Degradation of subcells and tunnel junctions during growth of GaInP/Ga(In)As/GaNAsSb/Ge 4‐junction solar cells

A GaInP/Ga(In)As/GaNAsSb/Ge 4J solar cell grown using the combined MOVPE + MBE method is presented. This structure is used as a test bench to assess the effects caused by the integration of subcells and tunnel junctions into the full 4J structure. A significant degradation of the Ge bottom subcell emitter is observed during the growth of the GaNAsSb subcell, with a drop in the carrier collection efficiency at the high energy photon range that causes a ~15% lower J_sc and a V_oc drop of ~50 mV at 1‐sun. The V_oc of the GaNAsSb subcell is shown to drop by as much as ~140 mV at 1‐sun. No degradation in performance is observed in the tunnel junctions, and no further degradation is neither observed for the Ge subcell during the growth of the GaInP/Ga(In)As subcells. The hindered efficiency potential in this lattice‐matched 4J architecture due to the degradation of the Ge and GaNAsSb subcells is discussed.