Organic Light-Emitting Diodes with Ultrathin Emitting Nanolayers

Organic light-emitting diodes (OLEDs) are promising for displays and lighting technologies because of their excellent advantages, such as high efficiency, high luminance, low power consumption, light weight, and flexibility. In recent years, ultrathin emitting nanolayers (UENs) have been used to develop OLEDs without the doping technique, which can simplify device structure, reduce material loss, achieve good exciton utilization, and realize comparable performance to doped devices such as the external quantum efficiency of 28.16%, current efficiency of 63.84 cd/A, and power efficiency of 76.70 Lm/W for white OLEDs. In this review, we comprehensively summarize the recent progress in the field of UEN-based OLEDs. Firstly, the host–guest-doped OLEDs and doping-free UEN-based OLEDs are compared. Then, various effective approaches for designing UEN-based OLEDs are presented, including both monochromatic and white devices. In particular, the properties of materials, the design of device structures, and the main working mechanisms of UEN-based OLEDs are highlighted. Finally, an outlook on the future development of UEN-based OLEDs is provided.