Epitaxial Lift-off (ELO) of InGaP/GaAs/InGaAs solar cells with quantum dots in GaAs middle sub-cell

We report the first demonstration of MOVPE-grown inverted metamorphic (IMM) cells with QDs embedded in the middle GaAs sub-cell. The IMM cells were fabricated on full 4 '' wafer using Epitaxial Lift off (ELO) technology. GaAs sub-cell embedded with 10 and 20 periods of InAs/GaP strain compensated QDs showed increase in current with number of QD periods. The single junction GaAs sub cell embedded with 20 periods of InAs/GaP strain compensated QDs showed 3.2% relative increase in J(sc) in comparison with control sample without QDs. Integrated short circuit (Jsc) from measurements of external quantum efficiency (EQE) of currents showed a 65% increase in sub-band collection in the GaAs sub-cell when the number of QD layers increased from 10 to 20. IMM cells with QD's embedded in the middle cell showed minimal loss in open circuit voltage (V-OC) in comparison to control sample without QDs. An efficiency of 30% under 1-sun AMO spectrum was obtained for IMM cells with 10 xs of InAs/GaP QDs in GaAs sub-cell. Quantum efficiency remaining factor of > 95% in the QD absorption region (940 nm) was measured for IMM devices with InAs/GaAs QD enhanced GaAs sub-cells irradiated with 1 MeV electrons under 2E15 /cm(2) fluence.