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 Ga_0.37In_0.63P (MM GaInP) grown on GaAs by molecular beam epitaxy. A low threading dislocation density of ∼6 × 10⁵ cm⁻² was achieved through the use of an In_xGa_1-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 lattice-matched 1.9 eV Ga_0.51In_0.49P (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 (V_OC) of 1.17 V. We also demonstrate the first MM 1.7 eV GaInP rear-heterojunction cells with high fill factor and V_OC of 85% and 1.21 V, respectively, by taking advantage of long carrier lifetime while eliminating majority carrier blocking. The high V_OC values for the 1.7 eV GaInP cells presented in this work indicate promising tolerance to threading dislocations in MM GaInP.