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

Abstract

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 surfacemore » 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.« less

Authors:

Carroll, Gerard Michael  ^[1];

• Search DOE PAGES for author "Carroll, Gerard Michael"
• Search DOE PAGES for ORCID "0000-0003-0195-8483"

Limpens, Rens  ^[1];

• Search DOE PAGES for author "Limpens, Rens"
• Search DOE PAGES for ORCID "0000-0002-2417-9389"

Pach, Gregory F.  ^[1];

• Search DOE PAGES for author "Pach, Gregory F."
• Search DOE PAGES for ORCID "0000-0002-5062-735X"

Zhai, Yaxin  ^[1];

• Search DOE PAGES for author "Zhai, Yaxin"
• Search DOE PAGES for ORCID "0000-0001-5862-1764"

Beard, Matthew C.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-2711-1355"

Miller, Elisa M.  ^[1];

• Search DOE PAGES for author "Miller, Elisa M."
• Search DOE PAGES for ORCID "0000-0002-7648-5433"

Neale, Nathan R.  ^[1]

• Search DOE PAGES for author "Neale, Nathan R."
• Search DOE PAGES for ORCID "0000-0001-5654-1664"

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+ Show Author Affiliations

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

Publication Date:

Mon Jan 25 00:00:00 EST 2021

Research Org.:

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

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE National Renewable Energy Laboratory (NREL), Laboratory Directed Research and Development (LDRD) Program

OSTI Identifier:

1769829

Report Number(s):

NREL/JA-5900-78046
Journal ID: ISSN 1932-7447; MainId:31955;UUID:df560b07-da48-40ee-a037-4d7f7fbb4543;MainAdminID:19782

Grant/Contract Number:  

AC36-08GO28308

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. C

Additional Journal Information:

Journal Volume: 125; Journal Issue: 4; Journal ID: ISSN 1932-7447

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

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