Cyano‐Enhanced Hot‐Exciton Utilization Efficiency for High‐Performance Red Organic Light‐Emitting Diode

ABSTRACT Red light‐emitting materials have extensive applications in many fields such as organic light‐emitting diodes (OLEDs), biological imaging, and night‐vision devices. In this work, we designed and synthesized two red emissive Donor‐Acceptor‐Donor’(D‐A‐D’) type molecules ( ICZNZPPI and ICZNZPPICN ), in which two different donors are introduced on both sides of naphthothiadiazole (NZ) to construct additional hot exciton channels for the improvement of triplet exciton utilization efficiency (EUE). The non‐doped OLEDs of ICZNZPPI and ICZNZPPICN exhibit the red electroluminescence (EL) with a maximum external quantum efficiency (EQE max ) of 0.93% and 3.12%, while their doped OLEDs demonstrate orange‐red EL with the EQE max of 7.32% and 13.52%, respectively. In essence, the higher EQE of ICZNZPPICN than ICZNZPPI is attributed to the introduction of the cyano (CN) group, which not only improves the charge‐transport balance and photoluminescence quantum yield (PLQY) but also significantly enhances the hot‐exciton utilization efficiency. Compared with ICZNZPPI (68%/65%), both non‐doped and doped OLEDs of ICZNZPPICN achieve an ultrahigh EUE of 91%/92%. This work not only demonstrates the feasibility and tunability of the hot‐exciton mechanism but also provides a novel approach for designing pure organic red electroluminescent materials with excellent comprehensive performance.