Emission and Absorption Tuning in TADF B,N-Doped Heptacenes: Toward Ideal-Blue Hyperfluorescent OLEDs

摘要

Developing high-efficiency purely organic blue organic light-emitting diodes(OLEDs) that meet the stringent industry standards is a major currentresearch challenge. Hyperfluorescent device approaches achieve in largemeasure the desired high performance by combining the advantages of ahigh-efficiency thermally activated delayed fluorescence (TADF) assistantdopant with a narrowband deep-blue multi-resonant TADF (MR-TADF)terminal emitter. However, this approach requires suitable spectral overlapto support F?rster resonance energy transfer (FRET) between the two.Here, a color tuning of a recently reported MR-TADF B,N-heptacene corethrough control of the boron substituents is demonstrated. While there islittle impact on the intrinsic TADF properties—as both singlet and tripletenergies decrease in tandem—this approach improves the emission colorcoordinate as well as the spectral overlap for blue hyperfluorescence OLEDs(HF OLEDs). Crucially, the red-shifted and more intense absorption allowsthe new MR-TADF emitter to pair with a high-performance TADF assistantdopant and achieve maximum external quantum efficiency (EQE_(max)) of 15%at color coordinates of (0.15 and 0.10). The efficiency values recorded for thedevice at a practical luminance of 100 cd m–2 are among the highest reportedfor HF TADF OLEDs with CIE_y ≤ 0.1.