore dependent of the synthesis of new efficient materials. In this work, N-doped TiO 2 thin films exhibiting a p-type conductivity (p-TiO 2 :N) are successfully synthesized by co-reactive magnetron sputtering. The p-type conductivity is correlated to the incorporation of N atoms in substitutional positions which is shown to be controllable by carefully tuning the ratio between O 2 and N 2 reactive gases during the growth of the material. Furthermore, we show that if p-TiO 2 :N films present a lower hole concentration (~ 10 15 -10 16 cm −3 ) and optical transmission in the visible (~ 36-40 %) than sputtered NiO, it reveals a 3 to 6 times higher mobility of the charge carriers (1.5 - 3.1 cm 2 .V −1 .s −1 ). These results are in particular interest for the future development of new “full TiO 2 ”-based t-DSSCs. the evolution of the chemical composition of the (empty as a function of φN 2 as well as, the evolution of both substitutional and interstitial nitrogen atoms based on the previously described analysis of the peak. These results show that whatever φN 2 , the N i remains relatively low and that

The control of the surface area enhancement and the ordering of the mesoporous photoanode is one of the key parameters to overcome the current limits of performance of dye sensitized solar cells (DSSCs). These parameters are expected to improve both the concentration of adsorbed dye molecules on the photoanode and the charge collection. In this paper, reactive magnetron sputtering at glancing angle is employed to synthesize nanostructured TiO2 thin films. A post-annealing treatment under an ambient atmosphere at 773 K allows recrystallization of the films to form individual single crystal-like anatase nanocolumns, as shown on a reference structure constituted by well-separated slanted nanocolumns. Even if the best cells provide an open circuit voltage of 0.8 V, a fill factor of 77%, and a short circuit current density of 4.6 mA/cm(2) (J(SC)) and permit to reach an overall efficiency up to 2.6%, it does not yet reach the performances of the reference TiO2 nanoparticle (NP)-based cell. This is explained by a poor carrier collection efficiency, as demonstrated by intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. The evaluation of other nanostructures such as zigzag and pillars shows the superiority of these structures on the NPs in terms of charge carrier collection efficiency. Nevertheless, the low penetration of the dye on these structures does not allow them to reach photovoltaic performances as good as those measured in NP-based DSSCs.

The interaction between 2,2'-bithiophene-5-carboxylic acid (PT2) sublimed under ultra-high vacuum conditions and anatase (101) and rutile (110) TiO2 single crystal surfaces is investigated by studying the electronic spectral density near the Fermi level with synchrotron-based spectroscopy. The experimental results are compared to density functional theory calculations of the isolated PT2 molecule and of the molecule adsorbed on an anatase TiO2 (101) cluster. The relative concentrations of Ti, C, and S atoms indicate that the adsorbed molecule remains intact upon deposition, which is typical of a Stranski-Krastanov growth mode. The analysis of the O1s spectrum suggests a predominant bidentate geometry of the adsorption with both rutile and anatase surfaces, as supported by previous theoretical simulations. It is also theoretically and experimentally demonstrated that the PT2 adsorption causes the appearance of new electronic states in the gap near the TiO2 valence band. A pinning effect of the LUMO level of the dye is also theoretically predicted.

TiO2 nanotube arrays (TNA) elaborated on transparent and conducting substrates are promising materials for photoanodes in dye-sensitized solar cells as the reduced dimensionality enhances their transport properties. TNA were obtained by anodization of Ti films deposited by magnetron sputtering on transparent conducting oxide-coated glass. This study presents the impact of introducing a compact TiO2 underlayer on the morphological, optical and electrochemical properties of the TNA photoanodes.

In this work, glancing angle deposition and magnetron sputtering are combined to synthesize nanostructured Ti films. Different type of microstructures (tilted columns, straight pillars, zigzags) are obtained as a function of the experimental conditions. As a support, kinetic Monte Carlo simulations are performed to understand the observed trends using the NASCAM (NAnoSCAle Modeling) code. The latter is used to simulate the growth of the films and to explain the effect on the obtained structures of experimental parameters such as the substrate temperature, the gas pressure as well as the substrate tilting and rotation speed. NASCAM enables quantitative prediction of the density, the surface roughness, and the column shape asymmetry. In addition, the effective porosity (ϕe) of the structures was evaluated from the simulation data for two molecules presenting different size (0.64 and 3.20nm). The results show that ϕe decreases with the size of the adsorbed molecule, from above 50% for the small molecule to below 10% for the larger one. This is understood by considering the accessibility of the pore as a function of the size of the molecules. These data are correlated to experimental results obtained by transmission electron microscopy.

Crystallized nanoporous TiO2 thin films were synthesized by combining reactive magnetron sputtering and Glancing Angle Deposition (GLAD). The growth temperature, the bias voltage and the rotation speed of the substrate were studied with the aim to grow nanoporous films presenting anatase constitution which are suitable for Dye Sensitive Solar Cells (DSSC) applications.By fixing the tilt angle at 85 degrees, we have shown that an increase of the growth temperature up to 450 degrees C leads to the formation of nanoporous anatase film with a grain size up to 24 nm while by applying a bias voltage leads to a densification of the films as evidenced by scanning electron microscopy and by X-ray diffraction. On the other hand, by rotating the substrate (from 0.1 to 10 degrees/s) during the deposition process, films with larger columns and higher surface roughness (from 45 to 60 nm) were obtained due to an enhanced shadowing effect.Preliminary dye impregnation experiments have shown that the highest light absorption values are obtained for the films prepared without bias and with no rotation, which is supported by the microstructure of these films presenting the highest porosity. These films, presenting an anatase constitution, are potentially good candidates as an anode in DSSC applications. (C) 2014 Elsevier Ltd. All rights reserved.

Au nanoparticles (NPs) were prepared by laser ablation in liquid. Different solutions containing the NP were prepared by varying the pulse number (N) and the fluence (F) of a 248 nm KrF excimer laser. The absorption spectra of those solutions were studied. We observed that the concentration of the NP solution does not increase linearly with the ablation rate. This behavior is explained by the notion of a negative feedback effect. In this report, we discuss this notion and the influence of different solvents on the size and shape of the gold NPs. Finally, suitable experimental parameters to obtain nearly spherical NPs presenting diameters around 6 nm are defined.