A study of carrier generation mechanism in x-metal-free phthalocyanine

Combined pulsed photoconductivity and electric field induced fluorescence quenching measurements have been used to study carrier generation mechanism in x-metal-free phthalocyanine. It was found that at low fields fluorescence quenching is a quadratic function of the applied field and saturates at unity at very high fields. Carrier generation is finite at zero applied field and has a linear component at low fields. Linear correlation between carrier generation and fluorescence quenching is observed for fields exceeding 60 V/μm. The results are interpreted by assuming field dependent charge transfer (CT) state formation which either dissociates into carriers or decays to the ground state. Fluorescence quenching data are in excellent agreement with theoretical predictions, while carrier generation at low fields cannot be explained by continuum theory of CT state dissociation probability. It is suggested that the development of a new theoretical framework may be needed which will take into account the discrete nature of charge hopping in the vicinity of the counterion.