와이어 바 코팅 된 반도체 폴리머 필름을 가진 고성능 유기 전계 효과 트랜지스터에 대한 연구

Abstract

Organic semiconductor-based field-effect transistors (OFETs) have been introduced by Ebisawa et al. in 1983 and later by Tsumura et al. in 1986. Since then, the performance of OFETs has made remarkable progress over the past three decades. Nowadays, it is highly anticipated that they will be available in a wide range of applications including flexible display, radio-frequency tags, functional sensors and so on. The development of OFET technology has been made possible thanks to many studies related to the synthesis and purification of various electronic materials such as organic (semi)conductors as well as dielectrics and the optimization of device fabrication processes. In particular, recent reports on donor (D)–acceptor (A)-type semiconducting copolymers with an alternating electron-donating unit and an electron-accepting unit along the polymer backbone confirm that it is possible to obtain a high charge-carrier mobility value of up to 30 cm2V−1s−1. The D–A type conjugated copolymers are intriguing materials because they exhibit high charge-carrier mobility as well as ambipolar characteristics despite their highly disordered microstructure that is in some cases close to an amorphous state. This is counterintuitive to conventionally well-known high-mobility polymers, such as liquid crystalline or semicrystalline thiophene-based semiconductors. In this thesis, the effect of the ordered alignment of the polymer chains on the charge transporting characteristics in the D-A type copolymers was investigated. In order to form more aligned D-A type conjugated copolymer films, a wire-bar coating process was applied to Cyclopentadithiophene-Benzothiadiazole (CDT-BTZ), that is D-A type conjugated copolymer known to have relatively high crystallinity, and other two CDT-based D-A type conjugated copolymers (Cyclopentadithiophene-Fluorinated benzothiadiazole (CDT-FBTZ), Cyclopentadithiophene –Thiadiazolopyridine, (CDT-PTZ)). We fabricated FETs with the wire-bar processed CDT-based D-A type conjugated copolymer film as an active semiconducting layer and compared to the performance with that of the FETs using thin-films obtained by spin coating the same CDT based D-A type conjugated copolymers. From our experimental results on electrical proeprties, it was revealed that the OFET with the wire bar-coated D-A type conjugated copolymer film had higher performance than the OFET with spin-coated semiconducting polymer film in terms of device parameters such as field-effect mobility. These results indicate that more aligned molecular chains have lower structural defects, which is still advantageous for the charge transporting properties even in the D-A type conjugated copolymer films.