OLED display cathode based on vacuum evaporation equipment and manufacturing method thereof

Abstract

The invention relates to a manufacturing technology of a light-emitting structure of an OLED (Organic Light Emitting Diode) display, in particular to an OLED display cathode based on vacuum evaporation equipment, which is applied to an OLED display with a top emission structure, and is characterized in that the cathode material adopts polyethylene dioxythiophene, and the manufacturing method comprises the following steps of: dissolving 3, 4-ethylenedioxythiophene in a mixed solvent of chloroform and acetic acid; adding a brominating agent N-bromosuccinimide to obtain a mixture, pouring the mixture into 1-3 times by volume of water, adding 0.2-1 times by volume of chloroform, stirring for 30 minutes, centrifuging the mixed solution in batches, taking out the organic matter by adopting a pipette, stirring and washing the obtained organic extract with a Na2CO3 solution to obtain a new mixed solution, and drying the new mixed solution to obtain a finished product. Purifying and distilling to obtain DBEDOT white powder; and finally, carrying out vacuum deposition in vacuum evaporation equipment to obtain the PEDO transparent cathode. The transparent cathode provided by the invention has the advantages of high conductivity, high light transmittance, simple preparation method and the like, and meanwhile, the display brightness can be improved to meet VR application requirements.

Description

Technical Field

[0001] The present invention relates to a manufacturing technology of a light-emitting structure of an OLED display, and in particular to a cathode of an OLED display based on a vacuum evaporation device and a manufacturing method thereof. Background Art

[0002] Organic light-emitting diode (OLED) has broad application prospects in the field of virtual reality (VR) displays due to its advantages such as high pixel density, high brightness, wide viewing angle and fast response speed.

[0003] In order to achieve the integration of light-emitting devices and circuits while avoiding the occlusion of the display area, OLED displays need to maintain a large aperture ratio as much as possible, so a top emission structure is selected. The existing top emission structure of OLED display structure consists of a semi-transparent metal cathode, an organic functional layer, a reflective anode, and a driving circuit from top to bottom. At present, the semi-transparent metal cathode usually uses a relatively thin Mg:Ag metal composite layer, which has a semi-transparent and semi-reflective property, resulting in a strong microcavity effect of the OLED organic light-emitting structure, which can greatly improve the luminous color purity of each single color of RGB; however, OLED displays usually use white light plus a color filter to achieve full-color display. If the microcavity effect is too significant, it will be difficult to match the filtering band of the color filter, resulting in a loss of luminous brightness and a deterioration of the overall display effect. At the same time, the necessary condition for the microcavity effect is that the organic functional layer has a specific cavity length thickness, usually 1000-3000Å. The thicker organic functional layer will greatly increase the operating voltage of the OLED display. However, the driving voltage of the silicon-based circuit is limited, which greatly limits the brightness of the organic functional layer. Summary of the invention

[0004] The purpose of the present invention is to provide a new OLED display cathode based on vacuum evaporation equipment and a manufacturing method thereof.

[0005] In order to achieve the above-mentioned purpose of the invention, the present invention provides an OLED display cathode based on a vacuum evaporation device, which is applied to an OLED display with a top emission structure, and is characterized in that the cathode material is polyethylene dioxythiophene (PEDOT).

[0006] The method for preparing the cathode of an OLED display based on a vacuum evaporation device is characterized by being achieved by the following steps: Step 1) dissolving 3,4-ethylenedioxythiophene (EDOT) in a mixed solvent of chloroform and acetic acid, wherein the volume ratio of the mixed solvent is 1-3:1; Step 2) Add brominating agent N-bromosuccinimide (NBS) at 0-10°C and argon, and then stir at 20-30°C for 2h~12h to carry out bromination reaction to obtain a mixture.

[0007] Step 3) The mixture was poured into 1-3 times the volume of water, and then 0.2-1 times the volume of chloroform was added and stirred for 30 minutes. The mixed solution was then centrifuged in batches at a centrifugal speed of 8000-12000 rpm to separate the organic matter from the water. The organic matter was removed by a pipette, and the obtained organic extract was washed with 1-2 times the volume of 1-5 wt% % The Na2CO3 solution was stirred and washed for 30 minutes to obtain a new mixed solution, and the new mixed solution was centrifuged in batches to extract the organic layer, and then the organic layer was concentrated by vacuum distillation, and the chloroform solution of 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) was obtained by silica gel column purification, and the DBEDOT white powder was obtained by vacuum distillation again; Step 4) placing DBEDOT powder in a vacuum evaporation device, and performing vacuum deposition in-situ polymerization on the substrate on which the OLED organic functional layer is deposited, to obtain a PEDOT transparent cathode composed of polyethylene dioxythiophene. The process conditions of the vacuum deposition in-situ polymerization are 40-100°C and the vacuum degree is 10 -5 ~10 -8 Torr; Specifically, the brominating agent in step 2) is an excess of copper bromide, hydrogen bromide, NBS, dimethyl bromide sulfide (DMBS), sodium bromide, potassium bromide, ammonium bromide or bromine chloride, etc. The above describes the specific steps and methods for preparing PEDOT into a polymer film layer as a transparent cathode of an OLED device. There are many methods for preparing a PEDOT polymer film layer, but none of them can prepare a transparent cathode of an OLED device on an organic functional layer substrate. The specific reasons and data are as follows: PEDOT is a common conductive polymer. Since PEDOT is a polymer film layer, its internal conjugated electron system has good connectivity, and electrons are quickly transmitted in the PEDOT molecular structure. Therefore, it has a conductivity of >1200S / cm, and its transmittance is ≥95%, making it an ideal electrode material. There are three main methods for preparing PEDOT electrodes: electrochemical polymerization, oxidative coupling polymerization (PEDOT, and coating PEDOT dispersion (PEDOT:PSS). The PEDOT electrode is prepared by applying PEDOT on the surface of a substrate to form an electrode.

[0008] Electrochemical polymerization method: Under the action of an external electric field, a solution containing monomer EDOT is electrolyzed to obtain a layer of conjugated polymer PEDOT on the surface of the working electrode. The solution is prepared from solvents such as acetonitrile, chloroform, benzonitrile, and carbonate propiolactone and solute EDOT. This method has two main features: (1) The substrate needs to have good conductivity; (2) It can withstand solvent dissolution. However, the OLED organic functional layer does not have good conductivity and can also be dissolved in solvents such as acetonitrile, chloroform, benzonitrile, and carbonate propiolactone. Therefore, it cannot be used as a substrate to prepare a polymer film layer as a transparent cathode for OLED devices.

[0009] Oxidative coupling polymerization method: The monomer EDOT is easily oxidized. EDOT first introduces a positively charged modifier (such as a sub-acid or sulfuric acid) through a chemical reaction, and then initiates a polymerization reaction through an oxidant (such as ammonium persulfate), so that multiple thiophene monomers are connected through conjugated bonds to form a polymer PEDOT on the substrate. The organic functional layer of OLED will fail when affected by water and oxygen, so the modifiers and oxidants involved in the oxidative coupling polymerization method will cause the organic functional layer of OLED to fail, so it cannot be used as a substrate to prepare a polymer film layer as a transparent cathode of the OLED device.

[0010] Coating PEDOT dispersion (PEDOT:PSS) method: water, water-soluble polymer electrolyte polystyrene-sulfonic acid (PSS) and PEDOT powder are reacted to form a solution containing PEDOT / PSS, which is then coated on the substrate by spin coating or inkjet method. After the water evaporates, a transparent electrode is formed. Its limitation is that the water and PSS solvent in PEDOT / PSS in this method will cause the failure of the OLED organic functional layer, so it cannot be used as a substrate to prepare a polymer film layer as a transparent cathode for OLED devices. At the same time, the product prepared by this scheme is PEDOT:PSS, and the conductivity decreases due to the presence of PSS, which is only about 550S / cm.

[0011] VR displays are developing rapidly at this stage. Currently, remote presentation and visual realism depend largely on their display brightness. In order to further increase the immersion of VR displays, so that users can see a "real" environment full of details instead of a glowing picture, it is necessary to further increase the display brightness of OLED displays. However, the presence of a translucent metal cathode will greatly limit the improvement of its brightness performance. The transparent cathode provided by the present invention has the advantages of high electrical conductivity, high light transmittance, and simple preparation method, and can also improve the display brightness to match VR application requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Figure 2 shows the chemical composition of PEDOT / PSS electrode in the conventional preparation scheme.

[0013] Figure 2 The synthetic route diagram of the PEDOT transparent cathode material of the present invention.

[0014] Figure 3 The infrared spectrum of the transparent cathode material of the present invention is shown in the figure. In the figure, the ordinate of the external spectrum is absorbance, which indicates the ability of the sample to absorb infrared radiation, and the abscissa is wave number, which indicates the reciprocal of the wavelength. -1 Asymmetric CC stretching peak, COC deformation peak and oxygen ring deformation stretching peak can be observed, proving the successful synthesis of PEDOT transparent cathode.

[0015] Figure 4 This is a spectrum diagram of the PEDOT transparent cathode of the present invention applied to an OLED display: in the figure, the ordinate is light intensity and the abscissa is wavelength; there are three bands of emitted light in the figure, corresponding to the emission of RGB three-color light, which proves that the device is working normally. DETAILED DESCRIPTION

[0016] The present invention will be described in more detail below through specific embodiments, but the protection scope of the present invention is not limited to the embodiments.

[0017] Embodiment 1: The driving substrate may be a glass substrate or a silicon-based driving substrate with a driving circuit such as α-Si / LTPS / LTPO / Oxide; the manufacturing process of the transparent cathode OLED display may be described as follows: Step 1: Using vacuum evaporation to sequentially deposit a hole layer and a blue light-emitting layer thin film on a substrate with a driving circuit and an anode pixel pattern; Step 2: Dissolve EDOT in a mixed solvent of chloroform and acetic acid. The volume ratio of the mixed solvent is 2:1; Step 3: Under low temperature and argon protection, add a brominating agent such as N-bromosuccinimide (NBS), and then stir at 25°C for 6 hours to carry out a bromination reaction to obtain a mixture; Step 4: Pour the mixture into water, and then extract the aqueous solution with chloroform. Wash the organic extract with Na2CO3 solution. Extract the organic layer and purify and concentrate to obtain a white powder of DBEDOT; Step 5: Place the DBEDOT powder in a vacuum evaporation device and deposit the The substrate of the OLED organic functional layer is in-situ polymerized by vacuum deposition at 60°C to obtain a high-purity PEDOT transparent cathode layer; Step 6: Use atomic layer deposition, chemical vapor deposition, molecular layer deposition, evaporation and other processes to complete the device thin film packaging process.

[0018] Embodiment 2: The driving substrate may be a glass substrate or a silicon-based driving substrate with a driving circuit such as α-Si / LTPS / LTPO / Oxide; the manufacturing process of the transparent cathode OLED display may be described as follows: Step 1: Using vacuum evaporation to sequentially deposit a hole layer and a blue light-emitting layer thin film on a substrate with a driving circuit and an anode pixel pattern; Step 2: Dissolve EDOT in a mixed solvent of chloroform and acetic acid. The volume ratio of the mixed solvent is 1:1; Step 3: Under low temperature and argon protection, N-bromosuccinimide (NBS) was added, followed by stirring at 25°C for 12 hours for bromination reaction to obtain a mixture; Step 4: Pour the mixture into water, and then extract the aqueous solution with chloroform. Wash the organic extract with Na2CO3 solution. Extract the organic layer and purify and concentrate to obtain a white powder of DBEDOT; Step 5: placing DBEDOT powder in a vacuum evaporation device, and subjecting the substrate on which the OLED organic functional layer is deposited obtained in step 1) to in-situ polymerization by vacuum deposition at 80° C. to obtain a high-purity PEDOT transparent cathode layer; Step 6: Use atomic layer deposition, chemical vapor deposition, molecular layer deposition, evaporation and other processes to complete the device thin film packaging process.

[0019] The present invention is described in detail above, but the present invention is not limited to the above-mentioned embodiments. Various changes or substitutions can be made within the knowledge of those skilled in the art without departing from the purpose of the present invention, and many other changes can be made without departing from the concept and scope of the present invention. It should be understood that the present invention is not limited to specific embodiments, and the scope of the present invention is defined by the claims.

Claims

1. The cathode of the OLED display based on the vacuum evaporation equipment is applied to the OLED display of the top emission structure, characterized in that The cathode material is polyethylene dioxythiophene.

2. A method for preparing an OLED display cathode based on a vacuum evaporation device, characterized in that This is accomplished by following these steps: Step 1) dissolving 3,4-ethylenedioxythiophene in a mixed solvent of chloroform and acetic acid, wherein the volume ratio of the mixed solvent is 1-3:1; Step 2) adding a brominating agent N-bromosuccinimide at 0-10°C and argon, followed by stirring at 20-30°C for 2h~12h for bromination reaction to obtain a mixture; Step 3) The mixture was poured into 1-3 times the volume of water, and then 0.2-1 times the volume of chloroform was added and stirred for 30 minutes. The mixed solution was then centrifuged in batches at a centrifugal speed of 8000-12000 rpm to separate the organic matter from the water. The organic matter was removed by a pipette, and the obtained organic extract was washed with 1-2 times the volume of 1-5 wt% % The Na2CO3 solution was stirred and washed for 30 minutes to obtain a new mixed solution, and the new mixed solution was centrifuged in batches to extract the organic layer, and then the organic layer was concentrated by vacuum distillation, and the chloroform solution of 2,5-dibromo-3,4-ethylenedioxythiophene was obtained by silica gel column purification, and the DBEDOT white powder was obtained by vacuum distillation again; Step 4) placing DBEDOT powder in a vacuum evaporation device, and performing vacuum deposition in-situ polymerization on the substrate on which the OLED organic functional layer is deposited, to obtain a PEDOT transparent cathode composed of polyethylene dioxythiophene. The process conditions of the vacuum deposition in-situ polymerization are 40-100°C and the vacuum degree is 10 -5 ~10 -8 Torr.

3. A method for preparing an OLED display cathode based on a vacuum evaporation device as claimed in claim 2, characterized in that The brominating agent in step 2) is copper bromide, hydrogen bromide, NBS, dimethyl bromide, sodium bromide, potassium bromide, ammonium bromide or bromine chloride, etc., which are added in excess.

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