Hiroyoshi Mizukami

Interpenetrating Interface in Organic Photovoltaic Cells with Heterojunction of Poly(3-hexylthiophene) and C60

The optical and photovoltaic properties of a photovoltaic cell with a structure of indium-tin-oxide (ITO)/C60/poly(3-hexylthiophene) (PAT6)/Au have been investigated. The C60/PAT6 heterojunction of this cell was fabricated by spin-coating the chloroform solution of PAT6 onto the C60 thin film formed on ITO. The photovoltaic cell fabricated by this method has demonstrated the high efficiency for a solar cell based on organic polymers. From the optical properties and the direct observation of the C60/PAT6 heterojunction, it has been clarified that the interpenetrating interface of PAT6 and C60 contributes to the high photovoltaic performance.

Improvement of sensitivity in long-wavelength range in organic thin-film solar cell with interpenetrating semilayered structure

Photovoltaic cells with interpenetrating interfaces between codeposited layers of small-molecular-weight materials and conducting polymer layers fabricated by the solvent corrosion method have been investigated. In order to improve photosensitivity in the long-wavelength range of the cells, the codeposited layers of C60:metal-free phthalocyanine (H2Pc) and C60:3,4,9,10-perylene tetracarboxylic bis-benzimidazole (PTCBI) have been fabricated instead of the monodeposited layer of C60. The short-circuit current under a white light and the energy conversion efficiency of the cell using the codeposited layer have been enhanced compared to the C60 monodeposited cell because of its high sensitivity in the long-wavelength range.

Surface and interface morphology observation and photovoltaic properties of C60/conducting polymer interpenetrating heterojunction devices

Optical and photovoltaic (PV) properties of PV cells with the structure indium tin oxide (ITO)/C60/conducting polymer (CP)/Au have been investigated. The C60/CP heterojunctions in the PV cells were fabricated by spin-coating an organic solution of CP onto the C60 underlying layer. Mixed organic solvents of chloroform and toluene were used to fabricate C60/CP interpenetrating interfaces. The C60/CP interfaces were controlled by adjusting the mixture ratio of chloroform to toluene. From the optical properties and SEM observation of C60/CP heterojunctions, it has been clarified that the interpenetrating interface of C60 and CP contributes to the balance of carrier generation and carrier transport, resulting in superior PV performance.

Ultraviolet light responses in photovoltaic properties of TiO2∕conducting polymer heterostructure devices

Photovoltaic properties of heterostructure devices of titanium oxide (TiO2) and conducting polymer thin films have been studied. Normal photovoltaic properties were stably observed upon the visible light irradiation of the wavelength range corresponding to the absorption of a conducting polymer, and unique photovoltaic properties were also observed upon the ultraviolet (UV) light irradiation of the wavelength range corresponding to the absorption of TiO2. UV light irradiation caused marked increases in the short-circuit current at the visible-wavelength range and in the open-circuit voltage. These properties have been discussed by considering the enhancement of the built-in field which originates from the hole accumulation caused by the trap levels in the TiO2 layer or TiO2∕conducting polymer interface.

Fabrication of Organic Photovoltaic Cells with Interpenetrating Heterojunction of Conducting Polymer and C60 by Spray Method

Organic photovoltaic cells with interpenetrating heterojunction of a conducting polymer and C60 have been fabricated by spray method. Photovoltaic cells fabricated by spray method and subsequent heat treatment have demonstrated a high photoconversion efficiency which is as the same as those fabricated by the spin coating method.

Effect of Indium-Tin Oxide Surface Micromodification and Improvement of Long-Wavelength Sensitivity on Photovoltaic Properties of Photovoltaic Cell with Conducting Polymer/C60 Interpenetrating Heterostructure

Photovoltaic cells, with a conducting polymer/C60 interpenetrating heterostructure fabricated by spin-coating a conducting polymer onto a C60 thin film, have been investigated and demonstrated a high efficiency as solar cells based on organic materials. The photovoltaic properties of the photovoltaic cell with a structure of indium-tin oxide (ITO)/C60/poly(3-hexylthiophene)/Au have been improved by the micromodification of the ITO surface and codeposition of metal-free phthalocyanine and C60.

Fabrication and Field Emission Properties of C60 Nanorod Formed by Spin-Cast Treatment

Nanorod-shaped surfaces of C60 films with thicknesses ranging from 100 to 400 nm and lengths ranging from 2 to 3 µm have been successfully obtained by a spin-cast treatment with trans-1,2-dichloroethylene. Results of observations by scanning electron microscopy and field emission (FE) measurements show an obvious correlation between the shape of the C60 nanorods and FE characteristics. By optimizing the conditions of the fabrication processes, the turn-on electric field was lowered from 25–30 to 17–20 V/µm. The nanorod-shaped surfaces of C60 films were still maintained even after a heat treatment under 250°C.

Formation of Nanorod-Shaped Surface of C60 Film and Its Field Emission Properties

The surface morphology of C60 films fabricated by vacuum deposition was modified by a spin-cast treatment process with various organic solvents and a nanorod-shaped surface was obtained in the case of spin-cast treatment with trans-1,2-dichloroethylene. The field emission properties of C60 films, the surfaces of which were modified, were found to depend on their surface morphology.