III-V quantum dot enhanced photovoltaic devices

Abstract

State of the art photovoltaics exhibiting conversion efficiency in excess of 30% (1-sun) utilize epitaxially grown multijunction III-V materials. Increasing photovoltaic efficiency is critically important to the space power, and more recently, the terrestrial concentrator PV communitiesThe use of nanostructured materials within photovoltaic devices can enable improved efficiency, potentially in excess of the Shockley-Queisser limit. The addition of nanostructures such as quantum dots (QDs) to photovoltaic devices allows one to extend the absorption spectrum of the solar cell and "tune" the bandgap to the spectral conditions. Multi-junction (MJ) solar cells would benefit from the additional short-circuit current within the middle current-limiting (In)GaAs cell via QD spectral tuning. While QD tuning is a potentially direct approach to increased efficiency of MJ solar cells, it has been reported that significant improvements can be achieved using QDs to form an intermediate band within the bandgap of a suitable matrix.We will discuss the potential for QD photovoltaic devices and examine the challenges associated with multi-junction device growth with the inclusion of quantum dot arrays. GaAs p-i-n solar cells, with and without InAs QD superlattices are used to demonstrate the potential benefits of QDs. The unique challenges associated with the characterization of this type of device will also be presented. Using strain-balanced Stranski-Krastanov QD formation, we have demonstrated sub-gap photon collection and increased current in QD-enhanced GaAs solar cells containing up to 100 periods. Finally, we will discuss the opportunities that these devices hold for high photovoltaic conversion efficiency.

Improving the voltage of GaAs solar cells with In0.4Ga0.6As nanostructures

“…We would also like to note that with an increase of n a red shift of P Q occurred which indicates deepening recombination levels in the QWDs and decreasing E . g Q Such behavior for nanostructures has been observed earlier 28,29) and was discussed by us in Ref. 16.…”

Light Emitting Devices Based on Quantum Well-Dots

“…Such effect was not revealed in case of stacking strain balanced QWs [7,61,62], where peak positions do not depend on the number of the layers. We attribute this effect, at least partly, to the elastic strain redistribution in the multilayer QWD medium, similar to the case of stacking several layers of self-organized QDs [63][64][65].…”