Temperature dependence of dark and photo-conductivity in single crystals of metal-free, iron and copper phthalocyanines from 300 to 85 K

Abstract

The temperature dependence of the photo- and dark conductivity in single crystals of metal-free, Cu and Fe phthalocyanines is reported, with the observation of thermally stimulated conductivity (t.s.c.) in the first two complexes. For the first two the conductivity decreased exponentially with temperature but photocurrent activation energy decreased sharply at ca. 220–250 K, the same temperature range in which t.s.c. was observed. Assuming electron conductivity, this behaviour is explained by a model involving electron donors ca. 1.1 eV below the conduction band and electron traps ca. 0.4 eV below the conduction band.

In contrast, in Fe phthalocyanine no t.s.c. was observed and the photo- and dark conductivity follow an Arrhenius plot, with no activation energy change down to 120 K. The exponent of the photocurrent–light-intensity relationship decreased with decreasing temperature.