A morphological study of random nanostructured external light extraction layers for enhancing optical characteristics of OLEDs

This study presents an in-depth investigation of nano-pillar-based external light extraction techniques, focusing on the analysis of light extraction characteristics based on the pillar and plane structures. The nano-pillar-based external light extraction structure is formed by a process technology that allows for the formation and control of the plane thickness. In this study, a random nanostructure layer based on SU-8 was fabricated, and the impact of variations in the overall height and plane height on the light extraction efficiency of the organic light-emitting diode (OLED) was analyzed. The nanostructure layer was easily formed using a low-temperature mask-free process, enabling control of diffraction and scattering effects in the visible wavelength range. The research results demonstrate that the fabricated nanostructure layer exhibited a total transmittance of over 85% in the visible spectrum, with higher light extraction efficiency observed as the thickness of the plane structure approached zero. Furthermore, compared to OLEDs without the random nano-pillar structure (RNPS), the external quantum efficiency and power efficiency were improved by up to 37.5% and 40.4%, respectively. These findings provide valuable insights into the design and optimization strategies for random nano-pillar-based external light extraction structures, contributing to the advancement of OLED technology.