Criticality of Electron and Hole Escape Sequence in Nano-Structured Photovoltaic Devices

Abstract

ABSTRACTIt has been empirically established that for quantum confined p-i-n solar cells a high electric field across the i-region is necessary for an optimal extraction of carriers from the well. This restriction imposes an upper limit for the total thickness of the i-region beyond which severe performance degradations are reported. For a given material system, the best efficiency trade-off is often achieved in the vicinity of this critical i-region thickness where the Voc degradation remains minimal and a higher photocurrent is afforded by the larger number of wells. But, even for devices that satisfy this condition, occasionally a severe Voc degradation occurs. Here, we show that this degradation is directly correlated to the carrier escape sequence from the wells and that a careful engineering of hole and electron confining potentials can be used to alleviate this shortcoming.