Koichi Wakita

Large-area CVD graphene as transparent electrode for efficient organic solar cells

Indium tin oxide (ITO) and related oxide based materials have been widely used as transparent electrode in optoelectronic devices and organic solar cells. Here, we demonstrate application of chemical vapor deposited (CVD) graphene films as transparent electrode for organic solar cells. Large area graphene films are deposited by control pyrolysis of botanical derivative camphor (C10H16O) and transparent electrode were fabricated by direct synthesis or transfer process. Raman spectroscopy and transmission electron microcopy studies are used to characterize the synthesized graphene based materials. Direct synthesized and transferred graphene films on glass or plastic substrates show very good optical transparency, electrical conductivity and mechanical stability. P3HT:PCBM bulk heterojunction solar cells are fabricated successfully on graphene based transparent electrode and compared with ITO based device. The dark light characteristic shows very good rectification with minimum leakage current. Under illumination of light the device shows very good open circuit voltage, short circuit current density and conversion efficiency.

Synthesis of continuous graphene on metal foil for flexible transparent electrode application

We demonstrate synthesis of large area graphene on a metal (Ni and Cu) foil by the thermal chemical vapor deposition (CVD) process using the solid camphor (C10H16O) as a carbon source. The graphene growth process on a polycrystalline metal foil significantly influence by the gas composition and quantity of solid precursor. Synthesis of high quality continuous graphene film is achieved in the developed technique. Fully flexible transparent conductor is fabricated by transferring the graphene film on a plastic substrate.