Transparent, Conductive and Flexible Carbon Nanotube Films and Their Application in Organic Light Emitting Diodes
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0936-L04-04
Transparent, Conductive and Flexible Carbon Nanotube Films and Their Application in Organic Light Emitting Diodes Koungmin Ryu1, Daihua Zhang1, Xiaolei Liu1, Evgueni Polikarpov2, Mark Tompson2, and Chongwu Zhou1 1 E.E.-Electrophysics, University of Southern California, 920 West 37th St., SSC514, Los Angeles, 90089 2 Chemistry, University of Southern California, Los Angeles, 90089
ABSTRACT
We have successfully used a transfer printing technique to directly transfer vacuum-filtered nanotube film to glass and plastic substrates. Our typical SWNT-film has a transparency of ~80% and a sheet resistance around 400 Ohm/square. Further improvement to the nanotube film includes SOCl2 doping and PEDOT passivation, which significantly improve the sheet conductance and surface quality of the nanotube films. We have applied the optimized SWNT films as hole injection electrodes to demonstrate OLEDs on both rigid glass and flexible substrates.
INTRODUCTION Evaluating the potential of carbon nanotubes (CNTs) as the basis of a future nanoelectronics technology has been the subject of intense research since their discovery. In one of the applications of carbon nanotubes, continuous CNT films could be a new class of transparent conducting material to replace indium-tin oxide (ITO) as the OLED electrodes for certain niche applications. For example, CNT films are superior to ITO in terms of the flexibility, as the former can be bent to acute angles without any breaking. In addition, while carbon is the most abundant element in nature, the world-wide production of indium is limited, which may soon find difficulty meeting the ever increasing demand for large-area transparent conductive electrodes. Furthermore, CNT-films may offer additional advantages such as tunable electronic properties through chemical treatment and enhanced carrier injection owing to the large surfacecontact area and field enhanced effect at the nanotube tips and surfaces.2 In spite of the fact that ITO films still lead CNT-films in terms of the sheet resistance and transparency, the abovementioned advantages have stimulated significant interest in exploiting carbon nanotube films as transparent conductive electrodes for OLEDs. OLED electrodes based on multi-walled nanotube films have been successfully demonstrated by Zhang et. al previously;3 however, multi-walled CNTs are an inferior transparent-conducting material compared to single-walled nanotubes (SWNTs) as the inner shells of multi-walled nanotubes that deteriorate the film transparency make little contribution to the sheet conductance. In this paper we report our systematic study on the preparation, chemical functionalization, and application of high-quality SWNT-film for OLED application. We have successfully used a transfer printing technique to directly transfer vacuum-filtered nanotube film to glass and polymer substrates. Our typical SWNT-film has a
transparency around 80% and a sheet resistance around 400 Ohm/square. Further improvement to the nanotube film includes SOCl2 doping, which l
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