Conjugated OFETs

In comparison with MOEP and H2TPP, the increased planarity and tt conjugate system associated with the attached benzene rings on the pyrroles of porphyrin core render tetrabenzoporphyrins (TBPs) the most widely studied molecules among porphyrin derivatives for OFET devices. In 2004, Ono and co-workers... 

In recent years great effort has been devoted to conjugated polymers as organic field-effect transistor (OFET) active layers [1]. An important parameter relevant to the operation of an OFET is the charge carrier mobility which determines the overall performance of any polymer-based devices. 

Fig. 1). In addition the jr-conjugated donor-acceptor organic functionalities should enhance electronic polarizabilities, which is attractive to achieve high permittivity materials. Pentacene OFETs based on v-SANDs exhibit excellent performance at low operating voltages. 

Interestingly, Vg-controlled electroluminescence and ambipolar characteristics have been recently observed in conjugated polymer OFETs [67,68], which indicates a balanced electron and hole injection. However, low hole and electron mobilities ( 10 cmWs), typical for polymer semiconductors, limit the channel current and therefore may present a serious problem for realizatiou of electrically pumped polymer lasers. For this reasou, ordered smaU-molecule orgauic semicouductors with higher mobilities are very promisiug for research in this direction. 

The semiconductive properties of conjugated polymers are also exploited for application in thin-film organic field-effect transistors (OFETs). The earliest materials examined were polyacetylene [17], polythiophene [18], and an oligomer of thiophene [19]. In these... 

The metal-like property of these polymers is based on their chemical nature, which consists of chains of conjugated double bonds. If these polymers are oxidized, they become electrical conducting. In the neutral state they can have properties like an inorganic semiconductor. This has now become as important as the metal-like conductivity. One example is the development of an organic field effect transistor (OFET). 

Ong et al. have synthesized solution-processable alkyl-substituted poly(ter- and quarterthiophenes) 203-205 [369-371] and realized OFETs with hole mobilities up to0.14cm V s and on/off ratio over 10 in the case of203 [369]. Similar results have been reported by others [372]. Another approach consists in limiting rr-electron delocalization by incorporation of building block, such as thieno[2,3-b]thiophene that interrupts the conjugated pathway in the chain. The solution-processable polymers 206 leads to OFETs with hole mobility of 0.12-0.15 cm V s [373]. 

FIGURE 7.1 Schematic description of the MOS-FET structure (a) and of the P-i-N diode structure (b). (c) The organic FET (OFET) top contact structure, using a conjugated organic material in the channel. 

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