Stabilization is one critical issue that needs to be improved for future application of colloidal quantum dot (QD)‐based light‐emitting diodes (QLEDs). This study reports highly efficient and stable QLEDs based on solution‐processsed, metal‐doped nickel oxide films as hole injection layer (HIL). Several kinds of metal dopants (Li, Mg, and Cu) are introduced to improve the hole injection capability of NiO films. The resulting device with Cu:NiO HIL exhibits superior performance compared to the state‐of‐the‐art poly(3,4‐ethylenedioxythiophene):poly(styrene‐sulfonate) (PEDOT:PSS)‐based QLEDs, with a maximum current efficiency and external quantum efficiency of 45.7 cd A−1 and 10.5%, respectively. These are the highest values reported so far for QLEDs with PEDOT:PSS‐free normal structure. Meanwhile, the resulting QLED shows a half‐life time of 87 h at an initial luminance of 5000 cd m−2, almost fourfold longer than that of the PEDOT:PSS‐based device.

light with the emission wavelength of 620-640 nm is an essential part for highdefinition display; however, compared with the green-counterpart, the electroluminescence (EL) performance of the colorsaturated red and blue perovskite emitters is much poorer. Ever since the first red-PeLED with an EL peak at 630 nm was demonstrated by Friend and coworkers, [1] efforts have been paid to improve the emitter photoluminescence quantum yield (PL QY) toward high-performing devices. Tan and coworkers applied a trimethylaluminum vapor-based crosslinking method to increase the PL QY of CsPb(Br/I) 3 nanocrystals (NCs) and gave rise to an EQE of 1.4%. [28] Brighter emitters leading to more efficient LEDs have been also observed in perovskite NCs of other colors and components, and strategies including doping, [29][30][31][32][33][34] surface capping, [35][36][37][38][39][40][41] core-shell structures, [42,43] and anion-exchange [25,[44][45][46][47] have been employed. For lead-halide perovskites, most charge recombination centers are localized on the crystal surfaces, and lead atoms who may cause strong exciton quenching are facile to form. [35,[38][39][40] Thus, the PL QY of red CsPb(Br/I) 3 NCs can increase through reducing the number of surface lead atoms. Aside from the excellent optical properties, the electric conductivity of perovskite NCs is another crucial factor for the performance of perovskite electroluminescent devices. Metal doping has been considered as a promising avenue to control over the electronic and optical performance of perovskite NCs. However, the limited improvement of metal doped CsPb(Br/I) 3 PeLEDs indicates that new methods are necessary. [32] Furthermore, doping perovskite with transition metal ions (Cu 2+ , Ni 2+ , Zn 2+ ) broadened the emission bands, and incorporation of Mn 2+ or lanthanide ions introduced new emission centers in perovskite NCs, leading to poor color purity of PeLEDs. [31,33,34] Here, benzyl iodide (BI) was chosen to passivate the CsPb(Br/I) 3 NC surface where the iodide can bond to the surface Pb atoms leading to reduced non-recombination centers. Interestingly, we found that the electrons tend to transfer from CsPb(Br/I) 3 NC to the surface electron acceptor-aromatic rings, leading to p-doping of the CsPb(Br/I) 3 NCs, thus allowing us to control over the energy levels and electrical conductivity. With the help of BI, the NC PL QY is greatly increased Color-saturated red light-emitting diodes (LEDs) with emission wavelengths at around 620-640 nm are an essential part of high-definition displays. Metal halide perovskites with very narrow emission linewidth are promising emitters, and rapid progress has been made in perovskite-based LEDs (PeLEDs); however, the efficiency of the current color-pure red PeLEDs-still far lags behind those of other-colored ones. Here, a simple but efficient strategy is reported to gradually down-shift the Fermi level of perovskite nanocrystals (NCs) by controlling the interaction between NCs and their surface molecular electron acceptor-benzyl iodide ...

Flexible information displays hold great promise for future optoelectronic applications. Herein, we report the fabrication of an efficient flexible white quantum dot (QD) light-emitting diode (QLED) with mixed red, green and blue QDs as emitters via an all-solution process. The resulting flexible QLED with a pure white emission shows high current efficiency of 10.5 cd A−1.

Despite the fast advances in monochrome quantum dots (QDs) based light‐emitting diodes (QLEDs), the performance for white QLEDs (WQLEDs) with great potential for illumination and backlight applications to date has fallen short of that of state‐of‐the‐art white organic LEDs. Here, a highly efficient all‐solution‐processed WQLED with a serially stacked red/green/blue tandem structure, which displays an almost perfect white emission with the Commission Internationale de l'Enclairage coordinates of (0.34, 0.33) is reported. The white device exhibits peak current efficiency of 79.9 cd A−1 and external quantum efficiency of 28.0%, which are the highest efficiency values ever reported in WQLEDs. The record performance for the WQLEDs is achieved by the effective interconnecting layer with excellent charge generation and the insertion of a polyethylenimine ethoxylated interlayer between the ZnO electron transport layer and QDs emissive layer in each unit for better balancing charge injection and suppressing the quenching of QDs emission due to the contact with ZnO.

Despite the rapid development in quantum-dot light-emitting diodes (QD-LEDs) with a single junction, it remains a big challenge to make tandem QD-LEDs with high performance. Here, we report solution-processed double-junction tandem QD-LEDs with a high external quantum efficiency of 42.2% and a high current efficiency of 183.3 cd A–1, which are comparable to those of the best vacuum-deposited tandem organic LEDs. Such high-efficiency devices are achieved by interface engineering of fully optimized single light-emitting units, which improves carriers’ transport/injection balance and suppresses exciton quenching induced by ZnO, and design of an effective interconnecting layer consisting of poly­(4-butylphenyl-diphenylamine) (poly-TPD)-mixed poly­(9-vinylcarbazole) (PVK)/poly­(3,4-ethylenedioxythiophene):polystyrene sulfonate/polyethylenimine ethoxylated-modified ZnO.

A Cu‐doped, NiO‐based quantum dot light‐emitting diode (QLED) reported by Xuyong Yang and co‐workers in article number https://doi.org/10.1002/adfm.201704278 exhibits a significant operating lifetime enhancement compared with organic PEDOT:PSS‐based QLEDs. Relying on an inorganic hole transport layer, the device's quantum dots retain their brightness for an extended time period. This is in contrast to light from a PEDOT:PSS‐based QLED shown in the upper‐left corner of the image.

No abstract

FA + = NH 2 CH = NH 2 + , X = Cl, Br, and I or their mixture) have been grown into the candidate materials for optoelectronic devices, such as light-emitting diodes (LEDs), liquid crystal display (LCD) backlight, solar cells, lasers, and photodetectors thanks to the excellent optical capabilities and low-cost solution processability. [1][2][3][4][5][6][7][8][9][10][11][12] Among the above-mentioned perovskites, FAPbBr 3 shows unique advantages: first, comparing to MAPbBr 3 , FAPbBr 3 performs better stability, which is crucial for the practical application. [13] The origin is that the ion diameter Metal halide perovskite nanocrystals (NCs) have shown significant potential in light-emitting applications due to the unique luminous properties, such as high color purity, tunability, and solution processability. However, the large-scale production of perovskite NCs with high-quality for meeting the commercial applications is still a challenge. Herein, a facile room-temperature synthesis of ten-gram-scale FAPbX 3 (FA + = HC(NH 2 ) 2 + , X = Br, or mixed halide system Cl/Br and Br/I) NCs by a high-power ultrasonic-assisted strategy and the electroluminescence for light-emitting diodes (LEDs) is reported. The uniform high-power radiation avoids the adverse effects caused by heating and stirring unevenness, and no inert gas is needed in the reaction process. Meanwhile, the room temperature reaction reduces the crystallization rate of the NCs, leading to the successful synthesis of ten-gram-scale high-quality FAPbX 3 perovskite NCs. The resulting NCs show size-focus distribution and high photoluminescence quantum yields of 93%, and the adjustable photoluminescence spectra from 453 to 695 nm by manipulating halide compositions. Attributed to the acquired FAPbBr 3 NCs, a highefficiency green LED with the maximum current efficiency of 61.3 cd A −1 and external quantum efficiency of 14.1% is also obtained.