High‐Performance Blue Quantum Dot Light‐Emitting Diodes with Balanced Charge Injection

Abstract

extensive attention in the field of optoelectronics, such as light emitting diodes (LEDs), photovoltaics, photodetectors, and lasers. [1][2][3] Among these, quantum dot LEDs (QLEDs) have attracted wide attention for their potential applications in thinfilm display and large-area lighting. [4] Since the QLEDs was first report in 1994, significant improvement has been achieved in both luminance and efficiency owing to the rapid development of QD materials and device architectures, [5][6][7] which foreshadows the commercialization of QLEDs in the future. [4,8] Among the various QD materials, Cd-based II-VI semiconductor QDs have relatively simple synthetic route [9] and highly visible-luminescent property, [10] making them the most attractive QDs for high-performance devices.In typical QLED geometry, the QDs emitting layer is sandwiched between the electron-transporting layer (ETL) and the hole-transporting layer (HTL). Early QLEDs drew a large amount of organic ETL and HTL materials from organic LEDs (OLED), [1,11] but were somehow restricted by them. Organic transporting materials generally suffer from low thermal stability and are easily eroded by oxygen and water, which deteriorates device performance. Besides, small-molecular organic layers are usually deposited through physical vapor deposition method, which increases the expense of production. Therefore, semiconducting metal oxides represented by ZnO, TiO 2 , and SnO 2 are gradually introduced in QLEDs as ETL. Metal oxides show superior physical and chemical stability and electronic conductivity in comparison with their organic counterparts. A wide variety of metal oxides can meet the requirements for energy band alignment with the neighboring layers. These properties enable metal oxides to be applicable for QLEDs as charge transport layer.People's understanding toward metal oxide ETL has experienced transfer over time. At first, the high free-carrier density in metal oxide crystal was thought to intensely quench the excitons formed in QDs. [12] Therefore, various methods were applied to fabricate amorphous metal oxide ETL, including zinc tin oxide (ZTO) deposited from magnetron sputtering [13] and sol-gel-made TiO 2 . [14] However, researchers then discovered the generally fairly low electron mobility in amorphous metal oxide (up to 4 orders of magnitude lower than the corresponding The balance of hole-electron injection is always a vital factor for the luminance, efficiency and working lifetime of quantum-dot light-emitting diodes (QLEDs), especially blue QLEDs. However, currently most approaches proposed to solve this issue involve tedious optimization of device architecture or material composition. Here, high-performance blue QLEDs are reported based on CdZnS/ZnS quantum-dot (QDs) by utilizing ZnO nanoparticles (NPs) and Al:Al 2 O 3 as electron-transporting layer (ETL) and cathode materials, respectively. The effect of post-annealing temperature on the trap state density in ZnO NPs and the related mechanisms are investigated through optical and photoelect...

Efficient and Stable Quantum‐Dot Light‐Emitting Diodes Enabled by Tin Oxide Multifunctional Electron Transport Layer

“…Compared to the low defect emission of SnO 2 , the ZnMgO shows a strong yellow emission, which is attributed to the defect emission originating from the recombination of electrons on the conduction band of ZnMgO and holes captured by defects. [14,26] As a result, the exciton quenching by SnO 2 is much weaker than ZnMgO, as revealed by the PL and time-resolved PL (TRPL) spectra shown in Figure 1b.…”

Effects of 1,2-ethanedithiol concentration on performance improvement of quantum-dot LEDs

“…Such traits have made colloidal QDs particularly promising candidates for next-generation displays and lighting systems, thus motivating many studies. [1][2][3][4][5][6][7][8][9] To this end, extensive efforts have been made to improve QD LED (QLED) performance toward the goal of simultaneously achieving high brightness, efficiency and durability.…”

Blue quantum dot-based electroluminescent light-emitting diodes

“…5a and b). 49 The electron mobility of the ZnO NPs can also be adjusted by controlling their particle size. Wang et al synthesized two types of ZnO NPs A (d = 3.626 nm) and B (d = 3.888 nm) and investigated the effect of different-sized ZnO NPs on device performance.…”