Variations in the Quantum Efficiency of Multiple Exciton Generation for a Series of Chemically Treated PbSe Nanocrystal Films

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• 作者：Matthew C. Beard ; Aaron G. Midgett ; Matt Law ; Octavi E. Semonin ; Randy J. Ellingson ; Arthur J. Nozik
• 刊名：Nano Letters
• 出版年：2009
• 出版时间：February 11, 2009
• 年：2009
• 卷：9
• 期：2
• 页码：836-845
• 全文大小：543K
• 年卷期：v.9,no.2(February 11, 2009)
• ISSN：1530-6992

文摘

We study multiple exciton generation (MEG) in two series of chemically treated PbSe nanocrystal (NC) films. We find that the average number of excitons produced per absorbed photon varies between 1.0 and 2.4 (±0.2) at a photon energy of 4E_g for films consisting of 3.7 nm NCs and between 1.1 and 1.6 (±0.1) at hν 5E_g for films consisting of 7.4 nm NCs. The variations in MEG depend upon the chemical treatment used to electronically couple the NCs in each film. The single and multiexciton lifetimes also change with the chemical treatment: biexciton lifetimes increase with stronger inter-NC electronic coupling and exciton delocalization, while single exciton lifetimes decrease after most treatments relative to the same NCs in solution. Single exciton lifetimes are particularly affected by surface treatments that dope the films n-type, which we tentatively attribute to an Auger recombination process between a single exciton and an electron produced by ionization of the dopant donor. These results imply that a better understanding of the effects of surface chemistry on film doping, NC carrier dynamics, and inter-NC interactions is necessary to build solar energy conversion devices that can harvest the multiple carriers produced by MEG. Our results show that the MEG efficiency is very sensitive to the condition of the NC surface and suggest that the wide range of MEG efficiencies reported in the recent literature may be a result of uncontrolled differences in NC surface chemistry.