Towards high efficiency GaAsP solar cells on (001) GaP/Si

We demonstrate metamorphic 1.66 eV GaAs_0.77P_0.23 solar cells grown by molecular beam epitaxy on exact (001) GaP/Si templates. Cascading such a cell with a 1.1 eV Si junction enables theoretical efficiencies of > 37% under the AM1.5G spectrum. We optimized the initial GaP growth on pseudomorphic GaP/Si templates to promote maximum strain relaxation with minimal nucleation of new threading dislocations. Electron beam-induced current studies of our cells reveal a threading dislocation density (TDD) of 7.8×10⁶ cm^-2, about 18% lower than our prior results on GaP/Si. The lower TDD has contributed to a low bandgap-voltage offset (W_OC=E_G/q-V_OC) of 0.55 V, which is 40 mV lower than our previous report, and represents significant progress for GaAs_yP_1-y/GaP/Si metamorphic solar cells.