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

We demonstrate metamorphic 1.66 eV GaAs0.77P0.23 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 7.8x10(6) 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(y)P(1-)y/GaP/Si metamorphic solar cells.