Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 56, Issue 52, Pages 16583-16587Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.201710224
Keywords
charge transfer; core-shell; photon upconversion; quantum dots; triplet energy transfer
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Funding
- National Science Foundation [CHE-1351663]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Solar Photochemistry Program [DE-FG02-12ER16347]
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A sub-monolayer CdS shell on PbS quantum dots (QDs) enhances triplet energy transfer (TET) by suppressing competitive charge transfer from QDs to molecules. The CdS shell increases the linear photon upconversion quantum yield (QY) from 3.5% for PbS QDs to 5.0% for PbS/CdS QDs when functionalized with a tetracene acceptor, 5-CT. While transient absorption spectroscopy reveals that both PbS and PbS/CdS QDs show the formation of the 5-CT triplet (with rates of 5.91 +/- 0.60 ns(-1) and 1.03 +/- 0.09 ns(-1) respectively), ultrafast hole transfer occurs only from PbS QDs to 5-CT. Although the CdS shell decreases the TET rate, it enhances TET efficiency from 60.3 +/- 6.1% to 71.8 +/- 6.2% by suppressing hole transfer. Furthermore, the CdS shell prolongs the lifetime of the 5-CT triplet and thus enhances TET from 5-CT to the rubrene emitter, further bolstering the upconverison QY.
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