Photocurrent spectra of phthalocyanine thin-film electrodes in the visible to near-infrared

Abstract

Photocurrent spectra in the visible to near-infrared (n.i.r.) region have been measured with thin-film electrodes of various phthalocyanines: CuPc, ZnPc, NiPc, VOPc, PbPc and H₂Pc. Only CuPc and PbPc exhibit clear n.i.r. photocurrent responses; these peak at 1100 and 1220 nm, respectively. These results correspond to the formerly reported photoconductive and luminescent properties of phthalocyanines in the n.i.r. and are consistent with their assignment to a singlet-to-triplet excitation. Photocurrent measurements determine the position of triplet excited states much more sensitively than do absorption measurements. The spectral behaviour of the visible photocurrent of CuPc is considered in connection with the process of photocarrier generation. ZnPc appears to show unusual behaviour, and this is attributed to its specific interaction with water. From the values of the quantum efficiencies of both the visible and n.i.r. photocurrents a singlet-to-triplet intersystem crossing efficiency is calculated using some simple assumptions.