Tomoki Shirakawa

Effect of ZnO layer on characteristics of conducting polymer/C60 photovoltaic cell

Photovoltaic properties of a photovoltaic cell with structure indium–tin oxide (ITO)/ZnO/C60/poly(3-hexylthiophene) (PAT6)/Au have been investigated. The C60/PAT6 heterojunction of this cell was fabricated by spin-coating a chloroform solution of PAT6 onto the C60 thin film formed on ZnO-coated ITO. Fabricated by this method, the photovoltaic cell has demonstrated a high efficiency for solar cells based on organic polymers, i.e. a monochromic external quantum efficiency of over 70% at the peak wavelength and a power conversion efficiency of 1.0% under AM1.5 spectral illumination of 100 mW cm−2.

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 Characteristics of Organic Photovoltaic Devices Composed of Conducting Polymer-Fullerene Systems by Introduction of ZnO Layer

Photovoltaic cells, which consist of a heterojunction of conducting polymer-fullerene systems and a zinc oxide (ZnO) thin film, have been studied. In this structure, an incident photon is used effectively because exciton generation and dissociation, which contribute to photocurrent, mainly occur on the light incident side in a conducting polymer layer. In the layered photovoltaic cells with the structure of indium-tin-oxide (ITO) / ZnO / fullerene / conducting polymer / Au, a monochromatic energy conversion efficiency of 5.2% under 0.6 mW/cm2 illumination at 500 nm and an external quantum efficiency reaching 74% at the peak wavelength have been realized, which can be explained by the interpenetrated fullerene / conducting polymer interface and the short distance between the electron-generation region and electrode enhancing electron collection to the electrode.

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.

Doping effects of novel fullerene derivatives in conducting polymer

The optical and electrical properties of novel fullerene derivatives, such as tetra(amino)fullerene epoxides (TAFEs) have been studied. The optical properties and photoconductivity in composite films and bilayer films of conducting polymers and fullerene derivatives have been also investigated. Donor-acceptor-type photovoltaic cells have been fabricated, and the photo-conversion properties have been discussed taking the photoinduced charge transfer into consideration.

Photocurrent Enhancement in Conducting Polymer Device by Doping with Endohedral Metallofullerene La@C82

Optical properties and photoconduction of composite films of poly(3-hexylthiophene) (PAT-6) and metallofullerene La@C82 have been studied. The photoluminescence intensity of PAT-6 has been quenched and its photocurrent intensity has been enhanced markedly with increasing La@C82 concentration, which has been explained by the photoinduced charge transfer from PAT-6 to La@C82.

Photoconduction Properties in Mono- and Disubstituted Polyacetylene Films

Absorption spectra, fluorescence spectra and photoconduction characteristics in thin films of polyacetylene (PA) derivatives such as monosubstituted PAs and disubstituted PAs have been studied. In disubstituted PAs, intense fluorescence is observed with Stokes shift from the absorption edge and photocurrent is observed at around the absorption edge. On the other hand, in monosubstituted PAs, photocurrent is observed at a much shorter wavelength than the absorption edge, but photoluminescence (PL) in the film is negligible. In the solution of monosubstituted PAs, weak fluorescence is observed at a shorter wavelength than the absorption edge. These differences in fluorescence and carrier generation processes have been discussed by taking the differences of the electronic states between monosubstituted PAs and disubstituted PAs into consideration.