Robust Hole Transport in a Thienothiophene Derivative toward Low-cost Electronics

Abstract

A new p-type organic semiconductor, bis(hexylthiophenyl)-thienothiophene, was synthesized and evaluated for its transport characteristics. A robust hole transport was observed even on bare SiO 2 /Si and on flexible substrates under dark air conditions. The discovered characteristics reduce the surface-preparation necessary for device fabrication for low-cost electronics.Recently, organic semiconductors have been extensively studied for practical use in electronic devices. In particular organic thin-film transistor (OTFT) is a key device for the realization of plastic electronics. Stable flexible OTFT are required for flexible displays, radio frequency identification tags, and large-area sensors at low cost. 1 One of the advantages in plastic electronics is providing low cost flexible circuits. A simple procedure to fabricate OTFT is very important for reducing cost. Besides this, the surface energy of gate-insulators commonly affect on the film morphology of organic semiconductor layer, in which the transport performance is drastically changed with the grain boundary population. Various SAM preparations therefore have been proposed to improve transport performance. 2 For realizing the plastic logic circuits, a thin uniform gate-insulator is indispensable to form the OTFT on a film. Control of the surface energy of the gate-insulator is also another requirement related to the surface energy control.Air stability of organic semiconductor is another key factor for plastic electronics. Air-stable organic semiconductors will accelerate the development of plastic electronics by allowing use under ambient conditions. Related to this, several types of sophisticated air-stable organic semiconductors have been synthesized and evaluated in the recent past. 3 From a manufacturing point of view, a small number of synthesis step is highly favorable for chemical vendors. In particular, a simple ³-conjugation system in the molecule providing a relative large band gap is highly desirable. Wide band-gap molecules are candidates to possess intrinsic airstability due to the lower energy level of the highest occupied molecular orbital (HOMO).Poly(2,5-bis(5-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT) is a well-known air-stable polymer showing relatively high hole transport performance. 4 Although the base unit of this polymer is a better candidate for an air-stable oligomer compared to quaterthiophene derivatives, there are no reports of the transport performance of this type of compound at the present stage. 5 In this report, a p-type organic semiconductor, 2,5-bis(5-hexylthiophen-2-yl)thieno[3,2-b]thiophene (BHT-TT) was synthesized ( Figure 1). It was revealed that the hole transport of BHT-TT is quite stable independent of the surface preparation of gateinsulator, by which the SAM process can skip from the fabrication procedure. Air-stability of the compound was also confirmed by the continuous measurement in dry air atmosphere in the dark.BHT-TT was synthesized by the Suzuki Miyaura coupling. 6 The detailed procedure is ...

Design and synthesis of proton-dopable organic semiconductors

“…2,5-Bis(3-dodecylthiophen-2-yl)thieno[3,2- b ]thiophene ( 3 ) was synthesized by the palladium catalyzed cross coupling reaction of 2,5-dibromothieno[3,2- b ]thiophene ( 1 ) with 3-dodecyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thiophene ( 2 ). 19 2,5-Bis(5-bromo-3-dodecylthiophen-2-yl)thieno[3,2- b ]thiophene ( 4 ) was obtained by bromination of 3 with N -bromosuccinimide (NBS). The final product BDTTT was synthesized by the palladium catalyzed cross coupling reaction of ( 4 ) with 2-(2,3-dihydrothieno[3,4- b ][1,4]dioxin-5-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane ( 5 ).…”

2,3-Thienoimide-ended oligothiophenes as ambipolar semiconductors for multifunctional single-layer light-emitting transistors

“…Indeed, while thiazole rings are expected to improve the electron charge transport behavior, the use of thienothiophene is associated with an enhanced hole charge transport as demonstrated in the case of linear oligothiophenes. 69 In detail, the new compound including the bithiazole core was named as NTzN, while the second one with thienothiophene was named as NThTN. A further derivative was synthesized by inserting electron rich methyl substituents into the two thiophene inner cores of NT4N (NTMeN) (Fig.…”