Yutaka Haga

Photoconductive properties of TiO2 films prepared by the sol–gel method and its application

The Photoconductive characteristics of TiO2 films prepared by the sol-gel method, and the photovoltaic characteristics fabricated with the resulting TiO2 film and phthalocyanine nickel (NiPc) are investigated. For a TiO2 film with hydroxypropyl cellulose (Hpc) heat treated at 500°C for 10 min, the relative sensitivity is about ten times higher than that without Hpc. A space-charge-limited current is observed in the dark current–voltage characteristic of the TiO2 film with Hpc. It is found that the TiO2 film with Hpc has a photosensitizing effect. The photovoltaic characteristics of TiO2(Hpc)/NiPc are as follows: the short-circuit current density, Jsc is 5.6×10-7 A cm-2, the open-circuit voltage, Voc is 0.24 V, the fill factor (F.F) is 0.64 and the power conversion efficiency, η is 0.73. Furthermore, the carrier transport mechanisms of the TiO2(Hpc)/NiPc photovoltaic cell are discussed.

Organic electroluminescent devices using deposited poly(p-phenylene) film as hole transport layer

Abstract We have fabricated organic electroluminescent devices with poly ( p -phenylene) as a hole-transporting layer, and with tris (8-hydroxy-quinoline) aluminum as an emitting layer by vacuum deposition. As a result, it is found that the deposited PPP film is an effective film as a hole transport layer, and that the characteristic of these devices changes remarkably with substrate temperature at vacuum deposition.

Photovoltaic Characteristics of Copper Phthalocyanine-poly(p-phenylene) Co-evaporation Films

Copper phthalocyanine (CuPc) and poly(p-phenylene) (PPP) composite films (CuPc–PPP) were produced by a simultaneous deposition method. Schottky barrier photovoltaic cells consisting of semitransparent aluminum and CuPc–PPP composite films were fabricated. The effects of composition and optimization on the photovoltaic properties of the CuPc–PPP composite films by simultaneous deposition were investigated. The short circuit photocurrent of the CuPc–PPP cells increased in comparison with that of the CuPc film. This behavior was described as follows. One is that an effective surface area of the CuPc is increased by the PPP, which functions as a binder polymer. The other is that the bulk conductivity of the composite film is improved by the PPP, which functions as a carrier transfer material (CTM) for CuPc. It is found that the optimum conditions for simultaneous evaporation are as follows; film thickness: 1200 A, deposition ratio: 5:1.25 A/s (CuPc:PPP), temperature: room-temperature. The power conversion efficiency under these conditions was found to be 2.33%.

The junction properties of the anionic surfactant doped polypyrrole with indium.

Summary form only given. Electrochemical polymerization of pyrrole was carried out in anionic surfactant aqueous solutions, and the Junction Characteristics of anionic surfactant doped polypyrrole with injium have been studied using sandwich devices. It has been observed that the Au/polypyrrole/In diode has unsymmetric, non-ohmic rectifying Characteristics. The analyses of the current-voltage and the capacitance-voltage characteristics have revealed that a Schttky barrier is formed between polypyrrole and indium.

Photovoltaic characteristics of TCNQ-incorporated CuPc-poly(p-phenylene) composite films

Composite films (CuPc–PPP–TCNQ) were produced by simultaneous deposition using copper phthalocyanine (CuPc) as a carrier generation material, poly(p-phenylene) (PPP) as a hole transport material, and tetracyanoquinodimethane (TCNQ) as a incorporation material. Schottky barrier photovoltaic cells, consisting of a semitransparent aluminum and the CuPc–PPP–TCNQ composite films, were fabricated. The junction properties and the photovoltaic properties on Al/CuPc–PPP–TCNQ/ITO sandwich cells were investigated. As well as a composite film of the CuPc and the PPP (CuPc–PPP), the conductivity of the CuPc–PPP–TCNQ composite film is improved as the TCNQ is simultaneously deposited in the CuPc–PPP composite film. Therefore, it is proven that the short circuit photocurrent density (Jsc) and the photovoltaic property increases significantly. The Jsc of the Al/CuPc–PPP–TCNQ/ITO cell is 2.60 μA/cm2, and it is found that the Jsc is about 20 times that of an Al/CuPc/ITO cell and double that of an Al/CuPc–PPP/ITO cell. Consequently, the power conversion efficiency of the Al/CuPc–PPP–TCNQ/ITO cell obtained was 3.68%.

Electrochromism of the Composite Film of Ethylene-Vinyl Alcohol Copolymer and Polypyrrole

Abstract The composite film of ethylene-vinyl alcohol copolymer (EVOH) and polypyrrole (PPy) were prepared by the electrochemical polymerization of pyrrole on an EVOH film containing lithium perchlorate coated on Indium-tin oxide (ITO). When a potential was varied from −1.0 V to 1.0 V, the color of the composite film changed reversibly from yellow to brown. The difference in absorbance (ΔA, 0.1—0.15) at 800 nm between the application of 1.0 V and −1.0 V in UV/VIS spectra of the composite film did not exhibit a pronounced decrease until ca.7000 cycles. In contrast to this behavior, the ΔA of a single PPy film rapidly dropped with an increasing cycle number and approached 0 within ca. 1000 cycles. This result indicates that the durability against the repeated application of potentials markedly improved in the composite film.

Copolymerization of vinyl monomers on the surface of CDS and photoconductivity properties of resulting composites

Abstract The reaction behaviour of CdS encapsulated copolymer (styrene-acrylonitrile copolymers; C-St · AN-CdS and styrene-methacryl acid copolymers; C-St · MAA-CdS) composites, their photoconductivity, and the mechanism of their photosensitivity were investigated. The results indicated that the reactivity ratios of the monomers for the encapsulated copolymer are considerably different from those of the homopolymer during encapsulation. The photoconductivities of C-St · AN-CdS showed a marked increase over that of CdS alone in the some range of the AN composition ratio. On the other hand, the photoconductivity of C-St·MAA-CdS was very low and showed a decrease. The dark current-voltage characteristic of CdS encapsulated in copolymer observed Ohms law at the test voltage for the composites of low photoconductivity, while space-charge limited current (SCLC) for C-St·AN-CdS and also for CdS alone was observed. The voltage index of the SCLC was about 2 for CdS alone, larger than 2 for the CdS encapsulated in polystyrene (C-St-CdS), and showed a tendency to increase to a larger value for the CdS encapsulated in the St-AN copolymers. These characteristics were explained with the distribution state of the energy levels of the traps and also with the increase of the characteristic temperature. Similar results were also observed for the light intensity index derived from the dependence of the photocurrent upon irradiation intensity. The decay characteristic of the photocurrent was delayed for C-St-CdS and that for C-St·AN-CdS was earlier compared with that for CdS alone.

Photoconductive properties of annealed TiO2 dispersion composites

Abstract It has been shown that the photoconductive characteristics of a dispersion composite of a photoconductive inorganic metal oxide, such as TiO2, with a polymer are significantly enhanced by annealing. For the poly(methyl methacrylate) (PMMA) dispersion composite TiO2-PMMA, the relative sensitivity is 101 ∼ 102 times higher than that of the unannealed sample. The space-charge limited current is observed in the dark current-voltage characteristics of the annealed TiO2-PMMA. From the light intensity index of the annealed TiO2-PMMA, it is found that the annealed sample has a large sensitizing effect.

A Various Properties on the Encapsulating Polymer.

カプセル化ポリマーと無機粉体との界面の相互作用を明らかにするために, 酸化チタン (TiO2) にポリメタクリル酸メチル (PMMA) 及びポリスチレン (PSt) をカプセル化した試料とTiO2にPMMA及びPStを分散した試料を作製し, これらの熱的挙動, 密度, 赤外スペクトル, 及び分子量分布を測定して比較検討した. カプセル化ポリマーは二つの熱緩和域をもっていた. さらに, GPC, 密度, 及び赤外スペクトル測定の測定結果は, カプセル化ポリマーが高密度・高分子量, かつタクティシティの大きい分子構造を有するポリマーであることを示していた.

Photoconductive Properties of Annealed ZnO/PMMA Dispersion Composities.

The influence of annealing on the photoconductivity of the composite materials of zinc oxide dispersed in polymethylmethacrylate (ZnO/PMMA) has been investigated. As a result, it was revealed that the photoconductivity of ZnO/PMMA composites was remarkably enhanced by annealing. From the experimental results of temperature dependences of the dark current, the dark current-voltage characteristics, the light wavelength characteristics and the photocurrent-light intensity characteristics, the photoconductive mechanism of the annealed ZnO/PMMA composites was discussed.