Article pubs.acs.org/JPCC
Effective Way To Enhance the Electrode Performance of Multiwall Carbon Nanotube and Poly(3,4-ethylenedioxythiophene): Poly(styrene sulfonate) Composite Using HCl−Methanol Treatment Dong-Jin Yun,† Yong Jin Jeong,† Hyemin Ra,† Jung-Min Kim,† Jong Hwan Park,† SungHoon Park,‡ Tae Kyu An,† Minsu Seol,† Chan Eon Park,† Jaeyoung Jang,*,§ and Dae Sung Chung*,∥ †
Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea Department of Mechanical Engineering, Soongsil University, Seoul 156-743 Korea § Department of Energy Engineering, Hanyang University, Seoul 133-791, Korea ∥ School of Chemical Engineering and Material Science, Chung-Ang University, Seoul 156-756, Korea ‡
ABSTRACT: In this study, the electrode performance of composite films composed of highly conductive multiwalled carbon nanotubes (MWCNTs) and poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) are improved with the use of HCl−methanol (HCl−met) treatment. The HCl−met treatment affects film properties, including surface morphology, optical transmittance, work function (Φ), and electrical conductivity, which are investigated using various kinds of MWCNT/ PEDOT:PSS composite systems. As a result of the HCl−met treatment, all MWCNT/PEDOT:PSS films undergo considerable changes in molecular ratio and arrangement between PEDOT and PSS, but their MWCNTs have no chemical/ structural transitions. This in turn enhances the electrical conductivity and catalytic activity of the MWCNT/PEDOT:PSS films without changing their other properties. Furthermore, because of these effects, the HCl−met treatment brings about noticeable enhancements in performance as the source/drain electrode in an organic thin-film transistor and as the catalytic counter electrode in a dye-sensitized solar cell.
1. INTRODUCTION For recent decades, many kinds of organic materials have been applied to organic electronics, such as organic thin-film transistors (OTFTs), organic photovoltaic (OPV) devices, dye-sensitized solar cells (DSSCs), and organic light-emitting diodes (OLEDs), due to cost and process advantages.1−4 Among them, the carbon nanotube (CNT) is one of most attractive candidate for electrode materials in various nextgeneration devices because of their excellent electrical (conductivity and catalytic activity), physical (flexibility and chemical/thermal stability), and optical properties (transmittance).5,6 Nevertheless, its poor dispersibility in common solvents is still a critical issue to be solved.7,8 Presently, for the purpose of enhancing its dispersion in solvents, the CNT oxidation or polymer grafting onto CNTs is widely utilized in most research groups.7−10 The CNT oxidation process involves degrading the electrical and physical properties, whereas a method based on polymer grafting onto CNTs allows of enhancing the solubility with undamaged inherent properties of CNTs. Moreover, in combination with various polymers, the film properties of the resulting CNT composite films can be controlled according to specific application.11,12 Among the diverse polymers used, poly(3,4-ethylenedioxythiophene) poly© XXXX American Chemical Society
merized with poly(4-styrenesulfonate) (PEDOT:PSS) has great merits for use as a CNT surfactant. By uniformly wrapping CNTs with PEDOT:PSS, the dispersion of the CNTs in polar/ organic solvents can be improved.13−15 Furthermore, the electrical properties of the CNT composite film, including electrical conductivity and work function (Φ), can be greatly enhanced.13−15 Recently, our group has made significant progress on an effective modification method for multiwalled carbon nanotube (MWCNT)/PEDOT:PSS composite electrodes.16−19 In accordance with our fabrication methods, the optimization of the MWCNT concentration allows for the preparation of MWCNT/PEDOT:PSS composite film with low-temperature (
