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

Abstract

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 J SC,IQE > 14 mA/cm 2 , suitable for high-efficiency multijunction cells, while RHJ cells showed diminished J SC,IQE < 11 mA/cm 2 due to limited diffusion length and high sensitivity to front-surface recombination. The RHJ cells on Si maintained a high open-circuit voltage (V OC ) of 1.292 V with threading dislocation density (TDD) of 1.0 × 10 7 cm −2 , a similar V OC value to FJ cells grown lattice-matched on GaAs. In addition, for a high TDD of 2.7 × 10 8 cm −2 , RHJ cells had a V OC of 1.223 V, greater than FJs with 10× lower TDD of 2.7 × 10 7 cm −2 , which further shows the high dislocation tolerance of n-GaInP. The high V OC , combined with the proposed work to boost IQE, could enable GaInP RHJs on Si for multijunction cell applications.