Novel InAs/GaAs QD subcell design for radiation hard 3-J ELO IMM solar cell

Abstract

InAs/GaAs quantum dots (QDs) have been investigated as a potential method of engineering the bandgap of the middle junction in triple junction solar cells to better match current generation and radiation tolerance to that of the InGaP top cell. While it is possible to successfully include QDs without inducing middle junction voltage degradation, they can lead to a slight reduction of minority carrier diffusion lengths in films grown after the QDs. Switching to an inverted metamorphic structure allows for the top cell to be grown first, but leads to challenges in maintaining current collection in the middle junction. In this work, a novel InAs/GaAs QD middle junction cell design is proposed for improving the efficiency of triple junction inverted metamorphic solar cells. Conventionally designed thin emitter devices as well as the proposed thick emitter devices were grown with and without InAs QDs in the uid region of the middle junction. The conventionally designed QDSC exhibited 1.8% relative increase in Jsc over the control device with no loss in VoC resulting in a 1.8% relative increase in efficiency over the control device.