ABSTRACT Multi‐resonant thermally activated delayed fluorescence (MR‐TADF) materials characterized by narrowband emission and high exciton utilization are promising for high‐performance organic light‐emitting diodes (OLEDs) with superior color purity. However, their rigid structures often lead to severe concentration quenching, spectral broadening, and poor solubility, thereby limiting their applicability in solution‐processed devices. To address these limitations, a core–shell design strategy was employed by shielding the planar MR‐TADF core with bulky peripheral substituents. This well‐defined configuration provides effective spatial segregation of the emitting cores, which not only suppresses detrimental π–π stacking and aggregation‐induced quenching but also ensures a high photoluminescence quantum yield and enhanced solubility. The corresponding solution‐processed OLEDs achieved a maximum external quantum efficiency (EQE max ) of 24.65%, with stable CIE coordinates of (0.17, 0.70) over a broad doping range (5–40 wt.%). Notably, the integration of a TADF‐type sensitizer led to a significant boost in efficiency, achieving a superior EQE max of 31.15%. Remarkably, the device maintained a high EQE of 24.63% even at a high doping concentration of 30 wt.%. This work paves the way for developing doping‐insensitive, solution‐processed MR‐TADF devices with exceptional efficiency and color purity.
Zhang et al. (Sun,) studied this question.