This work shows the potential of further optimization of phosphorus-doped emitters in p-type silicon solar cells. We investigate the impact of different combinations of phosphorus doping profiles and surface passivation qualities on the saturation current density J0e by considering boundary conditions based on published experimental data. Our simulation study shows that there are two possible ways to achieve J0e values below 10 fA/cm2. One is the reduction of the electrically active phosphorus concentration nsurf at the surface beneath 2×1019 cm-3 and simultaneously reducing the surface recombination velocity Sp to below 103 cm/s. The other contrarily increases nsurf to values of up to 1×1021 cm-3 while ensuring full activation of all phosphorus dopants. In the latter case, J0e values below 10 fA/cm2 seem possible, even for Sp = 107 cm/s which is equal to the thermal velocity.