Supercharging Silicon Solar Cell Performance by Means of Multijunction Concept

This study aims to comprehensively calculate the conversion efficiency limits of multijunction solar cells having crystalline silicon (c-Si) not only as a growth substrate but as the lowermost active subcell as well. The first set of efficiency limits is calculated based on the detailed balance principle, assuming a stepwise absorption profile. Practical limits are then calculated using Si absorption data and Auger recombination parameters from the literature. The Si wafer thickness is also considered in the two-stack tandem design. Performances of the tandems are compared when various Si solar cell technologies are used as the bottom subcells. The impact of external radiative efficiency and external quantum efficiency of the top subcell on the tandem performance is studied. Efficiency limits using state-of-the-art devices, and the effect of varying cell thickness on tandem efficiencies is also reported.