Photoconduction in Metal-Free Phthalocyanine Films

Abstract

By using pulsed photoconductivity techniques, transient action spectra have been recorded on vacuum-sublimed a metal-free phthalocyanine thin films in the wavelength range 350-700 nm. The transient photocurrents were determined at fields less than 10⁷ V m^-1 by range-limited transport of holes, the μ_T product of photogenerated holes being c. 2×10^-14 m² V^-1. The electron μ_T product was about 100 times smaller. Carrier generation was a bulk phenomenon. The quantum efficiency was about 1-2% at fields up to 10⁷ V m^-1, and it was increased several fold by the presence of a layer of the acceptor pyromellitic dianhydride. Photogeneration in phthalocyanine occurred by an Onsager -type process. When pyromellitic dianhydride was present, an additional process of carrier generation, not of Onsager type, occurred, possibly associated with an exciton reaction with a charge-transfer complex between α metal-free phthalocyanine and pyromellitic dianhydride .