Stacked GaAs(Sb)(N)-capped InAs/GaAs quantum dots for enhanced solar cell efficiency

Abstract

In this manuscript we carry out a comparative analysis of p-i-n junction solar cells based on 10 stacks of InAs/GaAs quantum dots (QDs) capped with GaAs(Sb)(N) capping layers (CLs). The application of such CLs allows to significantly extend the photoresponse beyond 1.3 μm. Moreover, a strong photocurrent from the CLs is observed so that the devices work as QD-quantum well solar cells. The GaAsSb CL leads to the best results, providing a strong sub-band-gap contribution, which is higher than that in a sample containing standard GaAs-capped QDs, despite giving rise to the highest accumulated strain. The use of a GaAsN CL reduces the photocurrent originating from GaAs, pointing to electron retrapping and hindered extraction and/or the introduction of point defects as possible reasons for this. Nevertheless, the addition of N helps to balance the accumulated strain, necessary to stack a higher number of QD layers. In addition, the possibility to independently tune the hole and electron confinements by the simultaneous presence of Sb and N in the CL is also confirmed for 10 stacked QD layers. This not only allows to further extend the QD ground state and, therefore, the photoresponse, but also offers the possibility to design an optimized structure facilitating carrier extraction from the QDs. Nevertheless, carrier losses seem to be stronger under the simultaneous presence of N and Sb in the CL.