Unraveling Non-Radiative Decay Channels of Exciplexes to Construct Efficient Red Emitters for Organic Light-Emitting Diodes

Abstract

Exciplex emitters naturally have thermally activated delayed fluorescence characteristics due to their spatially separated molecular orbitals. However, the intermolecular charge transfer potentially induces diverse non-radiative decay channels, severely hindering the construction of efficient red exciplexes. Thus, a thorough comprehension of this energy loss is of paramount importance. Herein, different factors, including molecular rigidity, donor-acceptor interactions and donor-donor/acceptor-acceptor interactions, that impact the non-radiative decay were systematically investigated using contrasting exciplex emitters. The exciplex with rigid component and intermolecular hydrogen bonds showed photoluminescence quantum yield of 84.1% and singlet non-radiative decay rate of 1.98×10⁶ s^-1 under optimized mixing ratio, respectively achieving a 3.3-fold increase and a 70% decrease than the comparison group. In the electroluminescence device, a maximum external quantum efficiency of 23.8% was achieved with an emission peak of 608 nm, which represents the state-of-the-art organic light-emitting diodes using exciplex emitters. Accordingly, a new strategy is finally proposed, exploiting system rigidification to construct efficient red exciplex emitters that suppress the non-radiative decay.