Ultrafast Charge Separation In Multiexcited Cdse Quantum Dots Mediated Byadsorbed Electron Acceptors

摘要

A lot of recent efforts aim to establish colloidal quantum dots (QDs) instead of organic molecules as light-emitters in electroluminescent devices, lasing materials, or light-absorbers in photovoltaics. A unique potential advantage of QDs over organic dyes in QD-sensitized solar cell is the production of multiexcitons by charge carrier multiplication (CM) that is not possible in organic molecules. Efficient generation of multiexcitons by one absorbed photon in QDs could improve performance of QD-sensitized cells beyond the efficiencies achievable with dye-sensitized solar cells. However, the successful application of CM in QD-based cells requires ultrafast charge separation in order to minimize the losses due to Auger recombination. Although the charge transfer between semiconductor QDs and the molecular electron or hole acceptors adsorbed on the surface has been previously observed on a subpicosecond and picosecond time scale, the possibility of charge extraction from QDs which contain multiexcitons has not been demonstrated yet. Recently, the energy transfer in QD conjugated with phthalocyanines was studied upon one- and two-photon excitation. The authors show that the energy transfer occurs mainly from the lowest one-exciton state and only to a minor extent from the multiexcited states.