π-Stacked host materials based on spirofluorene scaffolds for warm white OLEDs achieving 94.7 lm W −1 at 1,000 cd m −2

Power efficiency (PE) at high brightness is considered as the rigorous standard of high-quality white organic light-emitting diodes (WOLEDs), for which the host material plays a significant role in energy conservation for practical lighting applications. Herein, PE is successfully enhanced to a new level through the method of π-stacked host molecular with spirofluorene scaffold. We design host materials by confining two donor units in a very short distance to enlarge the π-electron spatial delocalization for facilitating the hole hopping process and engaging a rigid donor as the space-lock to suppress the quenching effect as well as induce host bipolar property. Based on this unique molecular design, the red, green, and blue (RGB) monochromic organic light-emitting diodes (OLEDs) demonstrate high external quantum efficiencies (EQEs) of 28.4%, 26.0%, and 31.2% with ultralow roll-off, respectively. More encouragingly, the warm WOLEDs achieve record-high current efficiency (CE) of 109.5 cd A −1 , PE of 109.1 lm W −1 , and EQE of 32.9%. Even under operating brightness of 1,000 cd m −2 , the devices can still realize 94.7 lm W −1 of PE, which represents the highest applicable PE value in the reported WOLEDs and for the first time single host based WOLEDs with a performance exceeding that of a conventional fluorescent tube (70 lm W −1 ) without any light extraction technique.