Polymer-coated moth-eye hybrid structure for broadband antireflection in the terahertz region.

A hybrid antireflective structure (ARS) is proposed for enhancing the transmittance of terahertz (THz) waves. This hybrid ARS was made by attaching a polymer-based two-layer coating onto a moth-eye structure on a silicon (Si) substrate. The measured power reflectance of this hybrid ARS remained below 6% in the frequency range of 0.6-2.5 THz, corresponding to the simulated results. The total power reflectance from 0.1 to 2.5 THz was 20% that of the unprocessed Si surface. Besides exhibiting a broadband AR characteristic, this hybrid ARS inherited the cleanable flat surface from the coating structure, which also acts as a protective shield for the moth-eye structures. This high-transmittance, cleanable, flat antireflective surface can not only improve the performance of numerous THz components but also promote the applications of THz waves in daily life.

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 cm(2) 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.

Transition between band and hopping transport in polymer field-effect transistors.

Hall effect and slightly negative temperature dependence of the mobility in polymeric transistors are demonstrated. The semiconductor channel is based on a polycyclopentadithiophene-benzothiadiazole (CDT-BTZ) donor-acceptor copolymer film whose chain direction is oriented by mechanical compression at the surface of an ionic liquid. The mobility is 5.6 cm(2) V(-1) s(-1) at room temperature, and is further improved to 6.7 cm(2) V(-1) s(-1) at 260 K.

Highly oriented polymer semiconductor films compressed at the surface of ionic liquids for high-performance polymeric organic field-effect transistors.

A novel and versatile method to align polymer semiconductors is demonstrated. Spreading and subsequent mechanical compression of a polymer thin film on an ionic liquid's surface yield a polymer thin film that has high uniaxial orientation of the polymer backbone, which is tested for typical polymer semiconductors of PB16TTT, PNDTBTC20, and P3HT. TFTs fabricated by the method exhibit significantly higher mobility compared to TFTs fabricated using a conventional spin-coating process.

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.

Furan fused V-shaped organic semiconducting materials with high emission and high mobility.

We report a facile synthetic protocol for preparation of dinaphtho[2,3-b:2',3'-d]furan (DNF-V) derivatives. DNF-V derivatives showed high emissive behaviour in solid. A solution-crystallized transistor based on alkylated DNF-V derivatives showed an excellent carrier mobility of up to 1.3 cm(2) V(-1) s(-1), thereby proving to be a new solution-processable active organic semiconductor with high emission and high mobility.

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.

Doping of organic semiconductors: impact of dopant strength and electronic coupling.

Molecular doping: The standard model for molecular p-doping of organic semiconductors (OSCs) assumes integer charge transfer between OSC and dopant. This is in contrast to an alternative model based on intermolecular complex formation instead. By systematically varying the acceptor strength it was possible to discriminate the two models. The latter is clearly favored, suggesting strategies for the chemical design of more efficient molecular dopants.

Naphtho[2,1-b:6,5-b']difuran: a versatile motif available for solution-processed single-crystal organic field-effect transistors with high hole mobility.

We here report naphtho[2,1-b:6,5-b']difuran derivatives as new p-type semiconductors that achieve hole mobilities of up to 3.6 cm(2) V(-1) s(-1) along with high I(on)/I(off) ratios in solution-processed single-crystal organic field-effect transistors. These features originate from the dense crystal packing and the resulting large intermolecular π-orbital overlap as well as from the small reorganization energy, all of which originate from the small radius of an oxygen atom.