The Strategies for High-Performance Single-Emissive-Layer White Organic Light-Emitting Diodes

White organic light-emitting diodes (WOLEDs) have been regarded as the most promising candidate for full-color display and solid-state lighting applications owing to their favorable merits of high efficiency, superior white color balance, simple fabrication, and large-area manufacturing possibility. Particularly, single-emissive-layer WOLEDs (SEL-WOLEDs) with the reduced structural complexity, lower process cost, and feasible solution processing have drawn particular attentions. Numerous strategies have been proposed in recent years to construct SEL-WOLEDs with improved device performance. This review focuses on the aspects, including: a) the molecular design methods for achieving a single-molecule WOLED; b) the energy transfer mechanisms in various multiple-molecule SEL-WOLEDs with all-fluorescence, all-phosphorescence, and fluorescence-phosphorescence hybrid structures; c) the combination of exciplex emitters and complementary fluorescent/thermally-activated delayed fluorescent/phosphorescent emitters to realize SEL-WOLEDs. Some future prospects on new opportunities and technological challenges in SEL-WOLEDs are also covered.