Solution-processed CsPbBr quantum-dot light-emitting diodes with a 50-fold external quantum efficiency improvement (up to 6.27%) are achieved through balancing surface passivation and carrier injection via ligand density control (treating with hexane/ethyl acetate mixed solvent), which induces the coexistence of high levels of ink stability, photoluminescence quantum yields, thin-film uniformity, and carrier-injection efficiency.

Highly efficient perovskite QLEDs can be realized when QD films possess two crucial synergistic parameters: highly luminescent features and effective electric transport properties. Regarding the emissive properties of QD films, although long organic ligands perfectly passivated the QD's surface and endowed ink with the near-unity luminescent properties with a PLQY approaching 100%, [11,12] the films generally exhibited a relatively low PLQY of about 40% due to the formation of nonradiative recombination centers. This phenomenon results from the dynamic characteristic of the bonding between the QD's surface and organic capping ligands, leading to the mismatched ligands during the film-forming process. [13,14] Meanwhile, these ligands act as electrically insulating layers on the QD's surface resulting in inefficient carrier injection and transportation, [15,16] which are detrimental to device performance. To enhance the electric properties of QD films, much attention [17,18] has been devoted to the development of ligand strategies that minimize the interparticle spacing. For example, Li et al. demonstrated an effective enhancement in electrical properties and EQE of CsPbBr 3 QLEDs through the control of surface ligand density. [9] Through ligand-exchange strategies, [8,19] a relatively short (C12) ligand, didodecyl dimethyl ammonium bromide (DDAB), was used to enhance device performance, obtaining an EQE of 8.73% under an effective washing process. Unfortunately, these methods are still based on long organic ligands, which cannot render the QD solid with ideal carrier injection and transportation features. Thus, it is significantly crucial to find an effective and feasible strategy to control the surface state of perovskite QDs, which could guarantee the high exciton recombination and carrier injection in constructing high-performance electroluminescent (EL) devices.Inorganic ligands with less space separation among particles could effectively enhance the electrical properties of QD films. [20,21] Meanwhile, they also improved the PL features through the reduce of the defect-related nonradiative recombination, which has been proven in traditional QDs. [22][23][24][25] For example, the halide-related ligands have improved the luminescent feature and radiative recombination in Cd-based QDs, which was realized by the ligand-exchange process. [20,26,27] But such a strategy is not feasible for perovskite QDs because they Perovskite quantum dots (QDs) with high photoluminescence quantum yields (PLQYs) and narrow emission peak hold promise for next-generation flexible and high-definition displays. However, perovskite QD films often suffer from low PLQYs due to the dynamic characteristics between the QD's surface and organic ligands and inefficient electrical transportation resulting from long hydrocarbon organic ligands as highly insulating barrier, which impair the ensuing device performance. Here, a general organic-inorganic hybrid ligand (OIHL) strategy is reported on to passivate perovskite QDs for highly efficient el...

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 CsPbBr 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 , respectively, which are the most-efficient perovskite QLEDs with colloidal CsPbBr 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.

Novel fluorescence with highly covert and reliable features is quite desirable to combat the sophisticated counterfeiters. Herein, we report a simultaneously triple-modal fluorescent characteristic of CsPbBr@CsPbBr/SiO by the excitation of thermal, ultraviolet (UV) and infrared (IR) light for the first time, which can be applied for the multiple modal anti-counterfeiting codes. The diphasic structure CsPbBr@CsPbBr nanocrystals (NCs) was synthesized via the typical reprecipitation method followed by uniformly encapsulation into silica microspheres. Cubic CsPbBr is responsible for the functions of anti-counterfeiting, while CsPbBr crystalline and SiO are mainly to protect unstable CsPbBr NCs from being destroyed by ambient conditions. The as-prepared CsPbBr@CsPbBr/SiO NCs possess improved stability and are capable of forming printable ink with organic binders for patterns. Interestingly, the fluorescence of diphasic CsPbBr@CsPbBr/SiO capsule patterns can be reversibly switched by the heating, UV, and IR light irradiation, which has been applied as triple-modal fluorescent anti-counterfeiting codes. The results demonstrate that the perovskite@silica capsules are highly promising for myriad applications in areas such as fluorescent anti-counterfeiting, optoelectronic devices, medical diagnosis, and biological imaging.

Owing to superior outstanding optical properties of perovskite nanomaterials in multiple dimensions, various perovskite nanocrystals (NCs) including quantum dots, nanoplates, nanorods, and polycrystalline film, with different characteristics have been integrated into perovskite LEDs. [18][19][20][21] Among them, most studies conducted are related to perovskite LEDs based on quantum dots and polycrystalline films. [16,17,22] A considerable number of studies have focused on increasing the modest efficiency of perovskite LEDs in the early stage. [22][23][24] Strategies concerning the optimization of both the emitting layer and the device structure were employed, which led to the realization of the highest external quantum efficiency (EQE) of 11.7% for perovskite LEDs. [7] However, the poor photostability, thermal stability, and ambient stability of perovskites have limited their practical application. [25] Surface passivation, composite structure, and composite design have been developed to improve the stability of perovskite NCs. [7,[26][27][28] However, most of the strategies are inadequate for electroluminance applications. The toxicity of Pb is considerably less than that of Cd in inorganic quantum dots (QDs), [29] but, such toxicity has obstructed the further applications of metal halide perovskites. The majority of studies are currently focused on the design of lead-free perovskites. Doped perovskites have also emerged as potential materials for perovskite LEDs. Despite the large difference in efficiency and long-term stability between perovskite LEDs and organic LEDs (OLEDs), perovskite LEDs show distinct advantage with respect to cost, synthesis, and color gamut. Compared with the decade of research spent to expand the practical application of OLEDs, the development of perovskite LEDs is relatively young; despite this, acceptable achievements have been accomplished in less than three years.Thus, we aimed to develop perovskite LEDs with high efficiencies as well as high long-term stability, nontoxicity, and reproducibility. A number of studies have been conducted on perovskite LEDs, [30][31][32][33] and a marked increase in EQE in perovskite LEDs has been observed in recent years, as shown in Figure 1. New strategies for improving both perovskite materials and device structures have been applied or considered. In addition, the long-term stability and lifetime of perovskite LEDs are rarely investigated. In this context, considering the Metal halide perovskites have drawn significant interest in the past decade. Superior optoelectronic properties, such as a narrow bandwidth, precise and facile tunable luminance over the entire visible spectrum, and high photoluminescence quantum yield of up to ≈100%, render metal halide perovskites suitable for next-generation high-definition displays and healthy lighting systems. The external quantum efficiency of perovskite light-emitting diodes (LEDs) increases from 0.1 to 11.7% in three years; however, the energy conversion efficiency and the long-term stability of perovsk...