Enhancing Narrowband Blue TADF OLED Performance with Adamantane Group-Integrated Spatially Hindered 1,3-Bis(N-Carbazolyl)Benzene-Based Host

In the past, considerable effort are focused on advancing blue organic light-emitting diodes (OLEDs) based on 1,3-bis(N-carbazolyl)benzene (mCP). To enhance and stabilize the device performance in vacuum-processed OLEDs, it is essential to optimize the thermally stable organic materials constituting the emitting layer. The proposed novel carbazole derivative, Ad-mCP, is designed and synthesized as a host material for blue thermally activated delayed fluorescence OLEDs, which are ideal for vacuum processing. Ad-mCP exhibits a high glass transition temperature and triplet energy (T₁), making it highly compatible with the blue dopant 2,11,14-tri-tert-butyl-N,N,5-tris(4-(tert-butyl)phenyl)−5H-5,8b-diaza-15b-borabenzo[a]naphtho[1,2,3-hi]aceanthrylen-7-amine emitter. The incorporation of a rigid adamantane unit into the carbazole group modifies the molecular structure of mCP, preserving crucial photophysical properties, such as T_1,while enhancing the morphological and thermal stability of the host material in its film state. Moreover, the spatially hindered molecular structure of Ad-mCP improves the photoluminescent quantum yield of the emissive layer and enhances charge balance, crucially contributing to the overall efficiency of the OLEDs. As a result, the exceptional performance of Ad-mCP as a host material for OLEDs resulted in a remarkably high maximum external quantum efficiency of 29.9%, demonstrating superior stability in efficiency even after thermal annealing compared to mCP devices.