Hybrid White OLEDs with High Electroluminescence Efficiency and High Color Rendering Index Achieved by a Sandwich Interlayer Sensitizing Configuration

White organic light-emitting devices (WOLEDs) exhibit promising applications as white illumination and background light, but achieving high efficiencies, and high color quality for the WOLEDs still remains difficult. Herein, to enhance exciton utilization and improve the color quality of WOLEDs, a new sandwich configuration of an ultrathin orange phosphorescent layer located between two blue thermally activated delayed fluorescence (TADF) layers is proposed, and the working mechanism is investigated. In this configuration, the interlayer sensitization from blue TADF layers to orange phosphorescent layer via efficient Förster energy transfer occurs, which effectively alleviates exciton quenching in emitting layers and thus results in excellent electroluminescence (EL) efficiencies and improved color quality. The obtained two-color hybrid WOLED exhibits an external quantum efficiency (η_ext) exceeding 27%, with Commission Internationale del'Eclairage (CIE_x,y) coordinates of (0.335, 0.396) and a color rendering index (CRI) of 63. By further incorporating an ultrathin red phosphorescent layer between the orange phosphorescent layer and the blue TADF layer, the η_ext maintains at 21.96% and the CRI increases to 91 (CIE_x,y = 0.380, 0.366). These results demonstrate the proposed sandwich interlayer sensitizing configuration is an effective and feasible strategy for realizing high EL efficiencies and high color quality simultaneously for hybrid WOLEDs.