Shiao-Wen Hwang

Highly efficient white organic electroluminescent devices based on tandem architecture

Two types of tandem organic light-emitting diodes (OLEDs) with white-light emission have been developed by using Mg:Alq3∕WO3 as the interconnecting layer. While the Commission Internationale d’Eclairage (CIE) coordinates of the tandem device with individual blue- and yellow-emitting OLEDs was sensitive to the viewing angle and the operating time, the tandem device connecting two white-emitting OLEDs was considerably less. At an optimal WO3 thickness of 5nm, the tandem two-unit device produced three higher luminance efficiency than that expected of a single-unit device. A maximum efficiency of 22cd∕A was achieved by the tandem device comprised of two white-fluorescent OLEDs, and the projected half-life under the initial luminance of 100cd∕m2 was over 80000h.

Highly power efficient organic light-emitting diodes with a p-doping layer

In this letter, the authors demonstrate p-i-n organic light-emitting diodes (OLEDs) incorporating a p-doped transport layer which comprises tungsten oxide (WO3) and 4,4′,4″-tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine (2-TNATA) to replace the volatile tetrafluro-tetracyanoquinodimethane. The authors propose the 2-TNATA:WO3 composition functions as a p-doping layer which significantly improves hole injection and conductivity of the device that leads to the fabrication of tris(8-quinolinolato)aluminum based p-i-n OLEDs with long lifetime, low driving voltage (3.1V), and high power efficiency (3.5lm∕W) at 100cd∕m2.

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.

Highly efficient p-i-n white organic light emitting devices with tandem structure

Highly efficient tandem p-i-n white organic light emitting devices have been fabricated. Utilizing an optical transparent bilayer with doped organic p-n junction that consists of 4,7-diphenyl-1,10-phenanthroline: 2% cesium carbonate (Cs2CO3)∕N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine: 50% v/v tungsten oxide (WO3) as the connecting layer, the tandem p-i-n white device achieved an electroluminescence efficiency of 23.9cd∕A and a power efficiency of 7.8lm∕W at 20mA∕cm2 with a Commission Internationale de l’Eclairage coordinates of (0.30, 0.43). The electroluminescent color of this tandem p-i-n white organic light-emitting diode device will not change significantly with respect to drive current variation and forward viewing angle.

White p-i-n organic light-emitting devices with high power efficiency and stable color

Highly efficient p-i-n two-component white organic light-emitting devices have been fabricated with a thin dual emission layer system comprised of one codeposited emitting layer with blue and yellow dyes and one blue emitting layer, which gives rise to a balance white emission. The p-i-n white device achieved an electroluminescence efficiency of 10cd∕A and a power efficiency of 9.3lm∕W at 1000cd∕m2 and a low voltage of 3.4V with a Commission Internationale de l’Eclairage coordinates of (0.32, 0.43). The electroluminescent color of this p-i-n white organic light-emitting diode device has been shown to be immune to drive current density variations.

Electrical characterization of organic light-emitting diodes using dipotassium phthalate as n-type dopant

An efficient n-doped electron transport layer composed of 4,7-diphenyl-1,10-phenanthroline (BPhen) and dipotassium phthalate (PAK2) has been developed. By temperature-dependent admittance spectroscopy, the incorporation of PAK2 into BPhen is found to raise the Fermi level from 1.7eV to only around 0.5eV below BPhen’s lowest unoccupied molecular orbital, which further enhances the efficiency of electron injection from an Al cathode. When this n-doped layer is adopted in an organic light-emitting diode device, the green fluorescent 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]-pyrano[6,7,8-ij]quinolizin-11-one do-ped device can achieve a current efficiency of 16cd∕A and a power efficiency of 10.9lm∕W at 1000cd∕m2.

Improved performance and stability of organic light-emitting devices with Al–Cu alloy cathode

We have developed a stable green organic electroluminescent (EL) device by using an Al–Cu alloy as a cathode, which has better performance and reliability than the device with an Al cathode. The device with an Al–Cu alloy cathode achieved an EL efficiency of 3.78cd∕A(2.18lm∕W) at 20mA∕cm2 and the operating voltage was 5.46 V, while device with Al cathode had an EL efficiency of 3.1cd∕A(1.34lm∕W) and 7.3 V at the same drive condition. The Al–Cu device achieved a 20% decay lifetime (t80) of 1234 h at an initial brightness of 756cd∕m2, which is twice the lifetime of conventional device with the state-of-the-art LiF∕Al cathode.

Thin-Film Encapsulation of Thin-Cathode Organic Light-Emitting Devices

We have developed a novel thin-film encapsulation method for thin-cathode organic light-emitting devices (OLEDs) by introducing organic (not polymer)/inorganic multiple thin films to protect devices, which is shown to slow down the permeation rate of moisture and oxygen. From the stability test of devices, the projected lifetime of thin-cathode OLEDs with thin-film encapsulation was similar to that of thin-cathode OLEDs with glass lid encapsulation.

17.4: Highly Power Efficient Organic Light-Emitting Diodes with a Novel P-Doping Layer

We demonstrate p-i-n organic light-emitting diodes (OLEDs) incorporating a p-doped transport layer which comprises tungsten oxide (WO3) and 4,4′,4″-tris(N-(2-naphthyl)-N-phenylamino) triphenylamine (2-TNATA) to replace the volatile and low Tg F4-TCNQ. We propose the 2-TNATA:WO3 composition functions as a p-doping layer which significantly improves hole-injection and conductivity of the Alq3 based p-i-n OLEDs with long lifetime, low driving voltage (3.1 V), and high power efficiency (3.5 lm/W) at 100 cd/m2

P-196: Controlling Recombination Zone in p-i-nWhite Organic Light-Emitting Diode

P-i-n Devices with 2% Cs2CO3 doped BPhen as the n-type transporting layer and WO3 doped triphenylamine derivatives as the p-type transporting layer, coupled with a modified composition of sky blue DSA doped MADN and yellow rubrene doped NPB emitters, are investigated to control the RZ of carriers in WOLED. We found the shift of recombination zone (RZ) as revealed by the amount of blue and yellow emissions produced is a dominant factor leading to the variation in white CIEx,y color coordinates with respect to luminance. A color stable p-i-n WOLED with CIEx,y coordinates of (0.32, 0.43) was achieved at a driving voltage of 3.4 V with a power efficiency of 9.2 lm/W at 1000 cd/m2.