High color purity blue quantum dot light-emitting diodes (QLEDs) have great potential applications in the field of ultra-high-definition display. However, the realization of eco-friendly pure-blue QLEDs with a narrow emission linewidth for high color purity remains a significant challenge. Herein, a strategy for fabricating high color purity and efficient pure-blue QLEDs based on ZnSeTe/ZnSe/ZnS quantum dots (QDs) is presented. It is found that by finely controlling the internal ZnSe shell thickness of the QDs, the emission linewidth can be narrowed by reducing the exciton-longitudinal optical phonon coupling and trap states in the QDs. Additionally, the regulation of the QD shell thickness can suppress the Förster energy transfer between QDs in the QLED emission layer, which will help to reduce the emission linewidth of the device. As a result, the fabricated pure-blue (452 nm) ZnSeTe QLED with ultra-narrow electroluminescence linewidth (22 nm) exhibit high color purity with the Commission Internationale de l'Eclairage chromatic coordinates of (0.148, 0.042) and considerable external quantum efficiency (18%). This work provides a demonstration of the preparation of pure-blue eco-friendly QLEDs with both high color purity and efficiency, and it is believed that it will accelerate the application process of eco-friendly QLEDs in ultra-high-definition displays.
ZnSeTe quantum dots (QDs) attract growing interest owing to their low threats to health and the environment. They are widely applied as emitters in displays and lighting devices. Previous findings have indicated that inorganic halides are excellent candidates for surface ligands on QDs. By incorporating inorganic halides during the synthesis process, the photoluminescence (PL) intensity and quantum yield (QY) of QDs can be significantly enhanced. However, the alteration of surface states in QDs induced by zinc halide modification and the mechanism of formation of trap-state radiative recombination processes have been less discussed. Herein, we proposed a synthesis strategy for ZnSeTe/ZnSe/ZnSeS/ZnS core/shell/shell/shell QDs modified with ZnCl2, and by comparing the morphology and elemental composition of QDs with different amounts of ZnCl2 added, we revealed the regulatory mechanism of nanocrystal growth in the presence of ZnCl2. QDs with modification of ZnCl2 exhibited broad yellow fluorescence, distinct from the intrinsic blue emission. Through spectroscopic and surface ligand analyses, we attributed this yellow emission to the intermediate state energy levels caused by the defects on the surface. Finally, we used the QDs with broad linewidth emission to fabricate a simple white-light-emitting diode (WLED). This work provided new insights into the role of inorganic ligands and the use of a single emitting material in solid-state lighting devices.
Colloidal quantum dots (QDs) usually surfer from incomplete ligand coverage due to the steric hinderance of bulky long-chain ligands used in the synthesis stage and ligand desorption during the purification process. In this work, a metal halide ligand-assisted purification (LAP) method is developed for the first time and applied to enhance the luminescence performance of eco-friendly ZnSeTe-based pure-blue QDs synthesized without HF. Compared to the traditional purification (TP) method, the LAP approach is capable of enhancing the photoluminescence quantum efficiency (PLQY) and environmental stability of the QDs without compromising their colloidal stability and solution processability for uniform thin-film fabrication. Among the three zinc halide ligands (ZnCl 2 , ZnBr 2 , and ZnI 2 ), ZnCl 2 -assisted purification achieved the most significant photoluminescence enhancement, increasing the QDs’ PLQY from 57% (obtained through TP) to 82%. This improvement is attributed to the fact that the small-sized chloride ligands effectively passivate QD surface defects via binding to undercoordinated surface atoms during purification. The pure-blue light-emitting diode based on the optimal LAP-QDs displayed a 4-fold increase in maximum luminescence intensity and a 1.5-fold enhancement in peak external quantum efficiency compared to that based on the TP-QDs. This study demonstrates a simple yet efficient purification strategy for improving colloidal QD luminescence.
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