Electrochemical Modulation of the Photophysics of Surface-Localized Trap States in Core/Shell/(Shell) Quantum Dot Films

Stam, Ward van der; Grimaldi, Gianluca; Geuchies, Jaco J.; Gudjonsdottir, Solrun; Uffelen, Pieter T van; Overeem, Mandy van; Brynjarsson, Baldur; Kirkwood, Nicholas; Houtepen, Arjan J.

doi:10.1021/acs.chemmater.9b02908

Cited by 41 publications

(65 citation statements)

References 64 publications

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“…The PL intensity drops severely upon electron injection into the conduction band, an expected consequence of increased Auger decay in the n - doped QDs. 17 Figure 2 d shows PL spectra at different potentials.…”

Section: Electrochemical Doping Of Qd Filmsmentioning

confidence: 99%

“…Furthermore, we observe that the absorption bleach increases at the same potential as the PL starts to quench, a good indication of trap-free and electrochemically stable QDs. 17 , 25 …”

Section: Electrochemical Doping Of Qd Filmsmentioning

confidence: 99%

“…When the QDs are sufficiently passivated with stable shells, this results in a stable and homogeneous doping density of the QD film. 17 , 18 …”

Section: Introductionmentioning

confidence: 99%

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Quantitative Electrochemical Control over Optical Gain in Quantum-Dot Solids

et al. 2020

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Solution-processed quantum dot (QD) lasers are one of the holy grails of nanoscience. They are not yet commercialized because the lasing threshold is too high: one needs >1 exciton per QD, which is difficult to achieve because of fast nonradiative Auger recombination. The threshold can, however, be reduced by electronic doping of the QDs, which decreases the absorption near the band-edge, such that the stimulated emission (SE) can easily outcompete absorption. Here, we show that by electrochemically doping films of CdSe/CdS/ZnS QDs, we achieve quantitative control over the gain threshold. We obtain stable and reversible doping of more than two electrons per QD. We quantify the gain threshold and the charge carrier dynamics using ultrafast spectroelectrochemistry and achieve quantitative agreement between experiments and theory, including a vanishingly low gain threshold for doubly doped QDs. Over a range of wavelengths with appreciable gain coefficients, the gain thresholds reach record-low values of ∼1 × 10 –5 excitons per QD. These results demonstrate a high level of control over the gain threshold in doped QD solids, opening a new route for the creation of cheap, solution-processable, low-threshold QD lasers.

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Section: Electrochemical Doping Of Qd Filmsmentioning

confidence: 99%

“…Furthermore, we observe that the absorption bleach increases at the same potential as the PL starts to quench, a good indication of trap-free and electrochemically stable QDs. 17 , 25 …”

Section: Electrochemical Doping Of Qd Filmsmentioning

confidence: 99%

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Quantitative Electrochemical Control over Optical Gain in Quantum-Dot Solids

et al. 2020

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“… 8 Much of the study geared toward improving the performance of these devices has been focused on reducing the density of surface traps via ligand capping 5 , 9 − 11 or core/shell synthesis. 12 , 13 …”

Section: Introductionmentioning

confidence: 99%

Effect of Ligands and Solvents on the Stability of Electron Charged CdSe Colloidal Quantum Dots

et al. 2021

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Many colloidal quantum dot (QD)-based devices involve charging of the QD, either via intentional electronic doping or via electrical charge injection or photoexcitation. Previous research has shown that this charging can give rise to undesirable electrochemical surface reactions, leading to the formation of localized in-gap states. However, little is known about the factors that influence the stability of charged QDs against surface oxidation or reduction. Here, we use density functional theory to investigate the effect of various ligands and solvents on the reduction of surface Cd in negatively charged CdSe QDs. We find that X-type ligands can lead to significant shifts in the energy of the band edges but that the in-gap state related to reduced surface Cd is shifted in the same direction. As a result, shifting the band edges to higher energies does not necessarily lead to less stable electron charging. However, subtle changes in the local electrostatic environment lead to a clear correlation between the position of the in-gap state in the bandgap and the energy gained upon surface reduction. Binding ligands directly to the Cd sites most prone to reduction was found to greatly enhance the stability of the electron charged QDs. We find that ligands bind much more weakly after reduction of the Cd site, leading to a loss in binding energy that makes charge localization no longer energetically favorable. Lastly, we show that increasing the polarity of the solvent also increases the stability of QDs charged with electrons. These results highlight the complexity of surface reduction reactions in QDs and provide valuable strategies for improving the stability of charged QDs.

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“…Since the representative work in 1993 [ 78 ], CdSe CQDs have functioned as a representative system for wet-chemical syntheses. Continuous endeavors enable the manipulation of size, shape, composition, and crystal structure of nanocrystals, giving rise to a large number of nanocrystals including core-only CQDs (e.g., CdSe, ZnS, ZnSe, CdS, and InP), core/shell CQDs (e.g., CdSe/ZnS, CdSe/ZnSe, and CdSe/CdS), and core/shell/shell CQDs (e.g., CdSe/ZnSe/ZnS, CdSe/CdS/ZnS, and CdTe/CdS/ZnS) [ 79 , 80 , 81 , 82 , 83 ]. Currently, the CQD-LED technology is entering the display market.…”

Section: Fundamental Concepts Of Impurity-doped Nanocrystal Ledsmentioning

confidence: 99%

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

Luo

Wang

Qiu³

et al. 2020

Nanomaterials

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In recent years, impurity-doped nanocrystal light-emitting diodes (LEDs) have aroused both academic and industrial interest since they are highly promising to satisfy the increasing demand of display, lighting, and signaling technologies. Compared with undoped counterparts, impurity-doped nanocrystal LEDs have been demonstrated to possess many extraordinary characteristics including enhanced efficiency, increased luminance, reduced voltage, and prolonged stability. In this review, recent state-of-the-art concepts to achieve high-performance impurity-doped nanocrystal LEDs are summarized. Firstly, the fundamental concepts of impurity-doped nanocrystal LEDs are presented. Then, the strategies to enhance the performance of impurity-doped nanocrystal LEDs via both material design and device engineering are introduced. In particular, the emergence of three types of impurity-doped nanocrystal LEDs is comprehensively highlighted, namely impurity-doped colloidal quantum dot LEDs, impurity-doped perovskite LEDs, and impurity-doped colloidal quantum well LEDs. At last, the challenges and the opportunities to further improve the performance of impurity-doped nanocrystal LEDs are described.

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Electrochemical Modulation of the Photophysics of Surface-Localized Trap States in Core/Shell/(Shell) Quantum Dot Films

Cited by 41 publications

References 64 publications

Quantitative Electrochemical Control over Optical Gain in Quantum-Dot Solids

Quantitative Electrochemical Control over Optical Gain in Quantum-Dot Solids

Effect of Ligands and Solvents on the Stability of Electron Charged CdSe Colloidal Quantum Dots

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

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