Study of ordered organic semiconductor films of pentacene and copper phthalocyanine

Abstract

Since the appearance of promising applications in low cost and flexible electronic devices, organic semiconductor materials have been widely studied in all aspects. The present work focuses on topics of ordered organic films and organic field effect transistor (OFET). Two organic semiconductors, pentacene and copper phthalocyanine (CuPc), were selected. The properties of thin film on various substrates and OFET devices based on these two materials were studied. CuPc was found to form ordered structure on three similar Van de Waals surfaces, Si(111):H, Si(100)(2x1):H and Highly Ordered Pyrolytic Graphite(HOPG), but with different morphologies. Despite the different morphologies, the films deposited on HOPG and Si(111):H at a high temperatures seem to have the same crystal structure. This structure is neither the α- nor the β- form crystal of CuPc. In this structure the CuPc molecules lie flat with their molecular plane parallel to the substrate surface. Two kinds of band bending behavior of CuPc film were observed. Pentacene forms ordered structures on both HOPG and Si wafer with native oxide layer (SiOx), but they are different from each other. On HOPG substrate the pentacene molecules always lie flat, while on SiOx substrate the pentacene molecules begin to lie flat from the second layer. A model is given to describe the growth of pentacene on SiOx substrate. Organic thin film transistor (OTFT) devices were fabricated by using both CuPc and pentacene as the active material. A device with a mobility of up to 0.187cm2/Vs and an on/off ratio of 2x103 was fabricated. The device made in Ultra-High Vacuum (UHV) shows better mobility but an unacceptable on/off ratio and the possible reason was given.

Date of Award	15 Jul 2004
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Shuit Tong LEE (Supervisor)