Photophysics and photochemistry of colloidal poly (p-phenylinevinylene) (PPV) polymer

The photophysical and photochemical behaviour of colloidal PPV polymers has been investigated by emission and photoelectrochemical studies. Emission studies indicated an increased conjugation length for PPV polymers on going from solution to the solid state. The quenching of the emission of PPV polymer by iodine can be used to probe the hole transfer by PPV–iodide complex with subsequent formation of I*−. To elucidate the role of hole trapping in the process of photo-generation charge separation in various PPV/OTE electrodes, various electrolytes have been used. The values of photon-to-photocurrent conversion efficiency (IPCE) were evaluated from the short circuit photocurrent measurements at different excitation wavelengths. The close match between the IPCE and the absorption spectra shows that the photosensitization mechanism is operative in extending the photocurrent response of OTE/PPV into the visible. The maximum IPCE observed in the present experiments was ∼1.5% in the wavelength region of 425 nm which commensurates well with the reported values [M. Jonforsen, I. Ahmad, T. Johansson, J. Larsson, L.S. Roman, M. Svensson, O. Inganas, M.R. Andersson, Synth. Met. 119 (2001) 185]. From the photoelectrochemical response of an OTE/PPV electrode to visible light irradiation, the generation of photovoltage and photocurrent was prompt and was reproducible under several on–off cycles of illumination. Optimization of redox couple, electrolyte and film thickness is essential for improving the performance of PPV-based photoelectrochemical cells.