Cascade Effect of a Dimerized Thermally Activated Delayed Fluorescence Dendrimer
Guimin Zhao, Shuai Lv, Yuheng Lou, Yuewei Zhang, Dongdong Zhang, Wei Jiang, Yueming Sun, Lian Duan
Abstract
Abstract Thermally activated delayed fluorescence (TADF) emitters with a high horizontal orientation are highly essential for improving the external quantum efficiency (EQE) of organic light‐emitting diodes; however, pivotal molecular design strategies to improve the horizontal orientation of solution‐processable TADF emitters are still scarce and challenging. Herein, a phenyl bridge is adopted to connect the double TADF units, and generate a dimerized TADF dendrimer, D4CzBNPh‐SF. Compared to its counterpart with a single TADF unit, the proof‐of‐the‐concept molecule not only exhibits an improved horizontal dipole ratio (78 %) due to the π‐delocalization‐induced extended molecular conjugation, but also displays a faster reversed intersystem crossing rate constant (6.08×10 6 s −1 ) and a high photoluminescence quantum yield of 95 % in neat film. Consequently, the non‐doped solution‐processed device with D4CzBNPh‐SF as the emitter achieves an ultra‐high maximum EQE of 32.6 %, which remains at 26.6 % under a luminance of 1000 cd/m 2 . Furthermore, when using D4CzBNPh‐SF as a sensitizer, the TADF‐sensitized fluorescence device exhibits a high maximum EQE of 30.7 % at a luminance of 575 cd/m 2 and a full width at half maximum of 36 nm.