Takuya Gotou

Carbon nanofilm with a new structure and property

We have prepared a carbon film of nanometer thickness, which is called here a carbon nanofilm (CNF), starting from the oxidation of graphite. The structure and thickness of the CNF are determined by high-resolution transmission electron microscopy and electron diffraction. The structure is of a new type (S.G.: P3), in which carbon six-membered-ring planes are stacked with the sequence of ...AA.... According to electron energy loss spectroscopy, a substantial amount of oxygen is detected but the molar ratio of oxygen to carbon is possibly decreased to less than 0.1. The CNF changes from an insulator to a semiconductor when reduced on heating at 250°C.

Single graphene sheet detected in a carbon nanofilm

In order to clarify the existence of a single sheet of carbon six-membered-ring plane (graphene) this letter presents a method by which the stacking number of the sheets in a carbon nanofilm (CNF) can be exactly counted, based on the quantitative analysis of electron diffraction intensity. Using the method we can detect a single graphene sheet in a CNF.

Efficient Crystalline Si/Poly(ethylene dioxythiophene):Poly(styrene sulfonate):Graphene Oxide Composite Heterojunction Solar Cells

Efficient crystalline silicon (c-Si) heterojunction solar cells with conductive poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and graphene oxide (GO) composite are demonstrated using a structure of Ag/PEDOT:PSS/PEDOT:PSS:GO composite/c-Si (100)(ρ: 3–5 Ωcm)/Al. The power-conversion efficiency η increased to 10.7% under illumination of AM1.5 100 mW/cm2 simulated solar light by adjusting the PEDOT:PSS and GO mixing concentration ratio. The GO addition to conductive PEDOT:PSS suppressed electron recombination and/or promoted the hole current at the anode. The soluble PEDOT:PSS:GO composite is promising as a hole-transporting transparent conducting layer for c-Si photovoltaic applications.

Fabrication of Transparent and Flexible Organic Field-Effect Transistors with Solution-Processed Graphene Source–Drain and Gate Electrodes

Transparent organic field-effect transistors with solution-processed graphene source–drain and gate electrodes were fabricated on flexible substrates. Graphene electrodes were formulated by chemical and thermal reduction of solution-processed graphene oxide films. A graphene gate electrode, a gate dielectric layer, and an organic active layer were coated on a transparent flexible polyimide film. Next, graphene source–drain electrodes, which had been formed on another glass substrate, were peeled off and transferred onto the active layer using a thermal release tape. The transparent and flexible poly(3-hexylthiophene) transistor with graphene electrodes showed p-type characteristics with hole mobility of 2.3×10-2 cm2V-1s-1.

Crystalline Silicon/Graphene Oxide Hybrid Junction Solar Cells

Soluble graphene oxide (GO) and plasma-reduced (pr-) GO were investigated using crystalline silicon (c-Si) (100)/GO/pr-GO hybrid junction solar cells. Their photovoltaic performances were compared with those of c-Si/GO/pristine conductive poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) heterojunction and c-Si/PEDOT:PSS:GO composite devices. The c-Si/GO/pr-GO and conductive PEDOT:PSS/Al heterojunction solar cells showed power conversion efficiencies of 6.5 and 8.2%, respectively, under illumination with AM 1.5 G 100 mW/cm2 simulated solar light. A higher performance of 10.7% was achieved using the PEDOT:PSS:GO (12.5 wt %) composite device. These findings imply that soluble GO, pr-GO, and the PEDOT:PSS:GO composite are promising materials as hole transport and transparent conductive layers for c-Si/organic hybrid junction solar cells.

Top-Contacted Organic Field-Effect Transistors with Graphene Electrodes Prepared by Laminate Transfer Method

Top-contacted organic field-effect transistors (OFETs) with graphene electrodes were fabricated by the laminate transfer method. Graphene electrodes were prepared on a different glass substrate and transferred onto an organic semiconductor layer of poly(3-hexylthiophene) (P3HT) using a double-layer laminate film of polyacrylonitrile (PAN) and poly(methyl methacrylate) (PMMA). The fabricated top-contacted OFET with graphene electrodes covered by the polymer film showed good p-type transistor characteristics with hole mobility of (3.7±0.5)×10-2 cm2 V-1 s-1, and 92% of the mobility was maintained even after exposure to ambient air for 250 h.