Electron Energy Level Alignment for Achieving Extremely Low‐Voltage and Voltage‐Stable p‐i‐n Type Sensitized Fluorescence Organic Light Emitting Diodes with Stable Lifetimes

Abstract Advancements of organic light‐emitting diodes (OLEDs) based on sensitized fluorescence have demonstrated promising efficiency and superior color purity. Nevertheless, overcoming the driving voltage issues, including low operating voltage and clarification of voltage increase during electrical aging, remains challenging. Here, it is disclosed that electron energy level mismatch at the hole‐blocking layer (HBL)/n‐doping electron transport layer (n‐ETL) interface dominates the voltage stability of device degradation. To address this interfacial bandgap, a frontier molecular orbital perturbation strategy is developed through integrating auxiliary electron‐withdrawing groups into the HBL skeleton, enabling low‐voltage and voltage‐stable phosphorescent‐ sensitized fluorescence (PSF) within a new conception of the p‐i‐n type OLED framework. Optimized pure‐green PSF OLEDs based on proof‐of‐concept achieve record‐high power efficiencies of 312.5 and 211.7 lm W −1 at maximum and 10 000 cd m −2 , with stabilized voltage drifts of 0.158 V after 500 h aging times and excellent T95 (lifetime to 95% of the initial luminance) of 43 300 h. Degradation analyses reveal that continuous voltage drifts stem from the electron transport deterioration by metal‐migration of n‐ETL, differing from the brightness decline mechanism (attributed to electron trapping centers). The findings provide critical insights into driving voltage bottlenecks, offering guidance for achieving high‐performance sensitized fluorescence OLEDs.