Highly Efficient and Long-Range Charge-Transfer Complex Emission Between Two Blue Phosphorescent Emitters for White Organic Light-Emitting Diodes

Herein, the authors report on charge-transfer (CT) complex emission-based organic light-emitting diodes (OLEDs), which emit light by electric field-induced intermolecular CT complex formation in the light-emitting layer. Two phosphorescent materials are chosen to have energy level offset for the CT complex formation. This process generates the CT complex, which efficiently emits only in the electroluminescent device by electric-field-induced complex formation. A phenylpyridine-ligand-based Ir compound and phenylimidazole-based Ir compounds are selected as the CT complex-forming materials, and the CT complex exhibits yellow emission under an electric field. Moreover, the doping of the two compounds in the host material produces white OLEDs, exhibiting both blue emission and yellow emission at a quantum efficiency of 13.7%. In particular, the color of the CT complex device can be tuned by the content of each material in the emitting layer. As an initial result, the quantum efficiency is acceptable, and further material development would enhance the quantum efficiency of the CT complex OLEDs. This light-emitting device can be used in various applications, e.g., a mono-color or a white-color light-emitting diode.