Reproducible high-efficiency and color stable single-emitting-layer cold WOLEDs based on inhibition of energy transfer and efficient exciton harvesting

Traditional white organic light-emitting diodes (WOLEDs) often rely on mechanism of incomplete energy transfer, which generally necessitate extremely low doping concentrations for low-energy emitters. This poses significant challenges in device fabrication reproducibility and color coordinate consistency. In this work, we developed a hot exciton yellow-emitting excited state intramolecular proton transfer (ESIPT) fluorophore, T4AC, featuring a large Stokes shift. The material achieves a high exciton utilization efficiency of up to 88.8 %, via high-energy-level reverse intersystem crossing (hRISC). By co-doping T4AC with a thermally activated delayed fluorescence (TADF) blue emitter, DMAc-MPM, we realized highly efficient and reproducible bluish WOLEDs employing a single emitting layer with complementary-color emissions. Minimal spectral overlap effectively suppressed energy transfer, thus ensuring independent triplet harvesting via hot exciton mechanism in T4AC and the TADF process in DMAc-MPM, respectively. The resulting device exhibits color stable and high-efficiency cold white emission, achieving maximum external quantum efficiency (EQE) of 11.50 % and current efficiency (CE) of 27.74 cd A⁻¹. More importantly, these bluish WOLEDs demonstrated excellent reproducibility across multiple batches, with small EQE variations within 11.15 % ± 0.62 % and CIE coordinate fluctuations confined to a narrow range of (0.181 ± 0.004, 0.351 ± 0.030). This study presents a viable strategy for the development of simple-structured, highly efficient, and reproducibly fabricated cold WOLEDs.