Transparent electrodes made from carbon nanotube polyelectrolytes and application to acidic environments
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Francesco Paolucci and Giovanni Valenti Dipartimento di Chimica, Università di Bologna, Via Selmi 2, I-40126, Bologna, Italy
Philippe Poulin and Alain Pénicauda) CNRS, Centre de Recherche Paul Pascal (CRPP), UPR 8641, F-33600, Pessac, France, Université de Bordeaux, CRPP, UPR 8641, F-33600, Pessac, France (Received 23 February 2015; accepted 27 May 2015)
Carbon nanotube (CNT)-based transparent conducting films (TCFs) have been prepared by filtration of (i) surfactant-based aqueous dispersions and (ii) organic solutions obtained by reductive dissolution of an alkali metal salt of polyelectrolyte nanotubes. Starting from the same source of nanotubes, it is shown that films obtained by the reductive dissolution route present up to one order of magnitude better conductivity for the same transmittance. Light scattering experiments show that the average CNT length is much larger for the reductive dissolution-based organic solutions than for the sonication aided aqueous dispersions. Values of surface resistivity of 200 ohm per square have been obtained for 80% transmittance. Additionally, it is shown that the CNT-based TCFs are undistinguishable from indium tin oxide (ITO) as electrodes in regular environments, whereas they perform efficiently in acidic environments where ITO fails.
I. INTRODUCTION
Carbon nanotubes (CNTs) are promising for applications in different fields, such as electronics,1–3 fibers,4–6 sensors,7,8 and composites.9,10 In particular, CNTs are considered as one of the most convincing alternative to inorganic oxides for future transparent electrodes. As CNTs are practically insoluble in all solvents, different methods have been developed, using sonication or high shear mixing, to disperse CNTs in water or in organic solvents. CNT aqueous dispersions can be obtained using surfactants and sonication.11 Nevertheless, these methods are known to damage CNTs, creating defects on the walls of nanotubes12 and shortening them.13,14 An alternative method known as reductive dissolution has been developed15–19 in which CNTs are reduced by potassium naphthalide in Tetrahydrofuran (THF).20 A negatively charged CNT salt is obtained, which is spontaneously soluble in polar aprotic solvents, such as Dimethyl sulfoxide (DMSO). No sonication is used. It has been shown that the reductive dissolution individualizes Contributing Editor: Mauricio Terrones a) Address all correspondence to this author. e-mail: [email protected] b) New address: Linde Nanomaterials, 1970 Diamond St., San Marcos 92078, CA, USA This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2015.166 J. Mater. Res., Vol. 30, No. 13, Jul 14, 2015
nanotubes without damaging them.21,22 Here we show that transparent conducting films (TCFs) prepared from CNT solutions obtained by reductive dissolution have far better performances than films prepared from aqueous, sonication-aided dispersions. The study is focused on understanding the effects of the reductive dissolution on film electrical performances and on highlighting the key paramete
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