Highly efficient fluorescence/phosphorescence hybrid white organic light-emitting devices based on a bipolar blue emitter to precisely control charges and excitons

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 8; no. 22; pp. 7543 - 7551
• Main Authors: Chen, Yuwen, Zhu, Jieji, Wu, Yibing, Yao, Jingwen, Yang, Dezhi, Qiao, Xianfeng, Dai, Yanfeng, Tong, Qingxiao, Ma, Dongge
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 14.06.2020
• Subjects: Chemical compounds; Devices; Efficiency; Emitters; Energy transfer; Excitons; Fluorescence; Organic light emitting diodes; Phosphorescence; Phosphors
• DOI: 10.1039/d0tc01549k
• ISSN: 2050-7526

Hybrid white organic light-emitting diodes (WOLEDs) combining blue fluorophores and green/red (or yellow) phosphors are still preferred for OLED production applications due to their advantages of good stability and high efficiency. One major challenge is to have a suitable blue fluorophore material to fully utilize the electrically generated excitons for fluorophore and phosphor emitters. Here, we employed an efficient blue fluorophore ( PBI-PPI-TPA ) with a high triplet energy of 2.48 eV as the blue emitter as well as the host for phosphors, whereby a series of highly efficient hybrid WOLEDs were successfully achieved. The two-color (BO) WOLEDs exhibited a maximum forward-viewing EQE/PE of up to 23.6%/77.8 lm W −1 , and retained 20.0%/49.5 lm W −1 at 1000 cd m −2 , thus exhibiting high-efficiency and low-efficiency roll-off. Furthermore, three-color (BYR) hybrid WOLEDs were also fabricated by adopting blue-yellow-red cascade energy transfer to ensure that all the excitons could be effectively utilized for the white emission. The resulting devices achieved a peak EQE/PE of 21.5%/53.2 lm W −1 , retained 17.2%/26.8 lm W −1 at 1000 cd m −2 , and the color rendering index (CRI) was doubled with respect to the two-color WOLEDs, showing a good trade-off between the efficiency and CRI. All these results are among the best reported for hybrid WOLEDs. Highly efficient fluorescence/phosphorescence hybrid WOLEDs have been realized by employing a new efficient blue fluorescent material.