Blue HLCT fluorophore for high-performance and color stable white OLEDs via balanced bipolar transport

White organic light-emitting diodes (OLEDs) hold a highly significant position in the fields of display and lighting. However, achieving both high efficiency and color stability in white OLEDs remains a persistent challenge. The recently developed hybridized local and charge transfer (HLCT) material PPIAn2N maximizes exciton utilization due to the bipolar nature of its PPI units and the efficient reverse intersystem crossing (RISC) from high-lying triplet states (T_n, n \ge 2) to the singlet state (S_1), suggesting its great potential for constructing high-performance white OLEDs. In this work, the blue HLCT material PPIAn2N is employed as a sensitizing host to fabricate red fluorescent and yellow phosphorescent OLEDs based on DCJTB and PO-01, respectively, by precise concentration control. The resulting devices achieve maximum external quantum efficiencies (EQEs) of 6.88% and 25.08%. Notably, the red device surpasses the theoretical EQE limit of 5% for conventional fluorescent OLEDs, and the yellow device exhibits negligible efficiency roll-off. Building upon this, a strategically designed dual-emission layer architecture enables PPIAn2N, with its bipolar carrier transport property, to function simultaneously as a blue emitter and as a sensitizing host for PO-01 in hybrid fluorescence/phosphorescence white OLEDs. The resulting device exhibits a maximum EQE of 17.03% and a maximum luminance of 74098 cd/m^2. Furthermore, a stable electroluminescence (EL) spectrum is maintained over a wide voltage range. We believe this work provides a new strategy for the development of high-performance doped monochromatic and color-stable white OLEDs.