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Advanced functional materials: High Performance Red quantum dot light emitting diodes based on organic electron transport layer

wallpapers News 2020-12-15
Compared with liquid crystal display (LCD) organic light-emitting diode (OLED) quantum dot light-emitting diode (qled) has the following advantages: 1. The emission spectrum of quantum dots (QDs) is adjustable the half peak width is narrow which supports the bt2020 stard with wider color gamut; 2. 3. The core-shell structure is easy to be finely controlled to obtain excellent optical properties thermal stability; 4. Good solution processability suitable for high-throughput low-cost printing process. Therefore in recent years qled has attracted extensive attention from academia industry. Based on organic / QDs / inorganic hybrid devices with organic hole transport layer inorganic electron transport layer blue green red qled with high performance have been reported one after another. The organic hole transport layer is mainly composed of poly TPD PVK or PFB the inorganic electron transport layer is mainly composed of ZnO nanocrystals or their derivatives. Because the electron mobility of ZnO is higher than that of polymer hole transport materials electrons will gather at the interface of hole transport layer / luminescent layer resulting in carrier transport imbalance non radiative Auger recombination. On the other h ZnO nanocrystals are greatly affected by the environment which leads to poor stability difficulty in batch synthesis storage which makes them incompatible with the ink-jet printing process in mass production.

to solve these problems Changchun Institute of Applied Chemistry Chinese Academy of Sciences Ding Junqiao team of Yunnan University have successfully assembled high-performance red quantum dot light-emitting diodes by using organic electron transport layer instead of traditional ZnO inorganic electron transport layer. Although

device structures based on organic hole transport layer organic electron transport layer (organic / QDs / organic) were proposed as early as 2002 there has been no substantial breakthrough in device performance. In this work the team selected nitrogen-containing heterocyclic compounds as organic electron transport layers fine tuned the molecular structure of the central core through b engineering. As shown in the figure when the central nucleus changes from benzene ring to pyrimidine triazine the lowest unoccupied molecular orbital (LUMO) energy level increases from - 2.28 ev to - 2.79 EV - 3.07 EV the electron injection ability gradually increases. Finally the organic electron transport layer tmpppytz with triazine core achieves the optimal carrier balance. The external quantum efficiency (EQE) of the device is as high as 13.4% (18.8 CD / A 23.9 LM / W) the CIE color coordinates are (0.68 0.32). These properties are comparable to those of devices based on inorganic electron transport layer indicating that organic electron transport layer also has great potential in high efficiency qled.

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