Quantum dot integrated LEDs using photonic and excitonic color conversion

Demir, Hilmi Volkan; Nizamoğlu, Sedat; Erdem, Talha; Mutlugün, Evren; Gaponik, Nikolai; Eychmüller, Alexander

doi:10.1016/j.nantod.2011.10.006

Cited by 257 publications

(208 citation statements)

References 48 publications

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“…In the last three decades since their fi rst reports appeared, [1][2][3][4][5] colloidal semiconductor quantum dots (QDs) attracted continuously increasing interest in different fi elds, including photonics [6][7][8][9][10] and optoelectronics. [11][12][13][14] Improving the characteristics and quality of QDs regarding synthetic Figure 1 a, a stable interface between the MeOH solution and the underlying NaCl-QD mixture instead of an instantaneous mixing is crucial for a successful crystallization.…”

Section: Introductionmentioning

confidence: 99%

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Adam

Wang

Dubavik

et al. 2015

Adv Funct Materials

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2638www.MaterialsViews.com wileyonlinelibrary.com approaches, [ 15,16 ] effi ciency, [ 17,18 ] extending their spectral range [19][20][21] and environmental friendliness using less toxic materials [22][23][24] sparked industrial applications. Those started with the demonstration of a 40 in. display prototype presented by Samsung [ 25 ] and followed by the foundation of QD Vision, Inc., [ 26 ] whose QDs are now used in the latest series of Sony products. All of the mentioned applications require long-term stability of the QDs under various conditions including high temperatures as well as high intensity illumination. Packaging of the QDs within polymer or inorganic matrices is one way to address these issues, while improving the processability of the QDs at the same time. Commonly used polymers, such as polystyrene and poly(methylmethacrylate) [ 27 ] are relatively less stable and tight in comparison to their inorganic counterparts. Inorganic matrices on the other hand can incorporate the QDs directly from their melt, e.g., using the Czochralski approach, [ 28 ] coated as a thin fi lm directly on their surface [ 29,30 ] or, as recently developed by our group, grown as mixed crystals at ambient temperatures from a saturated salt solution. [ 31 ] Using this method, different types of QDs can be incorporated due to the low thermal stress and, by choosing the proper matrix-QD system, the photoluminescence quantum yields (PL-QYs) are enhanced upon incorporation. [ 32,33 ] Here, a new, fast, and versatile method for the incorporation of colloidal quantum dots (QDs) into ionic matrices enabled by liquid-liquid diffusion is demonstrated. QDs bear a huge potential for numerous applications thanks to their unique chemical and physical properties. However, stability and processability are essential for their successful use in these applications. Incorporating QDs into a tight and chemically robust ionic matrix is one possible approach to increase both their stability and processability. With the proposed liquid-liquid diffusion-assisted crystallization (LLDC), substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process allows to incorporate even the less stable colloids including initially oil-based ligandexchanged QDs into salt matrices. Furthermore, in a modifi ed two-step approach, the seed-mediated LLDC provides the ability to incorporate oilbased QDs directly into ionic matrices without a prior phase transfer. Finally, making use of their processability, a proof-of-concept white light emitting diode with LLDC-based mixed QD-salt fi lms as an excellent color-conversion layer is demonstrated. These fi ndings suggest that the LLDC offers a robust, adaptable, and rapid technique for obtaining high quality QD-salts.

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Section: Introductionmentioning

confidence: 99%

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Adam

Wang

Dubavik

et al. 2015

Adv Funct Materials

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“…Acquiring a narrow emission is very essential for the displays and general lighting applications while high quantum efficiencies in particular in the blue and green colours are needed to address the green gap problem of the epitaxial LEDs. 4,5 As a solution, here we propose and demonstrate incorporation of the nonpolar NCs directly into the LiCl ionic salt without ligand exchange by benefiting from the solubility of LiCl in tetrahydrofuran (THF), which simultaneously disperses these nonpolar NCs. As a proof-of-concept demonstration, we integrated green-emitting CdSe/CdZnSeS/ZnS NCs into the LiCl host ( Fig.…”

Section: Introductionmentioning

confidence: 99%

Stable and efficient colour enrichment powders of nonpolar nanocrystals in LiCl

et al. 2015

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In this work, we propose and develop the inorganic salt encapsulation of semiconductor nanocrystal (NC) dispersion in a nonpolar phase to make a highly stable and highly efficient colour converting powder for colour enrichment in light-emitting diode backlighting. Here the wrapping of the as-synthesized green-emitting CdSe/CdZnSeS/ZnS nanocrystals into a salt matrix without ligand exchange is uniquely enabled by using a LiCl ionic host dissolved in tetrahydrofuran (THF), which simultaneously disperses these nonpolar nanocrystals. We studied the emission stability of the solid films prepared using NCs with and without LiCl encapsulation on blue LEDs driven at high current levels. The encapsulated NC powder in epoxy preserved 95.5% of the initial emission intensity and stabilized at this level while the emission intensity of NCs without salt encapsulation continuously decreased to 34.7% of its initial value after 96 h of operation. In addition, we investigated the effect of ionic salt encapsulation on the quantum efficiency of nonpolar NCs and found the quantum efficiency of the NCs-in-LiCl to be 75.1% while that of the NCs in dispersion was 73.0% and that in a film without LiCl encapsulation was 67.9%. We believe that such ionic salt encapsulated powders of nonpolar NCs presented here will find ubiquitous use for colour enrichment in display backlighting. © The Royal Society of Chemistry 2015

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“…In particular, core/shell heterostructures with type I straddling band offset exhibiting high photoluminescence (PL) quantum yields show much promise in imaging 3 , lighting 4,5 and display [6][7][8][9][10][11] applications. Although type II staggered band offset materials have also been achieved and have been shown to allow efficient photoinduced charge separation [12][13][14][15][16] and improved light amplification 17,18 , to date, the highly luminescent type I core/shell heterostructure is the predominant choice in emerging nanocrystal-based products.…”

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confidence: 99%

Double-heterojunction nanorods

et al. 2014

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As semiconductor heterostructures play critical roles in today's electronics and optoelectronics, the introduction of active heterojunctions can impart new and improved capabilities that will enable the use of solution-processable colloidal quantum dots in future devices. Such heterojunctions incorporated into colloidal nanorods may be especially promising, since the inherent shape anisotropy can provide additional benefits of directionality and accessibility in band structure engineering and assembly. Here we develop doubleheterojunction nanorods where two distinct semiconductor materials with type II staggered band offset are both in contact with one smaller band gap material. The double heterojunction can provide independent control over the electron and hole injection/ extraction processes while maintaining high photoluminescence yields. Light-emitting diodes utilizing double-heterojunction nanorods as the electroluminescent layer are demonstrated with low threshold voltage, narrow bandwidth and high efficiencies.

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Quantum dot integrated LEDs using photonic and excitonic color conversion

Cited by 257 publications

References 48 publications

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Stable and efficient colour enrichment powders of nonpolar nanocrystals in LiCl

Double-heterojunction nanorods

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