Abstract
Screen-printing inks containing various morphologies of carbon are used in the production of a variety of printed electronics applications. Particle morphology influences the rheology of the ink which will affect the deposition and therefore the electrical performance of a printed component. To assess the effect of both carbon morphology and concentration on print topography and conductivity, screen printable carbon inks with differing loading concentrations of graphite, carbon black and graphite nanoplatelets (GNPs) were formulated, printed and characterised, with rheological and novel print visualisation techniques used to elucidate the mechanisms responsible. Carbon morphology had significant effects on the packing of particles. The smaller carbon black particles had more interparticle interactions leading to better conductivities, but also higher ink viscosities and elasticities than the other morphologies. Increases in carbon concentration led to increases in film thickness and roughness for all morphologies. However, beyond a critical point further increases in carbon concentration led to agglomerations of particles, mesh marking and increases in surface roughness, preventing further improvements in the print conductivity. The optimal loading concentrations were identifiable using a custom-made screen-printing apparatus used with high speed imaging for all morphologies. Notable increases in filamentation during ink separation were found to occur with further increases in carbon concentration beyond the optimum. As this point could not be identified using shear rheology alone, this method combined with shear rheology could be used to optimise the carbon concentration of screen-printing inks, preventing the use of excess material which has no benefit on print quality and conductivity.
Highlights
Screen-printed carbon inks and pastes are widely used in the manufacture of a range of printed electronics applications due to their electrical conductivity and relatively low cost
The inks containing 25 wt% of graphite and 20 wt% carbon black could not be assessed at shear rates beyond 10 s-1 and 15 s-1 as the high viscosities of the inks prevented the rheometer from rotating at these speeds, with viscosities of 95.5 Pas and 48.5 Pa s, respectively, at these final shear rates
The smaller carbon black particles had more interactions leading to better electrical performance
Summary
Screen-printed carbon inks and pastes are widely used in the manufacture of a range of printed electronics applications due to their electrical conductivity and relatively low cost These include resistive heaters [1, 2], electrochemical sensors [3], printed batteries [4], Perovskite PV [5, 6], as well as energy harvesting in the form of printed pyroelectrics [7] and thermoelectrics [8]. These inks typically consist of a range of carbon morphologies to tailor the performance and cost of the inks. It is typically combined with larger carbon morphologies such as graphite or GNPs in inks, where they can be readily dispersed to form conductive bridges between neighbouring graphite flakes or GNPs to enhance the electrical conductivity of the ink [10, 14]
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