Enhanced Color Conversion Efficiency Of White Organic Light-emitting Diodes By Localized Surface Plasmon Resonance Effect Of Ag Nanoparticles

Down-conversion structure white organic light-emitting diodes (WOLEDs), in which white light is generated by a blue emission organic light-emitting diodes (OLEDs) in combination with a color conversion layer (CCL) outside the substrate, has attracted extensive interest due to its significant advantages in low cost and stabilized white-light emissions. However, low color-conversion efficiency of CCL is still a bottleneck for the performance improvement of down-conversion WOLEDs. Here, we demonstrate an approach to enhance the color-conversion efficiency of CCL-WOLEDs by localized surface plasmon resonance (LSPR) effect.(1) MEHPPV was characterized and was chosen to work as color conversion layer. Ag nanoparticles was prepared via polyol-mediated hydrothermal reduction from silver nitrate, and were characterized by TEM and UV-vis absorption. Although the absorption peak of Ag nanoparticles corresponded to blue LSPR excitation peak, it was necessary to insert an isolation layer due to the fluorescence quenching phenomenon. We tested series of isolation layers and eventually found that the mixture of Ag nanoparticles and polyvinyl alcohol (PVA) could be the most suitable isolation layer between blue organic light emitting diode and color conversion layer by spin-coating, which could benefit LSPR to the most extent.(2) Blue OLEDs devices were first optimized to obtain the maximum efficiency, and then white OLEDs devices were fabricated based on optimized blue OLEDs and previous PL results. The result of PL enhancement reached 1.8 times with PVA@Ag, leading to an obvious performance enhancement of white OLEDs. We also observed the enhancement range of LSPR by FEM simulation. Based on the LSPR effect of this modified structure, the color conversion efficiency has improved 32%, from 45.4% to 60%, resulting a 14.4% enhancement of the current efficiency, from 9.73 cd/A to 11.14 cd/A. Our work provides a simple and low-cost way to enhance the performance of down-conversion WOLEDs, which highlights its potential in illumination applications.