High-Efficiency Nondoped White Organic Light-Emitting Diodes Based on All-Exciplex Emission

A nondoped full-exciplex approach is applied in white organic light-emitting diodes (WOLEDs). Both the blue emission and yellow emission are from exciplex, which makes it possible to exceed the 25% internal quantum efficiency limit of normal fluorescent OLEDs via reverse intersystem crossing from triplet to singlet states because of the small energy gap between them. White emission can be realized by simply stacking the blue and yellow exciplex materials because the same acceptor material is used in the emitting systems. And a two-color WOLED with an external quantum efficiency (EQE) of 6.11% is demonstrated, exceeding the efficiencies of the exciplex-based blue and yellow monochrome devices. The higher efficiency is attributed to redistribution of the exciplex excitons, which suppresses the exciton concentration quenching at the emission interface. By adopting a quantum-well-like structure, the EQE can be further improved. This approach sheds light on the simple fabrication of high-efficiency WOLEDs in the future.