Thermally activated delayed fluorescence dendrimers with AIE property and functional dendrons for high-efficiency solution-processed white OLEDs

Thermally activated delayed fluorescence (TADF) materials with encapsulation dendrons have exhibited superior advantages in the solution-processed OLEDs. Herein, we utilized electron-donating carbazole and electron -withdraw phenylbenzimidazole as the peripheral wrapping unit to design and synthesize two TADF materials, TRZCz-Cz and TRZCz-Bz, to discuss the distinction about different encapsulations for one identical emissive core. The photophysical investigation demonstrate that both compounds have small LEST and clearly aggregation -induced enhancement (AIE) properties, which are benefit for enhancing the exciton unitization of electrolumi-nescence devices. Despite similar characters in photophysical property, the blue phosphorescence OLEDs host with TRZCz-Cz obtain the maximum current efficiency and external quantum efficiency of 38.6 cd A-1 and 18.4%, respectively, which far exceed TRZCz-Bz based one. Thanks to the high performance of blue device, the fully phosphorescent white OLEDs with Ir(MDQ)2(acac) as red phosphorescent dopant achieves the maximum luminescence, current efficiency, external quantum efficiency as high as 12874 cd m- 2, 33.8 cd A-1 and 16.5%, respectively, which are among the highest efficiency of solution-processed white OLEDs. Moreover, the hybrid white OLEDs with TADF as blue host and red phosphor as dopant was also achieved with a low turn-on voltage of 3.2 V, and more standard white emission with CIE coordinate of (0.34,0.33). Thus, this work significantly ex-tends the range of AIE TADF materials and paves the useful way for the fabrication of high efficiency white OLEDs through solution-process.

Automated summary

In this study, two Thermally Activated Delayed Fluorescence (TADF) materials, TRZCz-Cz and TRZCz-Bz, were designed and synthesized to investigate the distinction of different encapsulations for an identical emissive core. The results showed that despite similar photophysical properties, the blue phosphorescent OLEDs using TRZCz-Cz as the host achieved the highest current efficiency and external quantum efficiency, leading to the fabrication of high-efficiency white OLEDs.