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Electrospun Polythiophene Nanofibers and Their Applications for Organic Solar Cells Surawut Chuangchote, Michiyasu Fujita, Takashi Sagawa*, and Susumu Yoshikawa* Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan E-mail addresses: [email protected] (T.S.); [email protected] (S.Y.) ABSTRACT Poly(3-hexylthiophene) (P3HT) nanofibers were fabricated with an association of poly(vinyl pyrrolidone) (PVP) by electrospinning. A mixture of P3HT/PVP in a mixed solvent of chlorobenzene and methanol was electrospun to form composite fibers with 60 nm - 2 μm in diameter, followed by getting rid of PVP by selective extraction. After extraction, pure P3HT nanofibers were obtained as a spindle-like structure with wrinkled surface. The nanofibers obtained exhibit specific features of strong interchain contribution as investigated by UV-vis, fluorescence spectroscopic, X-ray diffraction (XRD), and photo-electron investigations. Bulk heterojunction P3HT:PCBM nanofibers with ~200 nm in diameters were also successfully fabricated by using the same technique. The preliminary results from the study of P3HT:PCBM nanofiber-based photovoltaic cells with conversion efficiency over 0.2% could be achieved. INTRODUCTION Since the discovery of efficient photoinduced charge separation at the interfaces of donor and accepter, organic solar cells based on conjugated polymers and soluble fullerenes have been widely studied [1]. Bulk-heterojunction organic photovoltaic device, which is based on the spontaneous phase separation between donor and acceptor materials, is commonly used because the simple device structure and easy processability for thin film fabrication. Recently, bulk heterojunction solar cells with high conversion efficiency has been demonstrated using a mixture comprising regioregular poly(3-hexylthiophene) (P3HT) as the donor and [6,6]-phenyl C61butyric acid methyl ester (PCBM) as the acceptor [2,3]. High conversion efficiencies require a thermal annealing of fabricated cells which is necessary to ensure optimal nanoscale phase separation between the donor and acceptor materials, and enables the efficient transport of excitons to the donor-acceptor interface [4]. One-dimensional (1D) fibers have been interested recently because when the diameters of polymeric materials are shrunk to sub-micrometers or nanometers, there appear to be several specific characteristics [5]. Electrospinning has become one of simple fiber-processing techniques, which uses electrostatic forces to produce polymeric, ceramics, and composite continuous ultrafine fibers with diameters ranging from a few nanometers to microns [6,7]. Due to large area of solar cells in the actual applications, the techniques for fabrication of organic solar cells in large area, have been received much attention. Recently, fiber-shaped devices are attractive for utilization in many applications, including photovoltaic devices. We have reported the fabrication of conductive polymer nanofibers of poly[2-methoxy-5-(2'ethylhexyloxy)-1,4-ph