White Top-emitting Organic Light-emitting Devices Research Articles

Efficient and angle-stable white top-emitting organic light emitting devices with patterned quantum dots down-conversion films

Abstract Efficient white top-emitting organic light-emitting devices (TEOLEDs) are fabricated by combining blue TEOLEDs with down-conversion films. Quantum dots (QDs) are integrated with polymethyl methacrylate (PMMA) to obtain freestanding composite films, and the films are used as down-conversion films to produce red emission by converting blue emission from blue TEOLEDs. The blue and white TEOLEDs exhibit the maximum current efficiency of 37.4 and 22.2 cd/A, respectively. Through integrating a microstructure QDs down-conversion film by transfer printing on blue TEOLED, the light extraction performance of white TEOLEDs is improved and the angular distribution of the white emission is almost Lambertian. The CIE color coordinates of white TEOLEDs with patterned QDs down-conversion films shift only (0.025, 0.005) from 0° to 60°.

Angle-stable inverted top-emitting white organic light-emitting devices based on gradient-doping electron injection interlayer

By adopting an 4,7-diphenyl-1,10-phenanthroline (Bphen):Ag interlayer with the gradient structure between the cathode and electron injection layer, the electron injection of white inverted top-emitting organic light-emitting devices (WITOLED) was enhanced. The structure of Ag–Ge–Ag anode capping with light outcoupling was used to ensure the spectral stability with the angles. The structure of the emission layer was carefully designed to guarantee the spectral stability with the voltages. The highest current efficiency of the WITOLED can reach 21.7cd/A. The CIE 1931 coordinates varies only 0.022 in X and 0.015 in Y (0o–60o).

Hybrid Tamm plasmon-polariton/microcavity modes for white top-emitting organic light-emitting devices

White top-emitting organic light-emitting devices (WTOLEDs), emitting white light through a transparent top metallic electrode, have emerged as promising candidates as energy-efficient solid-state lighting sources and full-color flat-panel displays. The microcavity effect due to usage of metallic electrodes results in emission enhancement solely at a particular color, and therefore sets an obstacle for WTOLEDs, where at least two colors with balanced intensity should be emitted. Current efforts solving the problem basically rely on the relaxation of the microcavity effect, resulting in sacrificed light outcoupling efficiency in the original resonance region. Here, we demonstrate that by integrating a photonic crystal structure upon the top metallic electrode, an additional emission enhancement peak other than the one determined by the microcavity resonance could be provided by the Tamm plasmon-polariton mode. Mode hybridization induced dual hybrid modes with comparable light outcoupling efficiency can then be excited, from which two colors with balanced intensity could be emitted. Both experimental and theoretical results demonstrate that the proposed mode hybridization strategy may pave the way for the realization of WTOELDs towards high white color quality, improved viewing characteristics, and electroluminescence efficiency.

Angle-stable top-emitting white organic light-emitting devices employing a down-conversion layer

Angle-stable white top-emitting organic light-emitting devices (WTEOLEDs) by the combination of a blue TEOLED with a down-conversion (DC) layer are demonstrated. The DC layer is composed of red fluorescent dye doped in a host of tris (8-hydroxy-quinolinato) aluminum. The TEWOLED shows a CIE coordinates of (0.240, 0.332) and a maximum current efficiency of 3.95 cd/A. Furthermore, the WTEOLED shows excellently angle-stable characteristic, the CIE coordinates at 20 mA/cm2 only shift by (0.023, −0.007) from 0° to 60°. It can be attributed to the angle-stable blue TEOLED based on the Ag/Ge/Ag transparent cathode.

High efficiency top-emitting white organic light-emitting devices with a (metal/organic) 2 cathode

White top-emitting organic light-emitting devices (TEOLEDs) were fabricated on a glass substrate with metal/organic multilayer of (Ag/Alq 3) 2 (Alq 3 is tris-(8-hydroxyquinoline) aluminum) as cathode. White TEOLEDs with high efficiency were obtained due to the microcavity effects. And the (Ag/Alq 3) 2 cathode, which adjusted the optical characteristics of the devices, played an important role. In addition, Alq 3–Ag–Alq 3 multilayer could work as a buffer layer, which would simplify the process of encapsulation for devices. We also calculated the electroluminescence spectrum of devices encapsulated with Al 2O 3 (150 nm) and Al 2O 3(75 nm)/ZrO 2(75 nm). And the results indicated that the CIE coordinates is almost the same between with and without encapsulating.

Optical simulation and optimization of ITO-free top-emitting white organic light-emitting devices for lighting or display

We present a simulation of the optical properties of ITO-free top-emitting white organic light-emitting devices (TEWOLEDs). Metals (Al, Ag, Mo, Cu, Au, Sm) are used as anode or cathode depending on their work functions. Besides, devices with 1D metallic–dielectric photonic crystal anode are also demonstrated. The influence of the capping layer or the metallic–dielectric multilayer structure on the optical properties (such as efficiency, angular emission characteristics, color gamut and color rendering index) of the devices has been investigated. The results indicated that TEWOLEDs can be used as lighting with high color rendering index or as a display with wide color gamut by carefully designing the structure of the devices.

P‐169: White Broadband Top‐emitting Organic Light‐emitting Diodes with a Novel Reflective and Conductive Bilayer Anode

AbstractWe demonstrate efficient white top‐emitting organic light emitting devices (WTOLEDs) with Al/ITO bilayer anode with which the sputtered‐ITO thin layer is found to improve hole injection into the organic hole‐transport layer. In addition, by capping with a transparent organic layer of NPB (n ∼ 1.6) on the semitransparent cathode to suppress the undesirable microcavity effect, a broadband white emission can be achieved. The WTOLEDs with two adjacent fluorescent blue/yellow emissive layers can achieve an EL efficiency of 13.7 cd/A at high luminance of 3,000 cd/m2 and a low driving voltage of 5.9 V with Commission Internationale d'Eclairage (CIE) coordinates of (x = 0.30, y =0.39).

High-contrast and high-efficiency microcavity top-emitting white organic light-emitting devices

Microcavity top-emitting white organic light-emitting devices (TEWOLEDs) with M/(Alq 3/Ag) 2 anode (M = Ag, Au or Al, Alq 3 is tris (8-hydroxyquinoline) aluminum) were investigated. All devices show white emission and the optical properties of the anode play an important effect on the efficiency and contrast of the devices. The maximum efficiencies of the top-emitting devices are comparable to the corresponding bottom one and the contrasts of top-emitting devices are much higher than that of the bottom one. The results indicated that such TEWOLEDs are compatible with complementary metal oxide semiconductor or organic thin film transistor techniques which using Au or Al as electrode.

Top-emitting white organic light-emitting devices with a one-dimensional metallic-dielectric photonic crystal anode

Top-emitting white organic light-emitting devices (TEWOLEDs) with 1D metallic-dielectric photonic crystal (1D MDPC) as an anode are investigated. A quasi-periodic 1D MDPC anode allowed for fabrication of multiple-peak TEWOLEDs. A two-peak or three-peak TEWOLED was obtained by simply adjusting the thickness of the dielectric layers in the MDPC. The efficiency of the TEWOLEDs are comparable to the corresponding bottom WOLED (11.1 cd/A), which are 9.9 (two-peak device) and 9.4 cd/A (three-peak device), respectively, and the contrast of the TEWOLEDs is about twice as high as the bottom device owing to the low reflection of the anode.

Spectrum study of top-emitting organic light-emitting devices with micro-cavity structure

Blue and white top-emitting organic light-emitting devices OLEDs with cavity effect have been fabricated. TBADN:3%DSAPh and Alq3:DCJTB/TBADN:TBPe/Alq3:C545 were used as emitting materials of microcavity OLEDs. On a patterned glass substrate, silver was deposited as reflective anode, and copper phthalocyanine (CuPc) layer as HIL and 4′-bis[N-(1-Naphthyl)- N-phenyl-amino]biphenyl (NPB) layer as HTL were made. Al/Ag thin films were made as semi-transparent cathode with a transmittance of about 30%. By changing the thickness of indium tin oxide ITO, deep blue with Commission Internationale de L'Eclairage chromaticity coordinates (CIEx, y) of (0.141, 0.049) was obtained on TBADN:3%DSAPh devices, and different color (red, blue and green) was obtained on Alq3:DCJTB/TBADN:TBPe/Alq3:C545 devices, full width at half maxima (FWHM) was only 17 nm. The spectral intensity and FWHM of emission in cavity devices have also been studied.

Top-emitting white organic light-emitting devices with down-conversion phosphors: Theory and experiment

White top-emitting organic light-emitting devices (TEOLEDs) with down-conversion phosphors are investigated from theory and experiment. The theoretical simulation was described by combining the microcavity model with the down-conversion model. A White TEOLED by the combination of a blue TEOLED with organic down-conversion phosphor 3-(4-(diphenylamino)phenyl)-1-pheny1prop-2-en-1-one was fabricated to validate the simulated results. It is shown that this approach permits the generation of white light in TEOLEDs. The efficiency of the white TEOLED is twice over the corresponding blue TEOLED. The feasible methods to improve the performance of such white TEOLEDs are discussed.

Highly efficient top-emitting white organic electroluminescent devices

We have developed highly efficient white top-emitting organic light-emitting devices with broad emission by modifying both the anode and cathode. To alleviate the undesirable microcavity effect and obtain “broad” white emission, a CFx-coated Ag anode and an index-matching layer (SnO2) capped on a thin Ca∕Ag cathode with a maximum transparency of 80% were employed. A top-emitting broad white-light device, based on the dual-layer architecture of light blue and yellow emitters with one of the highest EL efficiencies of 22.2cd∕A (9.6lm∕W) at 20mA∕cm2 and 7.3V with Commission Internationale d’Eclairage coordinates of (x=0.31,y=0.47), has been demonstrated.

4.2: Highly Efficient Top-Emitting White Organic Electroluminescent Devices

We have developed highly efficient white top-emitting organic light-emitting devices (TOLEDs) with broad emission by modifying both anode and cathode. To alleviate the undesirable microcavity effect and obtain “broad” white emission, CFx-coated Ag anode with modified reflectivity and an index-matching layer (SnO2) capped on thin Ca/Ag cathode with a maximal transparency of 80% were employed. A top-emitting broad white light device based on the dual layer architecture of light blue and yellow emitters with one of the highest EL efficiencies of 22.2 cd/A (9.6 lm/W) at 20 mA/cm2 and 7.3 V with Commission Internationale d'Eclairage (CIE) coordinates of (x=.0.31, y=0.47) has been demonstrated.