Multiple exciton generation(MEG), a process by which an absorbed photon generates multiple excitons (electron-hole pairs), was reported recently in a series of semiconductor quantum dots (QDs).  This process allows for over 100% quantum efficiency in generating electron-hole pairs, providing a potential way for dramatically improving the solar-to-electric power conversion efficiency in QD-based solar cells. Since MEG process allows the generation of multi-electron–hole redox centers under low photon flux, it may also find interesting applications in photocatalytic processes that require multiple electrons or holes. The next major scientific advance that enables these potential applications is the separation of electron-hole pairs before the exciton-exciton annihilation processes, which occurs on the 10s to 100s picosecond time scale for many QDs. Previous studies have reported that excitons in QD could dissociate by either electron or hole transfer, although the factors that control the dissociation pathways and rates remain not well understood.

       We are examining the mechanism of exciton dissociation in nanocomposites of QDs with various electron donor and acceptors (ranging from conjugated polymers, nanocrystalline thin films and molecules). We are investigating various factors that control the pathway and rate of exciton dissociation (electron vs hole transfer). Initial studies indicate that excitation dissociation on picosecond time scale can be achieved, suggesting the possibility of separating multiple excitons before the exciton-exciton annihilation process.