Reducing Emission Linewidth of Pure‐Blue ZnSeTe Quantum Dots through Shell Engineering toward High Color Purity Light‐Emitting Diodes

Abstract

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.

Repercussions of the Inner Shell Layer on the Performance of Cd-Free Quantum Dots and Their Light-Emitting Diodes

“…The QDs with thin ZnSe inner shell layer (QD-H1) showed a fast decay process as well as apparent bleach of absorption peaks (PB1), whereas the QDs with thick ZnSe inner shell layer (QD-H2) possessed a slow decay process and the absorption peaks (PB2) barely bleached. 59 As the thickness of the ZnSe inner shell layer further increased, the decay process was accelerated, and the absorption peaks bleached apparently again, as documented in their work. These phenomena indicate that for both InP-based QDs and ZnSeTe-based QDs, with suitable thickness of inner shell layer, the lattice strain could be balanced and diminished the interfacial defects, thereby improving their optical performances.…”

“…Furthermore, the transient absorption spectra of ZnSeTe-based QDs with a series of different thicknesses of the ZnSe inner shell layer exhibited distinct features and decay process (Figure l–n). The QDs with thin ZnSe inner shell layer (QD-H1) showed a fast decay process as well as apparent bleach of absorption peaks (PB1), whereas the QDs with thick ZnSe inner shell layer (QD-H2) possessed a slow decay process and the absorption peaks (PB2) barely bleached . As the thickness of the ZnSe inner shell layer further increased, the decay process was accelerated, and the absorption peaks bleached apparently again, as documented in their work.…”

“…(n) Bleach recovery kinetics of QD-H1 (top) and QD-H2 (bottom). Reproduced with permission from ref . Copyright 2021 Wiley-VCH.…”

“…Therefore, in this Perspective, we first collect and discuss the differences in the optical properties of these QDs with different compositions for the inner shell layer, including GaP, MgSe, ZnSe, ZnSeS, and multiple alloyed inner shell layers, as shown in Table . ,,,− Subsequently, we compare and elucidate the mechanism of how the typical inner shell components and thickness influence their optical properties. At last, we discuss the influence of inner shell components and thickness on the performance of as-fabricated QLEDs. ,,− We reckon that the inner shell layer is bifunctional, which can balance the lattice strain between the InP core and inner shell as well as that between the inner shell and outer shell and simultaneously change the energy barrier for the charge trapping process. Consequently, with appropriate components or thickness, the defects generated by valence mismatch or lattice strain can be effectively attenuated.…”

Blue-Emissive ZnSeTe Quantum Dots and Their Electroluminescent Devices

“…Zhao et al attributed the observed line width narrowing to the suppression of defect-related carrier trapping and exciton− phonon coupling by the ZnSe thick shell beyond a certain threshold. 50 Conversely, an excessively thick ZnSe shell introduces additional trap sites, leading to an expansion of fwhm and diminished PL QY. The influence of ZnSe shell thickness on PL properties was investigated by analyzing timeresolved PL decay profiles of ZnSeTe/ZnSe/ZnS QDs with varying inner ZnSe shell thickness (Figure 4b).…”