Metamorphic front- and rear-junction 1.7 eV GaInP solar cells with high open-circuit voltage

1.7 eV absorber materials are important in high-performance III-V multi-junction solar cells. Here, we show that rapid thermal annealing significantly improves the carrier lifetimes in lightly doped metamorphic 1.7 eV Ga0.37In0.63P (MM GaInP) grown on GaAs by molecular beam epitaxy. A low threading dislocation density of -6 x 105 cm-2 was achieved through the use of an InxGa1-xAs graded buffer. Annealing enables minority carrier lifetimes in 1.7 eV p- and n-GaInP of 3.9 and 28 ns, respectively, both of which are higher than annealed latticematched 1.9 eV Ga0.51In0.49P (LM GaInP) grown in the same chamber. With the benefit of annealing, MM 1.7 eV GaInP front-junction solar cells show a high peak internal quantum efficiency of 94.3% and an open-circuit voltage (VOC) of 1.17 V. We also demonstrate the first MM 1.7 eV GaInP rear-heterojunction cells with high fill factor and VOC of 85% and 1.21 V, respectively, by taking advantage of long carrier lifetime while eliminating majority carrier blocking. The high VOC values for the 1.7 eV GaInP cells presented in this work indicate promising tolerance to threading dislocations in MM GaInP.