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Multichannel Effect of Triplet Excitons for Highly Efficient Green and Red Phosphorescent OLEDs

With the inherent organic–metal system property, phosphorescent organic light‐emitting diodes (PhOLEDs) are capable of exhibiting high performance. However, the existence of unintended triplet–triplet annihilation (TTA), which is mainly originated from high triplet exciton density leading to inferio...

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Bibliographic Details
Published in:Advanced optical materials 2020-09, Vol.8 (17), p.n/a
Main Authors: Tian, Qi‐Sheng, Yuan, Shuai, Shen, Wan‐Shan, Zhang, Yuan‐Lan, Wang, Xue‐Qi, Kong, Fan‐Cheng, Liao, Liang‐Sheng
Format: Article
Language:English
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Summary:With the inherent organic–metal system property, phosphorescent organic light‐emitting diodes (PhOLEDs) are capable of exhibiting high performance. However, the existence of unintended triplet–triplet annihilation (TTA), which is mainly originated from high triplet exciton density leading to inferior device performance, is a current predicament. For mitigating the TTA in devices, reported herein is an effective host system with the role of precisely controlling the triplet excitons via the multichannel processes, in which a bipolar host material, a hole‐transporting material, and an electron‐transporting material are mixed to manage the triplet exciton transfer. The mixed‐host with so‐called “triplet excitons harvesting” strategy exhibits two concomitant reverse intersystem crossing (RISC) processes that simultaneously occur in the bipolar host material:electron‐transporting material and the host‐transporting material:electron‐transporting material exciplexes, respectively. Highly efficient green and red PhOLEDs are demonstrated by these multichannel processes, in which phosphorescent emitters bis(2‐phenylpyridine) (acetylacetonate) iridium(III) (Ir(ppy)2(acac)) and bis(2‐methyldibenzo[f,h]‐quinoxaline) (acetylacetonate) iridium(III) (Ir(MDQ)2(acac)) are doped into the mixed‐host, respectively. The green and red PhOLEDs realize nearly 30% of maximum external quantum efficiencies of 29.4% and 29.2%, respectively, and also maintain 29.1% and 28.3% at 1000 cd m−2. These excellent efficiencies and low roll‐offs confirm that the concomitant RISC processes effectively manage and utilize triplet excitons. Highly efficient green and red phosphorescent organic light‐emitting diodes with external quantum efficiencies close to 30% are achieved by employing a novel mixed host 26DCzPPy:TCTA:B4PyMPM, in which two reverse intersystem crossing processes are generated to mitigate the triplet–triplet annihilation with low energy loss.
ISSN:2195-1071
2195-1071
DOI:10.1002/adom.202000556