Affiliation:
1. Cavendish Laboratory Department of Physics University of Cambridge J J Thomson Avenue Cambridge CB3 0HE UK
2. Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering National Taiwan University 10617 Taipei Taiwan
3. State Key Laboratory of Supramolecular Structure and Materials College of Chemistry Jilin University Qianjin Avenue 2699 Changchun 130012 P. R. China
4. Department of Chemistry Swansea University Singleton Park Swansea SA2 8PP UK
Abstract
AbstractOrganic radicals have been of interest due to their potential to replace nonradical‐based organic emitters, especially for deep‐red/near‐infrared (NIR) electroluminescence (EL), based on the spin‐allowed doublet fluorescence. However, the performance of the radical‐based EL devices is limited by low carrier mobility which causes a large efficiency roll‐off at high current densities. Here, highly efficient and bright doublet EL devices are reported by combining a thermally activated delayed fluorescence (TADF) host that supports both electron and hole transport and a tris(2,4,6‐trichlorophenyl)methyl‐based radical emitter. Steady‐state and transient photophysical studies reveal the optical signatures of doublet luminescence mechanisms arising from both host and guest photoexcitation. The host system presented here allows balanced hole and electron currents, and a high maximum external quantum efficiency (EQE) of 17.4% at 707 nm peak emission with substantially improved efficiency roll‐off is reported: over 70% of the maximum EQE (12.2%) is recorded at 10 mA cm−2, and even at 100 mA cm−2, nearly 50% of the maximum EQE (8.4%) is maintained. This is an important step in the practical application of organic radicals to NIR light‐emitting devices.
Funder
Engineering and Physical Sciences Research Council
National Natural Science Foundation of China
National Science and Technology Council
Subject
Mechanical Engineering,Mechanics of Materials,General Materials Science