Effect of Threading Dislocations on GaInP Front-and Rear-Junction Solar Cells Grown on Si

We compare the performance of front-junction (FJ) and rear-heterojunction (RHJ) 1.9 eV GaInP solar cells grown on Si by molecular beam epitaxy. First, time-resolved photoluminescence showed a minority carrier lifetime of 11.7 ns for n-GaInP on Si, indicating a high tolerance to threading dislocations due to the low mobility of minority holes. GaInP solar cells were grown on both GaAs and Si substrates in FJ (p-type absorber) and RHJ (n-type absorber) configurations. The internal quantum efficiency (IQE) of FJ cells was identical on GaAs and Si substrates and showed high IQE-derived short-circuit current density JSC,IQE > 14 mA/cm2, suitable for high-efficiency multijunction cells, while RHJ cells showed diminished JSC,IQE < 11 mA/cm2 due to limited diffusion length and high sensitivity to front-surface recombination. The RHJ cells on Si maintained a high open-circuit voltage (VOC) of 1.292 V with threading dislocation density (TDD) of 1.0 × 107 cm-2, a similar VOC value to FJ cells grown lattice-matched on GaAs. In addition, for a high TDD of 2.7 × 108 cm-2, RHJ cells had a VOC of 1.223 V, greater than FJs with 10× lower TDD of 2.7 × 107 cm-2, which further shows the high dislocation tolerance of n-GaInP. The high VOC, combined with the proposed work to boost IQE, could enable GaInP RHJs on Si for multijunction cell applications.