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Even though lead halide perovskite has been demonstrated as a promising optoelectronic material for next-generation display applications, achieving high-efficiency and stable pure-red (620~635 nm) emission to cover the full visible wavelength is still challenging. Here, we report perovskite light-emitting diodes emitting pure-red light at 628 nm achieving high external quantum efficiencies of 26.04%. The performance is attributed to successful synthesizing strongly confined CsPbI3 quantum dots with good stability. The strong binding 2-naphthalene sulfonic acid ligands are introduced after nucleation to suppress Ostwald ripening, meanwhile, ammonium hexafluorophosphate exchanges long chain ligands and avoids regrowth by strong binding during the purification process. Both ligands enhance the charge transport ability of CsPbI3 quantum dots. The state-of-the-art synthesis of pure red CsPbI3 quantum dots achieves 94% high quantum efficiency, which can maintain over 80% after 50 days, providing a method for synthesizing stable strong confined perovskite quantum dots. Li et al. report the regulation of perovskite quantum dot growth after nucleation by designing ligand exchange utilising proton transfer. The Ostwald ripening and regrowth are prohibited with an external quantum efficiency of 26.04% achieved in the pure-red perovskite light-emitting diodes. [ABSTRACT FROM AUTHOR]

Hybrid lead halide perovskites have generated increasing attention for their high performance in optoelectronic applications. One main drawback of these materials is the sensitivity to moisture, which contributes heavily to the ultimate decomposition. Here, this study takes advantage of the reported representative white‐light emitting lead bromide perovskite and three‐dimensional (3D) perovskite as the subject of water‐stability study. It is reported here that other than observed phase transformation in one case, the majority of these perovskites break down in water rapidly, precipitating out as an inorganic salt compound Pb3Br6[H2O]·H2O. As these materials are studied in detail, it is discovered that better coverage of the hydrophobic organic cation enhances the water stability. Taking this idea further, it is demonstrated here that five new one‐dimensional (1D) lead bromide compounds have superior water stability, where the longest stability when completely immersed in water is more than one year and counting. This work provides a new mechanism regarding the degradation process when encountering moisture and general guidelines to increase the water stability for the lead bromide hybrids. [ABSTRACT FROM AUTHOR]

Core–shell perovskite nanocrystals (NCs) have emerged as a promising class of materials for optoelectronic applications due to their unique properties and stability. Although much research has been conducted on the shell growth mechanism and properties of the core–shell NCs, little is known about the role of shell thickness in determining their optical properties. Herein, a heteroepitaxial method is employed to prepare a series of core–shell FAPbBr3/CsPbBr3 NCs with different shell thicknesses. Through temperature‐dependent photoluminescence measurement, it is found that the electronic structure of core–shell FAPbBr3/CsPbBr3 NCs evolves from quasi‐type‐II to type‐I with the increase in shell thickness. This abnormal transition can be attributed to the thickened gradient alloy layer FA1‐xCsxPbBr3, which effectively relieves the lattice mismatch and releases strain in the NCs, resulting in variations in the bandgap between the core and the shell. Furthermore, the biexciton Auger lifetimes in these samples exhibit a non‐monotonic dependence on shell thickness, indicating the electronic structure transition. These results provide valuable insights into the relationship between shell thickness, electronic structure, and optical properties in core–shell perovskite NCs, which may offer guidance for the design of high‐performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

Perovskite nanocrystals for light‐emitting diodes are often synthesized by uncontrollable metathesis reactions, suffering from low product yield, nonuniform growth, and poor stability. Herein, by controlling the nucleation kinetics with high dissociation constant (Ka or Kb) acids or bases, homogenous one‐route nucleation of perovskite nanocrystals is achieved as the cluster intermediates are eliminated. The stable, shape uniform, and narrow size distribution green nanocrystals are synthesized. The perovskite nanocrystal film exhibites excellent stability in 80% humidity air with only a 10% photoluminescence intensity drop after 16 h. Efficient and stable electroluminescence is demonstrated with an FWHM of 16 nm at 517 nm. The green devices shows a peak EQE of 24.13% with a lifetime T50 of 54 min at 10 000 cd m−2. [ABSTRACT FROM AUTHOR]

Advances in thin film light-emitting devices have fueled the rapid growth of a new class of solid-state lighting devices, featuring low fabrication cost, high quantum efficiency, and broadband spectrum coverage, etc. In contrast to the conventional inorganic semiconductors that rely on lattice matched high crystalline quality substrate, solution processable thin films eliminate the dependence on the substrate, which is highly desired for the ease and versatility of integrations with foreign medium. By taking this advantage, this work developed an ultracompact solution to control the directionality of thin film emitters using integrated dielectric metasurface through one step spin-coating process. As a proof of concept, directional emissions from perovskite nanocrystal thin film, including collimated light emissions and two-dimensional beam steering, are experimentally demonstrated. Notably, our approach, where light emitters were integrated on the back side of substrate after the fabrication of metasurface, judiciously avoids any potential degradation of material optical quality caused by the multi-step nanofabrication. Therefore, it can serve as a generalized scheme to engage the advantageous properties of dielectric metasurface, including the compactness, high efficiency, and beam controllability with the emerging thin film light-emitting diodes (LEDs), which is applicable to a wide range of solution processable materials, including organic light-emitting diodes, quantum-dot light emitting diodes, polymer LEDs, and perovskite LEDs, opening up new pathways to develop low-cost and ultra-compact solid state light sources with versatile beams characteristics. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskite nanocrystals (NCs) have received extensive attention for next‐generation thin film devices due to their excellent optical properties, such as strong light absorption, high carrier mobility, and defect tolerance. However, significant challenges remain to obtain high‐quality perovskite thin films. Herein, a simple but effective post‐treatment by laser irradiation for CsPbBr3 NCs thin films is reported. Laser‐induced secondary crystallization is observed in CsPbBr3 NCs thin films after treatment. In addition, amplified spontaneous emission (ASE) with a low threshold (5.6 µJ cm−2) and a high gain value (743 cm–1) is achieved. Based on optical measurements, it is attributed to the low defect density, reduced Auger recombination, and weak exciton–phonon interactions, which greatly suppress the nonradiative recombination channels. The ASE from the film after treatment has a high characteristic temperature (134 K), showing a stable optical gain performance that maintains its intensity for 35 h at room temperature (and 12 h at 40 °C). Finally, the proof‐of‐concept demonstration of graphic coding is shown. This study deepens the understanding of the optical gain mechanism of CsPbBr3 perovskite films and provides a simple and convenient laser treatment that enables the fabrication of high‐quality CsPbBr3 perovskite thin films. [ABSTRACT FROM AUTHOR]

This document is a technical paper titled "Efficient Perovskite quantum dots Light Emitting Diodes." It discusses the use of CsPbI3 perovskite quantum dots (QDs) in light-emitting diodes (LEDs) and the challenges faced in their practical applications. The paper presents a new strategy of proton-prompted short-chain ligand exchange in the synthesis of CsPbI3 QDs and the design of interface layers with high electron affinity. These approaches result in improved device performance, with a champion-level external quantum efficiency (EQE) of 25.80% achieved. This study represents the highest reported performance for pure red perovskite quantum dot LEDs to date. [Extracted from the article]

Recently, thanks to their unique and attractive properties, such as tunable bandgap, high absorption coefficient, and long charge carrier diffusion length, metal halide perovskites have been recognized as one of the emerging candidates for next-generation optoelectronic devices. Optoelectronic devices based on perovskites have achieved significant breakthroughs in a relatively short period of time. However, their commercialization still faces various challenges, including stability, scalability, and reproducibility. Defects are often the culprits behind these problems, either inside the perovskites or at the device interfaces. Therefore, rational utilization of defect engineering to minimize the effect of defects on device performance and control of carrier behavior is the key to achieve efficient and stable perovskite-based optoelectronic devices (PODs). Given the important contribution to the rapid development of PODs, there is an urgent need to systematically investigate and summarize recent research advances in defect engineering. Therefore, in this review, defect physics in PODs are described in detail, the role and importance of defects in various PODs are highlighted, and various strategies for optimizing PODs are reviewed. Finally, based on the latest progresses and breakthroughs, the challenges facing in the future development of metal halide perovskites and their potential significance in the field of the optoelectronic are prospected. [ABSTRACT FROM AUTHOR]

[Display omitted] • WS 2 was used as the hole interface layer to improve the hole transport ability through energy level matching. • The crystal quality of perovskite film was improved by using WS 2 as the hole interface layer. • Obtained high-performance Quasi-2D blue perovskite light-emitting devices with EQE of 3.24%. Due to the deep energy levels, the external quantum efficiency (EQE) of the blue perovskite light-emitting diode (PeLED) is far lower than its green, red, and near-infrared counterparts, which has exceeded 20%. The mismatched energy levels between perovskites and the hole transporting layer (HTL) still hinder the hole injection and consequent improvement of blue PeLED device performance. Here, a two-dimensional material, WS 2 (Tungsten disulfide), was introduced to match the energy levels between perovskites and HTL and enhanced the hole injection. The WS 2 HTL-based perovskite FAPbBr 3-x Cl x blue LED achieved a luminance of 990 cd/m2 with an EQE of 3.24%, which surpasses the performance of previously reported for the formamidinium (FA) based system, indicating the potential of WS 2 for PeLEDs. [ABSTRACT FROM AUTHOR]