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J. Appl. Cryst.の発刊に際して

Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

Aggregation-Induced Emission: Together We Shine, United We Soar!

Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Printed electronics is a revolutionary technology aimed at unconventional electronic device manufacture on plastic foils, and will probably rely on polymeric semiconductors for organic thin-film transistor (OTFT) fabrication. In addition to having excellent charge-transport characteristics in ambient conditions, such materials must meet other key requirements, such as chemical stability, large solubility in common solvents, and inexpensive solution and/or low-temperature processing. Furthermore, compatibility of both p-channel (hole-transporting) and n-channel (electron-transporting) semiconductors with a single combination of gate dielectric and contact materials is highly desirable to enable powerful complementary circuit technologies, where p- and n-channel OTFTs operate in concert. Polymeric complementary circuits operating in ambient conditions are currently difficult to realize: although excellent p-channel polymers are widely available, the achievement of high-performance n-channel polymers is more challenging. Here we report a highly soluble ( approximately 60 g l(-1)) and printable n-channel polymer exhibiting unprecedented OTFT characteristics (electron mobilities up to approximately 0.45-0.85 cm(2) V(-1) s(-1)) under ambient conditions in combination with Au contacts and various polymeric dielectrics. Several top-gate OTFTs on plastic substrates were fabricated with the semiconductor-dielectric layers deposited by spin-coating as well as by gravure, flexographic and inkjet printing, demonstrating great processing versatility. Finally, all-printed polymeric complementary inverters (with gain 25-65) have been demonstrated.

A high-mobility electron-transporting polymer for printed transistors

Novel thiazole oligomers and thiazole/thiophene co-oligomers with trifluoromethylphenyl groups were developed as n-type semiconductors for OFETs. They showed excellent n-type performances with high electron mobilities. A 5,5'-bithiazole with trifluoromethylphenyl groups forms a closely packed two-dimensional columnar structure leading to a high performance n-type FET. The electron mobility was enhanced to 1.83 cm2/Vs on the OTS-treated substrate.

n-type organic field-effect transistors with very high electron mobility based on thiazole oligomers with trifluoromethylphenyl groups.

Novel π-electron systems with trifluoromethylphenyl groups and/or a thiazolothiazole unit were developed as n-type semiconductors for OFETs. They showed excellent n-type performances with high electron mobilities. The trifluoromethylphenyl group was found to be very effective in inducing n-type behavior. The thiazolothiazole unit was favorable for forming stacking structures leading to efficient intermolecular π−π interactions.

High performance n-type organic field-effect transistors based on π-electronic systems with trifluoromethylphenyl groups

https://iopscience.iop.org/article/10.1088/1468-6996/10/2/024313/pdf

Organic semiconductors for organic field-effect transistors

A series of new blue-phosphorescent iridium(III) complexes 1−14 with ligands of 2-phenylimidazo[1,2-a]pyridine (pip) derivatives were successfully prepared, and their electrochemical, photophysical, and electroluminescent (EL) properties were systematically investigated. It was found that the emission maxima are significantly dependent on the substituents on the phenyl ring in the range of 489−550 nm. For instance, electron-withdrawing groups such as F and CF3 shift the emission maxima to shorter wavelengths by lowering the HOMO levels (complexes 4−8), whereas the extended π-conjugation leads to bathochromic shifts (2, 3). To obtain further information about the frontier orbital, substitution effects on the imidazole part were also investigated here, and it was found that electron-withdrawing or -donating substituents on the imidazole ring affected the emission maxima (9, 557 nm; 10, 525 nm). These results including their oxidation potentials suggest that the HOMO of the pip-based complex is a mixture of ...

Phosphorescent iridium complexes based on 2-phenylimidazo[1,2-a]pyridine ligands: tuning of emission color toward the blue region and application to polymer light-emitting devices.

Novel anthracene derivatives were prepared as semiconductors for FETs to prove the effect of terminal groups on charge transport. The n- and p-type activities were achieved by introduction of acceptor or donor units into the anthracene structure.

Yoshiro Yamashita

Papers

n-type organic field-effect transistors with very high electron mobility based on thiazole oligomers with trifluoromethylphenyl groups.

High performance n-type organic field-effect transistors based on π-electronic systems with trifluoromethylphenyl groups

Organic semiconductors for organic field-effect transistors

Phosphorescent iridium complexes based on 2-phenylimidazo[1,2-a]pyridine ligands: tuning of emission color toward the blue region and application to polymer light-emitting devices.

Novel p- and n-Type Organic Semiconductors with an Anthracene Unit