Towards demonstration of GaAs 0.76 P 0.24 /Si dual junction step-cell

Here we present an initial demonstration of a dual junction step-cell using single junction (SJ) GaAs 0.76 P 0.24 cell, grown on Si 1−y Ge y /Si substrates, as the top cell and Si as the bottom cell. To demonstrate step-cell, two SJ cells are connected in series, without removing SiGe/Si carrier from III-V cell, and illuminated Si cell area is varied. Measured efficiency of optimized demo step-cell under 1 sun and without anti-reflective coating on III-V cell is ∼11.8% Using SJ cells characterization and optical data, we estimate maximum efficiency of bonded 1-μm GaAs 0.76 P 0.24 // 650-μm Si step-cell to be ∼26% at optimized total-to-top cell area ratio equal to 1.1. Results presented here show that step-cell can be used as added optimization design parameter for tandem cells.