4 years ago

PbS/CdS core/shell QDs suppress charge transfer and enhance triplet transfer

Tianquan Lian, Zihao Xu, Zhiyuan Huang, Hill Harman, Xin Li, MingLee Tang, Jordan Taylor, Melika Mahboub
Here, we observe that 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 rate constants 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 the hole transfer process. In addition, 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.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201710224

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