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 JSC 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 (VOC) in comparison to control sample without QDs. An efficiency of 30% under 1-sun AM0 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 /cm2 fluence.