Templated TiO2 mesoporous films used as highly efficient photoelectrode in Dye-Sensitized Solar Cells

Doctoral thesis (2013)

The present thesis is dedicated to the synthesis and characterization of the TiO2 semiconductor layer used as photoelectrode in dye-sensitized solar cells (DSSCs), with the aim to improve their ... [more ▼]

The present thesis is dedicated to the synthesis and characterization of the TiO2 semiconductor layer used as photoelectrode in dye-sensitized solar cells (DSSCs), with the aim to improve their photovoltaic efficiencies. DSSCs have been reported by O’Regan and Grätzel in the early nineties as a very promising alternative to conventional silicon devices. Main benefits of these cells are their low cost and their mild manufacturing process. In most of the specific literature, DSSCs are made of TiO2 films prepared by doctor-blade or screen-printing of anatase nanoparticles paste. However due to the random organization of the nanoparticles, pore accessibility by the dye and electrolyte could be incomplete and some anatase crystallites could be not connected impeding electron transfer. The strategy adopted to improve the films properties and thus PV efficiencies involves a surfactant-assisted process allowing the preparation of highly porous layers with well-ordered and accessibles pores as well as improved crystallites connectivity. The main goal of this work is to increase the film surface area and perfectly control the mesostructure in terms of thickness, pore size, pore organization and pore accessibility in order to maximize the adsorption of active dye and the electrolyte infiltration inside the porous network. Special attention was paid to the tuning of the experimental settings such as the relative humidity conditions, the withdrawal speed and the choices of substrate and surfactant. Moreover, for DSSCs applications, TiO2 film has to be crystallized in form of anatase. Perfect balance between high crystallinity and mesostructure preservation was studied in order to enhance the cells efficiencies. Besides, templated films challenge is to obtain thick layers. Indeed, monolayer films are only a few hundred nanometers thick. To increase the film thickness and thus the quantity of active material, a multilayer process was tuned. Special effort was paid to overcome the surface area limitation induced by the repeated thermal treatments applied during multilayer process. We propose an alternative thermal treatment in order to limit the mesostructure degradation. We also define the maximum crystal size compatible with the preservation of the mesoarchitecture initially induced by templating. Thick films up to 4 µm were prepared from this multilayer process and show excellent efficiency in combination with N-719 dye (6.1%) when compared to values reported in the literature. Such mesostructured templated films were compared in terms of photovoltaic performances with TiO2 nanoparticles films, generally used in DSSCs. In a second part, as the goal of this thesis is to improve the current nanoparticles-based DSSCs and prove the viability of the templating alternative, a comparison of the long-term stability of both technologies was performed. To our knowledge, long-term stability of templated DSSCs has never been reported at this time. However, in case of templated films, the surface area is highly improved and the negative effects of thermal stress, light soaking and UV exposure could be heightened. Due to their higher active interface, templated films are more sensitive than nanoparticles samples to UV illumination, what can be easily solved by the use of a UV filter. However, they are as stable as nanoparticles samples under visible light soaking (UV filtered) and under thermal stress. In addition, cells were characterized by electrochemical impedance spectroscopy (EIS). Templated cells show lower transfer resistance, as well as longer electron lifetime compared to nanoparticles DSSCs. Using templated films in DSSCs is therefore really promising because higher conversion efficiencies are reached without any increase in cells degradation. Finally, stability limitation encountered by DSSCs are mostly related to the use of liquid electrolytes, which can leak out the cell. Solid-state hole transporting materials are investigated in order to overcome this issue. However, in solid-state DSSCs, TiO2 films thickness is limited to a few microns allowing the adsorption of a limited amount of photoactive dye and thus leading to a poor light harvesting. Moreover, solid-state DSSCs are characterized by incomplete electrolyte filling, impeding the dye regeneration. Both limitations further lead to low photovoltaic efficiencies. Due to the surface area improvement as well as the perfect control of the pore organization and the pore size, the templating strategy was investigated to overcome light harvesting and pore filling limitations. Templated films were prepared from different structuring agents. They show an efficient electrolyte infiltration and a two times higher dye loading compared to nanoparticles layers. Corresponding photovoltaic performances in liquid-state and solid-state DSSCs have also been evaluated. While templating allows improving the liquid-state cells efficiencies, we cannot conclude for solid-state DSSCs due to device assembly issue and/or bad contacts between the electrodes and the sample holder during the I-V measurements. We hope that the achievements of this thesis brought a significant contribution to the field of DSSCs. Indeed, the templating strategy is proved to improve the liquid-sate cells efficiency. However, the assembly of solid-state devices and subsequent I-V tests have to be investigated further. Besides, new pathways are envisaged for interesting future work in both fundamental and applied research fields, such as the synthesis of templated films with hierarchical porosity or scale-up and industrialization of the templated devices. [less ▲]

Temple-Baraitser syndrome: a rare and possibly unrecognized condition.

in American Journal of Medical Genetics. Part A (2010), 152A(9), 2322-6

Temple-Baraitser syndrome, previously described in two unrelated patients, is the association of severe mental retardation and abnormal thumbs and great toes. We report two additional unrelated patients ... [more ▼]

Temple-Baraitser syndrome, previously described in two unrelated patients, is the association of severe mental retardation and abnormal thumbs and great toes. We report two additional unrelated patients with Temple-Baraitser syndrome, review clinical and radiological features of previously reported cases and discuss mode of inheritance. Patients share a consistent pattern of anomalies: hypo or aplasia of the thumb and great toe nails and broadening and/or elongation of the thumbs and halluces, which have a tubular aspect. All patients were born to unrelated parents and occurred as a single occurrence in multiple sibships, suggesting sporadic inheritance from a de novo mutation mechanism. Comparative genomic hybridization in Patients 1, 2 and 3 did not reveal any copy number variations. We confirm that Temple-Baraitser syndrome represents a distinct syndrome, probably unrecognized, possibly caused by a de novo mutation in a not yet identified gene. [less ▲]

Temporal and spatial expression of tumor-associated antigen RCAS1 in pregnant mouse uterus.

in American Journal of Reproductive Immunology (2010), 63(2), 137-43

PROBLEM: The tumor-associated antigen RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is considered to play a role in the inhibition of maternal immune response during pregnancy, and ... [more ▼]

PROBLEM: The tumor-associated antigen RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is considered to play a role in the inhibition of maternal immune response during pregnancy, and participates in the initiation of labor and placental detachment. The aim of our study was to investigate the expression of RCAS1 protein in the uteri of normal pregnant mice. METHOD: of study Uteri with fetuses were collected from pregnant ICR mice on days 1.5, 3.5, 5.5, 7.5, and 9.5 p.c., and uterine and placental tissues were obtained separately on days 11.5, 13.5, 15.5, and 17.5 p.c. Samples were examined using real-time (RT)-PCR, Western blotting, and immunohistochemical analyses. RESULTS: In normal pregnant mice, RCAS1 protein mRNA was significantly increased on day 7.5 p.c. Antigen localization was detected in the placenta, decidua, and fetus. CONCLUSION: The results of this study suggest the importance of day 7.5 p.c. for RCAS1 protein expression in connection with placentation as a possible target for future in vivo studies. [less ▲]

Temporal Control of Bovine Herpesvirus Type 4 Glycoprotein Synthesis

in Journal of General Virology (1991), 72((Pt 6)), 1429-34

The glycoprotein gp6/gp10/gp17, gp11/VP24 and gp8 are major bovine herpesvirus type 4 antigens. The temporal expression of these glycoproteins was studied and it was shown that gp6/gp10/gp17 appeared as ... [more ▼]

The glycoprotein gp6/gp10/gp17, gp11/VP24 and gp8 are major bovine herpesvirus type 4 antigens. The temporal expression of these glycoproteins was studied and it was shown that gp6/gp10/gp17 appeared as early as 6 h post-inoculation (p.i.), and gp11/VP24 and gp8 were detected 8 h p.i. Moreover, a precursor of two components of gp6/gp10/gp17 glycoprotein [p(gp10/gp17)] was a beta-gamma protein, whereas the gp11/VP24 and gp8 glycoproteins were gamma proteins. [less ▲]

Temporal differentiation in two strains of small rodents: a wood mouse (Apodemus sylvaticus) and an albino mouse (Mus musculus OF1)

in Behavioural Processes (2000), 52(2-3), 155-169

Wood mice (Apodemus sylvaticus) and OF1 albino mice (Mus musculus) were compared over durations ranging from 0.5 to 7 s, using the differential reinforcement of response duration schedule (DRRD) and a ... [more ▼]

Wood mice (Apodemus sylvaticus) and OF1 albino mice (Mus musculus) were compared over durations ranging from 0.5 to 7 s, using the differential reinforcement of response duration schedule (DRRD) and a 'platform' response, i.e. staying on a small platform for a specified criterion duration to be reinforced. Species-related differences were found for mean response durations, efficiency and the number of trials needed to reach a preset performance criterion. Coefficients of variation of response durations did not differ. Overall, OF1 mice needed more trials than wood mice to reach a temporal criterion. However, over 3-7 s, data from both strains almost fitted the behavioral assumptions of Scalar Timing theory. Performance of mongolian gerbils (Meriones unguiculatus) trained in a similar setting was shown for visual comparison. [less ▲]

Temporal evolution of biogeochemical properties of landfast sea ice at Barrow (Alaska)

Poster (2011, March)

Temporal evolution of sediment supply in Lago Puyehue (Southern Chile) during the last 600 yr and its climatic significance

in Quaternary Research (2005), 64(2), 163-175

Short-term climate changes in Southern Chile are investigated by a multi-proxy analysis of a 53-cm-long sedimentary sequence selected among eight short cores retrieved in Lago Puyehue (Chile, 40 degrees S ... [more ▼]

Short-term climate changes in Southern Chile are investigated by a multi-proxy analysis of a 53-cm-long sedimentary sequence selected among eight short cores retrieved in Lago Puyehue (Chile, 40 degrees S). This core contains a 600-yr-long undisturbed record of paleo-precipitation changes. Two measurement methods for sediment density, organic matter and biogenic silica contents are compared and the most appropriate techniques are selected. Together with aluminium and titanium concentrations, grain size and geochemical properties of the organic matter, these proxies are used to demonstrate paleo-precipitation changes around 40 degrees S. Increase of terrigenous particle supply between A.D. 1490 and A.D. 1700 suggests a humid period. Contemporaneously, delta C-13 data show increasing lake productivity, in response to the high nutrient supply. The A.D. 1700-1900 interval is characterized by a decreasing terrigenous supply and increasing delta C-13 values, interpreted as a drying period. The magnetic susceptibility signal, reflecting the terrigenous/biogenic ratio, demonstrates that similar variations occur in all the undisturbed sedimentary environments of Lago Puyehue. The A.D. 1490-1700 wet period is associated with the onset of the European Little Ice Age (LIA) and interpreted as its local signature. This work supports the fact that the LIA was a global event, not only restricted to the Northern Hemisphere. (c) 2005 University of Washington. All rights reserved. [less ▲]

Temporal Logic Can Be More Expressive

in Information and Control (1983), 56(1--2), 72--99

We first review Temporal Logic and prove that there are some properties of sequences that it cannot express, though these are expressible using for instance regular expressions. Then, we show how Temporal ... [more ▼]

We first review Temporal Logic and prove that there are some properties of sequences that it cannot express, though these are expressible using for instance regular expressions. Then, we show how Temporal Logic can be extended to express any property definable by a right-linear grammar and hence a regular expression. Finally, we give a complete axiomatization and a decision procedure for the extended Temporal Logic and examine its complexity. [less ▲]

Temporal parameters and behaviour

in Richelle, Marc; Lejeune, Helga (Eds.) Time in animal behaviour (1980)

Temporal reasoning and behavioral variability : proceedings of the 1st Interuniversity Poles of Attraction Workshop

Conference (1993)