Inkjet-printed PEDOT:PSS/SWCNTs on Paper: Substrate Effects on Conductivity
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Inkjet-printed PEDOT:PSS/SWCNTs on Paper: Substrate Effects on Conductivity Peter D. Angelo1 and Ramin R. Farnood1 1 University of Toronto, Department of Chemical Engineering and Applied Chemistry Toronto, ON, M5S 3E5, Canada ABSTRACT Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), or PEDOT:PSS, and singlewalled carbon nanotubes (SWCNTs) were incorporated into an inkjet ink. The combination of PEDOT, a conjugated, conductive polymer, and highly conductive CNTs, yielded a conductive film after printing and curing of the ink. Several paper types were used as substrates for depositing printed patterns of the PEDOT:PSS/SWCNT ink. Wide variability in conductivity was observed for different commercial paper types, ranging from a maximum 0.9 S/cm on Epson® Premium Photo cast-coated glossy paper to 3 × 10-5 S/cm on Epson® Premium Presentation coated cardstock. Increasing the SWCNT content of the ink improved conductivity on a non-permeable cellulose acetate substrate to a point, after which the combined effects of ink filtration and jetting limited the number of nanotubes delivered to the substrate. On permeable paper, the irregularity of the substrate overcame the beneficial effects of SWCNTs as “bridges” between conductive PEDOT regions. Correlations between the substrates’ physical structure and conductivity were established for the printed sheets, with densely coated sheets presenting the highest conductivity, and porous sheets the lowest. INTRODUCTION Water-borne suspensions of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) micelles, also known as PEDOT:PSS, have attracted interest due to PEDOT’s relatively high electrical conductivity, optical translucency, and ease of processing by wet methods [1-16]. To enhance the conductivity of PEDOT:PSS films, the addition of single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs) have been considered in the literature [17-20]. In particular, it has been shown that aqueous dispersions of PEDOT:PSS/CNTs can be deposited relatively uniformly by inkjet printing to form translucent conductive films [20]. Because PEDOT:PSS is aqueous, and CNTs may be also be dispersed in water or other solvents, they can form films at relatively low temperatures, lending themselves to processing on temperaturesensitive substrates, including paper. Paper as a substrate presents a novel opportunity for environmentally conscious electronics manufacturing due to its low cost, biodegradability, and renewability. However, the irregularity of this material, in terms of topography, porosity, chemistry, and so on, makes it a challenging substrate on which to achieve good electrical performance in materials like PEDOT:PSS or CNTs. Furthermore, paper components may also interact physicochemically with electrically functional layers. The interaction of PEDOT:PSS with a paper substrate and its effect on film conductivity has been reported in the literature, although primarily for coated PEDOT:PSS layers rather than printed ones [21-24]. These physicochemical interactions make paper-b
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