n-Type doping of mixed single- and double-layer graphene grown by chemical vapor deposition (CVD) using decamethylcobaltocene reveals a local-quasilinear relationship between the work function and the logarithm of the dopant solution concentration. The relationship that arises from bandgap opening is deduced by comparing the relationship between the two factors for single-or double-layer graphene. This work has extensive applicability and practical significance in doping CVD-grown graphene.