A statistical understanding of multiple exciton generation in PbSe semiconductor nanostructures

We propose a simple statistical model, based on Fermi statistical theory and impact ionization mechanism, to resolve the controversies over the effects of multiple exciton generation (MEG) in PbSe quantum dots (QDs). We have confirmed that MEG indeed occurs in PbSe QDs. Also, we have found out that there exists a critical radius R-c (similar to 9 nm) such that the MEG efficiency of PbSe QDs is smaller than that of the bulk counterpart if R < R-c, but larger if R > R-c. Moreover, we have found out that the MEG threshold energy calculated for PbSe QDs shows a universal behavior. The present work provides a powerful theoretical means not only for further experimental investigations into the MEG effects in semiconductor nanostructures, but for their applications in photovoltaic devices. (C) 2012 Elsevier Ltd. All rights reserved.