Organic semiconductors, with their simple low-temperature processing and good mechanical flexibility, provide an ideal solution for the production of low-cost flexible electronic devices. Currently, p-type organic semiconductor materials are the main research interest of researchers, whose transport capacity for holes is better than that for electrons. The p-type organic semiconductor materials can be divided into polymers, oligomers and organic small molecule species. The most obvious difference between these three types of organic species lies in their different molecular sizes. The difference in molecular size in turn largely determines their film-forming mode and quality.
P-type polymers are typically represented by alkyl-substituted polythiophenes, such as region-regularized poly32 alkylthiophenes that can form highly three-dimensional ordered polymer molecular chains, but their field-effect behavior is strongly dependent on the solvent used for film formation. One of the most successful thiophene-based polymers is poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophenes, PBTTT). The first high-performance donor-acceptor semiconductor copolymer for OFET applications was a cyclopentadithiophene and benzothiadiazole (CDT-BTZ) polymer, and since then copolymers based on diketopyrrole (DPP) and isoindigo (IIG) have also been used in OFETs. Several common organic polymeric semiconductor materials are shown in Figure 1.
Figure 1. Several common p-type organic polymer materials
p-type oligomers are represented by thiophene and its derivatives. In fact, the first historical OFET was prepared using oligothiophene as the field-effect material. Oligomeric molecules play an important role in OFET because of the flexibility to adjust the molecular orbital energy level by changing the molecular chain length and introducing functional groups.
P-type organic small molecules have unparalleled advantages of polymers, such as easy purification, the intermolecular planar structure greatly reduces the intermolecular potential barriers, which is conducive to high-speed carrier migration; and because of its film-forming process process, the preparation of semiconductor films of better quality, some organic semiconductors, such as and pentacene have been prepared into a single crystal, which greatly improves the carrier field effect mobility, expanding the application of OFET space. Typical P-type organic small molecules are usually and pentacene, phenol turnip compounds, flowers, red fluorene, etc..
Organic semiconductor materials are dominated by P-type organic semiconductor materials, so the research on P-type field effect materials has progressed relatively rapidly and there are more types of P-type field effect materials. In addition, because of the carrier mobility and switching ratio of P-type organic semiconductor materials, the use of vacuum film-forming OFET performance is mostly excellent. Such as single crystal and pentacene OFET performance is the best, greatly exceeding other OFET performance, but also greatly exceeded the amorphous silicon thin-film transistors. The continuous development of organic thin-film electronic devices urgently requires comprehensive performance of high mobility organic semiconductor materials. Therefore, the development of new high mobility organic semiconductor materials through chemical synthesis and physical compounding is still a development direction of organic thin film transistors.