Fig 2 - uploaded by Chang Kwon Hwangbo
Content may be subject to copyright.
(a) Simulated EL spectrum of green OLEDs with pairs of (SiO2/TiO2) layers in the forward direction. (b) Simulated radiance with pairs of (SiO2/TiO2) layers in the forward direction.
Source publication
In this paper, the spectral characteristics of red (R), green (G), blue (B) organic light-emitting diodes (OLEDs) with a pair of (SiO2/TiO 2) dielectric layers are studied. Multilayer structures of small-molecule RGB OLEDs are designed using an optical model. Simulated and measured electroluminescence spectra, luminous efficiencies, luminances, and...
Contexts in source publication
Context 1
... as the number of quarterwave pairs of (SiO 2 /TiO 2 ) layers was increased, and the result is presented in Fig. 2(a). The full width at half maximum (FWHM) of the EL spectrum decreases and the peak intensity increases at the resonance wavelength, as the number of quarterwave pairs of (SiO 2 /TiO 2 ) layers is increased. The figure shows the typical microcavity effects due to the higher reflectance as the number of pairs of dielectric layers is ...
Context 2
... reflectance at interface B increases from 0.9 % for a conventional OLED to 28.5 % for RGB OLEDs with a pair of (SiO 2 /TiO 2 ) dielectric mirrors while the refelctance at interface A is fixed at approximately 87 %. Secondly, the radiance of the green OLED was calculated by integrating the EL intensity over the emitted wavelength. Interestingly, Fig. 2(b) shows maximum radiance for a pair of (SiO 2 /TiO 2 ) dielectric layers, so a pair of (SiO 2 /TiO 2 ) dielectric layers was deposited as the output coupling mirror of RGB OLEDs in the ...
Context 3
... the fabricated RGB OLEDs in Fig. 3 show similar intensity spectral behaviors with the simulated green OLED in Fig. 2(a); a narrower FWHM and a higher peak intensity compared to those of conventional OLEDs without dielectric mirrors. We note that these experimental EL spectra are in good agreement with the simulated EL spectra from Eq. (1), as presented in the insets of Fig. ...
Context 4
... conventional one in Fig. 5. The luminances of the red and the green OLEDs with (SiO 2 /TiO 2 ) layers are enhanced in the forward direction up to ±40 • and then reduced for larger viewing angle. The luminance of a blue OLED is reduced because the resonator is being tuned to 465 nm. The narrow FWHM of the RGB OLEDs with (SiO 2 /TiO 2 ) layers in Fig. 2 leads to higher color purity. The color gamut area is larger than that of conventional RGB OLEDs in Fig. 6 and closer to the NTSC standard CIE chromaticity ...
Citations
... 4,5 Jung has, for example, simulated RGB OLEDs with SiO 2 /TiO 2 dielectrics layers to optimize the efficiency and reduce the band pass. 6 Nevertheless, the occurrence of interference patterns produces angular variations of the emissive spectra that can be sensitive to the human eye. The polarization state of the light emitted by OLEDs also depends on the manufacturing technology. ...
Multispectral viewing angle and imaging characterization have been applied to different organic light-emitting diode (OLED) displays. Angular dependence of the OLED emission is always complex because of its multilayer structure. Spectral information is also related to the geometry of Fabry–Perot-like structure of each OLED. High-resolution viewing angle measurements of different OLED displays are reported and compared. Multispectral viewing angle polarization properties are also reported. Imaging measurements allow to detect wavelength shift on the surface of the displays probably related to thickness non-uniformities. Local radiance fluctuations from one pixel to the other more related to driving problems due to the dispersion of the electric properties of the driving thin-film transistors are also detected.
... This type of effect can be used to optimize the light emission. B. Jung has for example simulated RGB OLEDs with SiO2/TiO2 dielectrics layers to optimize the efficiency and reduce the band pass [4]. Nevertheless it produces angular variations of the emissive spectra that can be sensitive to the human eye. ...
OLED displays are more and more used for many applications because of their interesting characteristics. Nevertheless, in spite of their high contrast ratio, wide viewing angle, and very fast response time, OLED displays are not perfect and require good manufacturing control to achieve optimized optical properties. In the present paper, we apply different types of optical characterizations to such displays (viewing angle, homogeneity, and response time) and we point out their specificities with regards to other types of displays. Since each blue, green, or red sub-pixel is an independent emitter of light, it is useful to study the light emission of each type of sub-pixel separately.
... This type of effect can be used to optimize the light emission. B. Jung has for example simulated RGB OLEDs with SiO2/TiO2 dielectrics layers to optimize the efficiency and reduce the band pass [4]. Nevertheless it produces angular variations of the emissive spectra that can be sensitive to the human eye. ...
OLED displays exhibit luminance fluctuations and color shifts that can be sensitive to human eye in particular conditions. Using viewing angle and imaging multispectral measurements we show that color shifts are generally related to multilayered structure of each sub-pixel. Interference fringes result in angular variations and thickness variations in surface non-uniformities
... This type of effect can be used to optimize the light emission [4][5]. B. Jung has for example simulated RGB OLEDs with SiO2/TiO2 dielectrics layers to optimize the efficiency and reduce the band pass [6]. Nevertheless the occurrence of interference patterns produces angular variations of the emissive spectra that can be sensitive to the human eye. ...
Different types of optical characterizations, have been applied to OLED displays: multi-spectral viewing angle, multi-spectral imaging and response time. The interest of the spectral information is that the exact shape of the light emission for each sub-pixel can be precisely determined and analyzed. Wavelength fluctuations versus angle give direct information on the OLED structure of each sub-pixel. Imaging measurements allow to detect wavelength shift on the surface of the displays probably related to thickness non-uniformities. Local radiance fluctuations from one pixel to the other are more related to driving problems due to the dispersion of the properties of the driving TFTs. A new generation of temporal instrument is also used to measure response times shorter than 10µs. In this case collecting light coming from one pixel or one line of pixels is mandatory to avoid averaging.
... This type of effect can be used to optimize the light emission [4][5]. B. Jung has for example simulated RGB OLEDs with SiO2/TiO2 dielectrics layers to optimize the efficiency and reduce the band pass [6]. Nevertheless the occurrence of interference patterns produces angular variations of the emissive spectra that can be sensitive to the human eye. ...
OLED displays exhibit luminance fluctuations and color shifts that can be sensitive to human eye in particular conditions. Using viewing angle and imaging multispectral measurements we show that color shifts are generally related to the multilayered structure of each sub-pixel. Interference fringes result in angular variations while thickness variations result in surface non-uniformities.
... Using relatively simple optical multilayer models many authors have predicted the spectral and angular emissive properties but the comparison to experimental data is generally very limited. B. Jung has for example simulated RGB OLEDs with SiO2/TiO2 dielectrics layers to optimize the efficiency and reduce the band pass [6]. In the present paper we use a multispectral viewing angle system that has been introduced in 2008 for the characterization of LCDs [7]. ...
The angular emission of OLED displays is measured using a multispectral Fourier optics viewing angle system. The emission of red, green and blue states presents complex spectral changes versus angle. These changes probably related to interference fringes inside the OLED layered structure have small impact on color and luminance properties.
Within this work the major breakthroughs in the development of OLED technologies are described. There is a strong emphasis placed upon materials discovery. The basic OLED structure is shown and the plasmonic effect is detailed in the context of OLED technologies. Keywords-organic light emitting diode (OLED), outcoupling efficiency, plasmonic materials, singlet/triplet emissions. Air n=1.0 ITO n=2.0 Organics n≈1.7-1.9 Cathode Ideal reflector Figure 1: The above figure depicts a simplified, planar OLED structure. The cathode is assumed to be an ideal reflector, which the organic layers are directly adjacent to. The ITO hole-injecting contact and air are also shown. Each of these layers corresponds to a significant change of refractive index within the OLED. Furthermore, this is an example of a top-emitting structure.
The relations of the Ti-O binding states to the resistive switching behaviors of TiO2 thin films have been investigated. TiO2 thin films in a Pt/TiO2/Pt structure were prepared by reactive magnetron sputtering with various preparation conditions, such as the oxygen partial pressure (P(O2)) and the substrate temperature (T s). At the optimized preparation conditions for reproducible resistive switching TiO2 thin films (Ts = 100°C and P(O2) = 0.1 mTorr), the O/Ti ratio in the bulk was nearly stoichiometric, 1.95, but the surface Ti-O binding state was heavily oxidized in the form of TiO2.5. We suggest that the molar fraction of the Ti2O3 in the bulk is related to the reproducible resistive switching behaviors, which, in turn, may be related to the filamentary mechanism in TiO2 thin films.
In this work, impedance spectroscopy analysis was used to study the effects of plasma treatment on the surface of indium-tin oxide (ITO) anodes using CF4, O2 and Ar gases and to model an equivalent circuit for organic Ught-emitting diodes (OLEDs). The devices with an ITO/TPD/Alq 3/LiF/Al structure could be modeled as a simple combination of resistors and capacitors. For modifications of the ITO surface, the samples were treated in an inductively-coupled tubular reactor system. The OLEDs fabricated on plasma-treated ITO anodes showed a lower impedance and a higher capacitance. The changes in the impedance and the capacitance were attributed to removal of contaminants and to changes in the work function of ITO. The impedance spectroscopy analysis showed that the devices with plasma-treated ITO anodes had different values of the contact resistance (RC), the parallel resistance (RP) and the parallel capacitance (CP).
Two types of microcavity blue organic light-emitting diodes (OLEDs) with a dielectric Bragg mirror (two different center wavelengths, type-A≈465, type-B≈470nm) were designed to achieve the color coordinates of NTSC blue standard and enhance the quantum efficiency in the normal direction. A moderate microcavity OLED was defined as a microcavity OLED with a single pair of TiO2/SiO2 high/low dielectric layers inserted between an indium tin oxide (ITO) layer and a glass substrate. The moderate microcavity blue OLED doped with 9,10-bis(3′,5′-diphenylphenyl)-10-(3″′,5″′-diphenylbiphenyl-4″-yl)anthracene (TAT) exhibited excellent color coordinates (type-A; x=0.143,y=0.068,type-B; x=0.139,y=0.081), which were better than the color coordinates of the NTSC standard (0.140,0.080) and the TAT-doped conventional noncavity OLED (0.156,0.094). There were approximately 60% and 54% improvement in the relative quantum efficiency of the type-B TAT-doped moderate microcavity OLED, respectively, compared to those of the conventional noncavity reference OLED (ITO=150nm) and other reference type-II with an identical ITO layer thickness (ITO=85nm). These improvements in color coordinates and the relative quantum efficiency were attributed to the optimization of narrowed spectrum bandwidth and enhanced integrated spectrum intensity in the TAT-doped blue OLED, resulting from the effective microcavity effect.
