Annual energy yield: A comparison between various monolithic and mechanically stacked multijunction solar cells

Using EtaOpt the detailed balance efficiency of the classic lattice matched InGaP/GaAs/Ge 3-junction cell and those of optimized band gap combinations for both monolithic and mechanical stacks are calculated under 500×AM1.5D illumination. The results are 48.7% (mono) and 59.2% (mech) for the classic and 59.6% (mono) and 60.3% (mech) for the optimized band gap structures. For these devices we calculated the (ideal) annual energy yield (AEY) under realistic spectra that represent a typical meteorological year for a certain location. Both monolithic stacks have AEYs - 44.3% (class) and 56.1% (optim) - that are lower than those of the mechanical stacks - 60.1% (class) and 61.4% (optim). Mechanical stacks are found to be less sensitive to spectral variations caused by time of day changes and atmospheric conditions. In the quest for higher efficiencies monolithic solar cell manufacturers are looking towards increasing the number of junctions to up to 6. The performance of such a monolithic 6-junction cell is compared to that of the optimized 3-junction mechanical stack.