Progress toward a 30%-efficient, monolithic, three-junction, two-terminal concentrator solar cell for space applications

The component cell milestone goals for an AM0 30% efficient, three-junction, two-terminal cell operating at 70 to 100°C at 100X concentration are 16% top cell, 11% middle cell, and 3% bottom cell. The best values measured so far at 80°C and 100X are 15.27% for a 1.9 eV AlGaAs top cell, 9.87% for a 1.4-eV GaAs middle cell, and 2.40% for a 1.0 eV InGaAs bottom cell. At 25°C, these values increased to 15.42%, 10.79%, and 3.02%, respectively. The measured negative temperature coefficient for efficiency increases with decreasing bandgap so that higher bandgaps are preferred (such as a 1.0 eV bottom junction compared to a 0.7 eV one, other things being equal)