Exciplex Structure of Highly Efficient Tadf OLEDs
Wen-Yi Hung1*, Ken-Tsung Wong2
1Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung, Taiwan
2Department of Chemistry, National Taiwan University, Taipei, Taiwan
* Presenter:Wen-Yi Hung
Lighting materials with thermally activated delayed fluorescence (TADF), which may theoretically harvest 100% internal quantum efficiency, have been attracting vast attention in the field of organic light emitting diodes (OLEDs). The core of TADF lies in a small singlet−triplet energy splitting, which allows highly efficient population from the emission forbidden triplet states (T1) to the allowed singlet states (S1) via thermal activation. Besides single-molecule TADF emitters, TADF can also be achieved by an exciplex exciton which can be simply generated by two oppositely charged molecules with weak Coulomb interactions. In OLED, charge carriers accumulating in the physically contact electron-donor (D)/ electron-acceptor (A) interface can generate exciplex excitons. The HOMO and LUMO orbitals of the exciplex exciton are primarily distributed on D and A, respectively, giving a very low electron exchange energy and therefore a small ΔEST for efficient RISC. Hence, employ effective exciplex as an emitter just require the selection of suitable D and A molecules without the needs of sophisticated molecule design and tedious synthesis. Here, we report a record-high blue exciplex OLED (EQE: 16%) consisting of a new carbazole-based electron donor CN-Cz2 and an acceptor PO-T2T co-deposited as the solid film. Subsequently, this leads to the successful construction of a tandem white light OLED (WOLED) with excellent efficiencies (EQE: 23.5%) with CIE(0.35, 0.47) that are nearly independent of EL intensity.

Keywords: OLED, thermally activated delayed fluorescence (TADF), exciplex excitons