High efficiency OLEDs based on exciplex (Conference Presentation)

Organic materials that display thermally activated delayed fluorescence (TADF) are a striking class of functional materials that have witnessed a booming progress in recent years. The small ΔEST in TADF-based systems prompts highly efficient RISC from T1 to S1 states, and consequently both singlet and triplet excitons can be harvested for light emission. For the last five years, a tremendous amount of TADF molecules have been reported based on the manipulation of the intramolecular charge transfer as well as the HOMO-LUMO overlap. Beyond this strategy, there is an emerging approach that simply involves intermolecular charge transfer between physically blended electron donor and acceptor molecules for high efficiency TADF-based OLEDs (via exciplex formation). This is because the exciplex-based systems can realize relatively small ΔEST (0–0.05 eV) much more easily since the electron and hole are positioned on two different molecules, thereby giving small exchange energy. Consequently, exciplex-based OLEDs have the possibility to maximize the TADF contribution and achieve theoretical 100% internal quantum efficiency and solve the challenging issue of achieving small ΔEST in organic systems. However, research on exciplex-forming materials is still at a growing stage, and consequently, new molecules with remarkable electro and or photo-physical property are still being explored. Thus, by focusing on the development of exciplex systems, we shall have the prospective of achieving the demands for high-efficiency and high stability OLED devices. In this conference, we will report our updated results of new efficient exciplex systems, and exciplex-hosted fluorescent and phosphorescent OLEDs with high efficiency and high stability.