$\dot{\gamma}$ decreases as shear rate from the squeegee is removed while $\eta$ increases to form a solid, unbroken image on the substrate surface with a rectangular cross sectional profile. The narrowest printed lines we have achieved on PET are of 200$\mu$m width with a line edge roughness of 4.04 $\mu$ m.; Supplementary Fig. 5. To ensure our formulated ink has these properties, a combination of OFAT, for qualitative screening and DOE for quantitative optimisation are utilised. A detailed explanation on the use of OFAT and DOE is given in supplementary note 1.

We use OFAT to firstly optimise the rheology of the ink by varying the graphene content, thereby determining the maximum loading of graphene permissible in the EC binder before the ink becomes unprintable. OFAT is a method of experimentation that varies one factor at a time in order to find an optimum response and is highly useful for bi-variate analysis [@Ng2019e; @Jacquez1998]. We define the screen printability of the ink as having starting viscosity under zero shear being in between 2 to 10 Pa s [@Ng2019e; @Hu2018]. To derive the maximum loading of graphene, first 20 wt.% of EC powder is fully dissolved in terpineol *via* stator-rotor mill, 