DC conduction processes and electrical parameters of the organic semiconducting zinc phthalocyanine, ZnPc, thin films

Electronic conduction in thermally evaporated thin films of organic semiconductor zinc phthalocyanine (ZnPc) has been investigated in a broad temperature range using gold Ohmic contacts. Electronic conduction by charge carrier hopping was dominated at low temperatures and for all applied voltages. At higher temperatures and at voltages just below 2 V conduction was found to obey Ohm's law, while at higher voltages space-charge-limited conduction (SCLC) was the dominated mechanism, which was controlled by hole-trapping states distributed exponentially within the band gap. In freshly prepared samples adsorbed oxygen was responsible for lower hole mobility and higher charge carrier concentrations. Prolonged heating of ZnPc films at 425 K resulted in lower defect state density, and thus reduced trap concentration and higher charge carrier mobility. (C) 2003 Elsevier Science Ltd. All rights reserved.