Triplet-Triplet Annihilation Enhanced Deep-Blue Organic Light-Emitting Diodes by Naphtho[1,2-d]imidazole-Isomer Derivatives with Spin-Orbit Coupling

作者：Yang, Guo-Xi; Liu, Deng-Hui; Gu, Qing; Peng, Xiaomei; Li, De-Li; Li, Mengke; Liu, Ming; Chen, Jie; Liu, Kunkun^*; Su, Shi-Jian^*

来源：Advanced Optical Materials, 2023.

DOI：10.1002/adom.202300455

• deep-blue emission
• non-doped organic light-emitting diodes
• spin-orbit coupling
• triplet-triplet annihilation

The utilization of triplet excitons is of great importance for organic light-emitting diodes (OLEDs). Triplet-triplet annihilation (TTA) is one of the effective tactics to achieve high efficiency deep-blue organic electroluminescence emitters by converting two triplet excitons into one singlet exciton. Whereas, in addition to the 25% electrogenerated singlet excitons, the proportion of radiative singlet excitons (RSE) produced by the TTA process is usually only 15%; thus the total radiative excitons are 40%. In this study, approximate to 35% of RSE is achieved by the TTA process (total 60%) with two deep-blue emitters based on the isomeric naphthoimidazole (NI) unit and anthracene bridge. As a result, non-doped OLEDs based on the two NI derivatives as emitting layers achieve maximum external quantum efficiencies of 10.9% and 11.2% with an identical deep-blue emission peak of 452 nm, which are the best TTA OLEDs with a Commission Internationale de l'Eclairage chromaticity Y coordinate below 0.15. Theoretical and experimental results demonstrate that the TTA process can be improved owing to the efficient spin-orbit interactions, even though the energy levels of the triplet pairs are higher than the calculated second triplet excited states.