Control of energy transfer by tuning Donor/Acceptor interface for exciplex upconversion-type organic light-emitting diodes

Organic light-emitting diodes (OLEDs) generally require operating voltage corresponding to the energy gap of the emitter. To reduce operating voltage, exciplex upconversion-type OLEDs (ExUC-OLEDs) have been reported. ExUC-OLEDs emit light via triplet-triplet upconversion (TTU) by transferring the energy of the exciplex to T1 of the emitter. Therefore, a combination of donor and acceptor that form an appropriate exciplex for energy transfer is required, and the degree of freedom in material selection for ExUC-OLEDs is low. Herein, the insertion of the spacer at the donor/acceptor interface controls the coulombic attraction, the energy of the exciplex, and the energy transfer to the emitter. As a result, ExUC emission is maintained up to 3 nm spacer thickness, and the external quantum efficiency is improved. Therefore, it is possible to increase the degree of freedom in material selection for ExUC-OLEDs by using appropriate spacer materials.