Wide bandgap acceptor with high-lying triplet excited state for efficient upconversion organic light-emitting diode

Organic light-emitting diodes utilizing triplet–triplet annihilation upconversion (UC-OLEDs) enable low-voltage operation; however, they generally suffer from low efficiency. This issue stems from non-radiative deactivation via energy transfer to the acceptor’s low-lying triplet excited state (T 1 ). We introduced a wide-bandgap acceptor, naphthalene diimide derivative, with high T 1 energy (1.86 eV) to suppress this pathway. With an optimized layered structure, the device achieved an external quantum efficiency of 2.84%, 2.37 times higher than that of conventional perylene-tetracarboxylic-diimide devices, while significantly extending the operational lifetime by a factor of 2.7. Controlling T 1 energy of the acceptor is crucial for efficient and stable UC-OLEDs.