期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 119, 期 23, 页码 13314-13324出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.5b02880
关键词
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资金
- Air Force Office of Scientific Research under AFOSR [FA9550-12-1-0137]
- National Science Foundation under CAREER [CHE-1151151]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1151151] Funding Source: National Science Foundation
The ligands that passivate the surfaces of semiconductor nanocrystals play an important role in excited state relaxation and charge transfer. Replacement of native long-chain organic ligands with chalcogenides has been shown to improve charge transfer in nanocrystal-based devices. In this report, we examine how surface-capping with S2-, Se2-, and Te2- impacts photoexcited state relaxation in CdSe quantum dots (QDs). We use transient absorption spectroscopy with state-specific pumping to reveal the kinetics of electron and hole cooling, band edge electron relaxation, hole trapping, and trapped hole relaxation, all as a function of surface-capping ligand. We find that carrier cooling is not strongly dependent on the ligand. In contrast, band edge relaxation exhibits strong ligand dependence, with enhanced electron trapping in chalcogenide-capped QDs. This effect is the weakest with the S2- ligand, but is very strong with Se2- and Te2-, such that the average band edge electron lifetimes for QDs capped with those ligands are under 100 ps. We conclude that, unlike the case of S2-, improvements in electron transfer rates with Se2- and Te2- ligands may be overshadowed by the extreme electron lifetime shortening that may lead to low quantum yields of electron transfer.
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