Influence of Introduction of an Exciton Capture Layer in the Donor on the Performance of Exciplex Upconversion-Type Organic Light-Emitting Diodes

Further development of organic light-emitting diodes (OLEDs) requires a reduction in driving voltage. Exciplex upconversion-type OLEDs (ExUC-OLEDs), which are actively utilized to form exciplexes at the donor/acceptor interface, are an optimal solution for reducing the driving voltage. However, a phenomenon that cannot be explained by simple exciton diffusion is observed in these devices. Herein, an exciton capture layer is inserted into the emitter (donor) layer of ExUC-OLEDs to elucidate the exciton diffusion mechanism. All ExUC-OLEDs emit light via triplet–triplet upconversion (TTU) and at more than half the applied voltage (1 V) of the energy gap of the emitter material. In addition, long-range exciton diffusion of up to 40 nm is confirmed by TTU and singlet fission contributions.