Effects of Graded Buffer Design and Active Region Structure on GaAsP Single-Junction Solar Cells Grown on GaP/Si Templates

We investigated the effect of GaAs_yP_1-y graded buffer layer design and cell structure on GaAsP solar cells grown on GaP/Si templates. Heavy Si doping in the graded buffer layer increases threading dislocation density (TDD) by 2.7× compared to no doping, while heavy Be doping has little or no effect on TDD. Higher TDD increases the bandgap-voltage offset, but its effect on short-circuit current density is more complex. For example, by implementing an n⁺/i/p structure in cells with elevated TDD, we could obtain significantly higher internal quantum efficiencies at 500-750 nm compared to n⁺/p structures with low TDD. All cells investigated here achieved efficiencies of 15.5-15.9% despite TDD values ranging from 4.5×10⁶-1.2×10⁷ cm^-2.