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

We demonstrate metamorphic 1.66 eV GaAs 0.77 P 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 y P 1−y /GaP/Si metamorphic solar cells.