Thiophene quinoidal organic semiconductors for high performance n-channel organic field-effect transistors

Abstract

Organic field-effect transistors have found wide applications in flexible displays, smart cards, sensors and so on because they can be fabricated on flexible substrates with large scale and low cost. Though great progress has been made on p-channel organic field effect transistors, the development of n-channel organic field-effect transistors is largely lagged behind their p-channel counterparts. The lack of high performance n-channel organic semiconductors has become one of the bottlenecks for organic field-effect transistors. Low LUMO energy level is one of the characteristics of n- type organic semiconductors. The low LUMO level of organic semiconductors can not only reduce the electron injection barrier, in favor of electrons transferring from the electrode into the semiconductor layer, but also prevent the electron charge carriers being trapped by air and water and obtain ambient stability. Thiophene quinoidal organic semiconductors have attracted great attentions recently because they have low-lying LUMO energy levels and strong intermolecular interactions, and usually display high electron mobility. This review summarizes the application of the thiophene quinoidal organic semiconductors in organic transistors in recent years. According to the characteristic of the molecular structures, in the review, the thiophene quinoidal organic semiconductors are divided into two classes: the oligo- thiophene quinoidal organic semiconductors and fused-ring thiophene quinoidal organic semiconductors. Compared to the extensive studied aromatic diimide n-type organic semiconductors, the research on thiophene quinoidal organic semiconductors is not sufficient and the molecular species of thiophene quinoidal compounds is not rich. However, the excellent electron transport properties of thiophene quinoidal organic semiconductors support their potential applications as high performance solution processable n-channel organic semiconductors. In addition to the application in organic transistors, thiophene quinoidal compounds usually have reversible redox property, high electron affinity and other characteristics, and will have potential applications in organic solar cells, charge transfer salts, organic memories and sensors. We believe that the research of thiophene quinoidal organic semiconductors will make more progress.