Organic–Inorganic Hybrid Passivation Enables Perovskite QLEDs with an EQE of 16.48%

Abstract

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...

White Photoluminescent Ti3C2 MXene Quantum Dots with Two‐Photon Fluorescence

“…The unexpected and important TPFL properties of the Ti 3 C 2 MQDs were investigated using a near-infrared (NIR) femtosecond (fs) pulsed laser (800 nm). [45,46] However, Ti 3 C 2 MQDs have a great impact by ligands with largely of carbon, unique structure and composition. The twophoton luminescence under pulsed infrared laser excitation was confirmed by comparing excitation under different laser powers.…”

Light Generation in Lead Halide Perovskite Nanocrystals: LEDs, Color Converters, Lasers, and Other Applications

“…A clean bandgap structure enables LHP‐NCs to produce an energy‐efficient and narrow band emission, even in the absence of ligands for passivating surface defects . Any remaining shallow bandgap states caused by surface defects can be effectively passivated using ligands . The unique energy diagrams and the resulting high defect tolerance of LHP‐NCs result in superior optical and electrical characteristics even when LHP‐NCs are fabricated by a crude synthesis However, the low luminous efficiency of LHP‐NCs at low excitation densities suggests that there is still considerable loss from trap‐induced nonradiative recombination .…”

“…Any remaining shallow bandgap states caused by surface defects can be effectively passivated using ligands . The unique energy diagrams and the resulting high defect tolerance of LHP‐NCs result in superior optical and electrical characteristics even when LHP‐NCs are fabricated by a crude synthesis However, the low luminous efficiency of LHP‐NCs at low excitation densities suggests that there is still considerable loss from trap‐induced nonradiative recombination . Hence, the most efficient LHP‐NCs are crystalline and surrounded by passivating ligands …”

“…Light emission from lead halide perovskites (LHPs) was reported over a decade ago; however, weak emissions at room temperature hindered the application of LHPs in light‐emitting devices because LHPs did not show any electroluminescence at the time . In the past few years, LHPs have returned to the spotlight in the form of nanoscale emitters because of their superior features in light generation and resulting applications . Low‐cost solution processing techniques are used to fabricate LHP nanocrystals (LHP‐NCs), and impressive achievements have been made in using LHP‐NCs in high‐brightness light‐emitting diodes (LEDs) with high external quantum efficiency (EQE) and as color converters for lighting and full‐color displays that have a wide color gamut and near‐unity luminous efficiency .…”

“…The prompt emission of LHP‐NCs has resulted in their being selected as color converters for light indoor fidelity (Li‐Fi) in short‐distance wireless data transmission . As the most attractive application, red and green LEDs exhibit much higher performances with EQEs >20% and high brightness that are comparable to organic LEDs and CdSe quantum dot LEDs; however, blue LEDs still have an EQE of ≈5.7% and a maximum brightness of 3780 cd m −2 . LHP‐NCs have narrow band emissions and are therefore not the best color convertors for white LEDs in lighting; however, low‐cost phosphors exhibit similar performance to lanthanide based white LEDs .…”