%0 Journal Article
%T Effects of Molecular Structure on Intramolecular Charge Carrier Transport in Dithieno [3,2-b: -d] Pyrrole-Based Conjugated Copolymers
%A Yoshihito Honsho
%A Akinori Saeki
%A Shu Seki
%J International Journal of Spectroscopy
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/983523
%X Intramolecular mobility of positive charge carriers in conjugated polymer films based on dithieno [2,3-b: -d] pyrrole (DTP) is studied by time-resolved microwave conductivity (TRMC). A series of DTP homopolymer and copolymers combined with phenyl, 2, -biphenyl, thiophene, 2, -bithiophene, and 9, -dioctylfluorene were synthesized by Suzuki-Miyaura and Yamamoto coupling reactions. Polymers containing DTP unit are reported to show high value of hole mobility measured by FET method, and this type of polymers is expected to have stable HOMO orbitals which are important for hole transportation. Among these copolymers, DTP coupled with 9, -dioctylfluorene copolymer showed the highest charge carrier mobility as high as 1.7£¿cm2/Vs, demonstrating an excellent electrical property on rigid copolymer backbones. 1. Introduction Since the first observation of electrical conductivity in doped polyacetylene [1, 2], conjugated polymers have attracted much attention to intend a wide variety of optical and electrical applications such as batteries, sensors, photovoltaic cells, organic light-emitting diodes (OLEDs), and organic field effect transistors (OFETs) [3¨C12]. Maximization of charge carrier mobility plays a key role in the enhancement of the performance of these electronic devices. The charge carrier mobility has been usually measured by conventional direct current (DC) methods, for instance, time of flight (TOF), space-charge-limited current (SCLC), and field effect transistor (FET) techniques. In these DC measurements under strong and one-directional external electric field, charge carriers are forced to travel over a long distance between electrodes, and to repeat trapping and detrapping processes at impurities, defect sites, or interfacial barriers between semiconductors and electrodes. Accordingly, the mobility measured by DC methods is affected by extrinsic factors mentioned above leading to rate-determining processes which are not reflecting effective transport along the extended conjugation of molecules. In contrast to DC methods, time-resolved microwave conductivity (TRMC) technique is categorized into an AC method [13¨C19] and allows measurement of intrinsic mobility, because of proving nm-scale oscillating motion of charge carriers free from the above-mentioned extrinsic factors. In this AC measurement, the oscillating motion of charge carriers is induced by alternating electric field of microwave on conjugated molecules, and probed without electrodes (noncontact measurement). Dithieno£¿£¿[3,2-b: 2¡ä,3¡ä-d]£¿£¿pyrrole (DTP) has been expected as a new class of
%U http://www.hindawi.com/journals/ijs/2012/983523/