Suppressing Auger Recombination in Multiply Excited Colloidal Silicon Nanocrystals with Ligand-Induced Hole Traps

Journal Article · Mon Jan 25 00:00:00 EST 2021 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/acs.jpcc.0c11388· OSTI ID:1769829

Carroll, Gerard Michael ^[1]; Limpens, Rens ^[1]; Pach, Gregory F. ^[1]; Zhai, Yaxin ^[1]; Beard, Matthew C. ^[1]; Miller, Elisa M. ^[1]; Neale, Nathan R. ^[1]

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1. National Renewable Energy Lab. (NREL), Golden, CO (United States)

Nonradiative Auger recombination in multiply excited nanocrystals is a dominant efficiency loss pathway for nanocrystal-containing optoelectronic devices that rely on high-rate emission and absorption operating conditions. Overcoming Auger recombination in these quantum-confined systems is therefore a longstanding challenge to the synthetic nanocrystal as well as device manufacturing communities. Several successful strategies have been realized to reduce Auger recombination, but they rely on complex and time-consuming nanocrystal core/shell synthesis. Alternatively, controlling Auger rates by varying the nanocrystal–ligand-binding chemistry is a promising route to obtain functional tunability, which reduces the barrier to large-scale manufacturing. The covalent surface chemistry and the extremely long-lived photoexcited lifetimes of silicon nanocrystals (Si NCs) make them a unique system among colloidal semiconductor NCs to study the intersection between surface chemistry and photoexcited carrier dynamics. Here, we show that changing the functional group that binds a saturated dodecyl ligand to the surface of nonthermal plasma-synthesized Si NCs from alkyl to thiolate slows Auger recombination rates within multiply excited Si NCs. This reduction in Auger rate persists across Si NC sizes ranging from 3.5 to 8 nm in diameter, but the expected linear dependence of Auger rates on the NC volume is retained for both alkyl and alkylthiolate surface terminations. To understand the origin behind this elongation, we carry out steady-state and time-resolved photoluminescence measurements as well as time-resolved terahertz spectroscopy measurements. These measurements reveal that thiolate groups introduce mid-gap surface states, which, we argue, reduces the photoexcited electron–hole overlap and elongates Auger recombination times. These results highlight how a typically detrimental chemical species—mid-band gap NC surface states—can be beneficial under high-rate absorption/emission conditions.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE National Renewable Energy Laboratory (NREL), Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC36-08GO28308
• OSTI ID: 1769829
• Report Number(s): NREL/JA--5900-78046; MainId:31955; UUID:df560b07-da48-40ee-a037-4d7f7fbb4543; MainAdminID:19782
• Journal Information: Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 4 Vol. 125; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
nanocrystal
silicon
solar
spectroscopy
surface chemistry