Abstract The resistance of the top layer of a photovoltaic cell is calculated using a numerical solution of Poisson's equation. The boundary conditions of the side of the slab facing the depletion layer are determined using a distributed model for the photovoltaic cell. The series resistances in the model are obtained from the actual resistances of the flow line paths between mesh points and the top collector. The exact junction voltage at that mesh point is then used to obtain the flow line path. Iteration between the results of Poisson's equation and the junction voltage converged after three to four trials.