Conduction in lead phthalocyanine films with aluminium electrodes

Electronic conduction has been investigated in evaporated lead phthalocyani ne thin films with aluminium electrodes. In contrast to previously investig ated samples where the injecting electrode was a gold ohmic contact, these samples did not exhibit space-charge-limited conductivity, but showed carri er excitation via a field-lowering mechanism with a log J proportional to V -1/2 current density-voltage (J-V) characteristic. Both polarities showed t wo regions in the J-V characteristics having different slopes, leading to t he conclusion that conduction is via Schottky and Poole-Frenkel emission at lower and higher voltages, respectively. The Schottky barrier height was 1 .03 eV and the depletion region thickness was typically 100 nm for forward bias and 77 nm for reverse bias. In the presence of air there was a decreas e in conductivity, which was attributed to the effects of oxygen establishi ng an interfacial region at the electrodes. The reverse bias conductivity w as higher than that for forward bias when exposed to air; this effect was a ssociated with different values of the hole injection efficiency at the two electrodes consequent on the effects of the oxygen exposure. (C) 2000 Else vier Science S.A. All rights reserved.