Critical Role of High‐Lying Triplet States for Efficient Excitons Utilization in High‐Performance Non‐Doped Deep‐Blue Fluorescent and Hybrid White Organic Light‐Emitting Diodes

Abstract For organic light‐emitting diodes (OLEDs), the characteristics of high‐lying excited states of pure organic materials significantly affect the utilization of triplet excitons, which are critical in the process of electroluminescence. Herein, two novel molecules, PT‐1 and PT‐2, with deep‐blue emission are obtained, which exhibit nearly identical photophysical behavior in the photoluminescence process. However, the remarkable distinction in the characteristics of the high‐lying triplet excited states between PT‐1 and PT‐2 leads to a significant difference in the electroluminescence performance. Moreover, the non‐doped OLED based on PT‐1 exhibits maximum external quantum efficiency (η ext ) of 6.63% with a low efficiency roll‐off. In addition, the authors employ PT‐1 as the phosphorescent host materials to fabricate two‐color hybrid white OLEDs (WOLEDs), from which they can realize the transformation from warm‐white to quasi‐white light by tuning the thickness of emission layer, with maximum η ext and power efficiency (η p ) of 23.93%/84.37 lm W −1 and 10.49%/33.96 lm W −1 , respectively. These results deeply demonstrate the effects of high‐lying excited states on electroluminescence and facilitate the preparation of functional OLEDs.