Abstract
This paper presents the formulation, inkjet printing, and vacuum forming of a conductive and stretchable polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), ink on a stretchable and transparent thermoplastic polyurethane (TPU) substrate. The formulation of the conductive and stretchable ink is achieved by combining PEDOT:PSS with additional solvents, to achieve the right inkjet properties for drop-on-demand (DoD) inkjet printing. A conductive pattern can be printed from the 21 µm orifice on a flexible and stretchable TPU substrate, with a linewidth down to 44 µm. The properties of the printed pattern, in terms of sheet resistance, morphology, transparency, impact of weather conditions, and stretching are investigated and show sheet resistances up to 45 Ohm/sq and transparencies as high as 95%, which is comparable to indium tin oxide (ITO). Moreover, in contrast to ITO, one-time stretching up to 40% can be achieved, increasing the sheet resistance up to 214 Ohm/sq only, showing the great potential of this ink for one-time stretching. Finally, as a proof of this one-time stretching, the printed samples are vacuum formed around a 3D object, still showing sufficient conductivity to be applied as a capacitive touch sensor.
Highlights
The most attractive transparent conductive electrode applied in many organic electronic applications is indium tin oxide (ITO)
The PEDOT:PSS ink was inkjet printed on a stretchable and transparent thermoplastic polyurethane (TPU) substrate and the final printed pattern was characterized for its final properties of sheet resistance, transparency, morphology, impact of weathering, and stretching
The behaviour of the ink during jetting and droplet flight depends on dimensionless numbers, such as the Reynolds number (Re), Weber number (We), and Ohnesorge number (Oh) [45,46,47]
Summary
The most attractive transparent conductive electrode applied in many organic electronic applications is indium tin oxide (ITO). It is necessary to fabricate high performance stretchable inks by selecting the printing parameters meticulously to achieve formulations that can be printed with inkjet printing on stretchable substrates and that maintain their properties upon stretching. Developed an PEDOT:PSS ink that was suitable for inkjet printing with a DoD Dimatix 2800 inkjet printer from Fujifilm and the layer achieved a resistivity of 0.15 Ω.cm, corresponding to a conductivity of 6.6 S/cm [38]. The PEDOT:PSS ink was inkjet printed on a stretchable and transparent thermoplastic polyurethane (TPU) substrate and the final printed pattern was characterized for its final properties of sheet resistance, transparency, morphology, impact of weathering, and stretching. 3D forming using vacuum forming technology was achieved for the first time as a proof of the one-time stretching behaviour of the printed pattern, and the printed PEDOT:PSS structure was applied for a touch sensing application
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