Size-tunable infrared (1000–1600 nm) electroluminescence from PbS quantum-dot nanocrystals in a semiconducting polymer

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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mentioning

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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“…They enable bandgap tuning via adjustment of the nanoparticle size 1,2 . This has led to promising optoelectronic devices for lighting 3,4 , solar power conversion [5][6][7][8][9] and photon detection 10,11 .…”

mentioning

confidence: 99%

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

et al. 2014

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Colloidal quantum dots are attractive materials for efficient, low-cost and facile implementation of solution-processed optoelectronic devices. Despite impressive mobilities (1-30 cm 2 V À 1 s À 1 ) reported for new classes of quantum dot solids, it is-surprisingly-the much lower-mobility (10 À 3 -10 À 2 cm 2 V À 1 s À 1 ) solids that have produced the best photovoltaic performance. Here we show that it is not mobility, but instead the average spacing among recombination centres that governs the diffusion length of charges in today's quantum dot solids. In this regime, colloidal quantum dot films do not benefit from further improvements in charge carrier mobility. We develop a device model that accurately predicts the thickness dependence and diffusion length dependence of devices. Direct diffusion length measurements suggest the solid-state ligand exchange procedure as a potential origin of the detrimental recombination centres. We then present a novel avenue for in-solution passivation with tightly bound chlorothiols that retain passivation from solution to film, achieving an 8.5% power conversion efficiency.

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“…0.001% 1.3-1.55 µm PbSe nanocrystals in a monolayer [3] 0.0086% 1-1.6 µm core only PbS blended with a polymer [5] 0.27% ∼ 1.15 µm MEH-PPV-PbS and MEH-PPV-InAs [1] 0.5% 1-1.3 µm core-shell InAs/ZnSe and MEH-PPV polymer blend [4] 1.15% 1.3-1.5 µm PbS nanocrystals and a layer of pentacene [16] The electroluminescence EQE (η EL ) of QD-LEDs is expressed as the ratio of photons extracted into the viewing direction to electrons injected and can be written in simplified form as [17],…”

Section: Eqe Wavelength Qd Usedmentioning

confidence: 99%

“…Other applications for which infrared (IR) active NCs have been proposed to date include: IR luminescence LEDs [3][4][5], IR detectors [6][7][8][9], modulators in the extended telecommunications-wavelength band (1200-1700 nm) [10], photovoltaic [11], IR laser technologies [12,13], thermoelectrics devices [14], and long-wavelength labeling [15].…”

Section: Introductionmentioning

confidence: 99%

Electromagnetic Modeling of Outcoupling Efficiency and Light Emission in Near-Infrared Quantum Dot Light Emitting Devices

Farghal¹,

Wageh²,

Elazm³

2010

PIER B

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Abstract-We report an analytical exciton emission model based on Green function for simulating the radiation characteristics of nearinfrared Quantum Dot-light emitting devices (QD-LEDs). In this model the internally emitted light can be classified into the following modes: Substrate, indium tin oxide (ITO)/organic waveguided, surface plasmonic modes, and external emitted mode. We investigate the influence of the thickness of different layers and the distance between the emitting center and the cathode metal on the emitted power distribution among these modes. In addition, we study the angular radiation profile for the externally emitted radiation and substrate waveguided mode in comparison with Lambertian radiation profile. We show the change of the thickness of the different layers, and the positions of the emitting centers are critical to the optical performance of the device. The optimization of optical performance through device geometry increases the outcoupling efficiency more than five times.

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Size-tunable infrared (1000–1600 nm) electroluminescence from PbS quantum-dot nanocrystals in a semiconducting polymer

Cited by 366 publications

References 12 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

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

Electromagnetic Modeling of Outcoupling Efficiency and Light Emission in Near-Infrared Quantum Dot Light Emitting Devices

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