Transparent, conductive and flexible single-walled carbon nanotube films

Antti Kaskela

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Single-walled carbon nanotube (SWCNT) networks have a large application potential for future electronics as transparent conductive films. SWCNT networks (SWCNT-N) offer improved flexibility when compared to the current industry standard transparent conductive films (TCF), an example of which is indium tin oxide (ITO). SWCNTs can be synthesised from abundant raw materials, whereas indium supply is limited and has been a target of aggressive trade policies, thus increasing supply risks and price volatility. In order to make the SWCNT-Ns suitable for industrial applications, their performance must be made competitive with ITO and other TCF materials, whilst their manufacturing costs have to be minimised. Understanding the performance limiting factors is important when it comes to the development of high performance SWCNT networks. The results presented here show that the bundle length has a major impact on the electrical performance of SWCNT networks. Optimisation of SWCNT growth conditions in aerosol-CVD reactors used for SWCNT synthesis led to an increase in SWCNT bundle length from 1.3 μm to 9.4 μm. Bundle diameter distributions were found to overlap, with mean bundle diameter measuring approximately 10 nm, and mean SWCNT diameters ranging from 1.4 to 1.7 nm. The increased bundle length led to a reduction in the number of the highly resistive bundle-bundle contacts and to improved performance. When the SWCNT-TCFs were chemically doped by nitric acid, sheet resistance was reduced down to 84 Ω/sq. at 90% transparency, thus making the SWCNT TCFs competitive with ITO on polymer films. The intertube and interbundle contact resistances together with the effect of nitric acid treatment were studied by using conductive atomic force microscopy. The contact resistance values of pristine junctions were within the range of 29 kΩ - 532 kΩ for contacts between individual tubes and small bundles with less than 5 nm diameter. The contact resistance decreased with increasing tube or bundle diameter. Contact morphology had a major impact on the contact resistance values as X- contacts exhibited higher mean contact resistance of 180 kΩ, while the Y-contacts had mean contact resistance of 60 kΩ. When the contacts were exposed to strong nitric acid, the mean contact resistance was reduced by a factor of 3, although the length resistivity remained largely unchanged at around 8 kΩ/μm. The results indicate that the contact morphology and the diameter of contacting SWCNTs and bundles had a significant impact on the electrical transport across the contacts and that the nitric acid treatment mainly affected the network performance by modulating the contacts and reducing their contact resistances. Furthermore, a novel room-temperature press transfer technique was developed. This dry, ambient temperature deposition method allowed for the rapid and direct deposition of variable thickness SWCNT networks to a wide range of substrates, from flexible polymers to glass, silicon and metals. The developed process eliminates harsh and detrimental purification and dispersion steps, thus maintaining the high intrinsic performance of SWCNTs. Fabrication of novel freestanding SWCNT networks was also demonstrated. The freestanding SWCNT networks can be used for a wide range of novel applications. The aerosol-CVD synthesized SWCNTs were also demonstrated as flexible counter-electrodes in dye-sensitised solar cells. The SWCNT-network was combined with electrochemically deposited PEDOT, reaching comparable performance with standard platinum catalyst with energy conversion efficiencies of up to 4%. Fabrication and properties of hybrid materials consisting of SWCNT networks coated with amorphous carbon deposited by low energy plasma were studied. The carbon coating improved the mechanical durability of SWCNT films under nanoindentation and scratching.
Translated title of the contributionLäpinäkyvät, johtavat ja joustavat yksiseinäiset hiilinanoputkikalvot
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Kauppinen, Esko, Supervising Professor
  • Nasibulin, Albert, Thesis Advisor
Publisher
Print ISBNs978-952-60-5458-2
Electronic ISBNs978-952-60-5459-9
Publication statusPublished - 2013
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • single-walled carbon nanotube
  • contact resistance
  • transparent conductive film
  • network
  • applications

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