Marco-A. De Paoli

Dye-sensitized solar cells: a successful combination of materials

Dye-sensitized TiO2 solar cells, DSSC, are a promising alternative for the development of a new generation of photovoltaic devices. DSSC are a successful combination of materials, consisting of a transparent electrode coated with a dye-sensitized mesoporous film of nanocrystalline particles of TiO2, an electrolyte containing a suitable redox-couple and a Pt coated counter-electrode. In general, Ru bipyridyl complexes are used as the dye sensitizers. The light-to-energy conversion performance of the cell depends on the relative energy levels of the semiconductor and dye and on the kinetics of the electron-transfer processes at the sensitized semiconductor | electrolyte interface. The rate of these processes depends on the properties of its components. This contribution presents a discussion on the influence of each of the materials which constitute the DSSC of the overall process for energy conversion. An overview of the results obtained for solid-state dye-sensitized TiO2 solar cells assembled with polymer electrolytes is also presented.

High yield preparation of a soluble polyaniline derivative

The effect of pH, temperature, monomer/oxidant molar ratio, catalysts and ionic strength on the reaction yield and electrical conductivity of chemically synthesized poly (o-methoxyaniline) was studied. Based on this, poly (o-methoxyaniline) was prepared in the presence of p-toluene-sulfonic, dodecyl-benzene-sulfonic and dodecyl-sulfuric acids. Poly(o-methoxyaniline) was obtained with 90% yield and a conductivity of 0.1 S cm−1 when p-toluene-sulfonic acid was used. The use of functionalized acids increased the thermal stability of the polymer in relation to HCl with no changes in the electric conductivity. The polymer is soluble in common organic solvents, enabling the preparation of films by casting. We also discuss the polymerization kinetics of o-methoxyaniline in the presence of HCl and of the functionahzed acids as a function of monomer/oxidant ratio.

Synthesis in pilot plant scale and physical properties of sulfonated polystyrene

The homogenous sulfonation of polystyrene was developed in a pilot plant scale producing polymers with different sulfonation degrees (18 to 22 mole % of sulfonated styrene units). The reaction yield depends chiefly on the concentration ratio of acetyl sulfate and polystyrene. The morphological and thermal properties of the sulfonated polystyrene obtained by homogeneous sulfonation were studied by means of scanning electron microscopy, differential scanning calorimetry and thermogravimetry. The glass transition temperature of sulfonated polystyrene increases in relation to pure polystyrene and DCp was evaluated in order to confirm the strong interactions among the ~SO3H groups.

An elastomeric conductor based on polyaniline prepared by mechanical mixing

In this work we describe the conditions of preparation and the electrical, mechanical, thermal and morphological characteristics of a conductive blend prepared by combining the elastomer poly(ethylene-co-propylene-co-diene-monomer) and polyaniline doped with p-toluene sulfonic acid. Polymer mixtures were prepared in a mixer chamber (cam rotors) coupled to a rheometer. A higher mixing temperature improves the homogeneity of the mixtures, as seen by an increase in conductivity and in crosslinking efficiency. In spite of the good homogeneity, the mixtures are imiscible. Therefore, the formation of bonds between the high molar mass chains of polyaniline and the oligomers explain the increase of the conductivity with an increase in polyaniline content. The modulus values also increase by adding polyaniline to the rubber suggesting a reinforcement effect.

The role of ion exchange in the redox processes of polypyrrole/dodecyl sulfate films as studied by electrogravimetry using a quartz crystal microbalance

Abstract The electrochemical redox mechanism of a dodecyl sulfate-doped polypyrrole was studied in detail by electrogravimetry using a quartz crystal microbalance. In order to distinguish the nature of the inserted/deinserted species, different salts were used as aqueous electrolytes. A quantitative analysis of the results indicated that the surfactant counter anion was trapped in the polymer matrix and that both anions and cations of the electrolyte play an important role in the redox processes. Quantitative calculations showed that the hydration sphere of these ions must be taken into account when dealing with the redox processes of conductive polymers adhered to the surface of electrodes.

Electrochemical and Structural Characterization of Polymer Gel Electrolytes Based on a PEO Copolymer and an Imidazolium-Based Ionic Liquid for Dye-Sensitized Solar Cells

Polymer electrolytes based on mixtures of poly(ethylene oxide-co-propylene oxide) and 1-methyl-3-propyl-imidazolium iodide (MPII) were investigated, aiming at their application in dye-sensitized solar cells (DSSC). The interactions between the copolymer and the ionic liquid were analyzed by infrared spectroscopy and (1)H NMR. The results show interactions between the ether oxygen in the polymer and the hydrogen in the imidazolium cations. The ionic conductivities, electrochemical behaviors, and thermal properties of the electrolytes containing different concentrations of MPII were investigated. The electrolyte containing 70 wt % MPII presented the highest ionic conductivity (2.4 x 10(-3) S cm(-1)) and a diffusion coefficient of 1.9 x 10(-7) cm(2) s(-1). The influence of LiI addition to the electrolytes containing different concentrations of MPII was also investigated. The DSSC assembled with the electrolyte containing 70 wt % MPII showed an efficiency of 3.84% at 100 mW cm(-2). The stability of the devices for a period of 30 days was also evaluated using sealed cells. The devices assembled with the electrolyte containing less ionic liquid showed to be more stable.

Electrochemical study of polypyrrole/dodecyl sulphate

Abstract The electropolymerization reaction of pyrrole in the presence of sodium dodecyl sulphate has been studied and the electroactivity of the polymer investigated with respect to parameters such as the ionic nature of the electrolyte. Polypyrrole obtained in the presence of dodecyl sulphate shows a higher stability and electroactivity in comparison with polypyrrole doped with inorganic dopants.

A conductive elastomer based on EPDM and polyaniline: II. Effect of the crosslinking method

Abstract Electrically conductive heterogeneous binary polymer blends based on ethylene–propylene–diene-monomer (EPDM) and polyaniline (PAni) were prepared in a Haake Rheocord 90 rheometer, coupled with an internal mixer (counter rotating cam rotors) using different amounts of PAni doped with dodecylbenzenosulfonic acid (DBSA). Blends were crosslinked using two methods: (i) phenolic resin (SP-1045) as crosslinking agent and (ii) electron beam irradiation. The last method avoids the interference of the acid dopant in the crosslinking process and produces blends with higher conductivity.

A solid state artificial muscle based on polypyrrole and a solid polymeric electrolyte working in air

A solid state artificial muscle based on polypyrrole(PPy) and poly(epichlorohydrin-co-ethylene oxide) [P(ECH-co-EO)]/ LiClO4 (solid polymeric electrolyte) is developed; an angular movement in air with rate, direction and electrical control similar to those obtained in a liquid electrolyte (aqueous solution of LiClO4) is registered when an electrical current was applied.

Electrochemical, electrochromic and photoelectrochemical behavior of a highly soluble polyaniline derivative: poly(o-methoxyaniline) doped with functionalized organic acids

Poly(o-methoxyaniline) was chemically prepared in the presence of hydrochloric, p-toluene-sulfonic, dodecyl-benzene-sulfonic or dodecyl-sulfuric acids. Films of this polymer were prepared by casting and electrochemical, electrochromic and photoelectrochemical properties were studied. Cyclic voltammetry experiments show well-defined redox waves when the pH of the electrolyte is 1.0. Poly(o-methoxyaniline) films present high optical contrast in the visible range, when the potential is changed from the fully reduced to the fully oxidized state, independently of the dopant acid. The film obtained from the polymer doped with p-toluene-sulfonic acid, however, presents the highest contrast. Photoelectrochemical experiments also showed that this material yields photocurrent when irradiated with monochromatic light (330nm), and that the sign of the photocurrent depends on its oxidation state.