The first solid-state field-effect transistor has been fabricated utilizing a film of an organic macromolecule, polythiophene, as a semiconductor. The device characteristics have been optimized by controlling the doping levels of the polymer. The device is a normally off type and the source (drain) current can be modulated by a factor of 102–103 by varying the gate voltage. The carrier mobility and the transconductance have also been determined to be ∼10−5 cm2/V s and 3 nS, respectively, by means of electrical measurements.

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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.

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The photooxidation of iodide ions on n-type silicon electrodes highly doped with boron from the surface in hydrogen iodide or hydrogen iodide/iodine solutions was investigated. Two doping methods were employed: thermal diffusion and ion implantation. The electrode was remarkably stabilized by coating with a 2 to 3 nm-thick platinum layer, followed by heat-treatment at about 400 °C for ca. 10 min. The photocurrent was stable for more than 500 h at a density of the order of 10 mA cm−2. The boron-doped and Pt-coated n-Si electrode also generated a photovoltage much higher than that for a Pt-coated n-Si electrode, showing an advantage of forming the p-n junction. Photoelectrochemical cells made of a boron-doped-Pt-coated n-Si electrode, a platinized Pt counter electrode, and a commercial cation exchange membrane were found to photoelectrolyze hydrogen iodide without externally applied voltage into hydrogen and iodine with a solar-to-chemical energy conversion efficiency (φchems) under simulated AM 1 solar radiation of 8.2%, probably the highest of the φchems values observed for the cells working without external voltage.

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.