Recent advances in white organic light-emitting diodes

White organic light-emitting diodes (WOLEDs) are emerging as the most promising technology for the next-generation display and solid-state lighting applications owing to their merits of being high-efficiency, low-cost, easy-flexibility, and environment-friendly. In this review, we will discuss the fundamental working principles, the basics of exciton manipulation concepts, the architecture designs within the emissive region, the approaches to relieve the efficiency roll-off at high luminance, and the remaining challenges in all phosphorescent and hybrid WOLEDs. A comprehensive understanding of the exciton manipulation concept and the key factors dominating the WOLED performances is of great importance for advancing technological applications. We aim to provide an overview on the recent advances in WOLEDs with emphasis specifically on: (a) principles on how to manipulate singlet and triplet excitons for maximizing the exciton utilization efficiency; (b) exciton manipulation in all phosphorescent WOLEDs and hybrid WOLEDs based on conventional fluorophors or thermally activated delayed fluorescent emitters by finely designing the emitting layer architectures and selecting matched materials; and (c) strategies to mitigate the efficiency roll-off including the utilization of effective charge and exciton-confined structures, decreasing the exciton lifetime, reducing molecular aggregation, and broadening the exciton recombination zone.