experiments and results of the DOE are given in supplementary information and have also been plotted in Fig. \[panel1\]f in a ternary plot reflecting the interaction between the three ink components. An optimum formulation for the screen printing graphene ink is established as graphene (23 wt.%), EC binder (75 wt.%) and IPA (2 wt.%) with a R$_s$ response of 64 $\Omega$ $\square^{-1}$ while on PET. The formulated ink is stable and not prone to sedimentation for more than 1 month; Supplementary Fig. 4. The lowest measured value of R$_s$ at 25 $\mu$m is 24 $\Omega$ $\square^{-1}$ when deposited on glass (bulk conductivity = 0.17 $\times$ 10$^4$ S m $^{-1}$). We stress that this value represents the bulk conductivity of the screen printed ink without further annealing, compression, and partial or full decomposition of the non-conductive polymeric binder. As will be discussed later, this variation in R$_s$ is attributed to differences in surface roughness. We further note that the above process optimises the electrical conductivity while maintaining the ink printability, and to our knowledge, have not been methodically applied to formulation of graphene or other 2D material inks in published literature. Although the final conductivity value will vary depending on the 