PHOTOCONDUCTIVITY OF SILICON NAPHTHALOCYANINE THIN-FILMS

The relative photocurrent quantum efficiencies of four silicon naphthalocyanine compounds in vacuum-deposited thin films were found to depend on the axial substituents bonded to the central metal silicon. Electronic, infrared, fluorescence, and photoacoustic spectroscopies, together with measurements of short-circuit photocurrent and low-frequency capacitance, were used in combination to investigate the photoelectrical activity and to elucidate the mechanism of photocarrier generation. There appears to be competition between photocarrier generation and nonradiative decay. In addition, the relative photocurrent quantum efficiency appears to be governed by (i) the degree of stacking of naphthalocyanine molecules in the thin films, (ii) the lattice relaxation originating from the vibrational and rotational motions of axial substituents bound to silicon, and (iii) the local electric field at the interface between aluminum substrate and the silicon naphthalocyanine thin films.