Blue organic light-emitting diode (OLED) technology requires further advancements, and hyperfluorescent (HF) OLEDs have emerged as a promising solution to address stability and colour-purity concerns. A key factor influencing the performance of HF-OLEDs is Förster resonance energy transfer (FRET). Here we investigate the FRET mechanism in blue HF-OLEDs using contrasting thermally activated delayed fluorescence (TADF) sensitizers. We demonstrate that the molecular structure of the sensitizer profoundly impacts the FRET efficiency, exemplified by the spiro-linked TADF molecule ACRSA, which suppresses the dihedral-angle inhomogeneity and any lower-energy conformers that exhibit minimal FRET to the terminal emitter. Consequently, the FRET efficiency can be optimized to nearly 100%. Further, we demonstrate how the properties of a near-ideal sensitizer diverge from ideal TADF emitters. As a result, blue HF-OLEDs utilizing a greenish sensitizer exhibit a remarkable tripling of external quantum efficiency (~30%) compared with non-HF devices. This new understanding opens avenues for sensitizer design, indicating that green sensitizers can efficiently pump blue terminal emitters, thereby reducing device exciton energies and improving blue OLED stability.

蓝色有机发光二极管 (OLED) 技术需要进一步发展，而超荧光 (HF) OLED 已成为解决稳定性和颜色纯度问题的有前途的解决方案。影响 HF-OLED 性能的关键因素是福斯特共振能量转移 (FRET)。在这里，我们使用对比热激活延迟荧光 (TADF) 敏化剂研究蓝色 HF-OLED 中的 FRET 机制。我们证明敏化剂的分子结构深刻影响 FRET 效率，以螺连接的 TADF 分子 ACRSA 为例，它抑制二面角不均匀性和任何对终端发射器表现出最小 FRET 的低能构象。因此，FRET 效率可以优化至接近 100%。此外，我们还展示了近乎理想的敏化剂的特性如何与理想的 TADF 发射体不同。因此，与非 HF 器件相比，使用绿色敏化剂的蓝色 HF-OLED 的外部量子效率显着提高了三倍（约 30%）。这一新的认识为敏化剂设计开辟了途径，表明绿色敏化剂可以有效地泵浦蓝色终端发射器，从而降低器件激子能量并提高蓝色OLED稳定性。