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Intermediate band solar cells (IBSCs) are third-generation photovoltaic (PV) devices that can harvest sub-bandgap photons normally not absorbed in a single-junction solar cell. Despite the large increase in total solar energy conversion efficiency predicted for IBSC devices, substantial challenges remain to realizing these efficiency gains in practical devices. We evaluate carrier escape mechanisms in an InAs/GaAs quantum dot intermediate band p-i-n junction PV device using photocurrent measurements under sub-bandgap illumination. We show that sub-bandgap photons generate photocurrent through a two-photon absorption process, but that carrier trapping and retrapping limit the overall photocurrent. The results identify a key obstacle that must be overcome in order to realize intermediate band devices that outperform single junction photovoltaic cells.

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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.

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