Quantum dot light-emitting diodes with high efficiency at high brightness via shell engineering

Abstract

Quantum dot light-emitting diodes (QD-LEDs) have made great development in the performance. However, the efficiency droop at high brightness limits their applications in daylight displays and outdoor lightings. Herein, we systematically regulate the shell structure and composition, and the results indicate that CdSe-based QDs with ZnSe interlayer and thinner ZnSeS outermost layer as emitting layers (EML) enable high-performance QD-LEDs. Accordingly, the devices exhibit peak external quantum efficiency (EQE) of 22.9% with corresponding brightness of 67,840 cd/m2, and this efficiency can be still maintained > 90% of the maximum value even at 100,000 cd/m2, which satisfies the requirements for high-brightness display and lighting applications. This strong performance is mainly attributed to the ZnSe/ZnSeS graded shell that smooths the injection barrier between QD EML and the adjacent hole transport layers (HTL), and then improves the hole injection and charge injection balance, in particular at the high luminance and/or at high current density.

Gateway towards recent developments in quantum dot-based light-emitting diodes

“…In this regard, Ba et al demonstrated a high-efficiency CdSe-based QD-LED with a ZnSe interlayer and a ZnSeS outermost layer as emitting layers through shell engineering. 105 Core-shell QDs have been synthesized by regulating the shell structure and composition such as CdSe/ZnS, CdSe/ZnSe, CdSe/ZnSe/ZnS, and CdSe/ZnSe/ZnSeS. Fig.…”

“…Fig. 8 (a) Schematic illustration of multi-layered QD-LEDs, (b) the EQEluminance, and (c) the EQE-current density of different QD-LED types 105. …”

Stability Improvement in Quantum-Dot Light-Emitting Devices via a New Robust Hole Transport Layer

“…Among the organic HTLs, poly­[(9,9-dioctylfluorenyl-2,7-diyl)- alt -(4,4′-( N -(4-butylphenyl))-diphenylamine)] (TFB) is known to have relatively high hole mobility that seems to be a good candidate used for efficient devices with inorganic electron transport layers (ZnO/ZnMgO) that also have high electron mobility. There are several reports with red, green, and blue QDs using TFB as the HTL in all-solution processed QDLEDs that achieved very high external quantum efficiency (EQE). ,, However, several factors can influence the extent of cross-linking in TFB, often limiting its resistance to solvent damage, an issue that leads to a large variability in device performance, especially stability. , So, there is a need to explore other HTLs that can circumvent these issues.…”

Stable ZnS Electron Transport Layer for High-Performance Inverted Cadmium-Free Quantum Dot Light-Emitting Diodes

“…For the advancement of next-generation display and lighting applications, colloidal quantum dots (QDs) have been widely used as an emissive layer (EML) due to their excellent optical properties, such as a narrow full-width at half-maximum (FWHM), tunability of the emission wavelength, a high photoluminescence quantum yield (PLQY), and solution processability. − The performance of cadmium (Cd)-based quantum dot light-emitting diodes (QLEDs) has demonstrated a peak external quantum efficiency (EQE) of over 20%, which is almost equivalent with that of the best organic light-emitting diodes. − The toxicity of Cd-based QDs negatively impacts the environment; thus, alternative non-toxic cadmium-free indium phosphide (InP)-based QDs have gained increasing attention due to their environmental friendliness. − Recently, great efforts have been expended to develop cadmium-free InP QLEDs, which have led to excellent QLED device performance. , However, the device lifetime and efficiency of InP-based QLEDs are still inferior compared to those of Cd-based QLEDs. , Such an inferior performance of InP-based QLEDs can be attributed to the charge imbalance in the device caused by a mismatch in electron and hole mobilities and instability of the QD materials.…”