Blue HLCT Material Featuring Dual hRISC Channels for White Organic Light‐Emitting Diode Achieving Extremely Small Efficiency Roll‐Off of less than 2.5% at 10000 cd/m ²

ABSTRACT White organic light‐emitting diodes (OLEDs) are widely regarded as the promising candidates for next‐generation lighting technology. However, notorious efficiency roll‐off remains a crucial issue that severely restricts their lighting application under high luminance. Herein, we propose to use a novel blue hybridized local and charge‐transfer (HLCT) material as the emitter and sensitization host to develop all‐fluorescent white OLEDs. Specifically, both blue HLCT materials of PyIAnp and pCzAnN are employed, in which PyIAnp exhibits interesting dual reverse intersystem crossing from higher triplet states (hRISC), but pCzAnN emits deeper blue light with an electroluminescence peak of 440 nm. All‐fluorescent white OLEDs are structured by combining a pCzAnN blue non‐doped layer with complementary doping emitting layers featuring traditional fluorescent green and red molecules sensitized by PyIAnp host. The resulting device realizes a broad and balanced white spectrum with a high color rendering index of 87. Moreover, the proposed white device exhibits an extremely small efficiency roll‐off of only 2.38% at a high luminance of 10000 cd/m ² , which is the lowest efficiency roll‐off value in reported white OLEDs, demonstrating a huge potential application. The dual hRISC mechanism of PyIAnp maximizes the conversion of triplet excitons to singlet excitons, suppressing triplet‐triplet exciton quenching, which is responsible for negligible efficiency roll‐off.