Highly efficient and spectra stable warm white organic light-emitting diodes by the application of exciplex as the excitons adjustment layer

We aim to simplify the device structure due to the low concentration precision and repeatability of white organic light-emitting diodes (WOLEDs) based on exciplex host with phosphorescent dopant. Two layers of exciplex used here play the role of blue emitter and excitons adjustment layer, respectively, to manage the excitons. Green and red phosphorescent ultrathin layer are inserted into exciplex layer to form white light-emitting. The maximum efficiency values of current efficiency, power efficiency and EQE reach to 38.8 cd/A, 34.9 lm/W and 15.3%, and remain 29.7 cd/A, 20.4 lm/W and 11.6% at 1000 cd/m(2), respectively. Besides, the change of Commission Internationale de I'Eclairage coordinates is only (0.024, 0.013) with the enhanced driving voltages from 4 V to 6 V. Such a high performance of warm WOLEDs with simple structure demonstrates the reasonable excitons management and efficient energy transfer from exciplex and excitons adjustment layer to ultrathin phosphorescent emitters.