GaAsP on SiGe/Si material quality improvements with in-situ stress sensor and resulting tandem device performance

GaAsP solar cells have been grown on Si substrates facilitated by a SiGe graded buffer layer. Materials-based characterization demonstrates threading dislocation densities (TDD) as low as 8.0×106 cm-2 via cathodoluminescence in III-V layers from dual-junction solar cells. The difference in material quality and device performance between lattice-match conditions at room temperature and growth temperature are quantified. These improvements are primarily realized through the use of an in-situ optical stress sensor in order to evaluate lattice-mismatch during MOCVD growth. Thus, due to improved material quality, window layer design, and contact resistance, we have achieved GaAsP/SiGe tandem performance with an AM1.5G open-circuit voltage of 1.458 V, a top subcell external quantum efficiency-extracted short-circuit current density of 13.8 mA/cm2 (no AR), and a fill factor of 82.8%.