Viviana Figa

Symmetric naphthalenediimidequaterthiophenes for electropolymerized electrochromic thin films

A new symmetric naphthalenediimidequaterthiophene (s-NDI2ODT4) was synthesized and exhibited the capability to electropolymerize alone or with EDOT affording polymers with controlled donor/acceptor monomer ratios. s-NDI2ODT4-EDOT-based copolymers showed low band gaps, wide optical absorption ranges extending to the near IR region, tuned electrical properties, thin-film surface morphology and hydrophilicity as well as high coloration efficiency in electrochromic devices.

Electrochemical growth and physico-chemical characterization in organic medium of Nb 2 O 5 thin films

Investigations about the energetics and the electrical properties of niobium thin film, electrochemically grown, were performed in an organic solution of acetonitrile and lithium perchlorate. The study of the energetics of the Nb2O5/organic solution interface was performed by means of a non-destructive optical technique, photocurrent spectroscopy. By means of this technique, it was possible estimating the value of the flat band potential and locating conduction and valence band. A more cathodic value of flat band potential in respect with acidic solution was found in organic medium. From impedance spectra, the electrical circuit that gives best fitting values is constituted by two resistances in parallel with two constant phase elements and in series with the resistance of the electrolyte. On considering the exponential coefficient, the constant phase elements model distorted capacitances.

NOVEL BENZOFULVENES-BASED POLYMERS: CHARACTERIZATION AND EMPLOYMENT IN FLEXIBLE ELECTROCHROMIC DEVICES

Benzofulvenes-based monomers have been synthesized for the first time and have been polymerized by means of electrochemical methods onto different electrodic materials. Morphological investigation has been performed by using SEM; electrical and optical properties have been studied by means of both cyclic voltammetry, optical absorption and spectroelectrochemical techniques. Finally, solid state electrochromic devices have been fabricated. They have displayed high optical contrast.

Electrodeposition of novel poly(naphthalenediimide-quaterthiophene) thin films and applications in plastic optoelectronics devices

A novel symmetric naphthalenediimide-quaterthiophene derivative (NDIT4d) has been polymerized on different substrates including glassy carbon and ITO/PET electrodes by means of electrochemical methods. XPS and UV-VIS spectroscopy as well as cyclic voltammetry have been employed for characterizing the thin film chemical features, the band gap and the HOMO and LUMO levels. DFT computational studies were in close agreement with the experimental observables also showing intriguing geometrical effects on the band gap energy values. The comparison of the energy levels locations of the electrodeposited poly(naphthalenediimide-quaterthiophene) derivative (e-PNDIT4) and P3HT thin films transferred by the Inverse Langmuir-Schaefer (ILS) technique, demonstrates that e-PNDIT4 behaves as acceptor at the interface with P3HT. Steady state fluorescence studies have been performed in order to study the electron transfer in both planar (double layer) and bulk heterojunctions made of e-PNDIT4 and P3HT. The bulk heterojunction - obtained by thermal annealing of the double layer system - has shown a fluorescence quenching of about 97%, indicating an efficient electron transfer from the excited P3HT to e-PNDIT4. Furthermore, electrochromic properties of e-PNDIT4 thin films have been studied by means of spectroelectrochemical measurements. Transmittance versus time plots, recorded under an applied square wave potential, showed an optical contrast of about 20%. These studies open new possibilities in terms of all-polymer devices including the employment of a new class of symmetric push-pull derivatives and the development of fabrication processes exploiting the synergetic use of electrochemical and layer-by-layer deposition methods.