Recent Advances in White Organic Light‐Emitting Materials and Devices (WOLEDs)

WOLEDs offer new design opportunities in practical solid‐state lighting and could play a significant role in reducing global energy consumption. Obtaining white light from organic LEDs is a considerable challenge. Alongside the development of new materials with improved color stability and balanced charge transport properties, major issues involve the fabrication of large‐area devices and the development of low‐cost manufacturing technology. This Review will describe the types of materials (small molecules and polymers) that have been used to fabricate WOLEDs. A range of device architectures are presented and appraised.     

White Organic Light‐Emitting Devices for Solid‐State Lighting

White organic light‐emitting devices (WOLEDs) have advanced over the last twelve years to the extent that these devices are now being considered as efficient solid‐state lighting sources. Initially, WOLEDs were targeted towards display applications for use primarily as liquid‐crystal display backlights. Now, their power efficiencies have surpassed those of incandescent sources due to improvements in device architectures, synthesis of novel materials, and the incorporation of electrophosphorescent emitters. This review discusses the advantages and disadvantages of several WOLED architectures in terms of efficiency and color quality. Hindrances to their widespread acceptance as solid‐state lighting sources are also noted.     

Recent Advances in Alternating Current‐Driven Organic Light‐Emitting Devices

Organic light‐emitting devices (OLEDs), typically operated with constant‐voltage or direct‐current (DC) power sources, are candidates for next‐generation solid‐state lighting and displays, as they are light, thin, inexpensive, and flexible. However, researchers have focused mainly on the device itself (e.g., development of novel materials, design of the device structure, and optical outcoupling engineering), and little attention has been paid to the driving mode. Recently, an alternative concept to DC‐driven OLEDs by directly driving devices using time‐dependent voltages or alternating current (AC) has been explored. Here, the effects of different device structures of AC‐driven OLEDs, for example, double‐insulation, single‐insulation, double‐injection, and tandem structure, on the device performance are systematically investigated. The formation of excitons and the dielectric layer, which are important to achieve high‐performance AC‐driven OLEDs, are carefully considered. The importance of gaining further understanding of the fundamental properties of AC‐driven OLEDs is then discussed, especially as they relate to device physics.     

Recent Developments in Top‐Emitting Organic Light‐Emitting Diodes

Organic light‐emitting diodes (OLEDs) have rapidly progressed in recent years due to their unique characteristics and potential applications in flat panel displays. Significant advancements in top‐emitting OLEDs have driven the development of large‐size screens and microdisplays with high resolution and large aperture ratio. After a brief introduction to the architecture and types of top‐emitting OLEDs, the microcavity theory typically used in top‐emitting OLEDs is described in detail here. Then, methods for producing and understanding monochromatic (red, green, and blue) and white top‐emitting OLEDs are summarized and discussed. Finally, the status of display development based on top‐emitting OLEDs is briefly addressed.