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Patent Issued for Organic Electroluminescence Device and Manufacturing Method

September 9, 2014



By a News Reporter-Staff News Editor at Life Science Weekly -- According to news reporting originating from Alexandria, Virginia, by NewsRx journalists, a patent by the inventors Zhou, Mingjie (Shenzhen, CN); Wang, Ping (Shenzhen, CN); Huang, Hui (Shenzhen, CN); Feng, Xiaoming (Shenzhen, CN), filed on September 30, 2010, was published online on August 26, 2014 (see also Ocean's King Lighting Science & Technology Co., Ltd.).

The assignee for this patent, patent number 8816340, is Ocean's King Lighting Science & Technology Co., Ltd. (Shenzhen, CN).

Reporters obtained the following quote from the background information supplied by the inventors: "Organic electroluminescent devices, also known as organic light emitting diodes (OLEDs), are a type of devices which can directly convert electric energy to light energy. In 1987, C. W. Tang and collaborators first prepared a small-molecular organic electroluminescent device having a double-layer structure by using a hole transport material N,N'-diphenyl-N,N'-bis(3-tolyl)-4,4'-benzidine as a hole transport layer, and 8-hydroxyquinoline aluminum having electron transport capacity as an electron transport layer and a light-emitting layer.

"Organic electroluminescence may involve the following five processes: 1) injection of carriers, during which electrons and holes are injected from the cathode and the anode, respectively, to the organic functional film layer arranged between the electrodes under the effect of an applied electric field; 2) migration of carriers, during which the injected electrons and holes migrate to the light emitting layer from the electron transport layer and the hole transport layer, respectively; 3) recombination of carriers, during which electrons and holes combine in the light-emitting layer to produce excitons; 4) migration of excitons, during which excitons migrate under the effect of the electric field, transfer their energy to the luminescent molecules, and excite electrons to transit from ground state to excited state; and 5) electroluminescence, during which the excited state is deactivated through energy irradiation to generate photons and release energy.

"In these five processes, the energy-level match between the layers is very important, which directly affects the ultimate performance of the device. The HOMO value of the hole transport layer material is somewhat different from that of the anode material and the anode may release oxygen after long-time operation, which destroys the organic layer and results in dark spots. Therefore, a hole injection layer, which has a HOMO value between those of the anode and the hole transport layer, is normally inserted between the anode and the hole transport layer to facilitate hole injection. In addition, its film characteristics enable it to prevent oxygen in the anode from entering the OLED device, so as to prolong the life time of the device. Furthermore, the hole injection layer can also increase the adhesiveness of the hole transport layer and the anode, increase the hole injection contact, balance electron and hole injections, increase the proportion of exciton production from electron and hole, and control or reduce the number of holes which do not participate in light emission, thereby increasing the efficiency of the device. In conventional organic electroluminescent devices, due to the low contact area between the hole injection layer and an adjacent layer, the contact is poor, which results in reduction of hole injection efficiency, thereby affecting the luminescent efficiency and the luminescent brightness of the organic electroluminescent device."

In addition to obtaining background information on this patent, NewsRx editors also obtained the inventors' summary information for this patent: "In view of the above, it is necessary to provide an organic electroluminescent device with relatively high luminescent efficiency and luminescent brightness.

"An organic electroluminescent device comprises a sequentially laminated structure comprising a conductive substrate, a hole injection layer, a light emitting layer and a cathode layer; wherein the hole injection layer comprises a conductive polymer and an azo initiator, and the surface of the hole injection layer connecting to the light emitting layer has a nano-reticular structure formed by thermal decomposition of the azo initiator.

"Preferably, the azo initiator is oil-soluble azobisisobutyronitrile, and the conductive polymer is poly(3-hexylthiophene), poly(3-methylthiophene), poly(3-octyloxythiophene) or poly(3-dodecylthiophene).

"Alternatively, the azo initiator is water-soluble azobis(isobutyramidine) hydrochloride, azobis[2-(2-imidazolin-2-yl)isobutane]hydrochloride, azobis(cyanovaleric acid) or azobis[2-(2-imidazolin-2-yl)propane], and the conductive polymer is a mixture of poly(3,4-ethylenedioxythiophene) and poly(sodium-p-styrenesulfonate) in a mass ratio of from 1:2 to 1:6.

"Alternatively, the azo initiator is amphipathic azoisobutyronitrile formamide, and the conductive polymer is a mixture of poly(3,4-ethylenedioxythiophene) and poly(sodium-p-styrenesulfonate) in a mass ratio of from 1:2 to 1:6, poly(3-hexylthiophene), poly(3-methylthiophene), poly(3-octyloxy thiophene) or poly(3-dodecyl thiophene).

"Preferably, the organic electroluminescent device further comprises a hole transport layer between the hole injection layer and the light emitting layer, and the surface of the hole injection layer connecting to the light emitting layer has a nano-reticular structure formed by thermal decomposition of the azo initiator.

"Preferably, the organic electroluminescent device further comprises an electron transport layer or an electron injection layer between the light emitting layer and the cathode layer.

"Preferably, the organic electroluminescent device further comprises an electron transport layer and an electron injection layer between the light emitting layer and the cathode layer, and the electron transport layer is in contact with the light emitting layer.

"In addition, there is a need to provide a method for preparing the organic electroluminescent device described above.

"A method for preparing an organic electroluminescent device comprises the steps of: adding an azo initiator into a solution of a conductive polymer and stirring to prepare a conductive gel, wherein a mass ratio of the azo initiator and the conductive polymer is in a range of from 0.1:1 to 1.5:1; subjecting a surface of a conductive substrate to a pretreatment; spin-coating the conductive gel on the pretreated surface of the conductive substrate and drying to give a hole injection layer; providing a light emitting layer on the hole injection layer; and providing a cathode layer on the light emitting layer and drying to give the organic electroluminescence device.

"Preferably, the azo initiator is oil-soluble azobisisobutyronitrile, the conductive polymer is poly(3-hexylthiophene), poly(3-methylthiophene), poly(3-octyloxy thiophene) or poly(3-dodecyl thiophene), the solvent for the solution of the conductive polymer is toluene, chlorobenzene or xylene, and the step of spin-coating the conductive gel and drying comprises dripping the conductive gel on the conductive substrate, spin coating with a spin coater at a rotating speed of 500.about.4000 rpm, and heating at 150.about.200.degree. C. for 15.about.60 min.

"Preferably, the azo initiator is water-soluble azobis(isobutyramidine) hydrochloride, azobis[2-(2-imidazolin-2-yl)isobutane]hydrochloride, azobis(cyanovaleric acid) or azobis[2-(2-imidazolin-2-yl)propane], the conductive polymer is a mixture of poly(3,4-ethylenedioxythiophene) and poly(sodium-p-styrenesulfonate) in a mass ratio of from 1:2 to 1:6, the solvent for the solution of the conductive polymer is water, and the step of spin-coating the conductive gel and drying comprises dripping the conductive gel on the conductive substrate, spin coating with a spin coater at a rotating speed of 500.about.3000 rpm, and heating at 150.about.200.degree. C. for 15.about.60 min.

"Preferably, the azo initiator is amphipathic azoisobutyronitrile formamide, the conductive polymer is a mixture of poly(3,4-ethylenedioxythiophene) and poly(sodium-p-styrenesulfonate) in a mass ratio of from 1:2 to 1:6, poly(3-hexylthiophene), poly(3-methylthiophene), poly(3-octyloxy thiophene) or poly(3-dodecyl thiophene), the solvent for the solution of the conductive polymer is water, benzene, chlorobenzene or xylene; and the step of spin-coating the conductive gel and drying comprises dripping the conductive gel on the conductive substrate, spin coating with a spin coater at a rotating speed of 500.about.4000 rpm, and heating at 100.about.200.degree. C. for 15.about.60 min.

"Preferably, the pretreatment step comprises sonicating the conductive substrate sequentially in a detergent, deionized water, acetone, ethanol, and isopropanol, and subjecting the conductive substrate to oxygen plasma treatment, ozone-UV treatment, hydrogen peroxide treatment, aqua regia treatment or acid treatment.

"The hole injection layer of the organic electroluminescent device comprises an azo initiator. Since the azo initiator has a relatively low decomposition temperature, it would decompose to release N.sub.2 when being heated above its decomposition temperature, so that a layer of non-planar, three-dimensional, nano-reticular structure is formed on the surface of the hole injection layer. This structure can greatly increase the area of the contact interface between the hole injection layer and an adjacent layer, thereby improving the contact between the hole injection layer and the adjacent layer, increasing the hole injection efficiency, and increasing the probability of recombination between holes and electrons, so that the luminescent efficiency and the luminescent brightness of the organic electroluminescent device can be increased."

For more information, see this patent: Zhou, Mingjie; Wang, Ping; Huang, Hui; Feng, Xiaoming. Organic Electroluminescence Device and Manufacturing Method. U.S. Patent Number 8816340, filed September 30, 2010, and published online on August 26, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8816340.PN.&OS=PN/8816340RS=PN/8816340

Keywords for this news article include: Alkenes, Ethylenes, Ocean's King Lighting Science & Technology Co., Ocean's King Lighting Science & Technology Co. Ltd., Sulfur Compounds, Technology, Thiophenes.

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Source: Life Science Weekly


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