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[주간세미나] 2015년 10월 26일
관리자 2015-10-21
  575

<조성민 교수 Lab.>


* 발표자 : 신지연

* 제목 : Subwavelength-Patterned Electrode for Blue Organic Light-Emitting Diodes

* 내용 : Organic light emitting diode (OLED) used in displays and lighting takes advantage of excellent electroluminescence performances, thin thickness, good flexibility, and low power consumption. Conventional Indium tin oxide (ITO) transparent electrode in OLED has high conductivity and transparency, but alternative transparent electrodes have been studied due to its limitation such as unstable supply of rare metals resulting high cost. 
 Thin metal films with nanohole array pattern are promising replacement for ITO. Though metallic thin films have high conductivity and low transparency, nanometer-thin film could be transparent but the resistance could be high. Periodic subwavelength hole patterning compensates this problem because the coupling of light with plamons on the interface between dielectrics and patterned metal film enhances transmission of certain wavelength more than the increase of the aperture ratio.
 In this study, the perforated Ag films fabricated as the transparent anode for OLED by nanosphere lithography and then blue emission OLEDs were evaporated on the anodes. We investigated luminance, efficiency and angular dependency of OLEDs between the different types of anodes, ITO, Ag and Ag with nanohole array as well as the effects by the different size of period of array and cavity diameter.




* 발표자 : 채영기

* 제목 : Scattering layer for OLEDs

* 내용 : OLEDs suffer from incomplete extraction of the light generated within the device, the fundamental reason being the higher than unity refractive index of the active, each layer.  We know that in typical OLEDs 70%&821180% of the generated photons remain confined  within the device either trapped in the substrate, guided in the organic layers and the transparent electrode (dielectric modes), or bound as surface plasmon polaritons (SPPs) at the metallic contact.  The possible out-coupling enhancement is limited as such structures cannot access light trapped in dielectric and SPP modes, such as MLA. So, a light scattering structure can be integrated in close proximity to the active layers of the device. Without additional external out-coupling structures, blue OLEDs containing these scattering films achieve light extraction for anode (ITO).  To fabricate scattering layer, 12 wt% TiO2 nano-spheres disperse in polymer host (PMMA 7 wt%). Dispersion was achieved by ultra-sonic tip method. Scattering layer was fabricated by spin coating onto SAM (Self Assembled Monolayer). And we use transfer method. So scattering layer roughness is very good. Blue OLED structure consists of ITO/HAT-CN/NPB/TCTA/Blue EML/LG201:Liq(1:1)/Liq/Al. And these scattering films achieved power efficiency 12.6 lm/w at 1000 cd/m2. And EQE (External Quantum Efficiency) 11.8 %. Therefore Scattering layer can light extraction in OLED devices.

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