1
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Llusar J, du Fossé I, Hens Z, Houtepen A, Infante I. Surface Reconstructions in II-VI Quantum Dots. ACS NANO 2024; 18:1563-1572. [PMID: 38169474 PMCID: PMC10795476 DOI: 10.1021/acsnano.3c09265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 12/20/2023] [Accepted: 12/22/2023] [Indexed: 01/05/2024]
Abstract
Although density functional theory (DFT) calculations have been crucial in our understanding of colloidal quantum dots (QDs), simulations are commonly carried out on QD models that are significantly smaller than those generally found experimentally. While smaller models allow for efficient study of local surface configurations, increasing the size of the QD model will increase the size or number of facets, which can in turn influence the energetics and characteristics of trap formation. Moreover, core-shell structures can only be studied with QD models that are large enough to accommodate the different layers with the correct thickness. Here, we use DFT calculations to study the electronic properties of QDs as a function of size, up to a diameter of ∼4.5 nm. We show that increasing the size of QD models traditionally used in DFT studies leads to a disappearance of the band gap and localization of the HOMO and LUMO levels on facet-specific regions of the QD surface. We attribute this to the lateral coupling of surface orbitals and the formation of surface bands. The introduction of surface vacancies and their a posteriori refilling with Z-type ligands leads to surface reconstructions that widen the band gap and delocalize both the HOMO and LUMO. These results show that the surface geometry of the facets plays a pivotal role in defining the electronic properties of the QD.
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Affiliation(s)
- Jordi Llusar
- BCMaterials,
Basque Center for Materials, Applications, and Nanostructures, UPV/EHU Science Park, Leioa 48940, Spain
| | - Indy du Fossé
- Department
of Chemical Engineering, Optoelectronic Materials, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The
Netherlands
| | - Zeger Hens
- Physics
and Chemistry of Nanostructures, Department of Chemistry, and Center
of Nano and Biophotonics, Ghent University, B-9000 Gent, Belgium
| | - Arjan Houtepen
- Department
of Chemical Engineering, Optoelectronic Materials, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The
Netherlands
| | - Ivan Infante
- BCMaterials,
Basque Center for Materials, Applications, and Nanostructures, UPV/EHU Science Park, Leioa 48940, Spain
- Ikerbasque
Basque Foundation for Science, Bilbao 48009, Spain
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2
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Self-assembly of semiconductor quantum dots with porphyrin chromophores: Energy relaxation processes and biomedical applications. J Mol Struct 2021. [DOI: 10.1016/j.molstruc.2021.131239] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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3
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Chen W, Lu X, Fan F, Du J. Optical-Gain-based Sensing Using Inorganic-Ligand-Passivated Colloidal Quantum Dots. NANO LETTERS 2021; 21:7732-7739. [PMID: 34515491 DOI: 10.1021/acs.nanolett.1c02547] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Thanks to their extremely large surface-to-volume ratio, colloidal quantum dots are potential high-performance sensing materials. However, previous sensing works using their spontaneous emission suffer from low sensitivities. The absence of an amplification process and the presence of the steric hindrance of long-chain organic ligands are two possible causations. Herein we propose that these two issues can be circumvented by using the amplified spontaneous emission of colloidal quantum dots capped by short-chain inorganic ligands. To exemplify this concept, we performed humidity sensing and observed a ∼31 times enhancement in sensitivity. Meanwhile, we found that the amplified spontaneous emission threshold power was reduced by 34% in a high humidity environment. On the basis of our transient absorption measurements, we attribute these observations to the mitigation of ultrafast subpicosecond trapping processes, which are enabled by the absorption of water molecules.
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Affiliation(s)
- Weiguo Chen
- Hefei National Laboratory for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China
- CAS Key Laboratory of Microscale Magnetic Resonance, University of Science and Technology of China, Hefei 230026, China
- CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
| | - Xuechun Lu
- Hefei National Laboratory for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China
- CAS Key Laboratory of Microscale Magnetic Resonance, University of Science and Technology of China, Hefei 230026, China
- CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
| | - Fengjia Fan
- Hefei National Laboratory for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China
- CAS Key Laboratory of Microscale Magnetic Resonance, University of Science and Technology of China, Hefei 230026, China
- CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
| | - Jiangfeng Du
- Hefei National Laboratory for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China
- CAS Key Laboratory of Microscale Magnetic Resonance, University of Science and Technology of China, Hefei 230026, China
- CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
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4
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Kumari L, Kar AK. Excitonic enhancement of colour emission and Förster resonance energy transfer in chemically synthesized Mn-doped ZnS nanomaterials. Dalton Trans 2020; 49:16979-16992. [PMID: 33191422 DOI: 10.1039/d0dt03387a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
This study has been carried out to understand the mechanism of charge carrier dynamics and the existence of exciton-dopant energy transfer within Mn-doped ZnS nanomaterials. Improvement in the energy transfer efficiency and electroluminescence properties of these nanomaterials has been investigated for using them as an emissive layer of LEDs. A chemical co-precipitation method has been used to synthesize ZnS with varying Mn contents to achieve enhanced luminescence properties demonstrating the effect of Mn doping on excitonic luminescence intensity. X-ray powder diffraction analysis reveals the prepared materials to be cubic crystallites with size varying between 2 nm and 4 nm. Agglomerated clusters and a nanogranular morphology have been observed in SEM analysis. The UV-Vis spectra reveal that the band gaps slightly decrease with an increase in the Mn content in ZnS samples. The photoluminescence spectra show that upon Mn incorporation, the intensity of blue emission at 420 nm increases due to the surface states in ZnS; an orange emission at 588 nm is also observed due to a transition within Mn2+. The energy transfer efficiency of 3 to 6% was measured theoretically by using the FRET (Förster resonance energy transfer) model. Mn-doped ZnS shows high photoluminescence quantum yield (QY) in comparison with ZnS, where 0.04 mol% Mn-doped ZnS achieved the highest QY of about 28.94%. The CIE chromaticity coordinates accordingly shift toward white from the blue region upon Mn substitution. A kinetic model has been used to determine the energy transfer efficiency, which affects the luminescence properties of ZnS. The FRET model has suitably unraveled the Förster radius and interatomic distance, which make the energy transfer possible in these materials. We have found 0.04 mol% Mn-doped ZnS with an enhanced energy transfer efficiency. The maximum external quantum efficiency of about 0.643% can be achieved at 2.9 volts of operating voltage for this nanomaterial. These highly luminescent materials possess the characteristics of an emissive layer to be used for light-emitting applications.
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Affiliation(s)
- Lakshmi Kumari
- Micro and Nano Science Laboratory, Department of Physics, Indian Institute of Technology (Indian School of Mines), Dhanbad - 826004, India.
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5
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Ronchi A, Capitani C, Pinchetti V, Gariano G, Zaffalon ML, Meinardi F, Brovelli S, Monguzzi A. High Photon Upconversion Efficiency with Hybrid Triplet Sensitizers by Ultrafast Hole-Routing in Electronic-Doped Nanocrystals. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e2002953. [PMID: 32761660 DOI: 10.1002/adma.202002953] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2020] [Revised: 06/18/2020] [Indexed: 06/11/2023]
Abstract
Low-power photon upconversion (UC) based on sensitized triplet-triplet annihilation (sTTA) is considered as the most promising upward wavelength-shifting technique to enhance the light-harvesting capability of solar devices. Colloidal nanocrystals (NCs) with conjugated organic ligands have been recently proposed to extend the limited light-harvesting capability of molecular absorbers. Key to their functioning is efficient energy transfer (ET) from the NC to the triplet state of the ligands that sensitize free annihilator moieties responsible for the upconverted luminescence. The ET efficiency is typically limited by parasitic processes, above all nonradiative hole-transfer to the ligand highest occupied molecular orbital (HOMO). Here, a new exciton-manipulation approach is demonstrated that enables loss-free ET by electronically doping CdSe NCs with gold impurities that introduce a hole-accepting intragap state above the HOMO energy of 9-anthracene acid ligands. Upon photoexcitation, the NC photoholes are rapidly routed to the Au-level, producing a long-lived bound exciton in perfect resonance with the ligand triplet. This hinders hole-transfer leading to ≈100% efficient ET that translates into an upconversion quantum yield as high as ≈12% (≈24% in the normalized definition), which is the highest performance for NC-based upconverters based on sTTA to date and approaches the record efficiency of optimized organic systems.
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Affiliation(s)
- Alessandra Ronchi
- Dipartimento di Scienza dei Materiali, Università degli Studi Milano Bicocca, via R. Cozzi 55, Milan, 20125, Italy
| | - Chiara Capitani
- Dipartimento di Scienza dei Materiali, Università degli Studi Milano Bicocca, via R. Cozzi 55, Milan, 20125, Italy
- Glass to Power SpA, Via Fortunato Zeni 8, Rovereto, I-38068, Italy
| | - Valerio Pinchetti
- Dipartimento di Scienza dei Materiali, Università degli Studi Milano Bicocca, via R. Cozzi 55, Milan, 20125, Italy
| | | | - Matteo L Zaffalon
- Dipartimento di Scienza dei Materiali, Università degli Studi Milano Bicocca, via R. Cozzi 55, Milan, 20125, Italy
| | - Francesco Meinardi
- Dipartimento di Scienza dei Materiali, Università degli Studi Milano Bicocca, via R. Cozzi 55, Milan, 20125, Italy
- Glass to Power SpA, Via Fortunato Zeni 8, Rovereto, I-38068, Italy
| | - Sergio Brovelli
- Dipartimento di Scienza dei Materiali, Università degli Studi Milano Bicocca, via R. Cozzi 55, Milan, 20125, Italy
- Glass to Power SpA, Via Fortunato Zeni 8, Rovereto, I-38068, Italy
| | - Angelo Monguzzi
- Dipartimento di Scienza dei Materiali, Università degli Studi Milano Bicocca, via R. Cozzi 55, Milan, 20125, Italy
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6
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Califano M. Charge Dynamics in Quantum-Dot-Acceptor Complexes in the Presence of Confining and Deconfining Ligands. J Phys Chem Lett 2020; 11:280-285. [PMID: 31840507 DOI: 10.1021/acs.jpclett.9b03073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Nanocrystal surface functionalization is becoming widespread for applications exploiting fast charge extraction or ultrasensitive redox reactions. A variety of molecular acceptors are being linked to the dot surface via a new generation of organic ligands, ranging from neutral linkers to charge delocalizers. Understanding how core states interact with these molecular orbitals, localized outside the dot, is paramount for optimizing the design of efficient nanocrystal-acceptor conjugates. Here we look at two examples of this interaction: charge transfer to a molecular acceptor linked through either an exciton-delocalizing ligand or a more conventional localizing molecule. We find that such transfer can be described in terms of an Auger-mediated process whose rates can be tuned within a window of a few orders of magnitude (for the same dot-ligand-acceptor conjugate) by a suitable choice of the dispersion solvent and nanocrystal's dielectric environment. This result provides clear guidelines for charge extraction rate engineering in nanocrystal-based devices.
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Affiliation(s)
- Marco Califano
- Pollard Institute, School of Electronic and Electrical Engineering, & Bragg Centre for Materials Research , University of Leeds , Leeds LS2 9JT , United Kingdom
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7
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Yin J, Cogan NMB, Burke R, Hou Z, Sowers KL, Krauss TD. Size dependence of photocatalytic hydrogen generation for CdTe quantum dots. J Chem Phys 2019; 151:174707. [DOI: 10.1063/1.5125000] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Affiliation(s)
- Jiajia Yin
- Institute of Optics and Electronics Chinese Academy Science, Chengdu, Sichuan 610209, China
| | - Nicole M. B. Cogan
- Department of Chemistry, University of Rochester, Rochester, New York 14627, USA
| | - Rebeckah Burke
- Department of Chemistry, University of Rochester, Rochester, New York 14627, USA
| | - Zhentao Hou
- Department of Chemistry, University of Rochester, Rochester, New York 14627, USA
| | - Kelly L. Sowers
- Department of Chemistry, University of Rochester, Rochester, New York 14627, USA
| | - Todd D. Krauss
- Department of Chemistry, University of Rochester, Rochester, New York 14627, USA
- The Institute of Optics, University of Rochester, Rochester, New York 14627, USA
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8
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Califano M, Skibinsky-Gitlin ES, Gómez-Campos FM, Rodríguez-Bolívar S. New strategies for colloidal-quantum-dot-based intermediate-band solar cells. J Chem Phys 2019; 151:154101. [DOI: 10.1063/1.5121360] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Affiliation(s)
- Marco Califano
- Pollard Institute, School of Electronic and Electrical Engineering, and Bragg Centre for Materials Research, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Erik S. Skibinsky-Gitlin
- Departamento de Electrónica y Tecnología de Computadores, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
| | - Francisco M. Gómez-Campos
- Departamento de Electrónica y Tecnología de Computadores, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
- CITIC-UGR, C/ Periodista Rafael Gómez Montero, n 2, Granada, Spain
| | - Salvador Rodríguez-Bolívar
- Departamento de Electrónica y Tecnología de Computadores, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
- CITIC-UGR, C/ Periodista Rafael Gómez Montero, n 2, Granada, Spain
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9
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Sabatini RP, Bappi G, Bicanic KT, Fan F, Hoogland S, Saidaminov MI, Sagar LK, Voznyy O, Sargent EH. Temperature-Induced Self-Compensating Defect Traps and Gain Thresholds in Colloidal Quantum Dots. ACS NANO 2019; 13:8970-8976. [PMID: 31310518 DOI: 10.1021/acsnano.9b02834] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Continuous-wave (CW) lasing was recently achieved in colloidal quantum dots (CQDs) by lowering the threshold through the introduction of biaxial strain. However, the CW laser threshold is still much higher than the femtosecond threshold. This must be addressed before electrically injected lasing can be realized. Here we investigate the relationship between threshold and temperature and find a subpicosecond recombination process that proceeds very efficiently at temperatures reached during CW excitation. We combine density functional theory and molecular dynamics simulations to explore potential candidates for such a process, and find that crystal defects having thermally vibrating energy levels can become electronic traps-i.e., they can protrude into the bandgap-when they are sufficiently distorted at higher temperatures. We find that biaxially strained CQDs, which have a lower femtosecond laser threshold than traditional CQDs, result in less heat for a given transparency/gain level and thus undergo this trapping to a lower extent. We also propose methods to tailor CQDs to avoid self-compensating defect traps.
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Affiliation(s)
- Randy P Sabatini
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
| | - Golam Bappi
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
| | - Kristopher T Bicanic
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
| | - Fengjia Fan
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
| | - Sjoerd Hoogland
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
| | - Makhsud I Saidaminov
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
| | - Laxmi K Sagar
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
| | - Oleksandr Voznyy
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
| | - Edward H Sargent
- Department of Electrical and Computer Engineering , University of Toronto , 10 King's College Road , Toronto , Ontario M5S 3G4 , Canada
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10
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Ronchi A, Brazzo P, Sassi M, Beverina L, Pedrini J, Meinardi F, Monguzzi A. Triplet–triplet annihilation based photon up-conversion in hybrid molecule–semiconductor nanocrystal systems. Phys Chem Chem Phys 2019; 21:12353-12359. [DOI: 10.1039/c9cp01692a] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Photon up-conversion based on triplet–triplet annihilation (TTA) in a hybrid system exploits the annihilation of optically dark triplets of an organic emitter, sensitized by a semiconductor nanocrystal, to produce high-energy singlets that generate high energy emission.
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Affiliation(s)
- Alessandra Ronchi
- Dipartimento di Scienza dei Materiali
- Università degli Studi Milano Bicocca
- 20125 Milan
- Italy
| | - Paolo Brazzo
- Dipartimento di Scienza dei Materiali
- Università degli Studi Milano Bicocca
- 20125 Milan
- Italy
| | - Mauro Sassi
- Dipartimento di Scienza dei Materiali
- Università degli Studi Milano Bicocca
- 20125 Milan
- Italy
| | - Luca Beverina
- Dipartimento di Scienza dei Materiali
- Università degli Studi Milano Bicocca
- 20125 Milan
- Italy
| | - Jacopo Pedrini
- Dipartimento di Scienza dei Materiali
- Università degli Studi Milano Bicocca
- 20125 Milan
- Italy
| | - Francesco Meinardi
- Dipartimento di Scienza dei Materiali
- Università degli Studi Milano Bicocca
- 20125 Milan
- Italy
| | - Angelo Monguzzi
- Dipartimento di Scienza dei Materiali
- Università degli Studi Milano Bicocca
- 20125 Milan
- Italy
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11
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Kirkwood N, Monchen JOV, Crisp RW, Grimaldi G, Bergstein HAC, du Fossé I, van der Stam W, Infante I, Houtepen AJ. Finding and Fixing Traps in II-VI and III-V Colloidal Quantum Dots: The Importance of Z-Type Ligand Passivation. J Am Chem Soc 2018. [PMID: 30375226 DOI: 10.1021/ja-2018-07783h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/17/2023]
Abstract
Energy levels in the band gap arising from surface states can dominate the optical and electronic properties of semiconductor nanocrystal quantum dots (QDs). Recent theoretical work has predicted that such trap states in II-VI and III-V QDs arise only from two-coordinated anions on the QD surface, offering the hypothesis that Lewis acid (Z-type) ligands should be able to completely passivate these anionic trap states. In this work, we provide experimental support for this hypothesis by demonstrating that Z-type ligation is the primary cause of PL QY increase when passivating undercoordinated CdTe QDs with various metal salts. Optimized treatments with InCl3 or CdCl2 afford a near-unity (>90%) photoluminescence quantum yield (PL QY), whereas other metal halogen or carboxylate salts provide a smaller increase in PL QY as a result of weaker binding or steric repulsion. The addition of non-Lewis acidic ligands (amines, alkylammonium chlorides) systematically gives a much smaller but non-negligible increase in the PL QY. We discuss possible reasons for this result, which points toward a more complex and dynamic QD surface. Finally we show that Z-type metal halide ligand treatments also lead to a strong increase in the PL QY of CdSe, CdS, and InP QDs and can increase the efficiency of sintered CdTe solar cells. These results show that surface anions are the dominant source of trap states in II-VI and III-V QDs and that passivation with Lewis acidic Z-type ligands is a general strategy to fix those traps. Our work also provides a method to tune the PL QY of QD samples from nearly zero up to near-unity values, without the need to grow epitaxial shells.
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Affiliation(s)
- Nicholas Kirkwood
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Julius O V Monchen
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Ryan W Crisp
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Gianluca Grimaldi
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Huub A C Bergstein
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Indy du Fossé
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Ward van der Stam
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Ivan Infante
- Department of Theoretical Chemistry, Faculty of Science , Vrije Universiteit Amsterdam , de Boelelaan 1083 , 1081 HV Amsterdam , The Netherlands
| | - Arjan J Houtepen
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
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12
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Kirkwood N, Monchen JOV, Crisp RW, Grimaldi G, Bergstein HAC, du Fossé I, van der Stam W, Infante I, Houtepen AJ. Finding and Fixing Traps in II-VI and III-V Colloidal Quantum Dots: The Importance of Z-Type Ligand Passivation. J Am Chem Soc 2018; 140:15712-15723. [PMID: 30375226 PMCID: PMC6257620 DOI: 10.1021/jacs.8b07783] [Citation(s) in RCA: 93] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
![]()
Energy levels in
the band gap arising from surface states can dominate
the optical and electronic properties of semiconductor nanocrystal
quantum dots (QDs). Recent theoretical work has predicted that such
trap states in II–VI and III–V QDs arise only from two-coordinated
anions on the QD surface, offering the hypothesis that Lewis acid
(Z-type) ligands should be able to completely passivate these anionic
trap states. In this work, we provide experimental support for this
hypothesis by demonstrating that Z-type ligation is the primary cause
of PL QY increase when passivating undercoordinated CdTe QDs with
various metal salts. Optimized treatments with InCl3 or
CdCl2 afford a near-unity (>90%) photoluminescence quantum
yield (PL QY), whereas other metal halogen or carboxylate salts provide
a smaller increase in PL QY as a result of weaker binding or steric
repulsion. The addition of non-Lewis acidic ligands (amines, alkylammonium
chlorides) systematically gives a much smaller but non-negligible
increase in the PL QY. We discuss possible reasons for this result,
which points toward a more complex and dynamic QD surface. Finally
we show that Z-type metal halide ligand treatments also lead to a
strong increase in the PL QY of CdSe, CdS, and InP QDs and can increase
the efficiency of sintered CdTe solar cells. These results show that
surface anions are the dominant source of trap states in II–VI
and III–V QDs and that passivation with Lewis acidic Z-type
ligands is a general strategy to fix those traps. Our work also provides
a method to tune the PL QY of QD samples from nearly zero up to near-unity
values, without the need to grow epitaxial shells.
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Affiliation(s)
- Nicholas Kirkwood
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Julius O V Monchen
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Ryan W Crisp
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Gianluca Grimaldi
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Huub A C Bergstein
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Indy du Fossé
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Ward van der Stam
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
| | - Ivan Infante
- Department of Theoretical Chemistry, Faculty of Science , Vrije Universiteit Amsterdam , de Boelelaan 1083 , 1081 HV Amsterdam , The Netherlands
| | - Arjan J Houtepen
- Optoelectronic Materials Section, Faculty of Applied Sciences , Delft University of Technology , Van der Maasweg 9 , 2629 HZ Delft , The Netherlands
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13
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Wang HI, Infante I, Brinck ST, Cánovas E, Bonn M. Efficient Hot Electron Transfer in Quantum Dot-Sensitized Mesoporous Oxides at Room Temperature. NANO LETTERS 2018; 18:5111-5115. [PMID: 30039708 DOI: 10.1021/acs.nanolett.8b01981] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Hot carrier cooling processes represent one of the major efficiency losses in solar energy conversion. Losses associated with cooling can in principle be circumvented if hot carrier extraction toward selective contacts is faster than hot carrier cooling in the absorber (in so-called hot carrier solar cells). Previous work has demonstrated the possibility of hot electron extraction in quantum dot (QD)-sensitized systems, in particular, at low temperatures. Here we demonstrate a room-temperature hot electron transfer (HET) with up to unity quantum efficiency in strongly coupled PbS quantum dot-sensitized mesoporous SnO2. We show that the HET efficiency is determined by a kinetic competition between HET rate ( KHET) and the thermalization rate ( KTH) in the dots. KHET can be modulated by changing the excitation photon energy; KTH can be modified through the lattice temperature. DFT calculations demonstrate that the HET rate and efficiency are primarily determined by the density of the state (DoS) of QD and oxide. Our results provide not only a new way to achieve efficient hot electron transfer at room temperature but also new insights on the mechanism of HET and the means to control it.
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Affiliation(s)
- Hai I Wang
- Max Planck Institute for Polymer Research , Ackermannweg 10 , Mainz 55128 , Germany
- Graduate School of Material Science in Mainz , University of Mainz , Staudingerweg 9 , Mainz 55128 , Germany
| | - Ivan Infante
- Department of Theoretical Chemistry, Faculty of Sciences , Vrije Universiteit Amsterdam , De Boelelaan 1083 , HV Amsterdam 1081 , The Netherlands
| | - Stephanie Ten Brinck
- Department of Theoretical Chemistry, Faculty of Sciences , Vrije Universiteit Amsterdam , De Boelelaan 1083 , HV Amsterdam 1081 , The Netherlands
| | - Enrique Cánovas
- Max Planck Institute for Polymer Research , Ackermannweg 10 , Mainz 55128 , Germany
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia) , Faraday 9 , Madrid 28049 , Spain
| | - Mischa Bonn
- Max Planck Institute for Polymer Research , Ackermannweg 10 , Mainz 55128 , Germany
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14
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Giansante C, Infante I. Surface Traps in Colloidal Quantum Dots: A Combined Experimental and Theoretical Perspective. J Phys Chem Lett 2017; 8:5209-5215. [PMID: 28972763 PMCID: PMC5651579 DOI: 10.1021/acs.jpclett.7b02193] [Citation(s) in RCA: 133] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2017] [Accepted: 10/03/2017] [Indexed: 05/19/2023]
Abstract
Surface traps are ubiquitous to nanoscopic semiconductor materials. Understanding their atomistic origin and manipulating them chemically have capital importance to design defect-free colloidal quantum dots and make a leap forward in the development of efficient optoelectronic devices. Recent advances in computing power established computational chemistry as a powerful tool to describe accurately complex chemical species and nowadays it became conceivable to model colloidal quantum dots with realistic sizes and shapes. In this Perspective, we combine the knowledge gathered in recent experimental findings with the computation of quantum dot electronic structures. We analyze three different systems: namely, CdSe, PbS, and CsPbI3 as benchmark semiconductor nanocrystals showing how different types of trap states can form at their surface. In addition, we suggest experimental healing of such traps according to their chemical origin and nanocrystal composition.
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Affiliation(s)
- Carlo Giansante
- Dipartimento
di Matematica e Fisica ‘E. De Giorgi’, Università del Salento, via per Arnesano, 73100 Lecce, Italy
- NANOTEC−CNR
Istituto di Nanotecnologia, via per
Arnesano, 73100 Lecce, Italy
| | - Ivan Infante
- Department
of Theoretical Chemistry, Faculty of Science, Vrije Universiteit Amsterdam, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
- E-mail:
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15
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Olshansky JH, Balan AD, Ding TX, Fu X, Lee YV, Alivisatos AP. Temperature-Dependent Hole Transfer from Photoexcited Quantum Dots to Molecular Species: Evidence for Trap-Mediated Transfer. ACS NANO 2017; 11:8346-8355. [PMID: 28759718 DOI: 10.1021/acsnano.7b03580] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The effect of temperature on the rate of hole transfer from photoexcited quantum dots (QDs) is investigated by measuring the driving force dependence of the charge transfer rate for different sized QDs across a range of temperatures from 78 to 300 K. Spherical CdSe/CdS core/shell QDs were used with a series of ferrocene-derived molecular hole acceptors with an 800 meV range in electrochemical potential. Time-resolved photoluminescence measurements and photoluminescence quantum yield measurements in an integrating sphere were both performed from 78 to 300 K to obtain temperature-dependent rates for a series of driving forces as dictated by the nature of the molecular acceptor. For both QD sizes studied and all ligands, the Arrhenius plot of hole transfer exhibited an activated (linear) regime at higher temperatures and a temperature-independent regime at low temperatures. The extracted activation energies in the high-temperature regime were consistent across all ligands for a given QD size. This observation is not consistent with direct charge transfer from the QD valence band to the ferrocene acceptor. Instead, a model in which charge transfer is mediated by a shallow and reversible trap more accurately fits the experimental results. Implications for this observed trap-mediated transfer are discussed including as a strategy to more efficiently extract charge from QDs.
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Affiliation(s)
- Jacob H Olshansky
- Material Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
- Kavli Energy NanoScience Institute , Berkeley, California 94720, United States
| | - Arunima D Balan
- Material Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
- Kavli Energy NanoScience Institute , Berkeley, California 94720, United States
| | - Tina X Ding
- Material Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
- Kavli Energy NanoScience Institute , Berkeley, California 94720, United States
| | | | | | - A Paul Alivisatos
- Material Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States
- Kavli Energy NanoScience Institute , Berkeley, California 94720, United States
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16
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Kotin PA, Bubenov SS, Mordvinova NE, Dorofeev SG. AgCl-doped CdSe quantum dots with near-IR photoluminescence. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2017; 8:1156-1166. [PMID: 28685116 PMCID: PMC5480357 DOI: 10.3762/bjnano.8.117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 05/08/2017] [Indexed: 06/07/2023]
Abstract
We report the synthesis of colloidal CdSe quantum dots doped with a novel Ag precursor: AgCl. The addition of AgCl causes dramatic changes in the morphology of synthesized nanocrystals from spherical nanoparticles to tetrapods and finally to large ellipsoidal nanoparticles. Ellipsoidal nanoparticles possess an intensive near-IR photoluminescence ranging up to 0.9 eV (ca. 1400 nm). In this article, we explain the reasons for the formation of the ellipsoidal nanoparticles as well as the peculiarities of the process. The structure, Ag content, and optical properties of quantum dots are also investigated. The optimal conditions for maximizing both the reaction yield and IR photoluminescence quantum yield are found.
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Affiliation(s)
- Pavel Aleksandrovich Kotin
- Department of Chemistry, Lomonosov Moscow State University, 1 building 3 Leninskie Gory, Moscow 119991, Russia
| | - Sergey Sergeevich Bubenov
- Department of Chemistry, Lomonosov Moscow State University, 1 building 3 Leninskie Gory, Moscow 119991, Russia
| | - Natalia Evgenievna Mordvinova
- Department of Chemistry, Lomonosov Moscow State University, 1 building 3 Leninskie Gory, Moscow 119991, Russia
- Laboratoire CRISMAT, UMR6508, CNRS-ENSICAEN, 6 boulevard Marechal Juin, Caen 14050, France
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17
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Walsh BR, Saari JI, Krause MM, Nick R, Coe-Sullivan S, Kambhampati P. Surface and interface effects on non-radiative exciton recombination and relaxation dynamics in CdSe/Cd,Zn,S nanocrystals. Chem Phys 2016. [DOI: 10.1016/j.chemphys.2015.11.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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18
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Leontiadou MA, Al-Otaify A, Kershaw SV, Zhovtiuk O, Kalytchuk S, Mott D, Maenosono S, Rogach AL, Binks DJ. Ultrafast Exciton Dynamics in Cd x Hg (1 − x ) Te alloy Quantum Dots. Chem Phys 2016. [DOI: 10.1016/j.chemphys.2016.02.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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19
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Niezgoda JS, Rosenthal SJ. Synthetic Strategies for Semiconductor Nanocrystals Expressing Localized Surface Plasmon Resonance. Chemphyschem 2016; 17:645-53. [DOI: 10.1002/cphc.201500758] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Revised: 10/30/2015] [Indexed: 11/08/2022]
Affiliation(s)
- J. Scott Niezgoda
- Department of Chemistry and Vanderbilt Institute for Nanoscale Science and Engineering; Vanderbilt University; Nashville TN 37235 USA
| | - Sandra J. Rosenthal
- Department of Chemistry and Vanderbilt Institute for Nanoscale Science and Engineering; Vanderbilt University; Nashville TN 37235 USA
- Departments of Interdisciplinary Materials Science, Physics and Astronomy, Chemical and Biomolecular Engineering; Vanderbilt University; Nashville TN 37235 USA
- Materials Science and Technology Division; Oak Ridge National Laboratory; Oak Ridge TN 37831 USA
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20
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Miller JB, Dandu N, Velizhanin KA, Anthony RJ, Kortshagen UR, Kroll DM, Kilina S, Hobbie EK. Enhanced Luminescent Stability through Particle Interactions in Silicon Nanocrystal Aggregates. ACS NANO 2015; 9:9772-9782. [PMID: 26348831 DOI: 10.1021/acsnano.5b02676] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Close-packed assemblies of ligand-passivated colloidal nanocrystals can exhibit enhanced photoluminescent stability, but the origin of this effect is unclear. Here, we use experiment, simulation, and ab initio computation to examine the influence of interparticle interactions on the photoluminescent stability of silicon nanocrystal aggregates. The time-dependent photoluminescence emitted by structures ranging in size from a single quantum dot to agglomerates of more than a thousand is compared with Monte Carlo simulations of noninteracting ensembles using measured single-particle blinking data as input. In contrast to the behavior typically exhibited by the metal chalcogenides, the measured photoluminescent stability shows an enhancement with respect to the noninteracting scenario with increasing aggregate size. We model this behavior using time-dependent density functional theory calculations of energy transfer between neighboring nanocrystals as a function of nanocrystal size, separation, and the presence of charge and/or surface-passivation defects. Our results suggest that rapid exciton transfer from "bright" nanocrystals to surface trap states in nearest-neighbors can efficiently fill such traps and enhance the stability of emission by promoting the radiative recombination of slowly diffusing excited electrons.
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Affiliation(s)
- Joseph B Miller
- North Dakota State University , Fargo, North Dakota 58108, United States
| | - Naveen Dandu
- North Dakota State University , Fargo, North Dakota 58108, United States
| | - Kirill A Velizhanin
- Theoretical Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Rebecca J Anthony
- University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Uwe R Kortshagen
- University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Daniel M Kroll
- North Dakota State University , Fargo, North Dakota 58108, United States
| | - Svetlana Kilina
- North Dakota State University , Fargo, North Dakota 58108, United States
| | - Erik K Hobbie
- North Dakota State University , Fargo, North Dakota 58108, United States
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21
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Smith CT, Leontiadou MA, Page R, O'Brien P, Binks DJ. Ultrafast Charge Dynamics in Trap-Free and Surface-Trapping Colloidal Quantum Dots. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2015; 2:1500088. [PMID: 27980905 PMCID: PMC5115313 DOI: 10.1002/advs.201500088] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 05/22/2015] [Indexed: 05/03/2023]
Abstract
Ultrafast transient absorption spectroscopy is used to study subnanosecond charge dynamics in CdTe colloidal quantum dots. After treatment with chloride ions, these can become free of surface traps that produce nonradiative recombination. A comparison between these dots and the same dots before treatment enables new insights into the effect of surface trapping on ultrafast charge dynamics. The surface traps typically increase the rate of electron cooling by 70% and introduce a recombination pathway that depopulates the conduction band minimum of single excitons on a subnanosecond timescale, regardless of whether the sample is stirred or flowed. It is also shown that surface trapping significantly reduces the peak bleach obtained for a particular pump fluence, which has important implications for the interpretation of transient absorption data, including the estimation of absorption cross-sections and multiple exciton generation yields.
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Affiliation(s)
- Charles T Smith
- School of Physics and Astronomy and Photon Science Institute University of Manchester Manchester M13 9PL UK
| | - Marina A Leontiadou
- School of Physics and Astronomy and Photon Science Institute University of Manchester Manchester M13 9PL UK
| | - Robert Page
- School of Chemistry University of Manchester Manchester M13 9PL UK
| | - Paul O'Brien
- School of Chemistry University of Manchester Manchester M13 9PL UK
| | - David J Binks
- School of Physics and Astronomy and Photon Science Institute University of Manchester Manchester M13 9PL UK
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22
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Meixner AJ, Jäger R, Jäger S, Bräuer A, Scherzinger K, Fulmes J, Krockhaus SZO, Gollmer DA, Kern DP, Fleischer M. Coupling single quantum dots to plasmonic nanocones: optical properties. Faraday Discuss 2015; 184:321-37. [PMID: 26404008 DOI: 10.1039/c5fd00074b] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Coupling a single quantum emitter, such as a fluorescent molecule or a quantum dot (QD), to a plasmonic nanostructure is an important issue in nano-optics and nano-spectroscopy, relevant for a wide range of applications, including tip-enhanced near-field optical microscopy, plasmon enhanced molecular sensing and spectroscopy, and nanophotonic amplifiers or nanolasers, to mention only a few. While the field enhancement of a sharp nanoantenna increasing the excitation rate of a very closely positioned single molecule or QD has been well investigated, the detailed physical mechanisms involved in the emission of a photon from such a system are, by far, less investigated. In one of our ongoing research projects, we try to address these issues by constructing and spectroscopically analysing geometrically simple hybrid heterostructures consisting of sharp gold cones with single quantum dots attached to the very tip apex. An important goal of this work is to tune the longitudinal plasmon resonance by adjusting the cones' geometry to the emission maximum of the core-shell CdSe/ZnS QDs at nominally 650 nm. Luminescence spectra of the bare cones, pure QDs and hybrid systems were distinguished successfully. In the next steps we will further investigate, experimentally and theoretically, the optical properties of the coupled systems in more detail, such as the fluorescence spectra, blinking statistics, and the current results on the fluorescence lifetimes, and compare them with uncoupled QDs to obtain a clearer picture of the radiative and non-radiative processes.
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Affiliation(s)
- Alfred J Meixner
- Center for Light-Matter Interaction, Sensors & Analytics (LISA+), Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany.
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23
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Boehme SC, Azpiroz JM, Aulin YV, Grozema FC, Vanmaekelbergh D, Siebbeles LDA, Infante I, Houtepen AJ. Density of Trap States and Auger-mediated Electron Trapping in CdTe Quantum-Dot Solids. NANO LETTERS 2015; 15:3056-66. [PMID: 25853555 DOI: 10.1021/acs.nanolett.5b00050] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Charge trapping is an ubiquitous process in colloidal quantum-dot solids and a major limitation to the efficiency of quantum dot based devices such as solar cells, LEDs, and thermoelectrics. Although empirical approaches led to a reduction of trapping and thereby efficiency enhancements, the exact chemical nature of the trapping mechanism remains largely unidentified. In this study, we determine the density of trap states in CdTe quantum-dot solids both experimentally, using a combination of electrochemical control of the Fermi level with ultrafast transient absorption and time-resolved photoluminescence spectroscopy, and theoretically, via density functional theory calculations. We find a high density of very efficient electron traps centered ∼0.42 eV above the valence band. Electrochemical filling of these traps increases the electron lifetime and the photoluminescence quantum yield by more than an order of magnitude. The trapping rate constant for holes is an order of magnitude lower that for electrons. These observations can be explained by Auger-mediated electron trapping. From density functional theory calculations we infer that the traps are formed by dicoordinated Te atoms at the quantum dot surface. The combination of our unique experimental determination of the density of trap states with the theoretical modeling of the quantum dot surface allows us to identify the trapping mechanism and chemical reaction at play during charge trapping in these quantum dots.
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Affiliation(s)
- Simon C Boehme
- †TU Delft, Chemical Engineering, Optoelectronic Materials, Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Jon Mikel Azpiroz
- §Kimika Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU) and Donostia International Physics Center (DIPC), P.K. 1072, 20018 Donostia, Euskadi, Spain
| | - Yaroslav V Aulin
- †TU Delft, Chemical Engineering, Optoelectronic Materials, Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Ferdinand C Grozema
- †TU Delft, Chemical Engineering, Optoelectronic Materials, Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Daniël Vanmaekelbergh
- ‡Utrecht University, Debye Institute, Condensed Matter and Interfaces, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands
| | - Laurens D A Siebbeles
- †TU Delft, Chemical Engineering, Optoelectronic Materials, Julianalaan 136, 2628 BL Delft, The Netherlands
| | - Ivan Infante
- §Kimika Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU) and Donostia International Physics Center (DIPC), P.K. 1072, 20018 Donostia, Euskadi, Spain
| | - Arjan J Houtepen
- †TU Delft, Chemical Engineering, Optoelectronic Materials, Julianalaan 136, 2628 BL Delft, The Netherlands
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24
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Zenkevich E, Stupak A, Göhler C, Krasselt C, von Borczyskowski C. Tuning electronic states of a CdSe/ZnS quantum dot by only one functional dye molecule. ACS NANO 2015; 9:2886-2903. [PMID: 25703788 DOI: 10.1021/nn506941c] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Self-assembly of only one functionalized porphyrin dye molecule with one CdSe/ZnS quantum dot (QD) not only modifies the photoluminescence (PL) intensity but also creates a few energetically clearly distinguishable electronic states, opening additional effective relaxation pathways. The related energy modifications are in the range of 10-30 meV and show a pronounced sensitivity to the specific nature of the respective dye. We assign the emerging energies to surface states. Time-resolved PL spectroscopy in combination with spectral deconvolution reveals that surface properties of QDs are a complex interplay of the nature of the dye molecule and the topography of the ligand layer across a temperature range from 77 to 290 K. This includes a kind of phase transition of trioctylphosphine oxide ligands, switching the nature of surface states observed below and above the phase transition temperature. Most importantly, our findings can be closely related to recent calculations of ligand-induced modifications of surface states of QDs. The identification of the optical properties emerged from a combination of spectroscopy on single QDs and QDs in an ensemble.
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Affiliation(s)
- Eduard Zenkevich
- †Department of Information Technologies and Robotics, National Technical University of Belarus, Nezavisimosti Ave., 65, 220013 Minsk, Belarus
| | - Aleksander Stupak
- ‡B.I. Stepanov Institute of Physics, National Academy of Science of Belarus, Nezavisimosti Ave., 70, 220072 Minsk, Belarus
| | - Clemens Göhler
- §Institute of Physics, Technische Universität Chemnitz, Reichenhainerstr. 70, 09107 Chemnitz, Germany
| | - Cornelius Krasselt
- §Institute of Physics, Technische Universität Chemnitz, Reichenhainerstr. 70, 09107 Chemnitz, Germany
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25
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Califano M. Origins of photoluminescence decay kinetics in CdTe colloidal quantum dots. ACS NANO 2015; 9:2960-2967. [PMID: 25716138 DOI: 10.1021/nn5070327] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Recent experimental studies have identified at least two nonradiative components in the fluorescence decay of solutions of CdTe colloidal quantum dots (CQDs). The lifetimes reported by different groups, however, differed by orders of magnitude, raising the question of whether different types of traps were at play in the different samples and experimental conditions and even whether different types of charge carriers were involved in the different trapping processes. Considering that the use of these nanomaterials in biology, optoelectronics, photonics, and photovoltaics is becoming widespread, such a gap in our understanding of carrier dynamics in these systems needs addressing. This is what we do here. Using the state-of-the-art atomistic semiempirical pseudopotential method, we calculate trapping times and nonradiative population decay curves for different CQD sizes considering up to 268 surface traps. We show that the seemingly discrepant experimental results are consistent with the trapping of the hole at unsaturated Te bonds on the dot surface in the presence of different dielectric environments. In particular, the observed increase in the trapping times following air exposure is attributed to the formation of an oxide shell on the dot surface, which increases the dielectric constant of the dot environment. Two types of traps are identified, depending on whether the unsaturated bond is single (type I) or part of a pair of dangling bonds on the same Te atom (type II). The energy landscape relative to transitions to these traps is found to be markedly different in the two cases. As a consequence, the trapping times associated with the different types of traps exhibit a strikingly contrasting sensitivity to variations in the dot environment. Based on these characteristics, we predict the presence of a sub-nanosecond component in all photoluminescence decay curves of CdTe CQDs in the size range considered here if both trap types are present. The absence of such a component is attributed to the suppression of type I traps.
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Affiliation(s)
- Marco Califano
- Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, United Kingdom
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26
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Espinobarro-Velazquez D, Leontiadou MA, Page RC, Califano M, O'Brien P, Binks DJ. Effect of Chloride Passivation on Recombination Dynamics in CdTe Colloidal Quantum Dots. Chemphyschem 2015; 16:1239-44. [PMID: 25630838 PMCID: PMC4501323 DOI: 10.1002/cphc.201402753] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Revised: 12/17/2014] [Indexed: 11/18/2022]
Abstract
Colloidal quantum dots (CQDs) can be used in conjunction with organic charge-transporting layers to produce light-emitting diodes, solar cells and other devices. The efficacy of CQDs in these applications is reduced by the non-radiative recombination associated with surface traps. Here we investigate the effect on the recombination dynamics in CdTe CQDs of the passivation of these surface traps by chloride ions. Radiative recombination dominates in these passivated CQDs, with the radiative lifetime scaling linearly with CQD volume over τr=20–55 ns. Before chloride passivation or after exposure to air, two non-radiative components are also observed in the recombination transients, with sample-dependent lifetimes typically of less than 1 ns and a few ns. The non-radiative dynamics can be explained by Auger-mediated trapping of holes and the lifetimes of this process calculated by an atomistic model are in agreement with experimental values if assuming surface oxidation of the CQDs.
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Affiliation(s)
- Daniel Espinobarro-Velazquez
- School of Physics and Astronomy and Photon Science Institute, University of Manchester, Oxford Road, Manchester M13 9PL (UK)
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27
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Krause MM, Kambhampati P. Linking surface chemistry to optical properties of semiconductor nanocrystals. Phys Chem Chem Phys 2015; 17:18882-94. [DOI: 10.1039/c5cp02173a] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
This perspective gives insight into how the chemistry occurring at the surface of semiconductor nanocrystals is crucial to tailoring their optical properties to a myriad of applications.
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28
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Cadirci M, Masala O, Pickett N, Binks D. Ultrafast charge dynamics in CuInS2 nanocrystal quantum dots. Chem Phys 2014. [DOI: 10.1016/j.chemphys.2014.05.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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29
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Voznyy O, Sargent EH. Atomistic model of fluorescence intermittency of colloidal quantum dots. PHYSICAL REVIEW LETTERS 2014; 112:157401. [PMID: 24785069 DOI: 10.1103/physrevlett.112.157401] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Indexed: 06/03/2023]
Abstract
Optoelectronic applications of colloidal quantum dots demand a high emission efficiency, stability in time, and narrow spectral bandwidth. Electronic trap states interfere with the above properties but understanding of their origin remains lacking, inhibiting the development of robust passivation techniques. Here we show that surface vacancies improve the fluorescence yield compared to vacancy-free surfaces, while dynamic vacancy aggregation can temporarily turn fluorescence off. We find that infilling with foreign cations can stabilize the vacancies, inhibiting intermittency and improving quantum yield, providing an explanation of recent experimental observations.
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Affiliation(s)
- O Voznyy
- Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada
| | - E H Sargent
- Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada
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