Highly Efficient and Color‐Stable Thermally Activated Delayed Fluorescence White Light‐Emitting Diodes Featured with Single‐Doped Single Emissive Layers

Abstract Despite their merits of environmental friendliness, low cost, and large‐scale production, thermally activated delayed fluorescence (TADF) based white organic light‐emitting diodes (WOLEDs) for daily lighting applications still face the formidable challenges of structural simplification and controllable exciton allocation. Here, the state‐of‐the‐art full‐TADF WOLEDs with features of the single‐doped single emissive layers (EMLs) and ultrasimple trilayer structure are demonstrated. The EMLs are binary systems as yellow TADF emitter (4CzTPNBu) doped blue TADF matrix ( p tBCzPO 2 TPTZ) with the large steric hindrance and mismatched frontier molecular orbital energy levels to effectively restrain excessive blue‐to‐yellow triplet exciton transfer and host‐dopant interaction induced triplet quenching. Simultaneously, Förster resonance energy transfer is utilized to optimize exciton allocation for the balance of blue and yellow emissions, giving rise to the photoluminescence quantum yield beyond 90%. Consequently, these single‐doped EMLs endow their cool white, pure white, and warm white diodes with the high‐quality and ultrastable white light and the 100% exciton utilization efficiencies through the extremely simple structures, making them competent for the diverse daily lighting applications.