Enhancing External Quantum Efficiency of Non‐Doped Deep‐Blue OLEDs by Optimizing Hybridized Local and Charge‐Transfer States

ABSTRACT Owing to the combination of high color purity of localized excited states and the benefits of inherent exciton utilization of charge‐transfer states, hybridized local and charge‐transfer (HLCT) states present significant potential for non‐doped organic light‐emitting diodes (OLEDs). However, it remains challenging to achieve efficient deep‐blue HLCT emitters, since strong charge transfer (CT) character leads to red shifted emission. Herein we demonstrated that the intensity of CT state can be modulated through strategic incorporation of phenyl rings to regulate the spatial separation between building blocks. Detailed investigations revealed that the new emitter CPChN, which exhibits a moderately enhanced charge transfer contribution, undergoes an efficient high‐lying reverse intersystem crossing process. This results in an external quantum efficiency exceeding 14% for a non‐doped device with Commission Internationale de l'Éclairage (CIE) coordinates of (0.160, 0.043), which is one of the highest efficiencies achieved for non‐doped OLEDs with the CIE _y < 0.05. In contrast, the emitter CPPChN, which is predominantly characterized by local excited states, achieves a significantly lower efficiency of about 6%. This comparative analysis highlights that precise control of the charge transfer proportion in emitters with HLCT states represents a strategic approach for advancing the development of high‐efficiency deep‐blue OLEDs.