Photocurrent kinetics in metal phthalocyanine crystals, films and pellets

The rise and decay kinetics of photoconductivity are reported for copper phthalocyanine [Cu(pc)], lead phthalocyanine [Pb(pc)] and chloro-(phthalocyaninato)-aluminium [Al(pc)Cl] single crystals. These show the rise to the first order (τ < 0.004, 0.68 and 0.36 (platelet), 0.071 (needle) s, respectively). The decay generally fits two consecutive first-order processes, both slower than the rise. The differences in lifetimes are interpreted in terms of trapping at defect lattice sites. The effects of ambient atmosphere and physical form are also reported. Exposure to NO2 or O2 decreases the rise time and increases the decay time. ‘Photocurrent kinetics’ of Pb(pc) pellets are shown to be due to thermal effects, as are those of poly-(phthalocyaninato siloxane). Thin films of these phthalocyanines show faster kinetics than single crystals. These results would not be expected for a polycrystalline structure and are discussed with reference to X-ray diffraction data obtained using synchrotron radiation.