Solar cells for NASA RAINBOW concentrator

The RAINBOW concentrator system is based on a concept of splitting the solar spectrum and focussing each portion on a solar cell having a bandgap matching the input spectral portion. Efficiencies over 40% are predicted for systems using a four-bandgap cell assembly under 20/spl times/ concentration. Reported here are the results of materials growth, processing, and testing of four different solar cells designed to populate the RAINBOW testbed, under development at JPL. The cells are 0.74-eV InGaAs on lattice-matched InP, 1.1-eV InGaAs on lattice-mismatched GaAs, 1.43-eV GaAs on GaAs, and 1.85-eV InGaP on lattice-matched GaAs. Quantum efficiencies between 0.8 and 1.0 have been realized for the spectral region from 0.5 to /spl sim/1.5 /spl mu/m.