High Efficiency 3‐Tandem Top Emitting Pure‐Blue OLEDs Beyond the BT.2020 Blue Standard

Tandem Top‐emitting Organic Light Emitting Diodes (TEOLEDs) have been in the spotlight for the past two decades due to their high efficiency, color purity, and longer operational lifetime. However, a systematic optimization method for reaching outstanding performance remains unexplored. Herein, we report a high‐efficiency, ultrapure‐blue three‐tandem TEOLED by leveraging the advantages of a narrowband emitter through synergistic optimization of the cavity structure and cathode design. By considering the Purcell effect, systematic optical simulations were performed for a multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitter (4F‐m‐ν‐DABNA) with intrinsically narrow emission to optimize the emitting dipole position and maximize cavity‐enhanced emission in microcavity conditions for single to 3‐tandem devices. Furthermore, a pure Ag cathode was used instead of the conventional Ag:Mg cathode, resulting in higher reflectance and lower parasitic absorption by carefully tuning the cathode and capping layer (CPL) thickness to balance cavity resonance and light out‐coupling efficiency. As a result, the optimized 3‐tandem device exhibits an emission peak at 463 nm, a narrow full width at half maximum (FWHM) of 10 nm, a CIE y coordinate of 0.040, and a maximum blue index of 1,596 cd/A/y, surpassing the BT.2020 blue standard.