Carbazole‐Based Iridium(III) Complexes for Electrophosphorescence with EQE of 32.2% and Low Efficiency Roll‐Off

• Published in: Advanced optical materials 2021-02, Vol.9 (3), p.n/a
• Main Authors: Luo, Xu‐Feng, Qu, Zhong‐Ze, Han, Hua‐Bo, Su, Jian, Yan, Zhi‐Ping, Zhang, Xiao‐Min, Tong, Jing‐Jing, Zheng, You‐Xuan, Zuo, Jing‐Lin
• Format: Article
• Language: English
• Subjects: carbazole; Carbazoles; Charge injection; Current efficiency; Efficiency; electrophosphorescence; Emitters; high external quantum efficiency; Iridium compounds; iridium(III) complex; low efficiency roll‐off; Materials science; Multilayers; Optics; Organic light emitting diodes; Phosphorescence; Photoelectric effect; Photoelectricity; Photoluminescence; Quantum efficiency; Thin films
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202001390

The integration of carbazole (Cz) unit and emissive iridium(III) complexes is a wise choice to facilitate hole injection/transport, charge balance, and achieve phosphorescent emitters for high‐performance organic light‐emitting diodes (OLEDs). Herein, three efficient Cz‐based Ir(III) complexes are synthesized and applied for OLEDs. The introduction of trifluoromethyl and trimethylsilyl units alter the photoelectric properties of these complexes, achieving photoluminescence (PL) from yellow (559 nm) to orange‐red (600 nm) with high PL quantum yields between 75% and 93% and short excited state lifetimes between 1.09 and 1.90 µs in doped thin films. Multilayer OLEDs using the three emitters exhibit highest current efficiency as high as 100.4 cd A−1 and maximum external quantum efficiency (EQEmax) up to 32.2% with very low efficiency roll‐off. Even at high brightness of 5000 and 10 000 cd m−2, the device D3 still can maintain the EQE at 28.2% and 27.9%, respectively. These results indicate that these complexes incorporating Cz units are potential substituents for efficient OLEDs. Three carbazole‐based iridium(III) complexes are efficiently obtained. The introduction of trifluoromethyl and trimethylsilyl achieve photoluminescence from yellow (559 nm) to orange‐red (600 nm) with high photoluminescence quantum yields. Utilizing these dopants, multilayer organic light‐emitting diodes exhibit turn‐on voltage as low as 2.7 V, high current efficiency up to 100.4 cd A−1, and external quantum efficiency up to 32.2% with low efficiency roll‐off.