50‐2: Invited Paper: Highly Efficient OLEDs using Exciplex Hosts

An exciplex is an excited state charge transfer complex formed between a donor molecule and an acceptor molecule upon excitation of the donor or acceptor molecule. Because of the charge transfer characteristics, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the exciplex are considered to be located on the donor and acceptor molecules, respectively. Since the overlap between the HOMO and the LUMO of the exciplex is small, the energy difference between the singlet and the triplet excited states can be very small. Therefore, exciplex forming materials have been used to harvest triplet as well as the singlet energy in OLEDs. Exciplex forming systems can also be used as co‐hosts of phosphorescent dyes for efficient OLEDs. An exciplex forming co‐host can be considered as a quasi‐host material possessing its singlet and triplet excited state energy close to the energy difference between the LUMO of the electron transporting material (acceptor) and the HOMO of the hole transporting material (donor) of the co‐host materials, which can be utilized to achieve high efficiency and low driving voltage in OLEDs. In this talk, we will present highly efficient phosphorescent and TADF OLEDs using exciplex host doped with phosphorescent dyes with preferred emitting dipole orientation along horizontal direction to realize the external quantum efficiency over 30%, low driving voltage, and low efficiency roll‐off by doping.