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Alleviating Efficiency Roll-Off of Hybrid Single-Emitting Layer WOLED Utilizing Bipolar TADF Material as Host and Emitter

Wang, Qiang, Zhang, Ye-Xin, Yuan, Yi, Hu, Yun, Tian, Qi-Sheng, Jiang, Zuo-Quan, Liao, Liang-Sheng
ACS applied materials & interfaces 2018 v.11 no.2 pp. 2197-2204
fluorescence, iridium, light emitting diodes, lighting, materials science, moieties
Hybrid single-emitting layer (SEML) white organic light-emitting diodes (WOLEDs) incorporating blue thermally activated delayed fluorescent (TADF) or fluorescent materials and yellow phosphors have been widely utilized for solid-state lighting. Nonetheless, developing appropriate host materials to reduce the large efficiency roll-off at high luminance is still an unsolved issue. Here, two TADF materials denoted as TRZ-CF and TRZ-CzF were synthesized, with electroluminescent emission peaking at 476 and 460 nm, respectively. In particular, TRZ-CF, using 7,7-dimethyl-5,7-dihydroindeno[2,1-b]carbazole (CF) as donor moiety, maintained both highly efficient blue emission (EQEₘₐₓ = 20.0%) and excellent charge transport abilities. The WOLED utilizing TRZ-CF as host material, doped by 0.8 wt % iridium(III) bis(4-phenylthieno[3,2-c]pyridinato-N, C2′) (PO-01), has EQEₘₐₓ of 20.3%, realizing the lowest roll-off to date of less than 2% at a luminance of 10 000 cd/m². The efficiency roll-off is alleviated through the reduction the exciton quenching and triplet–triplet annihilation (TTA) within the light-emitting layer, benefited from the TADF effect and bipolar property. The hybrid SEML WOLED exhibits Commission Internationale de L’Eclairage (CIE) coordinates of (0.38, 0.45), providing a practical way to simplify the production complexity and to reduce efficiency roll-off for solid-state lighting.