Marco-Aurelio De Paoli

New insights into dye-sensitized solar cells with polymer electrolytes

Polymer electrolytes or gel polymer electrolytes are interesting alternatives to substitute liquid electrolytes in dye-sensitized solar cells (DSSC). The interest in this research field is growing continuously, reflected in the increase in the number of papers published each year concerning these materials. This feature article presents a brief review of the history and development of polymer electrolytes aiming at applications in DSSC. Recent improvements achieved by modifications of the composition and by introduction of additives such as inorganic nanofillers, organic molecules and ionic liquids are described. The stabilities of DSSC assembled with these materials are also discussed and further improvements that can be introduced to maximize performance of the solar cell, such as photoelectrode modification, will also be presented.

Application of a composite polymer electrolyte based on montmorillonite in dye-sensitized solar cells

In this work we report for the first time the preparation and characterization of a novel composite polymer electrolyte based on montmorillonite clay and a poly(ethylene oxide) derivative plasticized with g-butyrolactone and its application in dye sensitized solar cells. Although the plasticizers enhance the ionic conductivity of the polymer electrolytes, they compromise the mechanical stability of the whole system and make the practical application of these devices difficult. Films with composite polymer electrolytes containing different clay content were analyzed by thermal and mechanical analysis and electrochemical impedance spectroscopy. We observed that the addition of the inorganic particles to the polymer matrix promotes not only an enhancement in the mechanical properties but also contributes to the increase the of ionic conductivity of the system. A solid-state dye-sensitized solar cell was assembled for this first time with the electrolyte containing montmorillonite clay, displaying efficiencies higher than 3% at 10 mW cm-2.

Polypropylene compounding with post-consumer material: II. Reprocessing

We have investigated extrusion moulding for 13 processing cycles, using formulations containing virgin polypropylene and 1:1 mixtures of virgin and post-consumer polypropylene containing, or not, the antioxidant Recyclostab 411™. The main effect of reprocessing for polypropylene was the decrease of molar mass due to degradation with chain scission, which was detected by the melt flow rate and the increase in crystallinity. Antioxidant consumption and material stability reduction with processing cycles were observed by the reduction of the thermo-oxidative stability detected by oxidative induction time measurements. The addition of antioxidants minimized degradation and maintained the stability of the material.

Photo-oxidation of polypropylene under load

Abstract We have studied the photo-oxidation of isotactic polypropylene films under mechanical load. These films were either slightly or highly oriented, with or without photoprotecting agents. The oxidation reactions were followed by carbonyl index determinations from IR spectra. The results indicate that the oxidation rate can be related to mechanical load, polymer morphology and the intensity of the light source. In the earlier stages of the photo-oxidation, the static load can act as a protector against oxidation, in a similar manner to that observed with highly oriented samples.

Dye-sensitized solar cells and solar module using polymer electrolytes: Stability and performance investigations

We present recent results on solid-state dye-sensitized solar cell research using a polymer electrolyte based on a poly(ethylene oxide) derivative. The stability and performance of the devices have been improved by a modification in the method of assembly of the cells and by the addition of plasticizers in the electrolyte. After 30 days of solar irradiation (100 mW cm-2) no changes in the cells efficiency were observed using this new method. The effect of the active area size on cell performance and the first results obtained for the first solar module composed of 4.5 cm2 solid-state solar cells are also presented.

Preparação de eletrodos opticamente transparentes

A simple experiment for the preparation of transparent conducting glass electrodes by deposition of pure and fluorine doped SnO2 films is described. This procedure was tested in the undergraduate inorganic course at IQ-UNICAMP. The success in achieving a conducting layer was easily checked using the standard probes of a volt-ohm meter. The optical transmittance and thickness were studied by UV-vis spectrophotometry. To discuss the experimental results we place significant emphasis on molecular orbital and energy band model theories. The undergraduate students can also discuss the concepts related to the electronic properties of solids and to interesting new materials, such as transparent conducting films, which are the subject of significant current research and technological applications.

Electrochemical impedance spectroscopy of dodecylsulphate doped polypyrrole films in the dark and under illumination

The morphology, thickness, oxidation and illumination effects in dodecylsulphate doped polypyrrole films can be qualitatively observed by EIS and consist in variations of interfacial and bulk resistances and capacitances of a proposed equivalent circuit. The circuit well with the measured spectra of films obtained with 190 mC cm-2 of synthesis charge density. For thinner films the calculated values observed by electrochemical impedance spectroscopy (EIS) deviate probably due to the absence of diffusion effects. The oxidation of the films diminishes the total impedance over the entire frequency range. The morphology effects are also observed in the entire spectra. The illumination effects are reversible and are observed as expected only in the reduced form of the polymer. The illumination reduces the internal resistance and the space-charge capacitance and increases the charge transfer resistance and the double layer capacitance.

New polyaniline/porous glass composite

Abstract In this work we report the preparation of a glass-polymer composite, obtained by the in situ oxidative polymerization of aniline, in the pores of Porous Vycor Glass (PVG). A piece of PVG was added to acid aniline solution. PVG adsorbs aniline via an ion-exchange process (H + from PVG porous surface/C 6 H 5 NH 3 + ). The impregnated PVG was added to a (NH 4 ) 2 S 2 O 8 acid solution. The glass gradually went to dark green with the formation of polyaniline in its conducting form, the emeraldine salt. The counter-anions are the SiO − groups on the pores surface of the glass, as confirmed by 29 Si-CP-MAS-NMR. Addition of the composite to an NH 4 OH solution leads do a change from dark green to dark blue (emeraldine base), and this process is reversible.

Polyaniline intercalation in α-Sn(HPO4)2-H2O

Abstract In this work we report the preparation of a inorganic-organic nanocomposite, obtained by the in situ oxidative polymerization of aniline inside the layers of α-Sn(HPO 4 ) 2 -H 2 O (α-SnP). Two approaches were used to obtain the α-SnP/polyaniline nanocomposite. Firstly, hydrogen atoms of a-SnP were exchanged with Fe 3+ cation to promote aniline polymerization. Secondly, aniline was intercalated in a-SnP and polymerization was performed by (NH 4 ) 2 S 2 O 8 solution. Both resulting material leads to formation of polyaniline in its conducting form, the emeraldine salt. The characterization results suggest the formation of linear polymer chains between the α-SnP layers.

Poliolefinas reforçadas com fibras vegetais curtas: sisal × curauá

There is growing interest in reinforced polymer composites using short vegetal fibers to replace glass fibers for several reasons. The composite fibers are produced from renewable resources, being biodegradable and less abrasive to the processing equipment, in addition to possessing a lower density than the glass fibers. Since their thermal degradation onset is at 200 °C, they can be used to reinforce thermoplastics processed below this temperature and thermosets. Several vegetal fibers have been used as reinforcing agent, including sisal and cuarua. However, there is controversy in the literature about the composites final properties. In this work we compare the properties of composites of high density polyethylene or polypropylene with 20 wt. (%) of short sisal or curaua fibers, with or without a coupling agent. All composites were processed by extrusion and molded by injection, under exactly the same conditions, and the mechanical properties were compared. The curaua fibers presented a higher tensile resistance than the sisal fibers, and the composites with curaua fibers had slightly higher tensile and flexural resistance compared to the sisal fiber composites. The situation is opposite in the impact resistance results, with sisal composites displaying higher impact resistance. Since sisal fibers are more fragile than curaua fibers, during processing there is a higher fracture of sisal in comparison to curaua, inducing these differences in composites mechanical properties.There is growing interest in reinforced polymer composites using short vegetal fibers to replace glass fibers for several reasons. The composite fibers are produced from renewable resources, being biodegradable and less abrasive to the processing equipment, in addition to possessing a lower density than the glass fibers. Since their thermal degradation onset is at 200 °C, they can be used to reinforce thermoplastics processed below this temperature and thermosets. Several vegetal fibers have been used as reinforcing agent, including sisal and cuaruá. However, there is controversy in the literature about the composites final properties. In this work we compare the properties of composites of high density polyethylene or polypropylene with 20 wt. (%) of short sisal or curauá fibers, with or without a coupling agent. All composites were processed by extrusion and molded by injection, under exactly the same conditions, and the mechanical properties were compared. The curauá fibers presented a higher tensile resistance than the sisal fibers, and the composites with curauá fibers had slightly higher tensile and flexural resistance compared to the sisal fiber composites. The situation is opposite in the impact resistance results, with sisal composites displaying higher impact resistance. Since sisal fibers are more fragile than curauá fibers, during processing there is a higher fracture of sisal in comparison to curauá, inducing these differences in composites mechanical properties.