Quantum dots are a unique class of emitters with size-tunable emission wavelengths, saturated emission colors, near-unity luminance efficiency, inherent photo- and thermal- stability and excellent solution processability. Quantum dots have been used as down-converters for back-lighting in liquid-crystal displays to improve color gamut, leading to the booming of quantum-dot televisions in consumer market. In the past few years, efficiency and lifetime of electroluminescence devices based on quantum dots achieved tremendous progress. These encouraging facts foreshadow the commercialization of quantum-dot light-emitting diodes (QLEDs), which promises an unprecedented generation of cost-effective, large-area, energy-saving, wide-color-gamut, ultra-thin and flexible displays. Here we provide a Progress Report, covering interdisciplinary aspects including material chemistry of quantum dots and charge-transporting layers, optimization and mechanism studies of prototype devices and processing techniques to produce large-area and high-resolution red-green-blue pixel arrays. We also identify a few key challenges facing the development of active-matrix QLED displays.

Quantum-Dot Light-Emitting Diodes for Large-Area Displays: Towards the Dawn of Commercialization.

Next-generation displays and lighting technologies require efficient optical sources that combine brightness, color purity, stability, substrate flexibility. Metal halide perovskites have potential use in a wide range of applications, for they possess excellent charge transport, bandgap tunability and, in the most promising recent optical source materials, intense and efficient luminescence. This review links metal halide perovskites' performance as efficient light emitters with their underlying materials electronic and photophysical attributes.

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Perovskites for Next-Generation Optical Sources.

Developing low-cost and high-quality quantum dots (QDs) or nanocrystals (NCs) and their corresponding efficient light-emitting diodes (LEDs) is crucial for the next-generation ultra-high-definition flexible displays. Here, there is a report on a room-temperature triple-ligand surface engineering strategy to play the synergistic role of short ligands of tetraoctylammonium bromide (TOAB), didodecyldimethylammonium bromide (DDAB), and octanoic acid (OTAc) toward "ideal" perovskite QDs with a high photoluminescence quantum yield (PLQY) of >90%, unity radiative decay in its intrinsic channel, stable ink characteristics, and effective charge injection and transportation in QD films, resulting in the highly efficient QD-based LEDs (QLEDs). Furthermore, the QD films with less nonradiative recombination centers exhibit improved PL properties with a PLQY of 61% through dopant engineering in A-site. The robustness of such properties is demonstrated by the fabrication of green electroluminescent LEDs based on CsPbBr3 QDs with the peak external quantum efficiency (EQE) of 11.6%, and the corresponding peak internal quantum efficiency (IQE) and power efficiency are 52.2% and 44.65 lm W-1 , respectively, which are the most-efficient perovskite QLEDs with colloidal CsPbBr3 QDs as emitters up to now. These results demonstrate that the as-obtained QD inks have a wide range application in future high-definition QD displays and high-quality lightings.

Room-Temperature Triple-Ligand Surface Engineering Synergistically Boosts Ink Stability, Recombination Dynamics, and Charge Injection toward EQE-11.6% Perovskite QLEDs

In recent years, substantial progress has been made in developing perovskite light-emitting diodes with near-infrared, red and green emissions and over 20% external quantum efficiency. However, the development of perovskite light-emitting diodes with blue emission remains a great challenge, which retards further development of full-color displays and white-light illumination based on perovskite emissive materials. Here, firstly, through composition and dimensional engineering, we prepare quasi-two-dimensional perovskite thin films with improved blue emission, taking advantages of reduced trap density and enhanced photoluminescence quantum yield. Secondly, we find a vertically non-uniform distribution of perovskite crystals in the PEDOT:PSS/perovskite hybrid film. Through modulating the position of the recombination zone, we activate the majority of quasi-two-dimensional perovskite crystals, and thus demonstrate the most efficient blue perovskite light-emitting diode to date with emission peak at 480 nm, record luminance of 3780 cd m−2 and record external quantum efficiency of 5.7%. Halide perovskite based light-emitting diodes attracted intensive research interest recently but the efficiency of blue diodes is much lower than the green and red ones. Here Li et al. push up the efficiency of blue diodes through composition engineering and vertical morphology control.

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Modulation of recombination zone position for quasi-two-dimensional blue perovskite light-emitting diodes with efficiency exceeding 5

Next-generation displays require efficient light sources that combine high brightness, color purity, stability, compatibility with flexible substrates, and transparency. Metal halide perovskites are a promising platform for these applications, especially in light of their excellent charge transport and bandgap tunability. Low-dimensional perovskites, which possess perovskite domains spatially confined at the nanoscale, have further extended the degree of tunability and functionality of this materials platform. Herein, the advances in perovskite materials for light-emission applications are reviewed. Connections among materials properties, photophysical and electrooptic spectroscopic properties, and device performance are established. It is discussed how incompletely solved problems in these materials can be tackled, including the need for increased stability, efficient blue emission, and efficient infrared emission. In conclusion, an outlook on the technologies that can be realized using this material platform is presented.

Perovskites for Light Emission.

Quick View Other Sources By Kim, Hyeong Pil; Kim, Jeongmo; Kim, Byung Soon; Kim, Hyo-Min; Kim, Jeonggi; bin Mohd. Yusoff, Abd. Rashid; Jang, Jin; Nazeeruddin, Mohammad Khaja From Advanced Optical Materials (2017), Ahead of Print.

High-Efficiency, Blue, Green, and Near-Infrared Light-Emitting Diodes Based on Triple Cation Perovskite

Zinc-oxide (ZnO) is widely used as an n-type electron transporting layer (ETL) for quantum dot (QD) light-emitting diode (QLED) because various metal doping can be possible and ZnO nanoparticle can be processed at low temperatures. We report here a Li- and Mg-doped ZnO, MLZO, which is used for ETL of highly efficient and long lifetime QLEDs. Co-doping, Mg and Li, in ZnO increases its band gap and electrical resistivity and thus can enhance charge balance in emission layer (EML). It is found also that the O–H concentration at the oxide surface decreases and exciton decay time of QDs on the metal oxide increases by co-doping in ZnO. The inverted green QLEDs with MLZO ETL exhibits the maximum current efficiency (CEmax) of 69.1 cd/A, power efficiency (PEmax) of 73.8 lm/W, and external quantum efficiency (EQEmax) of 18.4%. This is at least two times higher compared with the efficiencies of the QLEDs with Mg-doped ZnO ETL. The optimum Li and Mg concentrations are found to be 10% each. The deep-red, red, light-b...

Li and Mg Co-doped Zinc Oxide Electron Transporting Layer for Highly Efficient Quantum Dot Light-Emitting Diodes

We report highly efficient inverted quantum-dot light emitting diodes (QLEDs) using an Al doped ZnO (AZO)/Li doped ZnO (LZO) stack electron transport layer (ETL). An introduction of the LZO layer on AZO improved the current and power efficiencies of the green (G-) QLEDs from 10.5 to 34.0 cd A–1 and from 5.4 to 29.6 lm W–1, respectively. The red (R-), G-, and blue (B-) QLEDs fabricated in this work exhibited the maximum external quantum efficiencies (EQEs) of 8.4, 12.5, and 4.3%, respectively. It is found from time-resolved photoluminescence (PL) and transient electroluminescence (EL) decay that exciton loss at the interface between the ETL and the emission layer can be significantly reduced by introducing LZO.

Metal-Oxide Stacked Electron Transport Layer for Highly Efficient Inverted Quantum-Dot Light Emitting Diodes

Quantum dots (QDs) are a promising material for emissive display with low-cost manufacturing and excellent color purity. In this study, we report colloidal quantum-dot light emitting diodes (QLEDs) with an inverted architecture with a solution processed charge generation layer (CGL) of p-type polymer (tungsten oxide doped poly(ethylenedioxythiophene)/polystyrenesulfonate, PEDOT:PSS:WOx) and n-type metal oxide (lithium doped zinc oxide, LZO). The effective charge generation in solution processed p–n junction was confirmed by capacitance–voltage (C–V) and current density–electric field characteristics. It is also demonstrated that the performances of CGL based QLEDs are very similar when various substrates with different work functions are used.

Inverted Quantum-Dot Light Emitting Diode Using Solution Processed p-Type WOx Doped PEDOT:PSS and Li Doped ZnO Charge Generation Layer.

Zinc oxide (ZnO) nanoparticles (NPs) are widely used as electron-transport layers in quantum dots (QDs) light-emitting diodes (QLEDs). In this work, we show that the size of the NPs can be tuned wi...

Jeonggi Kim

Papers

High-Efficiency, Blue, Green, and Near-Infrared Light-Emitting Diodes Based on Triple Cation Perovskite

Li and Mg Co-doped Zinc Oxide Electron Transporting Layer for Highly Efficient Quantum Dot Light-Emitting Diodes

Metal-Oxide Stacked Electron Transport Layer for Highly Efficient Inverted Quantum-Dot Light Emitting Diodes

Inverted Quantum-Dot Light Emitting Diode Using Solution Processed p-Type WOx Doped PEDOT:PSS and Li Doped ZnO Charge Generation Layer.

ZnO Nanoparticles for Quantum Dot-Based Light-Emitting Diodes.