White Organic Light-Emitting Diodes with High Color-Rendering Index Based on Exciplex

The color rendering index (CR1) is an important evaluation parameter of white organic light-emitting diodes (WOLEDs). We fabricated a series of devices by vacuum evaporation to obtain WOLEDs with high CR1. The exciplex formed by NPH:TPHi(1:1) as a blue emission layer can reduce the difficulty and cost of fabrication of WOLEDs. Comparing this to a device with an exciplex emitting layer (3 nm), the device with the double-exciplex emitting layers (1. 5 nm X 2) helps to balance the exciton distribution and improves the CR1. Furthermore, the thickness of the spacer is changed to adjust the Dexter energy transmission of the exciton. When the thickness of the spacer layer 1 (Spacer 1) is 2 nm, the maximum power efficiency of the warm white light device B2 is 16.11 lm/W, the CR1 is as high as 95 under a driving voltage of 5 V, and its correlated color temperature is 2322 K.