The carbon based perovskite solar cell (C-PSC) has a strong commercial potential due its low manufacturing cost and its improved stability. A C-PSC consists of three mesoporous layers sandwiched between a Fluorine-doped tin oxide (FTO) substrate as bottom electrode and carbon as top electrode. However, the low conductivity of the two electrodes represents a real challenge when scaling from individual cells to modules. Here, 2D direct current simulation is used to investigate the influence of width of the active area on the performance of a single C-PSC. The same method is used to study the effect of the sub-cell's width, the interconnection's width and the contact resistance at the interconnection on the performance of a 10 sub-cells module connected in series. The intrinsic properties of the carbon cell are taken in account using experimental J(SC) and V-OC as an input to the modelling. The carbon conductivity is found to be critical in defining the optimum geometry. For a 10 Omega/sq carbon sheet resistance, the optimum interconnection width is 500 mu m and the sub cell width is 4.9 mm, leading to an optimum fill factor of 64%.