Hiroyuki Fuchigami

Polythienylenevinylene thin‐film transistor with high carrier mobility

A thin‐film transistor (TFT) with high carrier mobility has been fabricated using precursor‐route poly(2,5‐thienylenevinylene) (PTV) as semiconductor. The carrier mobility has been determined to be 0.22 cm2/V s, which is in the same level of that of amorphous silicon TFT. It has also been made clear that the carrier mobility is linearly proportional to the conversion ratio from the insulated precursor polymer to π‐conjugated PTV. The π‐conjugation length is crucial to obtain high carrier mobility in π‐conjugated polymer TFT.

Polythiophene field‐effect transistor with polypyrrole worked as source and drain electrodes

The field‐effect transistor has been fabricated, where polythiophene works as a semiconductor and a couple of polypyrrole layers act as a source and/or a drain electrode. The modulation ratio of the channel current with gate voltages has reached ca. 105, which is the largest one among organic FETs. This large modulation has been attributed to the depression of the channel current at no gate bias. It has been elucidated that the depression is caused by the barrier against hole transport formed inside the polythiophene layer and near the interface with polypyrrole.

Field-effect transistor with a conducting polymer film

Abstract Spin-coated conducting polymer films of poly(3-hexylthiophene) (PHT) and poly(2,5-thienylene vinylene) (PTV) have been demonstrated to be useful in a field-effect transistor (FET) as a semiconducting layer. The device with a doped PHT film shows enhance-type FET characteristics although they are unstable. On the other hand, the one with a non-doped PTV film shows very stable and excellent FET characteristics with large source current.

Macromolecular Electronic Device

Abstract A thin-film transistor (TFT) with high carrier mobility has been fabricated using poly(2,5-thienylenevinylene)(PTV) as semiconductor. The carrier mobility has been obtained to be 0.22cm2/Vsec, which is in the same level as that of amorphous silicon TFT. It has been indicated that the enlargement of the π-conjugation length is crucial for the improvement of the carrier mobility. It has been also demonstrated that the molecular orientation is another important factor in terms of the device characteristics.

Rear-emitter Si heterojunction solar cells with over 23% efficiency

We have developed highly crystallized n-type microcrystalline Si layers as window layers for rear emitter Si heterojunction solar cells. We introduce a seed layer between an n-type microcrystalline Si layer and an intrinsic amorphous Si layer to improve the crystallinity of the n-type microcrystalline Si layer. By using this stacked layer instead of an n-type amorphous Si layer, the contact resistance between the n-type thin layer and In2O3:H is reduced without Al-doped ZnO. As a result, we obtain a high short-circuit current and a high fill factor simultaneously, and achieve a solar cell efficiency of 23.43%.

Preparation and Characterization of 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) Films Deposited by Organic Molecular Beam Deposition Method.

The optical and structural properties for 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) films deposited on Au-coated substrates at the various growth temperatures by the organic molecular beam deposition (OMBD) method have been studied. The planar PTCDA molecules were oriented almost parallel to the substrate surface in the films deposited at the growth temperature of -160° C. Orientational disorder of the molecular planes occurred especially in the films grown at higher substrate temperatures. These films had basically large anisotropy of refractive indices which were evaluated by the prism attenuated total-reflection (ATR) method. The anisotropy of indices decreased for the film grown at the substrate temperature of 100° C. The optical anisotropy has been understood in terms of the molecular orientation.

Device characteristics and its operation mechanism of a FET-type waveguide modulator using α-sexithienyl

An optical waveguide modulator having a field-effect transistor-type electrode using a thiophene oligomer, α-sexithienyl (6T), has been fabricated and has functioned as an electro-absorption modulator with the modulation ratio of 20%. The optical modulation is directly related with the FET device operation, and has shown a maximum at 830 nm for propagating light wavelength. Therefore, the mechanism of the optical modulation has been clarified to be the increasing absorption due to polarons induced by negative bias. The linear relationship between the modulation ratios and the FET source currents has led to the conclusion that the polaron conversion efficiency η was introduced as the new parameter to understand the device operation, which has become clear. From the analysis, the nearly intrinsic value of carrier mobility of 6T was extrapolated, and the limit of the improving the carrier mobility was also shown. The possibility of enlarging the modulation ratio and its frequency dependence is also discussed.

Molecular orientation in vacuum-deposited poly(thiophene) film studied by second-harmonic generation

The molecular orientation of the vacuum-deposited polythiophene (PT) film has been studied by second-harmonic generation (SHG). The polythiophene main chain is preferably oriented to be perpendicular to the substrate normal. The chain tilt angle from the surface normal decreased with increasing substrate temperature during the vacuum deposition. These results are consistent with the reported electron diffraction results. It has been considered that the SHG originates from the modification of the electronic states of PT due to the interaction between PT and the glass substrate.

Large electro-optical modulation of a field-effect transistor-type waveguide modulator using α-sexithienyl

An optical waveguide modulator having a field-effect transistor-type electrode using a thiophene oligomer, α-sexithienyl, has been fabricated and has functioned as an electro-absorption modulator with the modulation ratio of 20%. The device also functions as a field-effect transistor (FET). The optical modulation is directly related with the FET device operation, and has shown a maximum at 830 nm for propagating light wavelength. Therefore, the mechanism of the optical modulation has been clarified to be the increasing absorption due to polarons induced or injected by negative bias.

Organic molecular beam deposition combined with laser-induced chemical reactions

In order to fabricate functional organic thin films, we investigated organic molecular beam deposition combined with laser-induced chemical reactions. Bis(ethynylstyryl) benzene (BESB) films of trans,trans-isomer were deposited by this new method. The cis,cis-BESB was sublimed and cis-to-trans photoisomerization was induced upon KrF excimer laser irradiation ((lambda) equals 248 nm). The growth of the well- oriented crystalline films was achieved upon the laser irradiation during the deposition at the substrate temperature of 60 degree(s)C. At this substrate temperature only trans,trans-BESB was deposited on the substrate surface, which indicated that unreacted cis,cis-isomer was re- evaporated from the substrates. It can be explained that the crystal growth favorably proceeded due to the enhancement of the surface migration of the trans,trans-isomer and no hindrance of the cis,cis-isomer. We also fabricated thin films of a reaction product by inducing an intermolecular reaction of BESB with biphenyl-dithiol upon the laser irradiation during the deposition. It is thus found that the new process made it possible to produce the functional organic thin films, which were difficult to be evaporated by the conventional vacuum process. We discussed the chemical reactions and the deposition behavior in our process.