A study of carrier generation in β-metal-free phthalocyanine

Photoinduced carrier generation has been studied in particle dispersions of β-metal-free phthalocyanine purified by temperature gradient sublimation. In addition to the photoconductive response measured by the delayed-collection-field technique, electric-field-induced fluorescence quenching and delayed fluorescence were also investigated. The results are consistent with the model which assumes that carrier generation proceeds through an intermediate, charge transfer (CT) state, which either dissociates into free carriers or predominantly decays to the ground state. Delayed-collection field and delayed-fluorescence experiments show that the geminate electron-hole pair is very long lived (tens of milliseconds) and has a non-exponential time decay. These results represent a new evidence for the observation of time-resolved carrier generation first reported by Mort et al. in polyvinyl carbazole. Field dependence of the geminate electron-hole pair dissociation yield is consistent with the Poole-Frenkel mechanism.