Enhancing the Efficiency of HLCT Emitter via External TTA Up‐conversion With Exciton Recycling Channel

Abstract Hybridized local and charge‐transfer (HLCT) materials exhibit great potential for high‐efficiency organic light‐emitting diodes (OLEDs) due to their rapid high‐energy reverse intersystem crossing (hRISC) and high photoluminescence quantum yield (PLQY). However, their exciton utilization efficiency (EUE) is constrained by energy loss from higher triplet states (T n , n ≥ 2) to T 1 via internal conversion and direct generation of T 1 excitons during device operation. To address this limitation, two HLCT blue emitters, PPIBA and PPIXO, are designed and synthesized. The PLQY of PPIBA and PPIXO reach 89.78% and 90.75%, whereas the EUE of their devices is only 39.7% and 31.4%. To further boost the EUE, a triplet‐triplet annihilation up‐conversion (TTA‐UC) material, 1‐(2,5‐dimethyl‐4‐(1‐pyrenyl)phenyl)pyrene (DMPPP), is introduced to recycle the T 1 excitons of the emitter. This strategy significantly enhances the EUE of the PPIBA‐ and PPIXO‐based devices, reaching 65.6% and 63.5%, respectively. Compared to non‐doped devices, incorporating TTA‐UC leads to substantial performance enhancements of 31.8% and 75.0% for PPIBA and PPIXO devices, respectively. Notably, the optimized devices exhibit negligible efficiency roll‐off until damage. This work demonstrates that TTA‐UC as an assistant host can overcome intrinsic limitations of HLCT materials in the emitting layer, providing a viable pathway for high‐performance OLEDs.