A recalculation of the efficiency limit in crystalline Si/Si tandem solar cells

We determine the limiting efficiency for monolithic tandem solar cells that employ crystalline silicon for the top-cell as well as for the bottom cell. In such a design, the top-cell extends over the region of very high generation rate that forms at the front of the device. Consequently, the design benefts from a high excess carrier density in the top-cell, resulting in a voltage in the tandem device that is more than twice the voltage of equally thick single junction solar cells. Considering Coulomb-enhanced Auger recombination coefficient, we find a maximum efficiency of 30.7% for a total device thickness of 500 μm wherein the top cell thickness amounts to 2.15 μm, representing gain of 1.1% (abs) with respect to the limiting efficiency of single junction devices.