Up to date, several kinds of thermally activated delayed fluorescence (TADF) host molecules have been rapidly developed to fulfill the increasing demand of high-efficiency phosphorescent organic light-emitting diodes (PHOLEDs). Herein, three wide-bandgap TADF materials BPCN-Cz2Ph, BPCN-2Cz, and BPCN-3Cz are newly designed and synthesized as host materials for sky-blue PHOLEDs. By modulation of carbazole-units in the molecular skeleton, we find that the optimized molecules can realize both high triplet energies and balanced carrier transport properties with obvious TADF properties. The sky-blue PHOLEDs with ultralow phosphor doping ratio employing BPCN-Cz2Ph, BPCN-2Cz, and BPCN-3Cz as host materials demonstrate really high performance with alleviated roll-offs and achieve impressive current efficiencies (CEs) of 46.5 cd A⁻¹, 50.0 cd A⁻¹, and 34.5 cd A⁻¹, power efficiencies (PEs) of 40.6 lm W⁻¹, 46.8 lm W⁻¹, and 34.8 lm W⁻¹, and external quantum efficiencies (EQEs) of 22.2%, 24%, and 15.8%, respectively. More encouragingly, even at an applied luminance of 1000 cd m⁻², the EQEs could maintain high levels of 21.0%, 21.5% and 12.8%, respectively, which represents the potential utility value of the new family of these molecules in blue PHOLEDs. Our molecular design strategy provides a practical way to construct promising wide-bandgap TADF host materials with an excellent combination of TADF property, high triplet energy, and balanced carrier-transporting ability for high-performance devices.

迄今为止，已经快速开发了几种热活化延迟荧光（TADF）主体分子，以满足对高效磷光有机发光二极管（PHOLED）的日益增长的需求。在此，新设计并合成了三种宽带隙TADF材料BPCN-Cz2Ph，BPCN-2Cz和BPCN-3Cz作为天蓝色PHOLED的主体材料。通过调节分子骨架中的咔唑单元，我们发现优化的分子可以实现高三线态能量和平衡的载流子传输特性，并具有明显的TADF特性。采用BPCN-Cz2Ph，BPCN-2Cz和BPCN-3Cz的具有超低磷光体掺杂率的天蓝色PHOLED主体材料证明符合缓解滚降的非常高的性能和取得不俗的电流效率46.5光盘的（CES）^-1，50.0光盘^-1和34.5光盘^-1 40.6流明的W，功率效率（PES）^{- 1}，46.8流明w ^ ^-1，和34.8流明w ^ ^-1，和分别为22.2％，24％，和15.8％，外部量子效率（EQEs）。更令人鼓舞的是，即使在施加的亮度为1000 cd m ^-2时，EQEs可以分别维持21.0％，21.5％和12.8％的高水平，这代表了这些新分子家族在蓝色PHOLED中的潜在实用价值。我们的分子设计策略为构建有前途的宽带隙TADF主体材料提供了一种实用的方法，该材料具有TADF特性，高三重态能量和平衡的载流子传输能力的优良组合，可用于高性能器件。