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Flexible perovskite light‐emitting diodes (LEDs) have been highly expected to realize advanced wearable optoelectronic applications due to the excellent optoelectronic properties of perovskites. However, the poor water and oxygen stability and limited flexibility of perovskites prevent their commercialization and applications in flexible LEDs. Herein, the low‐cost and green biomass materials‐ethyl cellulose (EC) is added in the CsPbI3 nanocrystals (NCs), acting as a cross‐linker between neighboring halide octahedra through hydrogen bonds and PbO coordination bonds. It reduces the defect densities of NCs, leading to improved photoluminescence quantum yield. Simultaneously, the synergistic effect of efficient defect passivation and hydrophobic ether groups of EC significantly improve the environment stability of NCs. Additionally, the favorable flexibility of EC and cross‐linking between EC and perovskite NCs improve the deformation resistance of the perovskite layer with stable photoluminescence and negligible cracks after repeated bending. Consequently, flexible LEDs based on the EC‐passivated CsPbI3 NCs achieved a record external quantum efficiency of 12.1% and significantly enhanced operational stability. Moreover, the flexible LEDs show small luminance degradation after bending for 1000 cycles at a radius of 3 mm, and still retain high performance even after repeatedly bending at an ultrasmall bending radius of 1 mm. [ABSTRACT FROM AUTHOR]

Although light‐emitting devices (LEDs) based on metal halide perovskite nanocrystals (PNCs) developed rapidly in recent years, the luminance of pure red LEDs with the Rec. 2020 standard Commission Internationale de l'Eclairage 1931 color coordinates of (0.708, 0.292) cannot meet the requirement of outdoor display. Herein, a facile in situ modification strategy is proposed to prepare the efficiently luminescent CsPb(Br/I)3 PNCs, where metal bromides are used to create a halide‐rich environment and inhibit the formation of nonradiative surface defects. Synchronously, appropriately increased surface ligands improved the effective exciton confinement. Hence, the modified CsPb(Br/I)3 PNCs exhibited a high photoluminescence quantum yield of 92.0%. Additionally, the electrical conductivity is improved due to the increased hole mobility, and the Auger process is inhibited caused by balanced carrier mobilities. Consequently, LEDs based on the modified CsPb(Br/I)3 PNCs exhibited a maximum luminance of 11233 cd m−2 with the pure red color coordinate (0.704, 0.292) and a peak external quantum efficiency value of 13.2%. Furthermore, the luminance reached 5198 cd m−2 under the driving voltage of 4.4 V. This is the first study to realize a pure red PNC LED with high luminance under low bias, which can meet the requirement of outdoor display. [ABSTRACT FROM AUTHOR]

The unbalanced charge transport is always a key influencing factor on the device performance of quantum dot light-emitting diodes (QLEDs), particularly for the blue QLEDs due to their large optical band gap. Here, a method of electron transport layer (ETL) doping was developed to regulate the energy levels and the carrier mobility of the ETL, which resulted in more balanced charge injection, transport and recombination in the blue emitting CdZnS/ZnS core/shell QLEDs. Consequently, an enhanced performance of blue QLEDs was achieved by modulating the charge balance through ETL doping. The maximum external quantum efficiency and luminance was dramatically increased from 2.2% to 7.3% and from 3786 cd m−2 to 9108 cd m−2, respectively. The results illustrate that charge transport layer doping is a simple and effective strategy to regulate the charge injection barrier and carrier mobility of QLEDs. [ABSTRACT FROM AUTHOR]

2D transition metal carbides, nitrides, and carbonitrides called MXenes show outstanding performance in many applications due to their superior physical and chemical properties. Herein, a ZnO–MXene mixture with different contents of Ti3C2 is applied as electron transport layers (ETLs) and the influence of the Ti3C2 MXene in all‐inorganic metal halide perovskite nanocrystal light‐emitting diodes (perovskite NC LEDs) is explored. The addition of Ti3C2 makes more balanced charge carrier transport in LEDs by changing the energy level structure and electron mobility of ETL. Moreover, lower surface roughness is obtained for the ETL, thus guaranteeing uniform distribution of the perovskite NCs layer and further reducing leakage current. As a result, a 17.4% external quantum efficiency (EQE) with low efficiency roll‐off is achieved with 10% Ti3C2, which is a 22.5% improvement compared to LEDs without Ti3C2. [ABSTRACT FROM AUTHOR]

The external quantum efficiencies (EQEs) of perovskite quantum dot light‐emitting diodes (QD‐LEDs) are close to the out‐coupling efficiency limitation. However, these high‐performance QD‐LEDs still suffer from a serious issue of efficiency roll‐off at high current density. More injected carriers produce photons less efficiently, strongly suggesting the variation of ratio between radiative and non‐radiative recombination. An approach is proposed to balance the carrier distribution and achieve high EQE at high current density. The average interdot distance between QDs is reduced and this facilitates carrier transport in QD films and thus electrons and holes have a balanced distribution in QD layers. Such encouraging results augment the proportion of radiative recombination, make devices with peak EQE of 12.7%, and present a great device performance at high current density with an EQE roll‐off of 11% at 500 mA cm−2 (the lowest roll‐off known so far) where the EQE is still over 11%. [ABSTRACT FROM AUTHOR]

With the development of the display technology, there are higher requirements for color saturation and vividness. As a base unit, light-emitting diode (LED) has become a primary object of study. Perovskite quantum dots with high photoluminescence quantum yield, narrow emission, and wide color gamut have attracted special attention in recent years. Although LEDs based on perovskite exhibit excellent performance, there are few applications of perovskite LEDs in display. Herein, LEDs based on CsPbI3 perovskite were used as basic units for fabricating eight-segment LED displays. The LEDs exhibited a luminance of 780 cd/m2 and an external quantum efficiency of 6%. The current-density and luminance vs driving voltage confirms the uniformity of these LEDs in the eight segments, which will promote the application of perovskite nanocrystalline LEDs in the field of full color display. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phase transformation was achieved via an insertion reaction with additive ZnBr 2. • Nonlumi nescent Cs 4 PbBr 6 were transformed to green Zn-doped CsPbBr 3 /Cs 4 PbBr 6 NCs. • The transformed Zn-doped CsPbBr 3 /Cs 4 PbBr 6 NCs exhibited high PL QY of 77.5%. • The transformed NCs based EL LED was fabricated with a record EQE of 3.2%. Zero-dimensional (0D) perovskites have attracted a great deal of attention over the last few years due to their fascinating properties. However, their application in electroluminescent (EL) Light-emitting diodes (LEDs) is limited and suffering from extremely low device performance. Herein, the nonluminescent Cs 4 PbBr 6 nanocrystals (NCs) were successfully transformed to highly luminescent Zn-doped CsPbBr 3 /Cs 4 PbBr 6 NCs via an insertion reaction with ZnBr 2 , which changed the atomic molar ratios of NCs and promoted the formation of CsPbBr 3. In this reaction, the Zn2+ ions provided by ZnBr 2 together with the Pb2+ ions can occupy the B-site due to the similar ion radius. The extra Br- ions not only can facilitate the transformation process, but also can passivate the surface defects of the NCs, resulting in high photoluminescence quantum yield (PL QY) of 77.5%. Furthermore, as-synthesized Zn-doped CsPbBr 3 /Cs 4 PbBr 6 NCs were used as emitters to fabricate EL LEDs. The device achieved the maximum current efficiency of 9.8 cd/A and a peak external quantum efficiency of 3.2%, which is the best performance of the CsPbBr 3 /Cs 4 PbBr 6 based LEDs. This reveals the great application potential of CsPbBr 3 /Cs 4 PbBr 6 NCs as EL emitters in LEDs. [ABSTRACT FROM AUTHOR]

• OPA improved the PL QY and enhanced the electrical conductivity of CsPbI 3 QDs. • Top-emitting device structure improved the light extraction efficiency of LEDs. • OPA-optimized CsPbI 3 QD LEDs achieved 10171 cd m−2 luminance and 12.6% EQE. All-inorganic CsPbX 3 (X = Cl, Br, I) quantum dots (QDs) are promising materials for light-emitting diodes (LEDs), but the long insulating ligands such as oleic acid (OA) and oleylamine (OLA) on the QD surface limit the device performances. They reduce the electrical conductivity of QDs, while their loss deteriorates the photoluminescence and stability. To overcome these issues, octylphosphonic acid (OPA) with a shorter carbon chain was added in the synthesis of perovskite QDs to partially replace OA ligands. Owing to the strong interaction between OPA and Pb atoms, the under-coordinated Pb atoms on the surface of CsPbI 3 QDs can be effectively passivated by OPA, leading to improved fluorescence quantum efficiency (close to unity) and solution stability. Furthermore, the electrical conductivity of QD films was also enhanced from 5.3 × 10−4 to 1.1 × 10−3 S/m by using shorter chain OPA ligands. Finally, highly efficient red perovskite QD LEDs with peak external quantum efficiency (EQE) of 12.6% and maximum luminance of 10171 cd m−2 were achieved in a top-emitting device structure, a nearly 3-fold enhancement in luminance compared with pristine CsPbI 3 QDs based LEDs. [ABSTRACT FROM AUTHOR]