High-Efficiency Red Organic Light-Emitting Diodes with External Quantum Efficiency Close to 30% Based on a Novel Thermally Activated Delayed Fluorescence Emitter
Yuan-Lan Zhang,1 Quan Ran,1 Qiang Wang,1 Yuan Liu,2 Christian H?nisch,2 Sebastian Reineke,2 Jian Fan,1* and Liang-Sheng Liao1*
1Institute of Functional Nano & Soft Materials (FUNSOM), Collaborative Innovation Center of Suzhou Nanoscience and Technology, Soochow University, 199 Ren-AiRoad, Suzhou 215123, China.
2Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universit?t Dresden, Hermann-Krone-Bau, N?thnitzer Str. 61, 01187 Dresden, Germany.
Researchers have spared no effort to design new thermally activated delayed fluorescence (TADF) emitters for high-efficiency organic light-emitting diodes (OLEDs). However, efficient long-wavelength TADF emitters are rarely narrated. Herein, we report a red TADF emitter TPA-PZCN, which possesses a high photoluminescence quantum yield (ΦPL) of 97% and a small singlet-triplet splitting (ΔEST) of 0.13 eV. Based on the superior properties of TPA-PZCN, red, deep-red, and near-infrared (NIR) OLEDs are fabricated by utilizing different device structure strategies. The red devices obtain a remarkable maximum external quantum efficiency (EQE) of 27.4% and an electroluminescence (EL) peak at 628 nm with the Commission Internationale de L'Eclairage (CIE) coordinates of (0.65, 0.35), which represents the best result with a peak wavelength longer than 600 nm among those of the reported red TADF devices. Furthermore, an exciplex-forming cohost strategy is adopted. The devices achieve a record EQE of 28.1% and a deep-red EL peak at 648 nm with the CIE coordinates of (0.66, 0.34). Last, nondoped devices exhibit 5.3% EQE and an NIR EL peak at 680 nm with the CIE coordinates of (0.69, 0.30).