Characterization of Titanyl Phthalocyanine Films by the Surface Photovoltage Method

Abstract

Titanyl phthalocyanine (TiOPc) thin films were prepared using evaporation and surface polymerization by ion-assisted deposition (SPIAD) which causes dimerization between adjacent TiOPc molecules. All films were characterized by the surface photovoltage method using absorption coefficients evaluated from measurement of the optical transmission and reflection. The surface photovoltage method is applied here to these organic films, allowing determination of exciton diffusion length, which characterizes signal from the bulk. Drift lengths of the charge carriers in the space charge region (SCR) showed recombination, influencing the voltage from this depletion region. Typically, the thickness of the SCR was higher than that of the bulk and the diffusion length of excitons was ~15 nm. No differences in the surface photovoltage spectra or the exciton diffusion lengths were observed between the SPIAD and evaporated TiOPc films more than one year after the samples preparation. An aging process was indicated at the evaporated films.