Photocarrier generation processes of phthalocyanines studied by photocurrent and electroabsorption measurements

We have studied the photocarrier generation processes of copper, oxotitanium, and [tau]-metal-free phthalocyanines (Pcs) by measuring the temperature dependence of transient photocurrent, lifetime of precursor of free carrier, and electroabsorption spectra. No distinct correlation was observed between the photocurrent activation energy and the charge generation efficiency. The lifetimes of some Pcs with different charge generation efficiencies had little difference. In phase II and Y-form oxotitanium Pc (TiOPc), electroabsorption signals assignable to CT exciton bands could be observed, while in amorphous TiOPc only the Frenkel exciton band was observed. The phase II and Y-form TiOPc showed much higher photoconductivities than the amorphous one. These results indicated that the nature of the excited states, namely the strength of the CT interaction, should dominate the free carrier generation efficiency in the photocarrier generation processes of Pcs. 14 refs., 8 figs.