Xiuling Zhu

High-efficiency microcavity top-emitting organic light-emitting diodes using silver anode

Top-emitting organic light-emitting diodes (TOLEDs) employing highly reflective Ag as anode and semitransparent LiF∕Al∕Ag as cathode were fabricated. The hole injection efficiency of Ag anode can be significantly improved with surface modification using a CF4 plasma. With C545T-doped Alq3 emitter, the top-emitting device shows a low turn-on voltage of 2.65V. The optimized microcavity TOLED shows a current efficiency enhancement of 65% and a total outcoupling efficiency enhancement of 35%, compared with a conventional OLED. No color variation was observed in the forward 140° forward viewing cone. Strong dependence of efficiency on Ag cathode thickness was observed, in good agreement with numerical simulations.

Effective Intermediate Layers for Highly Efficient Stacked Organic Light-Emitting Devices

Effective intermediate electrode layers comprising of LiF(1nm)∕Ca(25nm)∕Ag(15nm) or LiF(1nm)∕Al(3nm)∕Au(15nm) were studied in stacked organic light-emitting devices (OLEDs). Stacked OLEDs with two identical emissive units consisting of NPB∕Alq3: C545T/BCP exhibited superior luminous efficiency-current density characteristics over conventional single-unit devices. At 20mA∕cm2, the luminous efficiency of the stacked OLEDs using the intermediate layers of LiF∕Ca∕Ag and LiF∕Al∕Au were about 19.6cd∕A and 17.5cd∕A, respectively, almost doubling that of the corresponding control devices, as expected.

Efficient organic light-emitting diode using semitransparent silver as anode

A semitransparent silver layer is investigated as the anode for organic light-emitting devices (OLEDs). By pretreating the silver layer in a CF4 plasma, hole injection into the hole-transport layer is greatly enhanced. A bottom-emitting OLED using the modified, semitransparent silver anode, demonstrates improved current density-voltage characteristics and a 20% higher external quantum efficiency, compared to a conventional OLED using indium tin oxide as an anode. The superior optical characteristics are attributed to a higher outcoupling efficiency in the microcavity structure.

Efficiency improvement of phosphorescent organic light-emitting diodes using semitransparent Ag as anode

The emission efficiency in an organic light-emitting diode (OLED) based on fac tris(phenyl pyridine)iridium [Ir(ppy)3] is greatly improved using a semitransparent Ag anode. With surface modification of the Ag anode, excellent light coupling and hole injection properties can be realized. The Ag-based OLED exhibits a maximum current efficiency of 81cd∕A and a power efficiency of 79lm∕W, compared with 46cd∕A and 39lm∕W for an indium-tin oxide anode device, respectively.

Investigation of Al- and Ag-Based Top-Emitting Organic Light-Emitting Diodes with Metal Oxides as Hole-Injection Layer

Al- and Ag-based top-emitting organic light-emitting diodes (TOLED) are investigated. Both MoO3 and V2O5 have been used as hole-injection layer (HIL). The performance of the devices is significantly improved using the metal oxides as HIL. A C545T-doped Alq3 TOLED with Al and MoO3 can achieve a maximum current efficiency of 22 cd/A at 20 mA/cm2. The power efficiency is 20 lm/W at a low brightness and about 8.9 lm/W at 1000 cd/m2. For the Ag-based TOLED using V2O5 as HIL, very low operating voltages are obtained. For instance, 1000 cd/m2 can be obtained at a voltage of 4.7 V with a power efficiency of about 10 lm/W. From the analysis of the current–voltage characteristics of the single hole transport layer devices, it is believed that the hole injection from the metal anodes was greatly enhanced because of the lowering of the injection barrier induced by the metal oxides. The interface dipole theory was applied to the metal-metal oxide interface to explain the experimental observations.

Syntheses, photophysical, electroluminescence and computational studies of rhenium(i) diimine triarylamine-containing alkynyl complexes

A series of triarylamine-containing rhenium(I) diimine alkynyl complexes has been synthesized and some of their X-ray crystal structures have been determined. Low-energy transition bands at 402–444 nm were observed in the electronic absorption spectra and were tentatively assigned as an admixture of [dπ(Re) → π*(diimine)] metal-to-ligand charge-transfer (MLCT) and [π(CC−C6H4–R) → π* (diimine)] ligand-to-ligand charge-transfer (LLCT) transitions. They were found to give emission upon photo-excitation in the solid state and in fluid solution at room temperature and their emissive origins were assigned as derived predominantly from the triplet 3MLCT excited state, mixed with 3LLCT character as well as the 3IL state. Electrochemical studies revealed that the first oxidation process was mainly alkynyl ligand-based with mixing of the metal-centred contribution, whereas the first reduction was attributed to the ligand-centred reduction of the diimine ligand. Computational studies have been performed to provide further insight into the electrochemical and photophysical properties. The photochemical properties with triphenylamine were also studied by quenching experiments and time-resolved transient absorption spectroscopy. Some of these complexes were able to act as emitters in OLED devices and their electroluminescence (EL) behaviour was investigated.

Improving the performance of organic light-emitting diodes containing BCP/LiF/Al by thermal annealing

In this paper, we examined the effect of post-packaging annealing on the performance of organic light-emitting diodes containing tris-(8-hydroxyquinoline) aluminum (Alq,) or 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) in direct contact with a LiF-Al bilayer cathode. The detailed electroluminescent (EL) characteristics were compared before and after annealing at 70 degC for 5 hrs. It was found that better luminous efficiency as well as greater power efficiency could be achieved for devices with BCP/LiF/Al structure. However, other devices consisting of Alq3/LiF/Al were less affected. It is believed that the thermal treatment helps to enhance the electron injection for the former, and less helpful for the latter

P-230: Novel Electrical-Chemically Polished Stainless Steel Anode Organic Light Emission Device with Long Lifetime at High Luminance for Flexible Lighting

Stainless Steel (s.s.) sheet substrate was electrical-chemically polished. Afterwards its average surface roughness reached 1.93nm. Then Organic Light Emission Devices (OLEDs) were fabricated on it with Alq3 as the light emission material (EM) (called Devices SSA). So high-thermal-conductive s.s. was made use of directly as anode in Devices SSA. Lighted at initial luminance intensity 1135 cd/m2, Devices SSA decayed to its half luminance after 18 hours (hrs) in the vacuum which has pressure of 5×10−3 Pa. At the same time, top emission OLEDs with evaporated aluminum anode on glass (called Devices AA) were fabricated with the same EM. Devices AA have 20.5 hrs half lifetime but much lower initial luminance intensity 296cd/m2, as measured in the same vacuum condition. The maximum luminance (Lmax) of Devices SSA is 61,200cd/m2, which is 2.3 times as high as Lmax of Devices AA. In this paper, Device SSA with s.s. substrate thickness 0.05mm and bending radius 2mm is demonstrated. It indicates a bright future of flexible lighting application. White OLEDs on this substrate is being researched and longer lifetime could be achieved soon under better condition.

29.3: Very Bright and Efficient Top‐Emitting OLED with Ultra‐Thin Yb as Effective Electron Injector

Very bright and efficient top-emitting organic light-emitting diodes (TOLEDs) using an ultra-thin ytterbium (Yb) layer capped with a semitransparent Ag layer as the effective electron-injection cathode were demonstrated. TOLED with Yb/Ag cathode exhibited lower operation voltage and higher power efficiency, as compared to the one with commonly used Ca/Ag cathode. With bis(2-phenylpyridine)iridium [(ppy)2Ir(acac)] as the phosphorescent dopant, the Yb/Ag based TOLED showed a current efficiency of 88 cd/A and a power efficiency of 67 lm/W, considerably greater than those (56 cd/A and 44 lm/W) obtained from the corresponding bottom-emitting one. The good performance of these TOLEDs is attributed to the efficient electrons injection from the Yb/Ag cathode as well as a micro-cavity effect.

22.3: High Efficiency Electrophosphorescent Organic Light Emitting Diodes using Semitransparent Ag as Anode

We have significantly improved the emission efficiency in an organic light emitting diode (OLEDs) based on tris(phenyl pyridine)iridium [Ir(ppy)3]. Using a semitransparent Ag with surface modification as anode to replace conventional ITO, excellent light outcoupling and hole injection properties have been realized. The Ag based OLED exhibits a maximum current efficiency of 81 cd/A and power efficiency of 79 lm/W, compared with 46 cd/A and 39 lm/W for an ITO anode device. The improvement is due to a carefully designed microcavity.