High-CRI warm white OLEDs based on TADF-Doped Exciplex Co-host Structure enabled by efficient reverse intersystem crossing

In this work, we present a high-performance warm white organic light-emitting diode (WOLED) achieving a maximum color rendering index (CRI) of 95, based on a novel TADF-Doped Exciplex Co-host Structure. The device design integrates a blue exciplex (mCP:PO-T2T) as the host material, sensitizing ultrathin phosphorescent layers emitting green, yellow, and red light. By systematically varying the thickness of spacer and ultrathin layers, the position of the exciton recombination zone was finely tuned, revealing its critical role in exciton transport dynamics and energy transfer efficiency. To optimize exciton transport pathways, the TADF material 4CzTPN was strategically incorporated into the spacer layers. This incorporation significantly altered the exciton transfer mechanism by facilitating efficient reverse intersystem crossing (RISC) and promoting Förster energy transfer from the exciplex to phosphorescent emitters. Consequently, this approach not only reduces triplet exciton density, mitigating Dexter transfer losses, but also enhances exciton utilization efficiency. As a result, the WOLED achieves warm white light emission with a high CRI closely aligned with the Planckian locus on the CIE chromaticity diagram. These findings demonstrate the transformative potential of the TADF-Doped Exciplex Co-host Structure for developing efficient and color-stable WOLEDs, paving the way for next-generation lighting and display technologies.