Fig. 1. (a) Relationship between grinding time and sheet resistance of each group of conductive inks. (b) Comparison of conductivity of inks prepared by different conductive fillers. (c and d) Schematic diagram of CNTs network and graphite, CB filled CNTs network. (e) SEM image of the pure MWNT-f-OH, (f) SEM image of the CB, graphite and MWNT-f-OH are mixed conductive ink filled with each other. (g) SEM images of the cross-section of the ink layer. (h) TEM images of the few-layer graphene in ink.