Random rubbed structure for enhanced light extraction in organic light-emitting diodes

Abstract

In this study, we demonstrated a nanoscale random rubbed structure (nRRS) as an internal scattering layer for organic light-emitting diodes (OLEDs) through an innovative fabrication method. Random corrugation above the SU-8 polymer surface can be simply formed using the rubbing technique commonly employed for liquid crystal alignment. A random structure that is optimized to a nanoscale that does not deteriorate electrical stability can be engineered by controlling the rubbing process. The nRRS exhibited high transmittance (>97%) in the visible wavelength range of 380–700 nm, making it suitable for use as an internal functional layer for OLEDs. Compared to that of the reference device, the external quantum efficiency of the optimized nRRS device increased by 35.47%, and the current and power efficiencies at 3000 cd/m2 were 1.27 times higher. As the viewing angle increased from 0° to 70°, the nRRS-inserted OLED showed a negligible International Commission on Illumination 1931 coordinate shift (Δ (x, y) = (0.016, 0.022)), successfully expressing the alleviation of the viewing-angle dependency. By utilizing finite-difference time-domain simulation tool, the optical results of the device are predicted and verified. This manufacturing approach has the advantages of being applicable to large-scale production and processability at room temperature without the use of a vacuum equipment.