Study on enhanced quantum efficiency of organic light-emitting diodes by utilizing localized surface plasmon resonance

Abstract

Organic light-emitting diodes (OLEDs) have studied over last few decades due to their many advantages for potential applications in displays, and lightings, etc. Although OLED have developed for some level by synthesis of efficient emissive materials and optimization of device structure, electronics and optics, further improvement of the efficiency is still needed. One possible and remarkable way to fulfill this purpose is to introduce the physical phenomenon called localized surface plasmon resonance (LSPR) into OLEDs. Localized surface plasmons (LSP) means the collective oscillations of electrons in noble metal nanoparticles embedded in a dielectric matrix, and LSPR is the resonance interaction of LSPs with incident electromagnetic waves. By LSPR, internal quantum efficiency of OLEDs can be enhanced due to the enhancement of spontaneous emission rate by creating new recombination path of excitons. In this thesis, new and simple methods to couple LSPs from Ag nanoparticles (NPs) with various emissive materials are suggested. In Chapter 2, first of all, PVP-capped Ag nanoparticles having a size of 30nm were successfully synthesized and analyzed by scanning electron microscope (SEM) and UV-Vis spectrophotometer. To attach the Ag NPs on the ITO substrate, ITO surface was treated self-aseembled-monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) which is bi-functional molecule having thiol and carboxylic acid functional groups in the both ends because carboxylic functional group have affinity to indium. Then Ag NPs with PVP was drop-casted on the ITO surface, so ligand-exchange reaction occurred at surface. Properties of Ag NPs film was measured by various techniques. In chapter 3, to introduce silver nanoparticles to ITO surface, silver NPs was synthesized with new method that poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT:PSS) was used as a stabilizing agent. Newly synthesized NPs were introduced on the ITO surface by simple spin-casting...