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 ▲]

Retour au travail après une longue absence...

E-print/Working paper (2013)

Effects of chondroitin sulfate on the gene expression profile in IL-1β stimulated synovial fibroblast cells cultures

in Osteoarthritis and Cartilage (2013, April), 21(Supplement April 2013),

Purpose: Chondroitin sulfate (CS) is one the most used molecules in the management of OA. In this study, we performed a microarray analysis and identified a differential expression profile between control ... [more ▼]

Purpose: Chondroitin sulfate (CS) is one the most used molecules in the management of OA. In this study, we performed a microarray analysis and identified a differential expression profile between control and IL-1β stimulated synovial fibroblast cells cultures. In a second step, we investigated the effects of CS on this gene expression profile. Methods: OA synovial specimens were obtained from 12 patients undergoing knee replacement. At the surgery time, the synovial membrane was dissected. Synovial fibroblast cells (SFC) were enzymatically isolated and used after four passages (P4). SFC were pre-treated 1 hour with highly purified bovine CS (200 µg/ml, Bioibérica S.A., Barcelona, Spain) before treatment with IL-1β (1 ng/ml) for 24 hours. Total RNA was extracted using the RNeasy Mini Kit. RNA purity and quality were evaluated using the Experion RNA StdSens Analysis kit (Bio-rad Laboratories). Gene expression profiling was performed using Illumina’s multi-sample format Human HT-12 BeadChip (Illumina Inc.). Differential analysis was performed with the BRB array tools software. Class comparison test between control (Ctl) and interleukin (IL)-1β conditions, Ctl and Ctl/CS and IL-1β and IL-1β/CS conditions was based on paired t-test where Ctl and IL-1β, Ctl and Ctl/CS and IL-1β and IL-1β/CS were paired for each patient. The biological relevance of up- and down-regulated genes was analyses with Ingenuity Pathways Analysis (Ingenuity® Systems). Probes with a p-value below 0.001 were chosen and classified as up- or down-regulated ones. Results: 3308 genes were identified as differentially expressed genes between Ctl and IL-1β conditions. We observed a differential profile of expression of major pathways involved in OA pathogenesis. The key identified pathways were related to inflammation, complement cascade, angiogenesis, cartilage catabolism and anabolism and Wnt signaling. In the inflammatory network, the most upregulated cytokines were IL-8 and IL-6 with a fold change of 156.25 and 58.8 respectively. We also identified several chemokines, enzymes and metallothioneins (MTs). Complement factor B (CFB) and complement component 3 (C3) are two factors upregulated in the inflammatory complement cascade. We also identified some genes implicated in the angiogenesis pathway. The most upregulated was Stanniocalcin 1 (STC1) with a fold change of 9.09. The differential expression of intermediates involved in both cartilage anabolism and catabolism was revealed by the IL-1β stimulation, showing an imbalance in favour of catabolism. MMP-3 was largely upregulated (fold change of 62.5). Wnt 5A and low density lipoprotein receptor-related protein (LRP8) were significantly upregulated while frizzled homolog 2 (FZD2) and dickkopf homolog 3 (DKK3) were downregulated in the Wnt signaling pathway. We next performed a class comparison test between Ctl and Ctl/CS in one hand and IL-1β and IL-1β/CS on the other hand. 660 genes were identified as differentially expressed between Ctl and Ctl/CS conditions while 241 genes were identified between IL-1β and IL-1β/CS. Among them, our attention was focused on two genes upregulated in the presence of CS: lysyl oxidase-like 4 (LOXL4) and claudin 11 (CDLN11), two genes that negatively regulate cell invasion. Conclusions: We here evidenced in synovial fibroblast cells the modulation of gene expression following IL-1β stimulation. We also demonstrated the modulatory effects of CS on gene expression and isolated several CS-modulated genes of interest such as LOXL4 and CDLN11, which could constitute new mechanisms of action of the molecule and contribute to explain the symptomatic efficacy of CS in the treatment of OA. [less ▲]

SOUTHERN BLUES NIGHT , Heerlen (NL) 17e ed. , 15 mars 2013

E-print/Working paper (2013)

C.R. de la 17e Southern Blues Night , le 15 mars 2013 à Heerlen ( Nl) + photos ; Khalif Wailin' Walter , Mud Morganfield, Heritage Blues Orchestra, James Harman, Enrico Crivellaro, Gene Taylor, ....

ON THE MODELING OF ADHESIVE CONTACT AND STICTION FAILURE IN MICRO-SWITCHES

in Ouisse (FEMTO-ST – ENSMM, France); Deü (CNAM, FR), J.F. (Eds.) MEDYNA 2013 Proceedings (2013, April)

Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. Indeed the adhesive forces can become so important that the two surfaces remain permanently ... [more ▼]

Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. Indeed the adhesive forces can become so important that the two surfaces remain permanently glued, limiting the life-time of the MEMS. This is especially true when contact happens between surfaces where elasto-plastic asperities deform permanently until the surfaces reach plastic accommodation, increasing the surface forces. To predict this behavior, a micro adhesive-contact model is developed, which accounts for the surfaces topography evolutions during elasto-plastic contacts. This model can be used at a higher scale to study the MEMS behavior, and thus its life-time. For illustration purpose, an electrostatic-structural analysis is performed on a micro-switch. [less ▲]

Conception des pseudo-articulations à col paraboique

in Agiuzoul, Mohammed (Ed.) 11ème Congrès de Mécanique - Actes du Congrès (2013, April)

The elastic behaviour of parabolic notch hinges submitted to the classical sollicitations of a beam is studied. For each sollicitation, an analytical solution is given first. Its asymptotic expression for ... [more ▼]

The elastic behaviour of parabolic notch hinges submitted to the classical sollicitations of a beam is studied. For each sollicitation, an analytical solution is given first. Its asymptotic expression for very narrow hinges is then obtained and finally,, an approximate factor relating the exact solution to the asymptotic one is proposed. [less ▲]

Extensions of Superalgebras of Krichever-Novikov type

Poster (2013, April)

Adenomas Pituitarios Familiares Aislados (FIPA)

Scientific conference (2013, April)

Supervening Events and Contract Law: A Comparative and Critical Analysis

Conference (2013, April)

The binding force of contracts (pacta sunt servanda) is a basic rule in most – if not all – legal systems. Parties will therefore be liable in the event they failed to perform an obligation provided ... [more ▼]

The binding force of contracts (pacta sunt servanda) is a basic rule in most – if not all – legal systems. Parties will therefore be liable in the event they failed to perform an obligation provided within the contract. However, there are situations which excuse non-performance due to unforeseen circumstances that occurred subsequently to the conclusion of a contract. While most jurisdictions excuse the debtor's non-performance in case of impossibility to perform, only a few provide for remedies when performance has become by far more burdensome for one contracting party. It is to be noted that there is an increasing trend to adopt a general doctrine of hardship, as illustrated by the European codification projects. As a counterexample, Belgium remains attached to the pacta sunt servanda principle and rejects the so-called “theory of imprévision”. The English frustration doctrine seems to provide for an in-between position. In a first part, this paper will briefly discuss the mechanisms dealing with unexpected events which have been adopted in two different legal systems (England and Belgium) and in one European soft law instruments (PECL). In a second part, the paper will critically compare the mechanisms applied in the observed legal systems. [less ▲]

Amenability for processing of oolitic iron ore concentrate for phosphorus removal

in Minerals Engineering (2013), 46-47

Beneficiation routes aimed at dephosphorisation of oolitic gravity magnetic concentrate and involving a combination of roasting, re-grinding, magnetic separation and water and acid leaching are ... [more ▼]

Beneficiation routes aimed at dephosphorisation of oolitic gravity magnetic concentrate and involving a combination of roasting, re-grinding, magnetic separation and water and acid leaching are investigated. Roasting was carried out at 900ºC for one hour without or with lime or sodium hydroxide as roasting additives. When additives were used, cement phases of Si-Al-Na-Ca-O type were detected as well as the mineral giuseppettite. During the thermal process sodium silicate is liquefied and the newly formed phases coat the oolites and penetrate inside the cracks. Energy Dispersive Spectroscopy analysis has indicated that the zone surrounding the oolites consists of Na, Al and Si phases with part of phosphorus being captured there. As a result of the alkaline roasting, goethite is partly transformed to magnetite and this reduction is reinforced with an increase in sodium hydroxide dosage. Investigation of redistribution of phosphorous shows that it could be only partly separated if leaching is not accompanied by re-grinding and physical separation. The recommended dosage of the reductive agent for the final flowsheet is 8 % mass ratio to concentrate. Grinding to a mean size of 0.040 mm, with water and acid leaching and double magnetic separation creates conditions to obtain a high-quality iron concentrate with 65.97 % Fe and recovery of 92.43 %, with simultaneous decrease in the phosphorus content from 0.71 % to 0.05 %. [less ▲]