Chikahiko Mitsui

V‐Shaped Organic Semiconductors With Solution Processability, High Mobility, and High Thermal Durability

V-shaped organic semiconductors have been designed and synthesized via a large-scale applicable synthetic route. Solution-crystallized films based on such molecules have demonstrated high-performance transistor properties with maximum mobilities of up to 9.5 cm(2) V(-1) s(-1) as well as pronounced thermal durability of up to 150 °C inherent in the V-shaped cores.

High‐Performance Solution‐Processable N‐Shaped Organic Semiconducting Materials with Stabilized Crystal Phase

N-shaped organic semiconductors are synthesized via four steps from a readily available starting material. Such semiconductors exhibit preferable ionization potential for p-type operation, thermally stable crystalline phase over 200 °C, and high carrier mobility up to 16 cm(2) V(-1) s(-1) (12.1 cm(2) V(-1) s(-1) on average) with small threshold voltages in solution-crystallized field-effect transistors.

Modular Synthesis of 1H-indenes, Dihydro-s-Indacene, and Diindenoindacene―a Carbon-Bridged p-Phenylenevinylene Congener

A variety of 1H-indenes, dihydro-s-indacenes, and diindenoindacenes, carbon-bridged phenylenevinylene derivatives, can be synthesized in good to high yields using as a synthetic module a 3-lithioindene compound made available by reductive cyclization of an alkynylbenzene derivative. The planar analogues of oligophenylenevinylene compounds thus synthesized show physical properties beneficial for use as ambipolar organic semiconductor materials.

Inch-Size Solution-Processed Single-Crystalline Films of High-Mobility Organic Semiconductors

A method for continuously growing large-domain organic semiconductor crystals is developed to fabricate multi-array high-mobility organic transistors. An organic semiconductor solution is held at the edge of a moving blade to grow a large-area crystalline thin film. The continuous evaporation of the solvent at around 100 °C, while the solution is supplied at the same rate, allows the organic crystals to grow steadily on the substrate to several inches in size. The performance of the arrays of field-effect transistors based on the large-domain crystal films is excellent, with mobility of 5–10 cm2 V-1 s-1.

Tetraaryl‐Substituted Benzo[1,2‐b:4,5‐b′]dipyrroles: Synthesis, Properties, and Applications to Hole‐Injection Materials in OLED Devices

Yes, HIMs can! A series of 2,3,6,7-tetraarylbenzo[1,2-b:4,5-b′]dipyrroles (BDPs) were synthesized using zinc-mediated double cyclization. Organic light-emitting diodes consisting of BDP:PPB as a hole-injection layer could be driven at a lower voltage than a PEDOT:PSS-based device. Correlation of the IP values with the driving voltage shed some light on the mechanism of hole-injection processes.

Suppressing molecular vibrations in organic semiconductors by inducing strain

Organic molecular semiconductors are solution processable, enabling the growth of large-area single-crystal semiconductors. Improving the performance of organic semiconductor devices by increasing the charge mobility is an ongoing quest, which calls for novel molecular and material design, and improved processing conditions. Here we show a method to increase the charge mobility in organic single-crystal field-effect transistors, by taking advantage of the inherent softness of organic semiconductors. We compress the crystal lattice uniaxially by bending the flexible devices, leading to an improved charge transport. The mobility increases from 9.7 to 16.5 cm2 V−1 s−1 by 70% under 3% strain. In-depth analysis indicates that compressing the crystal structure directly restricts the vibration of the molecules, thus suppresses dynamic disorder, a unique mechanism in organic semiconductors. Since strain can be easily induced during the fabrication process, we expect our method to be exploited to build high-performance organic devices.

Modular synthesis of polybenzo[b]silole compounds for hole-blocking material in phosphorescent organic light emitting diodes.

A diversity-oriented synthetic strategy allowed us to design a series of conjugated molecules containing multiple benzosilole units that can be utilized as efficient hole-blocking materials for phosphorescent organic light emitting diodes (OLEDs). Some of these compounds showed a performance surpassing that of the current standard, bathocuproine. The new compounds were easily synthesized in a modular fashion from a previously reported 3-stannyl benzosilole building unit. Studies on the properties of these compounds in solution and in the solid state indicate that they possess high electron affinity, high ionization potential, and form stable amorphous films that show high electron-drift mobility. The correlation between their molecular properties and the efficiency of the OLED device performance is also investigated.

Split-gate organic field-effect transistors for high-speed operation.

Split-gate organic field-effect transistors have been developed for high-speed operation. Owing to the combination of reduced contact resistance and minimized parasitic capacitance, the devices have fast switching characteristics. The cutoff frequencies for the vacuum-evaporated devices and the solution-processed devices are 20 and 10 MHz, respectively. A speed of 10 MHz is the fastest device reported so far among solution-processed organic transistors.

Wafer-scale, layer-controlled organic single crystals for high-speed circuit operation

A wafer-scale, 2D organic single-crystalline semiconductor revolutionizes near-field communication. Two-dimensional (2D) layered semiconductors are a novel class of functional materials that are an ideal platform for electronic applications, where the whole electronic states are directly modified by external stimuli adjacent to their electronic channels. Scale-up of the areal coverage while maintaining homogeneous single crystals has been the relevant challenge. We demonstrate that wafer-size single crystals composed of an organic semiconductor bimolecular layer with an excellent mobility of 10 cm2 V−1 s−1 can be successfully formed via a simple one-shot solution process. The well-controlled process to achieve organic single crystals composed of minimum molecular units realizes unprecedented low contact resistance and results in high-speed transistor operation of 20 MHz, which is twice as high as the common frequency used in near-field wireless communication. The capability of the solution process for scale-up coverage of high-mobility organic semiconductors opens up the way for novel 2D nanomaterials to realize products with large-scale integrated circuits on film-based devices.

High performance oxygen-bridged N-shaped semiconductors with a stabilized crystal phase and blue luminescence

Here, we describe an oxygen-bridged N-shaped π-electron core, dinaphtho[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]difuran (DNBDF), as a new entity of organic semiconducting materials. Interestingly, by introduction of flexible alkyl chains at appropriate positions, DNBDF π-cores exhibit solution processability, a highly stabilized crystal phase, high mobility, and blue luminescence as a solid.