Nanostructures in Organic Light‐Emitting Diodes: Principles and Recent Advances in the Light Extraction Strategy

Organic light‐emitting diodes (OLEDs) in recent years have emerged as a leading display technology and the popularity of OLEDs is attributed to their numerous advantages, including the ability to produce natural color, achieve a true black state, consume low consumption, exhibit fast response, and be compatible with flexible devices. However, limitations in the performance persist, e.g., the out‐coupling efficiency, which currently stands at ≈20% due to issues such as trapped modes and plasmon loss. Many researchers, therefore, have actively proposed the integration of various nanostructures to address the challenges and enhance OLED performance. The structures play a crucial role in facilitating strong optical interaction with surface plasmon and waveguide modes, thereby improving the extraction of trapped modes. To mitigate the confinement, layers to modulate the refractive index are introduced to extract the confined light and redirect it into the out‐coupled mode. In this review, a comprehensive overview of the principle and effectiveness of these nanostructures in enhancing OLED performance is provided. Various applications of OLEDs are explored based on nanostructures such as nanoparticles, nanomeshes, metasurface, bioinspired structures, and scattering layers. By implementing and refining these nanostructures, significant advancements in OLED performance are anticipated. Principles and latest breakthroughs with nanostructures enabling the extraction of confined light from organic light‐emitting diodes (OLEDs) by facilitating strong optical interactions between nanostructures and trapped modes are reviewed. Four types of extraction strategies are examined: periodic nanostructures, randomly distributed nanostructures, metamaterials, and bioinspired nanostructures. Insights of the design parameters of nanostructures are also discussed for optimizing OLED performance.