(80d) Layer-by-Layer (LBL) Assembled Highly Conductive, Transparent and Robust Thin Carbon Nanotube Films for Optoelectronics

Thin Conductive transparent films (TCFs) play an essential role in many optoelectonic devices, including Touch Screens, Liquid Crystal Displays (LCDs), Organic Light-Emitting Diodes (OLEDs), and Photovoltaics (PV) as electrodes. Indium Tin Oxide (ITO) was selected as an appropriate candidate for this application long ago in industry, due to its low resistivites[1] at the magnitude of 10^-4 ohms-cm with high transmittance in the visible spectrum. However, it falls short in several aspects, such as increasing price due to limit of availability, high patterning cost, brittleness, and low transmittance to the infrared region of solar spectrum[2], challenging the research and marketing in the field of flexible OLEDs and PVs. Two alternative materials, conductive polymers and composites with conductive fillers, are proposed to fulfill the challenge. After a decade of research and development, conductive polymers like Poly(3,4-ethylenedioxythiophene) (PEDOT) has comparable properties in conductivity and transmittance to ITO (according to product information on Baytron PH500[3]), however, they suffer from thermal and environmental stability problems[4] and are usually colored, which prevent their widespread use in commercial applications. Currently, more interest is drew upon making highly transparent, conductive thin composite electrode using highly conductive fillers, like Single Walled Carbon Nanotubes (SWNTs). Networks of SWNTs combine many advantageous properties such as mechanical flexibility, optical transparency, high electrical conductivity, simple preparation.

Layer-by-layer (LBL) Assembly, well known for its potential to build highly tuned, functional thin films with nanometer-level control of film composition and structure, has demonstrated its significance in building ultrastrong nanocomposites[5, 6], biomaterials[7] and other materials like species-selective thin films[8] and electrochromic thin films[9], etc. We propose here that this technology can be applied to make thin SWNTs electrodes with properties equivalent to ITO, based on the understanding that it can enable the homogenous distribution of SWNTs, which is fundamental to extend nanoscale properties, like high strength and high conductivities of individual SWNTs, to the bulky composite materials.

Reference:

[1] C. G. Granqvist, Solar Energy Materials and Solar Cells 2007, 91, 1529.

[2] Z. C. Wu, Z. H. Chen, X. Du, J. M. Logan, J. Sippel, M. Nikolou, K. Kamaras, J. R. Reynolds, D. B. Tanner, A. F. Hebard, A. G. Rinzler, Science 2004, 305, 1273.

[3] www.baytron.com.

[4] G. P. Crawford, Flexible Flat Panel Displays, John Wiely and Sons, 2005.

[5] A. A. Mamedov, N. A. Kotov, M. Prato, D. M. Guldi, J. P. Wicksted, A. Hirsch, Nature Materials 2002, 1, 190.

[6] P. Podsiadlo, A. K. Kaushik, E. M. Arruda, A. M. Waas, B. S. Shim, J. D. Xu, H. Nandivada, B. G. Pumplin, J. Lahann, A. Ramamoorthy, N. A. Kotov, Science 2007, 318, 80.

[7] E. Jan, N. A. Kotov, Nano Letters 2007, 7, 1123.

[8] D. M. Sullivan, M. L. Bruening, Chemistry of Materials 2003, 15, 281.

[9] C. A. Cutler, M. Bouguettaya, J. R. Reynolds, Advanced Materials 2002, 14, 684.