Modeling of two-junction, series-connected tandem solar cells using top-cell and coating thicknesses as adjustable parameters

Theoretical efficiencies are calculated for two-junction, series-connected solar cells using AM1.5 global and direct irradiance spectra. For (bandgap combinations) previously limited by a low bottom-cell current, thinning of the top cell is shown to result in significant increases in the theoretical efficiencies. The increases are primarily due to increased short-circuit currents resulting from (current matching). Smaller gains are also seen in the (open-circuit voltages) of the thinner cells with low surface-recombination velocities. Some current matching can also be achieved by adjusting the antireflection coating thicknesses. This model has important implications for the design of GaInP/GaAs, AlGaAs/GaAs, and GaAs/Ge tandem cells