Takao Nagatomo

Characterization of vacuum-evaporated tin sulfide film for solar cell materials

Abstract Tin sulfide (SnS) films were prepared by vacuum evaporation. As-grown SnS films showed p-type conduction with a resistivity of 13 ∼ 20 Ω cm, a carrier density of 6.3 × 10 14 ∼ 1.2 × 10 15 cm −3 , and a Hall mobility of 400 ∼ 500 cm 2 /Vs. The absorption coefficients of the films were an order of 10 4 cm −1 at the fundamental absorption edge. The n-CdS/p-SnS heterojunctions were made by depositing n-CdS, p-SnS and Ag ohmic electrode on the transparent electrode (indium-tin oxide, ITO) in the order ITO/n-CdS/p-SnS/Ag structure. The photovoltaic properties of a short-circuit current of 7 mA/cm 2 , an open-circuit voltage of 0.12 V, a fill factor of 0.35, and a conversion efficiency of 0.29% were obtained under the illumination of 100 mW/cm 2 .

Properties of Ga1-xInxN Films Prepared by MOVPE

Epitaxial films of the solid solution Ga1-xInxN (up to X=0.42) have been fabricated on (0001) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) at 500°C. The properties of the films have been studied by the reflection high-energy electron diffraction technique, X-ray diffraction, and electrical and optical measurements. The fundamental absorption edge of the film decreases linearly with composition (up to X=0.42) from 3.20 eV to 2.01 eV at room temperature.

Fabrication and Characterization of SnO2/n-Si Solar Cells

SnO2/n-Si solar cells fabricated by the spray pyrolysis technique display significant photovoltaic effects when exposed to sunlight. These solar cells have a thin insulating layer at the SnO2/n-Si interface. The presence of the thin insulating layer can increase the open-circuit voltage by increasing the diode quality factor and by reducing the dark saturation current. The performance of this heterojunction solar cell was an open-circuit voltage of 0.52 V, short-circuit current of 21.0 mA/cm2, fill factor of 0.53 and conversion efficiency of 7.2%. The relative photospectral response above fifty percent spreads in a range of 420 to 1020 nm and is wider than that of conventional Si p-n solar cells. One possibility for cost reduction lies in the method of junction fabrication, and the idea of a simply deposited SnO2/n-Si junction is very attractive.

Electrical and optical properties of vacuum-evaporated indium-tin oxide films with high electron mobility

Abstract Tin-doped In 2 O 3 films with high electron mobility (180 cm 2 V −1 s −1 ) were obtained by reactive evaporation of indium and tin in oxygen, compared with In 2 O 3 and tin-doped In 2 O 3 films prepared by various fabrication techniques. The high electron mobility of tin-doped In 2 O 3 films is due to the improvement in the crystallinity and the preferential orientation of the (222) crystal plane. The electrical and optical properties of tin-doped In 2 O 3 and undoped In 2 O 3 films are described.

Polyacetylene batteries -scaling up and problems

Abstract There is no significant difference between the charge-discharge characteristics of the large-scaled polyacetylene battery (27 cm 2 -cell x 4) and that of 2 cm 2 battery. However, the doping inhomogeneity and the non-uniformity of the film thickness cause trouble to enlarge the cathode area. The several problems to be improved, such as self-discharge, degradation of polyacetylene film, decomposition of organic solvent and others are described.

The effect of rubrene as a dopant on the efficiency and stability of organic thin film electroluminescent devices

Rubrene was doped into the hole transport layer of an organic thin film electroluminescent (OTFEL) device with a double-layered structure. It was found that the dopant has a profound influence on the EL characteristics - it changed the region of light emission, increased the luminescence efficiency by more than 50% and improved the device stability tenfold. The reasons for these effects are discussed based on injection theory and the energy level diagram of the device.

Large‐Scaled Polyacetylene Batteries

Polyacetylene, (CH) /SUB x/ film is the simplest conjugated polymer consisting of parallel chains of CH groups. It has recently been of considerable interest as the electrode active material of secondary batteries, with many superior features: (it contains an interwoven network of ca. 200A (CH) /SUB x/ fibrils; (the electrical conductivity of (CH) /SUB x/ films can be varied over 12 orders of magnitude from insulator to metal when suitably doped with donor or acceptor species; it is very stable chemically; there are other attractive features. This battery promises to be lighter and has higher power and energy densities as compared to conventional batteries such as lead-acid batteries. This paper describes the charge-discharge characteristics of large-scaled polyacetylene secondary batteries with electrode areas of 20 about 54 cm/sup 2/. The cis-(CH) /SUB x/ films were polymerized by the Shirakawa technique. Care was taken to achieve pure (CH) /SUB x/ starting material through extensive washing to remove all catalyst, with subsequent storage and handling in inert atmosphere to minimize oxygen content.

Fabrication of BaTiO3 films by RF planar-magnetron sputtering

Abstract BaTiO3 films have been fabricated onto platinum and fused-quartz substrates by rf planar-magnetron sputtering using BaTiO3 ceramic target. For the substrate temperatures above 500 °C, the films have the perovskite structure. Preferential orientations, grain sizes and lattice constants of these films vary with the substrate temperatures and gas pressures. Ferroelectric properties are observed for BaTiO3 films fabricated at the substrate temperature of 700 °C and the gas pressures above 10−2 Torr.

The Response of TiO2 Photocatalysts Codoped with Nitrogen and Carbon to Visible Light

We successfully achieved deposition of Ti(O,C,N) 2 films codoped with nitrogen (N) and carbon (C) using dc reactive sputtering utilizing a Ti target in an Ar/N 2 /CO 2 ambient. The crystallinity and surface morphology of the films were observed using X-ray diffraction (XRD) and field-effect scanning electron microscopy. Interstitial N and C in the films were also measured using X-ray photoelectron spectroscopy (XPS), from which the doping level was calculated. The photocatalytic activity was evaluated using methylene blue decomposition under visible and ultraviolet irradiation. All the films were transparent yellow, and it was confirmed using XRD that the crystal form was polycrystalline anatase. Two peaks resulting from Ti-N bonding (397 eV) and Ti-C bonding (282 eV) were observed using XPS. Thus, N and C were considered to be at substitutional O sites. It was verified that the Ti(O,C,N) 2 films deposited in this study undergo a photocatalystic reaction when exposed to visible light in the wavelength range of 400-500 nm.

Stability enhancement of organic electroluminescent diode through buffer layer or rubrene doping in hole-transporting layer

Abstract The stability of organic electroluminescent devices is significantly improved by inserting a buffer layer between ITO and the holetransporting layer or by doping rubrene in the hole layer. The durabilities of the improved devices increase by a factor of about 10. The reasons for the improvements are discussed based on tunnelling theory and the energy-level diagram of the device.