Semiconductors ambipolar

Due to the great potential applications and the widespread interests of OFETs, several review articles with emphasis on different aspects of OFETs have been published [8-13], However, despite the extensive studies and increasing research interests in phthalocyanine as well as porphyrin semiconductors, there is still no review article that systematically generalizes the research achievements in the field of tetrapyrrole organic semiconductors for OFETs. Thus, the present contribution should interest scientists in both industrial and theoretical fields. The main contents of this chapter is as follows Firstly, some basic introduction of the structure and characteristics of OFET is provided then theoretical factors that influence the performance of OFET devices is discussed finally, the progress in phthalocyanine-based OFETs in the order of p-type, n-type, and ambipolar semiconductors is summarized. 

Fig. 5.6. Schematic drawing of a bulk heterojunction device. Charge generation occurs throughout the bulk, but the quality of the two transport networks (p-and n-type channels) is essential for the functionality of the blend as an intrinsic, ambipolar semiconductor. Light emission occurs at the semi-transparent ITO electrode. Electron transport on the fullerenes is marked by full arrows and hole transport along the polymer by dotted arrows...

This is of particular interest since for all pentacene-based thin film transistors using high work function electrodes (such as gold) only p-type transport has been found although pentacene is intrinsically an ambipolar semiconductor. Note, that previously n-type transport has only been observed in connection with low work function electrodes such as calcium [80] (see also Chapter 24 by Benson et al.). In accord with previous findings by Friend and coworkers [78] we propose that we can observe n-conduction in our model device because the presence of any OH-groups at the SAM/pentacene interface can be safely excluded by the use of ultra-clean electrodes. 

Charge-transfer type co-polymers comprised of electron-donating and electron-withdrawing units are considered to be potentially useful as ambipolar semiconductors. With this in mind, co-polymers of thiophene (-electron donor) and thiazole or... 

Most semiconductors can be selectively made (by doping) either n type or p type, in which case they are called ambipolar semiconductors. Some semiconductors can be selectively made only n type or only p type. For example, ZnTe is always p type whereas CdS is always n type. Such semiconductors are called unipolar semiconductors. 

Ambipolar semiconductors Semiconductors that can be selectively doped to achieve either type or p type material. 

Usta H, Newman C, Chen Z, Facchetti A (2012) Dithienocoronenediimide-based copolymCTs as novel ambipolar semiconductors for organic thin-film transistors. Adv Mater 24 3678-3684... 

Since the benzothiadiazole units are often found in p-type/ambipolar semiconductors as described above, additional electron-accepting units are required to achieve n-type-dominated behavior. Introduction of the benzothiadiazole units in n-type semiconductors is advantageous to acquire low-lying LUMO levels and enhance intermolecular interactions through heteroatom contacts. The perfluo-roalkylated compound 81c showed an electron mobility of 4.7 x 10 cm s ... 

Further evidence for the crucial role of the dielectric was brought by reports on n-channel operation with pentacene through the use of PVA as gate dielectric [71, 72]. Hence the concept of ambipolar semiconductor, where the type of the charge carriers (electrons or hole) is not dictated by the nature of the semiconductor instead, it will depend on the nature of the gate dielectric and of the contacts. 

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