Highly efficient green and red electroluminescence with an extremely low efficiency roll-off based on iridium( iii ) complexes containing a bis(diphenylphorothioyl)amide ancillary ligand

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 7; no. 9; pp. 2570 - 2576
• Main Authors: Ma, Xiao-Feng, Xia, Jing-Cheng, Yan, Zhi-Ping, Luo, Xu-Feng, Wu, Zheng-Guang, Zheng, You-Xuan, Zhang, Wen-Wei
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2019
• Subjects: Crystallography; Current efficiency; Diodes; Efficiency; Electroluminescence; Iridium compounds; Ligands; Organic light emitting diodes; Phosphorescence; Quantum efficiency
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/C8TC06346J

In this study, two iridium( iii ) complexes named Ir(tfpmd)2(stpip) and Ir(tfpqz)2(stpip) were synthesized, in which 2-(4-(trifluoromethyl)phenyl)pyrimidine (tfpmd) or 4-(4-(trifluoromethyl)phenyl)quinazoline (tfpqz) was used as the cyclometalated ligand and bis(diphenylphorothioyl)amide (stpip) as the ancillary ligand, respectively. The Ir(tfpmd)2(stpip) complex shows green light, peaking at 501 nm with a high phosphorescence quantum efficiency of 0.83. The organic light-emitting diode (OLED) with a double-emissive-layer structure using the (tfpmd)2(stpip) complex displays good performances with a maximum luminance ( L max ) above 39 000 cd m −2 , a maximum current efficiency ( η c,max ) of 90.5 cd A −1 , a maximum external quantum efficiency (EQE max ) of 30.8% and an extremely low efficiency roll-off. Even at the high luminance of 10 000 cd m −2 , the efficiency roll-off ratio is below 5%. The Ir(tfpqz)2(stpip) complex shows red light, peaking at 624 nm, and its corresponding device with a single-emissive-layer structure also shows decent characteristics with a L max of 33 732 cd m −2 , a η c,max of 28.6 cd A −1 , an EQE max of 18.3% and also a very low efficiency roll-off. These results suggest that the green and red Ir( iii ) complexes with bis(diphenylphorothioyl)amide as the ancillary ligand have the potential for use in high-efficiency OLEDs with a low efficiency roll-off.