Fabrication and photoelectrochemical properties of polythiophene-porphyrin composite films

Polythiophene-porphyrin composite films consisting of bithiophene and meso-tetrathienylporphyrin were prepared on transparent indium tin oxide (ITO) electrodes. First, a polythiophene film was fabricated on the ITO electrode by electrochemical polymerization in the bithiophene solution with repeated oxidation-reduction cycles in the 0-+2V region. Then, porphyrin was assembled on the polythiophene-modified electrode by using the same electrochemical polymerization in the porphyrin solution, to give polythiophene-porphyrin modified electrodes. The amount of porphyrin increased with increasing number of scanning cycles for electrochemical polymerization. In the presence of oxygen, irradiation of the polythiophene-porphyrin modified electrodes resulted in stable cathodic photocurrents. Photocurrent increased with increasing amount of porphyrin. Large cathodic photocurrents were observed in the negatively applied potentials. The photocurrent action spectra of modified electrodes strongly suggested the photochemical cooperation of porphyrin and polythiophene for photocurrent generation. The combination of polythiophene and porphyrin in the electrochemically modified electrode is quite effective for generating large photocurrents.