Optoelectronic Properties of Orientation-controlled Lead Phthalocyanine Films

We investigated the optoelectronic properties of orientation-controlled lead phthalocyanine (PbPc) films on (0001) sapphire and (001) KCl substrates prepared by vacuum deposition. The results obtained from X-ray diffraction measurements indicate that the orientations of the molecular planes in the PbPc films on the sapphire and KCl substrates are perpendicular and parallel to the substrate surface, respectively. It is found from current-voltage characteristics under dark and illumination conditions that the in-plane conductivity of the PbPc film on the sapphire substrate is about 20 times as large as that on the KCl substrate. This finding indicates that the in-plane conductivity is dominated by the molecular-plane orientation, which is considered to be due to their one-dimensional conduction nature via Pb ions. Furthermore, we discuss the contribution of excitons to the photocarriers based on the results of the absorption and photocurrent spectra.