The optimum emitter surface dopant concentration (Ns) in passivated silicon solar cells is found for different base resistivities with the help of a computer model. The model takes into account not only the band‐gap narrowing, Auger and surface recombination effects on the dark saturation current, but it also considers the variation of series resistance as the impurity concentration changes. The results obtained with the model show different behavior for passivated and nonpassivated solar cells. The open‐circuit voltage and the conversion efficiency of nonpassivated solar cells is almost independent of the surface impurity concentration when this parameter is greater than 2×1019cm−3. On the other hand, for passivated solar cells the optimum value is in the range 2.5×1019cm−3≤Ns<5×1019cm−3for typical base resistivities. Furthermore, it is confirmed that even whenNsis high (Ns>1×1020cm−3) there is an advantage in efficiency of passivated solar cells over those which have a high recombination at the surface. However, in order to increase the efficiency appreciablyNshas to be optimized. The model also gives a procedure to optimize the grid design simultaneously with the surface concentration, assuming the other parameters are optimum.