Fabrication and Optical Properties of Electrospun Organic Semiconductor Nanofibers from Blended Polymer Solution
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1091-AA07-85
Fabrication and Optical Properties of Electrospun Organic Semiconductor Nanofibers from Blended Polymer Solution Surawut Chuangchote, Takashi Sagawa, and Susumu Yoshikawa Institute of Advanced Energy, Kyoto University, Gokasho, Uji, 611-0011, Japan ABSTRACT Ultrafine organic semiconductor fibers with the average diameters ranging in sub-microdown to nanometers (43 nm - 1.7 µm) were fabricated by electrospinning of a mixture of poly(2methoxy-5-(2 -ethylhexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) and polyvinylpyrrolidone (PVP) in various mixed solvents. The average diameter of the as-spun fibers decreased into nanometer scale with decreasing the concentration of PVP. Addition of a volatile organic salt (pyridinium formate, PF) or utilization of three-mixed solvent system was also effective to reduce the size of the diameter of as-spun fibers. After the removal of PVP from as-spun fibers by Soxhlet extraction, pure MEH-PPV fibers were obtained as a ribbon-like structure aligned with wrinkled surface in fiber direction. As-spun fibers showed relatively higher crystallinity, higher conjugation length, and a remarkable blue shift of photoluminescence (PL) peak was observed, in comparison with the cast film. The increase in composition of MEH-PPV and the removal of PVP from as-spun MEH-PPV/PVP fibers resulted in a significant blue-shift in UVVis absorption peak and red-shift in PL peak. ′
INTRODUCTION Electronic and optoelectronic devices based on organic semiconductors have been restricted by problems of material processing. However, conjugated or conductive polymers have been shown to have mechanical, optical and electronic properties with easy processing. A range of devices have been fabricated from conjugated polymers, such as photovoltaic cells, fieldeffect transistors, and electroluminescent diodes [1]. Recently, 1-direction nanomaterials, including organic nanofibers, are growing broad interest because of their specific properties, e.g. large surface to volume ratio, improved mechanical properties, and flexibility in surface functionalities [2]. Conductive polymers have also been fabricated in nanofiber form by various methods. Among them, electrospinning which utilizes electrostatic force to produce continuous ultrafine fibers with diameters ranging from microns down to a few nanometers has become one of the simple techniques for fabrication of conductive polymer nanofibers [3,4]. Because of the limitations of solvents to dissolve the polymers and suitable molecular weight of the polymers for electrospinning, electrospinning of neat conductive polymers resulted in non-uniform fibers with large amount of beads [4]. Therefore, various techniques have been developed to solve such those problems.
In this contribution, a simple technique for improvement in the uniformity of electrospun nanofibers of a conductive polymer, i.e. poly[2-methoxy-5-(2 -ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV), by blending with poly(vinyl pyrrolidone) (PVP), an easily spinnable and easily extractable polymer, has been re
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