Effective Energy Transfer for Green, Orange, and Red Phosphorescent Organic Light‐Emitting Diodes Based on a Bipolar Deep‐Blue Emitter with Low Efficiency Roll‐Off at High Brightness
Guo‐Xi Yang, Jie‐Ji Zhu, Shan‐Shun Tang, Hong‐Ji Tan, Xin He, Jing‐Xin Jian, Xu‐Hui Zheng, Qing‐Xiao Tong
Abstract
Of paramount significance in phosphorescent organic light‐emitting diodes (PHOLEDs) are the facts that Förster resonance energy transfer (FRET) must be sufficient and back energy transfer should be prohibited. Herein, the FRET efficiencies for high‐performance PHOLEDs based on a simple bipolar luminogen 1‐phenyl‐2‐(5′‐phenyl‐[1,1′:3′,1″‐terphenyl]‐4‐yl)‐1 H ‐phenanthro[9,10‐ d ]imidazole ( PHT‐PPI ) with high triplet energy of 2.44 eV are systematically investigated. As a result, with PO‐01 as dopant, the high‐performance orange PHOLED is achieved with maximum external quantum efficiency (EQE max ) of 26.14% and ultrahigh brightness of 152 000 cd m −2 , which are the highest reported efficiencies for orange OLEDs with such high brightness. In addition, the green and red PHOLEDs are also fabricated with EQE max of 15.38% and 16.12%, respectively. Furthermore, the nondoped device based on PHT‐PPI as a deep‐blue emitter is also obtained with an EQE max of 5.12% and the Commission Internationale de L’Eclairage (CIE) index of (0.15, 0.08). More importantly, the blue, green, orange, and red devices exhibit low efficiency roll‐off, particularly, of which the orange PHOLED is extremely small (<9%) even at the brightness of 10 000 cd m −2 .