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Colloidal quantum dot (QD) light-emitting diodes (QLEDs) hold the promise of next-generation displays and illumination owing to their excellent color saturation, high efficiency, and solution processability. For achieving high-performance lightemitting diodes (LEDs), engineering the fine compositions and structures of QDs is of paramount importance and attracts tremendous research interest. The recently developed continuously graded QDs (cg-QDs) with gradually altered nanocompositions and electronic band structures present the most advanced example in this area. In this Perspective, we summarize the current progress in LEDs based on cg-QDs, mainly concentrating on their synthesis and advantages in addressing the great challenges in QLEDs, like efficiency roll-off at high current densities, short operation lifetimes at high brightness, and low brightness near the voltage around the bandgap. In addition, we propose accessible approaches exploiting the cutting-edge mechanisms and techniques to further optimize and improve the performance of QLEDs.

Lead-free double perovskites offer non-toxic properties and strong emission via alloying and doping. Herein, we report the synthesis of Bi-doped pure Rb2HfCl6 and Cs-alloyed RbCsHfCl6 microcrystals. The pure Rb2HfCl6 microcrystals are nearly non-emissive while alloying with Cs and Bi doping lead to strong deep blue emission at 466 nm with an increase in photoluminescence quantum yield from ∼0 to 66%. Density functional theory studies attest to the improved phase stability due to Cs-alloying and link photoluminescence to Bi3+ dopant-induced localized states.

The addition of aqueous hydrohalic acids (HX, X = F, Cl, Br) during the synthesis of colloidal quantum dots (QDs) is now widely employed to achieve high‐quality QDs. However, this reliance on the use of aqueous solutions is incompatible with oxygen‐ and water‐sensitive precursors such as those used in the synthesis of Te‐alloyed ZnSe QDs. Herein, we show this incompatibility, leads to phase segregation into Te‐rich and Te‐poor regions, causing spectral broadening and luminescence peak shifting under high laser irradiation and applied electrical bias. Here we report a synthetic strategy to produce anhydrous‐HF in‐situ by using benzenecarbonyl fluoride (BF) as a chemical additive. Through in‐situ 19F nuclear magnetic resonance spectroscopy, we find that BF reacts with surfactants in tandem, ultimately producing intermediary F···H···trioctylamine adducts. These act as a pseudo‐HF source that releases anhydrous HF. The controlled release of HF during the nucleation and growth steps homogenizes the Te distribution in the ZnSeTe lattice, leading to spectrally‐stable blue‐emitting QDs under increasing laser flux from ∼3 μW to ∼12 mW and applied bias from 2.6 to 10 V. Single‐dot photoluminescence (PL) spectroscopy and analyses of the absorption, PL and transient absorption spectra together with density functional theory point to the role of anhydrous HF as a Te homogenizer.This article is protected by copyright. All rights reserved

Quantum dot light-emitting diodes (QD-LEDs) are highly promising light sources with excellent figures of merit. Although great successes have been achieved in elevating some key parameters to an ideal level, QD-LEDs with superior performance in all aspects have rarely been realized. Herein, by exploring crystalline structure-dependent electronic properties, it is shown that QD-LEDs can simultaneously exhibit high external quantum efficiency, roll-off-free under high brightness, and dramatically improved operational stability. This improved performance stems from the crystal phase engineering of QD. Reduced structure symmetry in the wurtzite phase introduces an unneglectable internal crystal field compared with the zinc-blende one, which raises both the conduction and valence band energy levels, thus, facilitating a more balanced charge injection. The crystal phase-optimized superior-comprehensive performance in the QD-LED offers a novel degree of freedom for device engineering and promotes commercial applications for the upcoming display and illumination technologies.