Pulsed photoconductivity action spectra of β-metalfree phthalocyanine thin films

Using pulsed photoconductivity techniques, transient action spectra have been recorded on vacuum sublimed β-metalfree phthalocyanine thin films in the wavelength range 360♯740 nm. Quantum efficiencies for carrier generation and carrier ranges were deduced assuming (a) range limited transport and (b) wavelength and field independent quantum efficiency. Carrier generation is shown to be a bulk phenomenon and the lowest excited singlet state is the common intermediate in the carrier generation process. Two sets of measurements have been performed, 5 and 12 weeks after sample preparation. The quantum efficiency changed from 2.5×10−4 to 10−3, probably due to an increase in the amount of absorbed oxygen.