Highly efficient and stable blue fluorescent OLED using dual EML system

Abstract In 2022, we presented a high‐efficiency improvement for blue fluorescent OLEDs through Dual emitting layer (BH1/BH2 EML) technology to enhance performance. In this study, the light extraction efficiency was improved by controlling the molecular orientation and the spectral shape of the blue dopant (BD) in the blue host (BH) on the anode side. Additionally, through mechanism analysis, we confirmed that the clear functional separation of the two layers enhanced the Triplet‐Triplet Fusion (TTF) efficiency and each BHs deuteration impact resulting in a multiplicative extension of lifetime. Furthermore, by applying a dual‐hole transporting layer (HTL) that contributes to light extraction improvement, the bottom‐emission (BE) device achieved external quantum efficiency (EQE) = 16.3%, and top‐emission (TE) device reached BI = 350, LT95@50 mA/cm 2 > 200 h.