Teruyoshi Mizutani

Performance of poly(3-hexylthiophene) organic field-effect transistors on cross-linked poly(4-vinyl phenol) dielectric layer and solvent effects

Bottom-contact organic field-effect transistors (OFETs) were fabricated using a polymer gate insulator cross-linked poly(4-vinyl phenol) with regioregular poly(3-hexylthiophene) (RR-P3HT) as an active layer from different organic solvents. With this polymer dielectric, a field-effect mobility of 0.084±0.006cm2V−1s−1 was obtained. Solvents and interfacial properties have pronounced effects in determining the crystallinity and device performance of RR-P3HT on the polymer gate layer. Morphology correlation with the charge carrier mobility of RR-P3HT OFETs is investigated. Large nanoscale crystalline island densities of this polymer play an important role in the high charge carrier mobility of devices.

Film Properties of Nanocrystalline 3C–SiC Thin Films Deposited on Glass Substrates by Hot-Wire Chemical Vapor Deposition Using CH4 as a Carbon Source

Nanocrystalline cubic silicon carbide (3C–SiC) thin films have been successfully prepared on glass substrates (at a low temperature of around 325 °C) by hot-wire chemical vapor deposition using CH4 as a carbon source. It was found that using CH4, i.e., a SiH4/CH4/H2 system, is useful for the low-temperature deposition of nanocrystalline 3C–SiC thin films and that filament temperature (Tf) is a significant parameter. The structural transition from hydrogenated amorphous SiC (a-SiC:H) to nanocrystalline 3C–SiC occurred with increasing Tf from 1400 to 1600 °C. The mean crystallite size of the obtained films was 2.6 to 8.4 nm. The IR absorption peak due to Si–C bonds showed a single Lorentzian shape, and with increasing Tf, intensity increased and full width at half maximum decreased. This indicates that the crystallinity of 3C–SiC was improved. The SiH4/CH4/H2 system has enabled us to prepare nanocrystalline 3C–SiC thin films at a low H2 dilution ratio in comparison with the findings of other groups obtained thus far, resulting in a high deposition rate of over 0.15 nm/s.

Behavior of Charge Carriers in Organic Insulating Materials

Organic insulating materials have been widely used in electrical and electronic equipments and a large number of papers have been published for the past several decades. However, the behavior of charge carriers in organic insulating polymers is not well understood yet because insulating polymers have complicated physical/chemical structure and also various additives and impurities which strongly affect the behavior of carriers. The understanding of the physics behind the behavior of charge carriers is necessary for the development of high-performance materials and the further improvement of electrical apparatus and cables. In this paper, the author will try to find the physics behind fundamental carrier behavior in organic insulating polymers. I focus on carrier transport, carrier trap (localized state) and carrier injection of polyethylene (PE). Recent band calculation of PE provided useful hints to understand the carrier transport and carrier traps. The physical defects due to disordered chain folding and the chemical defects such as impurities and oxidation byproducts act as carrier traps and strongly affect the carrier transport and injection. The morphology and the molecular motion of a polymer also play an important role in carrier transport. The space charge measurement techniques such as the PEA method enable us to directly observe the behavior of carriers. Their results are very useful to understand what happens in real insulating polymers.

Third-order nonlinear optical characteristics and the morphologies of polythiophene derivative thin films fabricated by the solution method

The low, third-order nonlinear optical characteristics, as compared with the poly (3-hexylthiophene) [RRP3HT] thin film made on the fused silica substrate by the drop casting method, depend on the random orientation of the thin film prepared by the spin-coating method. The RR-P3HT thin film was made using the casting method, and in addition, the morphology of the RR-P3HT thin film and the effect on third-order nonlinear optical characteristics were evaluated and examined. The fast drying speed meant the thin film did not form by the casting method. Therefore, as the drying speed is suppressed with a saturated chloroform-gas, the RR-P3HT thin film was prepared with the same. In the RR-P3HT thin film made by the casting method, it was clarified as having third-order nonlinear optical characteristics for an excellent orientation compared with the spin-coating method. Furthermore, the third-order nonlinear optical characteristics for the orientation of the poly (3-octylthiophene)[P3OT] and poly (3-dodecylthiophene)[P3DDT] thin films were investigated and performed. The Χ(3) of P3DDT thin film is 1.03×10-10 [esu].

Performance of organic field effect transistor constructed with polycarbonate gate dielectric layer

In this paper, pentacene and metalphthalocyanine was deposited on polycarbonate (PC) thin film using vacuum deposition and their morphologies and molecular orientations were investigated using X-ray Diffraction (XRD) spectrometer and UV/Vis spectrometer. From these results, pentacene and metalphthalocyanine molecules were concluded to be perpendicular on the PC film. The organic field effect transistor (OFET) with pentacene thin film or copperphthalocyanine thin film as an active layer and PC thin film as a gate dielectric film was fabricated on the polyethylene naphtalate (PEN) film (substrate). The drain current versus drain voltage characteristics of the OFET were measured.

Optical bistability of terthiophene/polymethylmethacrylate composite film

In our previous data, following organic gas treatment in 1,2-Dichloroethane vapor, the third order nonlinear susceptibility of a tertiary-butyl vanadylphthalocyanine ((t-Bu)1.45VOPc)/polymethylmethacrylate (PMMA) composite film was observed to increase markedly, because the phase morphology of the composite film changed from Phase I to II. Therefore, the third order nonlinear optical property of the quasi-waveguide, comprised of composite film, was stronger than that before organic gas treatment. When irradiating the quasi-waveguide treated organic gas for 25 hrs with input laser power intensity, the output power had optical bistability. The optical bistability also displayed excellent stability and effective reproducibility. However, in terms of the input laser power intensity dependences of optical bistability, the switching on-off position shifted with the increase in input laser power intensity. In this study, we adopted a terthiophene(3T)/PMMA and poly(3-hexylthiophene)[P3HT]/PMMA composite films, possessing strong third-order optical nonlinearity, to decrease the change in the on-off position depending on the input laser power intensity. The optical bistability of the optical devices, fabricated using a prism, 3T/PMMA or P3HT/PMMA composite films were investigated. The shift in the on-off position in optical bistability characteristics caused by the refractive index change in the thermal effect was improved by the use of the terthiophene (3T)/PMMA or P3HT/PMMA composite films.

High field conduction and breakdown of ultra thin evaporated polypropylene films

The conduction current of an Al/thin PP film/Al structure are explained by tunneling injection and its breakdown strength was about 12 MV/cm without a self-healing breakdown. The surface structures of a conventional PP film and a thin PP film were measured with ESCA, and compared with each other. The degree of oxidation of the thin PP film surface was two times higher than that of a conventional PP film surface. X-ray diffraction studies showed that the thin PP film had high crystallinity and orientation.

Characteristics and performance of organic photovoltaic cells having the active layer fabricated by ternary organic semiconducting materials

The organic semiconductors of poly(3-hexylthiophene) (P3HT), poly(3-octylthiophene)(P3OT), poly(3-dodecylthiophene) (P3DDT) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) were used to make active layers. The active layers of an organic thin film solar cell were fabricated by the P3HT/PC71BM, P3HT/P3OT/PC71BM and P3HT/P3DDT/PC71BM fluid, respectively. Compared with the performances, the performance of the organic solar cell fabricated by P3HT/P3OT/PC71BM thin film indicates the best. The open circuit voltage is 0.61 V. The short-circuit current density is 6.55 mA cm2. The fill factor is 0.51. The power conversion efficiency is 2.07%.

Nano-structure control in the bulk heterojunction layer for organic solar cells

The power conversion efficiency of a polysilicon solar cell is nearly 20%, while that of an amorphous silicon solar cell exceeds 15%. However, as silicon material is inorganic, the simple fabrication of a flexible, lightweight and inexpensive inorganic solar cell is difficult. These limitations of inorganic materials have fuelled active study and considerable progress in the domain of organic thin film solar cells on a global scale. After a bulk-hetero junction structure was introduced in an organic thin film solar cell, one of the latter with power conversion efficiency exceeding 6% was reported. In this study, ethanol, a weak solvent, was added to the 0.01w%P3HT, the 0.01w%PCBM, and the mixed solution of the 0.01wt%P3HT respectively, all of which were dissolved in chloroform. From thin films fabricated by these solutions, P3HT grains and PCBM aggregations are observed with, and evaluated by AFM images and UV-vis spectra.

Organic solar cell performance and nano-morphology of poly(3- hexylthiophene-2,5-diyl) (P3HT)/PCBM thin film using poly(3- ocxylthiophene)

Organic solar cells have been attracting attention due to their economic and lightweight nature that facilitates processing. However, they also have low power conversion efficiency and short lifespans. Therefore, with practical organic solar cells in mind, solving these problems is important. To improve the power conversion efficiency of organic solar cells, the organic solar cell performance of poly(3-hexylthiophene-2,5-diyl)(P3HT)/PCBM thin film using poly(3-ocxylthiophene) was studied with the bulk heterojunction structure. It was shown that a red shift occurred by adding P3OT to the P3HT/PCBM mixture film at the absorption wavelength area of the active layer. This indicates that the formation of the P3HT grain and the aggregate of the PCBM molecule occur because of the P3OT addition. In the heat-treatment sample, it also emerges that the heat-treatment has an effect similar to the P3OT addition because it causes red shifts in both the P3HT/PCBM and P3OT/P3HT/PCBM thin films. This indicates that the formation of the P3HT grain and the aggregate of the PCBM molecule occur because of the P3OT addition. In the heat-treatment sample, the heat-treatment is understood to have an effect similar to the P3OT addition because it causes red shifts in both the P3HT/PCBM and P3OT/P3HT/PCBM thin film. Under preparatory conditions without thermal or solvent annealing, the power conversion efficiency, short circuit current, and open voltage and fill factor are 0.6%, Isc=3mA/cm2, Voc=0.7V and 0.28, respectively.