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We have developed a new method to obtain Ribbon-shaped floating films via dynamic casting of floating-film and transfer method (dynamic-FTM). Dynamic-FTM is a unique method to prepare oriented thin-film of conjugated polymers (CPs) which is quick and easy. This method has several advantages as compared to the other conventional casting procedure to prepare oriented CP films. In the conventional dynamic FTM appearance of large scale circular orientation poses difficulty not only for practical applications but also hinders the detailed analysis of the orientation mechanism. In this present work, pros and cons of this newly proposed ribbon-shaped floating-film have been discussed in detail from those of the conventional floating-film prepared by dynamic-FTM., 12th International Conference on Nanomolecular Electronics (ICNME-2016), December 14-16, 2016, Kobe International Conference Center, Kobe, Japan

Orientation characteristics of non-regiocontrolled poly (3-hexylthiophene) (NR-P3HT) films prepared by dynamic casting of floating film and transferring method (FTM) has been investigated. The film was first cast on liquid-substrate to obtain as a floating-film followed by its transfer on solid-substrate such as white-glass or Si-wafer in order to evaluate their optoelectronic characteristics. As a possible key-factor to generate the orientation of conjugated polymer in this method we focused on the components of liquid-substrate in this study. The orientation dependence upon various liquid-substrates reveals that dichroic ratio strongly changes with liquid-substrates. Pictures of floating-film show the change in size of floating-parts depending upon the liquid-substrate, representing the expansion length of casting solution upon the viscosity. These findings have indicated that spreading speed of polymer solution and solvent evaporation speed controls the size of floating-film leading to change in the orientation intensity. The multilayer coatings of oriented NR-P3HT films were used for polarized FTIR analysis exhibiting clear dichroism. The obtained dichroic characteristics were well corresponded with in-plane, out-of-plane and non-oriented vibronic modes of P3HT., India-Japan Expert Group Meeting on Biomolecular Electronics & Organic Nanotechnology for Environment Preservation (IJEGMBE 2015), December 23-26, 2015, Fukuoka, Japan

Poly(3-hexylthiophene) nanofibers were prepared under ambient conditions and applied in organic field-effect transistors (FETs). Top-contact FETs with spin-coated and nanofiber-based layers were fabricated to compare their transport performance. It was found that the nanofiber FET shows a higher performance than the spin-coated one. The effects of annealing on the device performance of the nanofiber FET were also investigated from room temperature to 120 °C. The key performance characteristics of the nanofiber FET, such as carrier mobility and ON/OFF ratio, were improved by low-temperature annealing up to 80 °C. However, they were degraded by high-temperature annealing at 120 °C. The modulation of the surface morphology observed by atomic force microscopy is consistent with the change in device performance. The results of the correlation analysis of the mobility, hysteresis, and OFF current indicate that the change in FET performance is due to the disappearance of nanofiber interspaces and the removal of adsorbed molecules by temperature-controlled annealing.

Uniaxially self-oriented centimeter-scale thin films of poly(9,9'-dioctylfluorene) (PFO) could be obtained with a one-step deposition by the floating-film transfer method (FTM) under ambient conditions. β-phase PFO was also generated along with the orientation direction during the film formation by FTM. Polarized β-phase electroluminescence having a maximum dichroic ratio of 7.7 was realized in bilayer polymer light-emitting diodes consisting of a self-oriented PFO film as the emission layer and a poly(9-vinylcarbazole) film as the hole-transporting and electron-blocking layer.

Ambipolar characteristics in an organic field-effect transistor (FET) with a bilayer structure consisting of poly(3-hexylthiophene) (P3HT) and a fullerene derivative (PCBM) are reported. P3HT was deposited by a floating film transfer method (FTM) with toluene solution on spin-coated PCBM. The FTM-deposited film was found to show relatively high hole mobility even when cast using toluene solution. Even after coating P3HT on PCBM by FTM, a relatively high n-type transport was obtained. This indicates that FTM employed in this study is a mild way to coat an organic thin film on an organic semiconductor layer in terms of minimizing the effect of carrier transport in the underlayer. The transport characteristics have been discussed in comparison with those of ambipolar FETs prepared by other methods previously reported.

Field-effect mobilities and threshold voltages in organic field-effect transistors (OFETs) were studied to elucidate the difference of the OFETs performance between Si/SiO2 and flexible polymer substrates. The polymer OFETs were built on poly(ethylene naphthalate) (PEN) film as the substrate with polyimide (PI) as the gate-insulators. Pentacene and N,N'-ditridecylperylene-3,4,9,10-tetracarboxylicdiimide (PTCDI-C13) were employed as p- and n-type semiconductors. The n-type OFET on polymer substrates exhibited higher electron mobility and smaller threshold voltages compared with those on Si/SiO2. On the contrary, the p-type OFET on the Si/SiO2 substrate showed better transport performance than that on the polymer substrate. The results are discussed taking the difference of surface potential between SiO2 and PI gate-insulator, which possibly modifies OFET characteristics.

A new solution-processed technique of floating film transfer method (FTM) is proposed for depositing organic thin film semiconductor. Organic field-effect transistors (OFETs) have been fabricated to evaluate the transport characteristics in poly(3-hexylthiophene) (P3HT) films deposited with FTM and spin-coating methodology. An enhancement of hole mobility was found in the FTM film by one order of magnitude as compared to that in spin-coated films. Absorption spectra as well as X-ray diffraction profiles represent well-grown lamella structures of P3HT with FTM transverse to the substrate, representing the advantage of this method suitable for the carrier transport.

A novel n-type organic semiconductor, cyano-substituted distyrylbenzene derivative, 1,4-bis2-[4-(trifluoromethyl)phenyl]acrylonitorilebenzene, was synthesized by Knoevenagel condensation with aldehyde and acetonitrile derivatives. Fabricated thin-film transistors (TFTs) exhibited high electron field-effect mobility of 10-2–10-1 cm2 V-1 s-1, on/off current ratio of 6×105. Hysteresis-free n-type transport characteristics observed in this device promises a steady operation of organic logic circuit. Almost same TFT characteristic was observed even after 1 month storage in ambient condition. The findings indicate that the material has a good resistance to atmospheric oxidants.

The time-of-flight technique has been used to study transports of photocarriers in regioregular and regiorandom poly(3-hexylthiophene) (P3HT) films by fabricating indium-tin-oxide/P3HT/Al sandwich cell. It has been found that regularity in the coupling of monomers, head-to-tail (HT) has a marked effect on electrical properties and photocarrier transport in P3HT. Both regular and random P3HT films exhibit a dispersive photocurrent response with the positive sign of photocarrier (hole). The room temperature hole mobility of regioregular P3HT is estimated to be 1.21 ×10-3 cm2/V·s and is one order of magnitude larger than that of the random one. The mobility in regioregular P3HT is almost independent of the applied field while that of random P3HT shows a positive field dependence at the field larger than 1.0 ×105 V/cm.