Fabrication and analysis of multijunction solar cells with a quantum dot (In)GaAs junction

InAs quantum dots (QDs) have been incorporated to bandgap engineer the (In)GaAs junction of (In)GaAs/Ge double-junction solar cells and InGaP/(In)GaAs/Ge triple-junction solar cells on 4-in. wafers. One sun AM0 current–voltage measurement shows consistent performance across the wafer. Quantum efficiency analysis shows similar aforementioned bandgap performance of baseline and QD solar cells, whereas integrated sub-band gap current of 10 InAs QD layers shows a gain of 0.20 mA/cm2. Comparing QD double-junction solar cells and QD triple-junction solar cells to baseline structures shows that the (In)GaAs junction has a Voc loss of 50 mV and the InGaP 70 mV. Transmission electron microscopy imaging does not reveal defective material and shows a buried QD density of 1011 cm−2, which is consistent with the density of QDs measured on the surface of a test structure. Although slightly lower in efficiency, the QD solar cells have uniform performance across 4-in. wafers. Copyright © 2013 John Wiley & Sons, Ltd.