Deep-Red Organic Light-Emitting Diodes with Increased External Quantum Efficiency and Extended Operational Lifetime by Managing the Composition of Mixed Cohosts

To achieve high-performance and stable deep-red (DR)/near-infrared (NIR) organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters, here, a mixed cohost structure with carrier regulating capability was constructed by combining 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy) with 1,3,5-tris(6-(3-(pyridin-3-yl)phenyl)pyridin-2-yl)benzene (Tm3PyP26PyB) and optimizing the mixing ratios and thicknesses. The results indicated that this structure is efficient in modulating the carrier balance and boosting recombination probability due to effective blocking of excess holes and increased electron mobility. By employing the NIR TADF dye 7,10-bis(4-(diphenylamino)phenyl)-2,3-dicyanopyrazino-phenanthrene (TPA-DCPP) as a dopant, the optimized device obtained DR emission (663 nm) with an increased external quantum efficiency (EQE) of 16.4% and extended device lifetime LT50 of 135 min, which are superior to those of reference and reported devices. Our investigations provide an effective and synergistic strategy for promoting the development of DR/NIR OLEDs.