Energy‐Efficient Stable Hyperfluorescence Organic Light‐Emitting Diodes with Improved Color Purities and Ultrahigh Power Efficiencies Based on Low‐Polar Sensitizing Systems

Abstract Multi‐resonance (MR) molecules with thermally activated delayed fluorescence (TADF) are emerging as promising candidates for high‐definition displays because of their narrow emission spectra. However, the electroluminescence (EL) efficiencies and spectra of MR‐TADF molecules are highly sensitive to hosts and sensitizers when applied to organic light‐emitting diodes (OLEDs), and the highly polar environments in devices often lead to significantly broadened EL spectra. In this study, a proof‐of‐concept TADF sensitizer (BTDMAC‐XT) with low polarity, high steric hindrance, and concentration‐quenching free feature is constructed, which acts as a good emitter in doped and non‐doped OLEDs with high external quantum efficiencies (η_exts) of 26.7% and 29.3%, respectively. By combining BTDMAC‐XT with conventional low‐polarity hosts, low‐polarity sensitizing systems with a small carrier injection barrier and full exciton utilization are constructed for the MR‐TADF molecule BN2. Hyperfluorescence (HF) OLEDs employing the low‐polar sensitizing systems successfully improve the color quality of BN2 and afford an excellent η_ext of 34.4%, a record‐high power efficiency of 166.3 lm W⁻¹ and a long operational lifetime (LT₅₀ = 40309 h) at an initial luminance of 100 cd m⁻². These results provide instructive guidance for the sensitizer design and device optimization for energy‐efficient and stable HF‐OLEDs with high‐quality light.