We have investigated GaAs-based p-i-n quantum dot solar cells (QDSCs) with 10 up to 20 stacked layers of self-assembled InAs quantum dots (QDs) grown by atomic hydrogen-assisted molecular beam epitaxy. The net average lattice strain was minimized by using the strain-compensation technique, in which GaNAs dilute nitrides were used as spacer layers. The filtered short-circuit current density beyond GaAs bandedge was 2.47 mA/cm2 for strain-compensated QDSC with 20 stacks of InAs QD layers, which was four times higher than that for strained QDSC with identical cell structure.

We have fabricated and compared the performance of GaAs-based p-i-n quantum dot solar cells with ten multilayer stacked structures of self-assembled InAs quantum dots embedded with GaNxAs1−x strain-compensating spacer layers. Reducing the thickness of the spacer layer, and hence increasing the nitrogen composition in GaNxAs1−x, from 40 nm (x=0.5%) to 15 nm (x=1.5%) thereby fulfilling the net strain-balanced condition, resulted in a steady increase in the short-circuit density, while a decreasing trend for the open-circuit voltage was observed. The observed results can be interpreted in terms of the difference in the quantum confinement structure.

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We characterized the optical absorption and solar cell characteristics of high‐density InAs self‐assembled quantum dots (QDs) grown on GaAs (001) substrates by atomic hydrogen‐assisted molecular beam epitaxy. The GaNAs material can be used as strain‐compensating layer (SCL) thereby minimizing the net strain, and thus is advantageous for multi‐stacking of InAs QDs structures. As a result, dislocations and coalesced islands were not observed in 100 layer‐stacked QDs. For QD solar cell characterization, the short‐circuit current density of QDSC increases with increasing number of QD stacks, and reaches as high as 26.4 mA/cm2 for 50 layer‐stacked sample under air‐mass 1.5 condition. However, the light absorption by QD superlattice as determined by optical absorption measurements at is limited to ∼ 10% even for 100 layer‐stacked samples. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)