Phosphorescent transparent organic light-emitting diodes with enhanced outcoupling efficiency: Reduction of surface plasmon losses

Abstract

In this work, we fabricated nanostructured transparent organic light-emitting diodes (TrOLEDs) using phosphorescent materials and a WO3 layer with various periods of perforation, to improve light extraction. Using these nanostructured TrOLEDs, higher external quantum efficiency (EQE) values were achieved, of 7.8% (bottom emission), and 2.0% (top emission) at 100 mA/cm(2). Compared to conventional TrOLEDs, these were 28% and 33% higher for bottom and top emission, respectively. In addition, by varying the periods of the nanostructures, we found that the extraction of the trapped surface plasmon mode was mainly responsible for enhancing outcoupling efficiency. When adopting light extraction methods in TrOLEDs, one should consider the influence of the optical clarity of devices. The nanostructured TrOLEDs in this study showed good optical clarity as the total transmittance was consistent with direct transmittance. Photographs of the TrOLEDs also showed neither optical blur nor haziness. Lastly, the total transmittance of the nanostructured TrOLEDs was similar to that of a conventional TrOLED except for two points where light coupling to the surface plasmon mode and waveguide mode occurred. (C) 2014 Elsevier B.V. All rights reserved.