D‐A1‐D‐A2 Backbone Strategy for Benzobisthiadiazole Based n‐Channel Organic Transistors: Clarifying the Selenium‐Substitution Effect on the Molecular Packing and Charge Transport Properties in Electron‐Deficient Polymers

Unipolar n‐type semiconducting polymers based on the benzobisthiadiazole (BBT) unit and its heteroatom‐substituted derivatives are for the first time synthesized by the D‐A₁‐D‐A₂ polymer‐backbone design strategy. Selenium (Se) substitution is a very effective molecular design, but it has been seldom studied in n‐type polymers. In this study, within the similar conjugated framework, the Se substitution effects on the optical, electrochemical, solid‐state polymer packing, electron mobility, and air‐stability of the target unipolar n‐type polymers are unraveled. Replacing the sulfur (S) atom in the thiadiazole heterocycles with the Se atom leads to narrower bandgaps and deeper lowest unoccupied molecular orbital (LUMO) levels of the n‐type polymers. Furthermore, the Se‐substituted polymer (pSeN‐NDI) shows shorter lamellar packing distances and stronger edge‐on π–π stacking interactions than its S‐counterpart (pSN‐NDI), as observed by the two‐dimensional grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) patterns. With the deeper LUMO level and thin‐film microstructures suitable for transistors, pSeN‐NDI exhibits four‐fold higher electron mobilities (μ_e) than pSN‐NDI. However, the other Se‐containing polymer, pSeS‐NDI, forms rather amorphous film structures, which is caused by its limited thermal stability and decomposition during the thermal annealing processes, thus giving rise to a lower μ_e than its S‐counterpart (pBBT‐NDI). Most importantly, pBBT‐NDI demonstrates an electron mobility of 0.039 cm² V^?1 s^?1, which is noticeable among the unipolar n‐type polymers based on the BBT and its analogs.     

Development of 170 GHz/500 kW gyrotron

A development of 170GHz/500kW level gyrotron was carried out as R&D work of ITER. The oscillation mode is TE_31,8. In a short pulse experiment, the maximum power of 750kW was achieved at 85kV/40A. The efficiency was 22%. In the depressed collector operation, 500kW/36%/50ms was obtained. The maximum efficiency of 40% was obtained at P_RF=470kW whereas the power decrease by the electron trapping was observed. Pulse extension was done up to 10s at P_RF=170kW with the depressed collector operation. The power was limited by the temperature increase of the output window.     

Numerical Analysis of the Boundary Scattering Effect on Transport Properties in Bi-Sb Nanowires

In this study, we have numerically analyzed the transport properties of Bi-Sb nanowires, taking into account wire boundary scattering. Wire boundary scattering slightly decreased the Seebeck coefficient of Bi-Sb nanowires. This effect is due to the observation that boundary scattering and the mobility ratio of L-point electrons to T-point holes in the nanowires are smaller than those in bulk Bi-Sb because the wire boundary scattering suppresses the mobilities of L-point electrons and heavy holes. The largest Seebeck coefficient for all wire diameters was obtained when the Sb concentration was 5 at.%. The effective mass approached zero near 5 at.% Sb, and the small effective mass led to a large subband shift in each band. Thus, a small effective mass enhances the quantum effect at a fixed wire diameter, even if wire boundary scattering is taken into account.     

Thin reduced graphene oxide interlayer with a conjugated block copolymer for high performance non-volatile ferroelectric polymer memory

Polymer ferroelectric-gate field effect transistors (Fe-FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next-generation non-volatile memory. For minimizing gate leakage current of a device which arises from electrically defective ferroelectric polymer layer in particular at low operation voltage, the materials design of interlayers between the ferroelectric insulator and gate electrode is essential. Here, we introduce a new solution-processed interlayer of conductive reduced graphene oxides (rGOs) modified with a conjugated block copolymer, poly(styrene-block-paraphenylene) (PS-b-PPP). A FeFET with a solution-processed p-type oligomeric semiconducting channel and ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) insulator exhibited characteristic source–drain current hysteresis arising from ferroelectric polarization switching of a PVDF-TrFE insulator. Our PS-b-PPP modified rGOs (PMrGOs) with conductive moieties embedded in insulating polymer matrix not only significantly reduced the gate leakage current but also efficiently lowered operation voltage of the device. In consequence, the device showed large memory gate voltage window and high ON/OFF source–drain current ratio with excellent data retention and read/write cycle endurance. Furthermore, our PMrGOs interlayers were successfully employed to FeFETs fabricated on mechanically flexible substrates with promising non-volatile memory performance under repetitive bending deformation.     

Detailed Analysis of Temperature Characteristics of an InGaP/InGaAs/Ge Triple-Junction Solar Cell

Temperature characteristics of an InGaP/InGaAs/Ge triple-junction solar cell were analyzed in detail using an equivalent circuit calculation. The current–voltage (I–V) characteristics of single-junction solar cells (InGaP, InGaAs, Ge solar cells) were measured at various temperatures. Fitting of I–V curves between measured and calculated data was carried out, and the diode parameters and temperature exponents of the single-junction solar cells were extracted. The parameters for each single-junction solar cell were used in the equivalent circuit model for the triple-junction solar cell, and calculations of solar cell performance were carried out. Measured and calculated results of the I–V characteristics at various temperatures agreed well.     

Synthesis of Nanohole‐Structured Single‐Crystalline Platinum Nanosheets Using Surfactant‐Liquid‐Crystals and their Electrochemical Characterization

Nanohole‐structured single‐crystalline Pt nanosheets have been synthesized by the borohydride reduction of Na₂PtCl₆ confined to the lyotropic liquid crystals (LLCs) of polyoxyethylene (20) sorbitan monooleate (Tween 80) with or without nonaethylene‐glycol (C₁₂EO₉). The Pt nanosheets of around 4–10 nm in central thickness and up to 500 nm or above in diameter have a number of hexagonal‐shaped nanoholes ∼1.8 nm wide. High‐resolution electron microscope images of the nanosheets showed atomic fringes with a spacing of 0.22 nm indicating that the nanosheets are crystallographically continuous through the nanoholed and non‐holed areas. The inner‐angle distributions for the hexagonal nanoholes indicate that the six sides of the nanoholes are walled with each two Pt (111), Pt (1 1) and Pt (010) planes. The formation mechanism of nanoholed Pt nanosheets is discussed on the basis of structural and compositional data for the resulting solids and their precursory LLCs, with the aid of similar nanohole growth observed for a Tween 80 free but oleic acid‐incorporated system. It is also demonstrated that the nanoholed Pt nanostructures loaded on carbon exhibit fairly high electrocatalytic activity for oxygen reduction reaction and a high performance as a cathode material for polymer‐electrolyte fuel cells, along with their extremely high thermostability revealed through the effect of electron‐irradiation.     

Network copolyesters from benzenepolycarboxylic acids and 1,6-hexanediol

Network copolyesters were prepared from trimesic (Y), pyromellitic (X) or mellitic (Y_H) acids and 1,6-hexanediol (6G). Prepolymers prepared by meltpolycondensation were cast from dimethylformamide solution and postpolymerized at 260°C for 6h to form a network. The resultant films were transparent, flexible and insoluble in any organic solvents. Degree of reaction estimated from the infrared absorbance of ester and methylene groups was almost the same for all films, 94–96%. X-ray diffraction intensity curves and densities showed that the ordering of networks was decreased by the copolymerization, which was remarkable for 6G–X/Y_H copolymer films and was consistent with the higher decreases of heat-distortion temperature for these copolymer films. The copolymerization also caused decrease of thermal stability, tensile properties and alkali resistance and increase of dye absorption.     

Characteristics of a-Si solar cells prepared by the super chamber at a high substrate temperature

A new approach to high-performance a-Si solar cells was studied. a-Si films prepared at a high substrate temperature (> 250°C) have a higher absorption coefficient and a low Si H₂ bond density. the effect of deposition temperature on the open-circuit voltage (V_oc) has been investigated systematically for glass/SnO2 Ipin/metal and glass/metal/nip/indium tin oxide (ITO) structure a-Si solar cells. The V_oc is found to depend strongly on the thermal history of the p/i interface. A short-circuit current of 19.5 mA/cm⁻⁻² was achieved for an a-Si solar cell using an a-Si i-layer with a thickness of 4000 Å, which was prepared at a substrate temperature of 270°C.     

Oscillation of a tilted circular pad on a droplet for the self-alignment process

The seesaw-oscillation of a small circular pad on a single droplet was studied both numerically and experimentally. The circular pad with a diameter of 2.0–3.8 mm onto a water or glycerol droplet with a volume of 1–10 μL, and a bottom substrate with a smaller diameter than that of the pad were used in the experiment. The pad was then tilted and then the tilting fixture was quickly removed. The pad alternately oscillated and then finally stabilized in a horizontal position. The numerical model considering the surface tension and the viscous force of the droplet was developed and calculated using the same configurations as those in the experiment. The experimental and numerical data showed good agreement not only in terms of the oscillating frequency and damping ratio but the transient motion of the circular pad and instantaneous droplet surface shape.