Jiaxin Sun

Aggregation-induced emissions of tetraphenylethene derivatives and their utilities as chemical vapor sensors and in organic light-emitting diodes

Nonemissive tetraphenylethene (TPE) 1 and its diphenylated derivative 2 were induced to emit intensely by aggregate formation. Crystalline aggregates of the dyes emitted bluer lights than their amorphous counterparts. The emissions of the TPE dyes could be switched off and on continuously and reversibly by wetting and dewetting with solvent vapors, respectively, manifesting their ability to optically sense volatile organic compounds. The light-emitting diodes fabricated from 1 and 2 were turned on at ∼2.9 and ∼5V and emitted blue lights with maximum luminance of ∼1800 and ∼11000cd∕m2, respectively.

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.

Vanadium pentoxide modified polycrystalline silicon anode for active-matrix organic light-emitting diodes

Recently, polycrystalline silicon (p-Si) has been demonstrated to be an efficient anode for organic light-emitting diode (OLED) [X. L. Zhu, J. X. Sun, H. J. Peng, Z. G. Meng, M. Wong, and H. S. Kwok, Appl. Phys. Lett. 87, 083504 (2005)]. In this letter, we show that, by depositing an ultrathin vanadium pentoxide (V2O5) layer on the p-Si anode, the performance of the OLED can be greatly improved. Detailed x-ray photoelectron spectroscopy study shows that strong band bending occurs at the p-Si∕V2O5 interface, leading to much stronger hole injection. This modified p-Si anode can be integrated with the active p-Si layer of thin-film transistors in active-matrix OLED displays.

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.

Aggregation-induced and crystallization-enhanced emissions of 1,2-diphenyl-3,4-bis(diphenylmethylene)-1-cyclobutene

1,2-Diphenyl-3,4-bis(diphenylmethylene)-1-cyclobutene can be induced to emit efficiently by aggregate formation, with the crystalline aggregates emitting brighter, bluer lights than their amorphous counterparts.

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.

Efficient organic light-emitting diodes using polycrystalline silicon thin films as semitransparent anode

Polycrystalline silicon (p-Si) is a good material for the construction of thin-film transistors (TFT). It is used for fabricating active-matrix organic light-emitting diode (AMOLED) displays. In this letter, we propose and demonstrate the application of boron-doped p-Si as a semi-transparent anode in making different color OLEDs. Without removing the ultrathin native oxide on the p-Si surface and employing p-doped hole transport layer to enhance holes injection, these OLEDs show comparable or even better performance to conventional OLEDs which use ITO as anodes. The present technique has the advantage of less masking steps in making AMOLED.

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