Abstract
Two new Zinc phtalocyanine, ZnPcR1 and ZnPcR4, with peripheral mono and tetra quinoleinoxy substituents of the phtalocyanine ring, were characterized to investigate their optical and electrical properties. The modification of the chemical structure allows the elongation of the pi-conjugation, leading to an enhanced solubility as well as a broadening of the ZnPcR1 and ZnPcR4 absorption spectra. The UV-Visible absorption spectra show a typical behavior of phtalocyanine for the two pi-conjugated systems with an optical band gap of 1.70 and 1.74 eV for ZnPcR1 and ZnPcR4 respectively and the Photoluminescence study exhibits a green emission for both compounds. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels were estimated using cyclic voltammetry analysis and the calculated electrochemical gap was found to be equal to the optical one. Current-voltage characteristics and impedance spectroscopy measurements performed on sandwich structures ITO/phtalocyanine derivatives/Al are used to elucidate the conduction mechanisms. The static electrical characterizations showed a space charge limited conduction with exponential trap distribution at high applied bias voltage. The impedance spectra were discussed in terms of an equivalent circuit model designed as a parallel resistor R-p and capacitor C-p network in series with a resistor R-s. The evolution of the electrical parameters deduced from fitting of the experimental data is discussed. The conduction mechanism revealed by I-V characteristics is in agreement with the impedance spectroscopy results.