Perspective on the prospects of a carrier multiplication nanocrystal solar cell

This article presents a perspective on the experimental and theoretical work to date on the efficiency of carrier multiplication (CM) in colloidal semiconductor nanocrystals (NCs). Early reports on CM in NCs suggested large CM efficiency enhancements. However, recent experiments have shown that CM in nanocrystalline samples is not significantly stronger, and often is weaker, than in the parent bulk when compared on an absolute photon energy basis. This finding is supported by theoretical consideration of the CM process and the competing intraband relaxation. We discuss the experimental artifacts that may have led to the apparently strong CM estimated in early reports. The finding of bulklike CM in NCs suggests that the main promise of quantum confinement is to boost the photovoltage at which carriers can be extracted. With this in mind, we discuss research directions that may result in effective use of CM in a solar cell.