High-brightness/high efficiency and long-life red, green and blue trichromatic QLED devices come out
2019-05-12

Recently, Henan University and the University of Science and Technology of China have cooperated to make breakthroughs in visible light quantum dot light-emitting diodes (QLEDs). This work has developed a new high-brightness, high-efficiency and long-life red-green-blue trichromatic QLED device by designing and synthesizing new core-shell quantum dots. Among them, many performance indicators have set a world record, including red and green brightness (356,000). Cd/m2 and 614,000 cd/m2) and efficiency (21.6% and 22.9%), blue brightness (62,600 cd/m2), and green and blue device lifetimes (1.7 x 106 h and 7000 h, respectively). The results of this study are expected to accelerate the process of QLED application in the field of high-brightness and efficient display and lighting.


The breakthrough of GaN-based high-brightness blue LEDs in the 1990s opened a new era of LED lighting and display (three Japanese scientists contributed to the 2014 Nobel Prize in Physics). Based on semiconductor quantum dot-based QLED, it has broad application prospects in the field of display and illumination due to its advantages of better monochromaticity, color saturation and lower preparation cost. After rapid development in recent years, the main performance indicators such as luminous brightness, external quantum efficiency (EQE) and life have been greatly improved. However, in the past work, the device has the contradiction that the efficiency is too low when the brightness is high and the brightness is too low under the high efficiency. How to make the device high in brightness while maintaining high efficiency, long life and high stability is an urgent problem to be solved in the field of QLED, and it is also a key technical bottleneck restricting its application in display and lighting.


The main reason for the above-mentioned 'fish and bear's palm can not have both' predicament is that the quantum dot valence band in the QLED luminescent layer is usually deeper, does not match the hole transport layer, resulting in low hole injection efficiency, and electron injection. unbalanced. In response to this problem, the research team started from the design of luminescent layer quantum dots, based on the technology of 'low temperature nucleation, high temperature long shell', synthesized a new core of CdSe/ZnSe with high fluorescence quantum yield and high stability. Shell structure quantum dots (Figure 1). Such high-quality core-shell quantum dots can be used as a light-emitting layer to improve the matching with the energy level of the transport layer, effectively reduce the hole injection barrier, improve the injection efficiency of carriers, and overcome the insufficiency of hole injection and electrons in QLEDs. A series of problems caused by excessive injection, which greatly improves the overall performance of the device.


兼具高亮度/高效率和长寿命红绿蓝三基色QLED器件问世

Fig.1 CdSe/ZnSe core-shell structure quantum dot spherical electron microscope and element distribution


Based on this new structural system, the research team obtained the highest brightness and external quantum efficiency of red, green and blue three-color QLED devices, reaching 356,000 cd/m2, 614,000 cd/m2, 62,600 cd/m2 and 21.6%, 22.9%, 8.05, respectively. %, the brightness and efficiency of the red and green colors and the brightness of the blue are the highest international records (Figure 2). This work breaks through the key problem of low brightness and low efficiency of QLED in the past with high brightness. For the first time, it has realized red, green and blue three-color QLED devices with high brightness and high efficiency.


兼具高亮度/高效率和长寿命红绿蓝三基色QLED器件问世

Figure 2 Red, green and blue three-color QLED device performance


To more accurately describe the luminescent properties of the new QLEDs, the research team introduced a new concept, 'Efficient Brightness (EFL),' defined as the product of the peak EQE and its corresponding illuminance. Figure 3 is a comparison of the EFL of the working three-color QLED and the reported work of the literature. It can be seen that the EFL of the green device is doubled, and the red and blue colors have a near-order improvement. Moreover, from the requirements of brightness and efficiency of illumination, the three-color QLED obtained in this work has exceeded the corresponding threshold.


兼具高亮度/高效率和长寿命红绿蓝三基色QLED器件问世

Figure 3 Red, green and blue QLED 'effective brightness' (EFL) compared with existing work


The stability (lifetime) of the device is another key factor that constrains its application. The new QLED devices developed in this work also excel in life. Red and green QLED devices have a lifetime of more than 1.6 × 106 h, and blue lifetimes of more than 7000 h. The life of green and blue devices is also the highest in the world. Long record.


These research results and the established device model not only demonstrate the possibility of QLED application in the high-brightness and high-efficiency display and illumination field, but also provide new ideas for the material system design and device structure optimization of QLED in the future.


Related research results


Visible quantum dot light-


The issue of emitting diodes with simultaneous high brightness and efficiency was published in Nature Photonics [2019, 13, 192–197]. Professor Shen Huaibin from Henan University is the first author of the paper. Professor Du Zuliang, Professor Li Linsong from Henan University and Professor Zhang Zhenyu from the University of Science and Technology of China are co-authors.


The work was funded by the National Natural Science Foundation of China and the Ministry of Science and Technology.


Source: Chinese laser