High-performance doping-free hybrid white organic light-emitting diodes: The exploitation of ultrathin emitting nanolayers (< 1 nm)

Doping-free organic light-emitting diodes (OLEDs) have aroused research interest due to their simple properties. However, their performances are unsatisfactory, particularly for doping-free white OLEDs (DF-WOLEDs). Herein, by exploiting ultrathin emitting nanolayers (< 1 nm), simplified but high-performance doping-free hybrid WOLEDs (DFH-WOLEDs), for the first time, have been developed. Firstly, it is found that interlayers play a new role in hybrid WOLEDs, called averting the concentration quenching. Then, unlike conventional concepts, unipolar interlayers are more beneficial than bipolar interlayers in DFH-WOLEDs. A two-color DFH-WOLED can exhibit high efficiency (similar to 40 lm W-1), stable color, low voltage and high luminance. Significantly, its phosphorescent layer is 109 times thinner than that of the representative DF-WOLED. Besides, unlike previous hybrid WOLEDs, the DFH-WOLED shows a unique emission mechanism. Moreover, three-color DFH-WOLEDs exhibit i) a wide color correlated temperature span (2325-8011 K), which is the first DF-WOLED showing sun-like emission; or ii) a color rendering index (CRI) of 91.3, which is the first three-color DF-WOLED with ultrahigh CRI (> 90). Such surprising findings will unlock a novel concept that ultrathin emitting nanolayers (< 1 nm) are promising to develop simplified but high-performance hybrid WOLEDs, which possess a bright prospect for the next generation lightings and displays. (C) 2016 Elsevier Ltd. All rights reserved.