We report on efforts to design high efficiency silicon sub-cells for use in multijunction stack devices. Both simulation and experimental work have been performed looking at a silicon solar cell under a truncated spectrum due to the optical filtering of the upper layers in the multijunction stack. The truncation for our case occurs for photon energies above 1.5 e V. Good agreement is seen between the modeling and experiments, with very different design features being identified, as compared to the design for a high efficiency solar cell under a full spectrum. When a well passivated front surface is achieved i.e. low interface recombination velocity, we see that a lightly-doped emitter profile maximizes the open circuit voltage (V oc ). When a high interface recombination is present, however, heavily-doped profiles exhibit the higher V oc values. The impact on short circuit current (J sc ) is seen to be minimal even with large variations in the interface recombination and emitter profiles.