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.