Recent Advances in Solution-Processed White Organic Light-Emitting Materials and Devices

Solution-processed white organic light-emitting diodes (WOLEDs) have drawn great attention both in the academic and industrial research communities due to the potential application in low-cost, large-area, solid-state lightings. Issues related to the device efficiencies are largely hampering progress in this field. Alongside the development of new materials and novel device architectures, distinct progress has been made for such white devices. In particular, the all-phosphorescent light-emitting strategy has been intensively developed in recent years, mainly focusing on a host-guest, doping-system-based, single-active-layer structure and a solution-processed, multilayer device structure. Novel approaches, including white single polymers and excimer-/exciplex-based white devices, have also appeared as a promising choice and received great attention. As a prerequisite, the issue of the morphology of the emissive layer is also important and has an influence on the optoelectronic behavior of the device. Herein, major advances in solution-processed WOLEDs based on polymers, dendrimers, or solution-processed small molecules are summarized. Special attention is focused on the main progress in high-efficiency, solution-processed WOLEDs with the key strategies mentioned above and the morphology issue in these systems. The remaining challenges in pursuing the development of reliable and energy-saving lighting devices are also discussed.