A. Geri

Electrochemical preparation and electrochromic characteristics of dithienopyrrole-dithienothiophene, dithienopyrrole-thionaphtheneindole and dithienothiophene-thionaphtheneindole copolymers

Abstract Poly(dithienopyrrole-dithienothiophene) copolymers can be obtained as good conducting electrode films by electrolytic oxidation of acetonitrile solutions of monomer mixtures (electrolyte: tetrabutylammonium perchlorate). They show good electrochromic characteristics. Films of poly(dithienopyrrole-thionaphtheneindole) and poly(dithienothiophene-thionaphtheneindole) copolymers can be obtained in the same way as the previous ones. They are adherent to the electrodes but are insulating and non-electrochromic; the reason for this behaviour is proposed to be the break of conjugation in the polymeric chain due to the thionaphtheneindole moiety.

Properties of the heterojunction between poly(dithienopyrrole)-poly(vinylchloride) composite and n-doped silicon

Using the temperature dependence of the forward-biased current-voltage characteristics as well as capacitance-voltage measurements, we calculated the contact barrier height of the heterojunction between poly(dithienopyrrole)-poly(vinylchloride) composite and n-Si. Analysis of the characteristics suggests that thermionic emission over the composite/inorganic contact barrier dominates at low current densities, whereas at high current densities the process is dominated by the series resistance. Very good reproducibility was observed for the junction characteristics.

Electrochromic properties of poly(N-methyl-10,10-dimethyl-phenazasiline)

Abstract A new conducting polymer was obtained by electrooxidation of N -methyl-10,10-dimethyl-phenazasiline (SIN). The electrochromic properties of poly(SIN) have been investigated. It was found that this material presents a good chemical stability and a reversible behaviour during many subsequent redox cycles.

Effect of hexadecyl groups in 4 position on the electrochemical polymerisation of 4H-cyclopenta[2,1-b:3,4-b′]dithiophene

Abstract Hexadecyl groups in 4 position of 4 H -cyclopenta[2,1- b :3,4- b ′]dithiophene (CPDT) molecule leads, by cyclic voltammetry (CV), to electrode films of polyconjugated polymers with a more regular morphology and higher interchain distance. The rate of film formation is lower for the alkyl-substituted compounds and, in this case, during the preparative cyclic voltammetry (PC), an induction step was observed inherent to the electrode covering process. The same induction step was observed also in the polymerisation of non-substituted molecule, but at lower concentrations.

Optimisation of the dark and photovoltaic properties of Schottky junctions between aluminium and conjugated polymers

Abstract The behaviour of ITO/poly(4,4′-dipentoxy-2,2′bithiophene)/Al and ITO/poly(3-butylthiophene)/Al Schottky junctions has been investigated in the dark and under white light illumination, both in the air and under dry argon flux. Both systems exhibit a battery in the dark and photoelectrochemical processes under illumination, when tested in wet atmosphere. The more hydrophobic structure, the polyPT4-based one, was found to be less affected by the ionic conductivity induced by the water absorbed from the environment and the aluminium oxidation.

Photoelectrical properties in poly(alkyl/alkoxy-terthiophenes): dependence on the alkyl-chain length

Abstract The length of the alkyl-groups affects both the spectrophotometric and the electrochemical properties of poly(alkoxy-alkyl-terthiophenes) films prepared by cyclic voltammetry. The maximum absorbance shifts towards higher wavelengths and the oxidation peak towards cathodic potentials as the alkyl-chain length increases. Moreover, it was found that the photoelectrical performance exhibited by poly(alkoxy-alkyl-terthiophenes)-based devices improved from poly(4,4″-dipenthoxy-3′-dodecyl-2,2′:5′,2″-terthiophene) to poly(4,4″-dipenthoxy-3′-hexyl-2,2′:5′,2″-terthiophene), probably due to an increasing hopping mobility, and remained constant or somewhat decreased by going from poly(4,4″-dipenthoxy-3′-hexyl-2,2′:5′,2″-terthiophene) to poly(4,4″-dimethoxy-3′-methyl-2,2′:5′,2″-terthiophene) possibly for a lower planarity of polythiophene chains.

Electrochemical preparation of conducting polymer composites: Poly(vinylchloride)/poly(dithienopyrrole) and poly(vinylchloride)/ poly(dithienothiophene)

Abstract With the aim of improving the processability of some electrochromic polymers, dithienopyrrole and dithienthiophene were polymerized by a potentiodynamic technique on platinum electrode coated by poly(vinylchloride). A composite was obtained in both cases, characterized by a good processability, typical for poly(vinylchloride), and by electrochromic features very similar to those of the conducting polymers.

Photovoltaic effect of heterojunctions between poly(4,4′-dipentoxy-2,2′-bithiophene) and n-doped silicon

Abstract The photovoltaic effect of poly(4,4′-dipentoxy-2,2′-bithiophene) (poly(ET2)) conducting polymer deposited on n-doped silicon has been investigated. The plots of short-circuit current, open-circuit voltage, fill factor and conversion efficiency as a function of incident light intensity are reported. Analysis of the photovoltaic characteristics suggests that an internal series resistance limits the junction performance.

Influence of the reaction medium on the polymerization mechanism of thionaphtheneindole

Abstract The oxidative polymerization of thionaphtheneindole is investigated. It is found that the nature of the resulting polymer depends on the reaction medium: in particular with perchlorate as electrolyte, the conducting polymer is the product of the thionaptheneindole oxidation; on the contrary, in the presence of p -toluenesulfonate, the same oxidation gives rise to the neutral polymer.

Reflection electrochromism of poly(4,4-dipentoxy-2,2' :5'2-dithiophene

Abstract Transmittance and reflectance spectra as a function of the electrode potential are reported for the title polymer, an electrochemically prepared thiophenic polymer with extremely good chemical stability and mechanical properties of its conductive state. An electrochromic effect both for the transmitted and for the reflected light is shown. The “reflection electrochromism” here reported, besides its relevant implications in the analysis of the electronic states of conducting polymers, is certainly an interesting effect for its possible application in energy saving systems.