CN100456527C - A method for improving the light-coupling efficiency of flat-panel light-emitting devices - Google Patents

Abstract

The invention belongs to the field of flat light-emitting devices, especially the field of organic electroluminescent devices, and specifically relates to a method for improving the light-coupling efficiency of flat light-emitting devices. To couple light efficiency, the microspheres are semi-pressed into the polymer pre-spin-coated on the organic light-emitting device substrate by using microcontact printing technology, and then the transparent electrode 1, organic material layer and electrode 2 are sequentially stacked on the other side of the substrate. Its characteristic is to keep the microspheres, the polymers pressed into the microspheres, and the refractive index of the substrate to be equal or close, so that the refraction and reflection effect of the light emitted by the device at the interface between the substrate and the polymer, and the polymer and the microspheres can be ignored , thereby improving the outcoupling efficiency of the device. The entire technological process of the present invention does not require photolithography, and is relatively simple. In addition, the diameter of the microspheres can be selected, so that the finally formed quasi-microlenses are uniform in size and uniform.

Description

A method for improving the light-coupling efficiency of flat-panel light-emitting devices

technical field

The invention belongs to the field of flat light-emitting devices, in particular to the field of organic electroluminescence devices, and specifically relates to a method for improving the light-coupling efficiency of flat light-emitting devices.

Background technique

Organic electroluminescent devices are devices that use injected carriers to emit light. They have the advantages of autonomous light emission, low-voltage drive, wide viewing angle, fast response, and rich colors. Therefore, they have attracted wide attention as next-generation display devices.

The typical structure of an organic electroluminescent device is: substrate/anode/organic light-emitting layer/cathode. Due to the difference in refractive index of the materials that make up each layer, refraction and reflection will be formed at the interface of each layer, and total reflection will also be formed when light is incident from a material layer with a high refractive index to a material layer with a low refractive index. As a result, the optical coupling output efficiency of the device is only about 20%, so most of the light is lost inside the device.

In order to solve such problems, a method is disclosed in the patent literature (US Patent: 6984934), that is, a layer of micro-lenses is fabricated on the substrate of the organic light-emitting device to improve the outcoupling efficiency of light. However, the process of fabricating the microlens is relatively complicated, and a traditional photolithography process is required, that is, a template is firstly fabricated, and then the microlens is fabricated on the template, and then transferred to the substrate of the organic light-emitting device. In order to improve the method of making microlenses, another patent document (Chinese Patent: Publication No. CN1719955A) mentions spraying microlens-forming materials on the surface of organic light-emitting device substrates and having low affinity with the surface of the substrate material. droplets, which are then allowed to solidify to form microlenses. The process of this method is relatively simple, but the size of the sprayed droplets is difficult to control, resulting in the microlenses formed on the surface of the substrate of the organic light-emitting device with different sizes and very irregular.

Contents of the invention

The purpose of the present invention is to provide a simple method for improving the light coupling efficiency of flat light-emitting devices. Aiming at the shortcomings of the complicated process of making microlenses in the past, or the shortcomings of difficult control of the size of microlenses, it is proposed to make microspheres first, and then use the screened microspheres Microspheres are semi-pressed into the polymer pre-spin-coated on the organic light-emitting device substrate to form a microlens-like structure.

To achieve the above object, the technical solution of the present invention comprises the following steps:

(1) preparing a microsphere colloidal liquid whose diameter is on the order of nanometers or micrometers;

(2) Use a centrifuge to separate microspheres of different diameters, and select a microsphere with a diameter to carry out the following steps;

(3) drop the colloidal liquid containing microspheres obtained in step (2) onto a slightly inclined substrate at a certain angle, and form multi-layered closely packed microsphere colloidal crystals on the substrate by evaporating the solvent;

(4) Using polymer 1 with relatively good elasticity to transfer the monolayer microspheres to the organic light-emitting device substrate that is pre-spin-coated with polymer 2 to form a close-packed or non-close-packed microsphere structure, the polymer 2 and microspheres The adhesion is greater than the adhesion between polymer 1 and microspheres;

(5) heating the substrate of the organic light-emitting device so that its temperature exceeds the glass transition temperature of polymer 2, and applying pressure to half-press the microspheres into polymer 2, and then removing polymer 1;

(6) Fabricate an electroluminescent device comprising an organic polymer layer or a small molecule layer on the other side of the substrate of the organic light-emitting device, thereby preparing a flat-panel light-emitting device with improved light coupling efficiency.

The microspheres described in the above method step (1) are inorganic material microspheres or polymer material microspheres, with a diameter of 100 nanometers to 1400 nanometers; are equal, the refraction and reflection effect of the light emitted by the device at the organic light-emitting device substrate and the polymer, the polymer and the microsphere interface can be ignored, thereby improving the outcoupling light efficiency of the device; by stretching the polymer 1 (such as polysiloxane; polyethylene; ethylene-propylene rubber; neoprene, etc.), so that the microspheres on the surface of the polymer 1 have a distance of 100 nanometers to 1000 nanometers, so that the semi-pressed polymer 2 (such as polyvinyl alcohol) ; Polyethylene glycol; Polymethyl methacrylate; Polyurethane) in the microspheres form a non-close packing structure, the distance between the microspheres is 100 nanometers to 1000 nanometers; it is also possible not to stretch the polymer 1, so that the semi-pressed polymer The microspheres in 2 form a close-packed structure; the organic light-emitting device includes a transparent substrate, first and second electrode layers, and an organic polymer layer or a small molecule layer sandwiched between the two electrode layers, wherein the organic polymer layer material Trapezoidal polyphenylene and its derivatives, polyphenylene vinylene and its derivatives, polyfluorene and its derivatives, etc. can be selected, and octahydroxyquinoline aluminum, triphenylamine and its derivatives, and phenolic pyridine complexes can be used as materials for the small molecule layer. substances, quinacridone derivatives, porphyrin metal complexes, etc.; the transparent substrate uses glass or flexible plastics (such as polyester, polyamide, etc.); the first electrode is a metal, alloy or electrode with a large work function and transparency. Conductive compounds (such as indium tin oxide, zinc oxide, indium zinc oxide, gold, copper, silver, etc.); organic polymer layers or small molecule layers are hole injection layers, hole transport layers, electron blocking layers, light emitting layers, One or more layers of hole blocking layer, electron transport layer, and electron injection layer; the second electrode uses a metal or alloy with low work function, such as metal lithium, magnesium, calcium, strontium, aluminum or their combination with copper, gold, Silver alloys etc.

The structure, materials and electrodes of the electroluminescence device are not the invention points of this patent. Regarding the device structure, there are typically double-layer or multi-layer structures (Appl. Phys. Lett. 1987, 51, 913).

The specific instructions are as follows:

(1) According to Stober's method (W.Stober, A.Fink.J.Colloid Interface Sci.26, 62 (1968)), prepare monodisperse colloidal silica microspheres with a diameter of 100nm to 1400nm in ethanol liquid;

(2) Use a centrifuge to separate silica microspheres of different diameters, and select microspheres with a diameter of 400 to 700 nanometers to carry out the following steps;

(3) Drop the colloidal liquid of microspheres obtained in step 2 onto a silicon substrate that is 3 to 12° from the horizontal plane, and then form a large microsphere on the silicon substrate by evaporating the solvent in an oven that can control temperature and humidity. Colloidal crystals of hexagonal close-packed microspheres with a single layer or multiple layers (2 layers and above);

(4) Using polymer 1 (polysiloxane; polyethylene; ethylene-propylene rubber; neoprene) with relatively good elasticity, poly(dimethylsiloxane) poly(dimethylsiloxane) is used here for short as PDMS, and the single-layer dioxide The silicon microspheres are transferred to the organic light-emitting device substrate that is pre-spin-coated with polymer 2, and polymer 2 (such as polyvinyl alcohol; polyethylene glycol; polymethyl methacrylate; polyurethane) is selected from polyvinyl alcohol poly(vinyl alcohol) Referred to as PVA, it can be tightly packed or non-close packed. Refer to our patent (Chinese patent: ZL200310110094.X);

(5) Heating the organic light-emitting device substrate at 95-105 degrees to make the temperature exceed the glass transition temperature of PVA (80 degrees), apply a pressure of about 0.1×10 ⁵ Pa to 0.5×10 ⁵ Pa, and press the microspheres into the Polymer PVA, and then peel off PDMS, because the adhesion of silica microspheres to PVA is greater than that of silica to PDMS, so the PDMS layer can be peeled off, leaving silica microspheres in PVA layer;

(6) On the other side of the substrate of the organic light-emitting device, an electroluminescent device comprising an organic polymer layer or a small molecule layer is fabricated by a conventional method.

The entire technological process of the present invention does not require photolithography, and is relatively simple. In addition, the diameter of the microspheres can be selected, so that the finally formed quasi-microlenses are uniform in size and uniform.

Description of drawings

Figure 1: Schematic diagram of multi-layer close-packed colloidal crystals of silica microspheres formed on a silicon substrate;

Figure 2: Schematic diagram of the compact compression process of polymer PDMS with relatively good elasticity and silica microspheres;

Figure 3: A schematic diagram of the process of uncovering the PDMS and sticking a layer of silica microspheres to the PDMS;

Figure 4: A schematic diagram of the process of tightly packing PDMS with a layer of silica microspheres and the polymer PVA pre-spin-coated on the organic light-emitting device substrate to form a dense stack of silica microspheres;

Figure 5: A schematic diagram of the process of stretching PDMS with a layer of silica microspheres in two directions and then compacting it tightly with PVA to form non-tight packing of silica microspheres;

Figure 6: Schematic diagram of the process of heating the organic light-emitting device substrate to make its temperature exceed the glass transition temperature of PVA, and applying pressure to half-press the microspheres into the polymer PVA;

Figure 7: Schematic diagram of the microlens-like structure formed after removing PDMS;

Figure 8: Electron micrograph of the structure shown in Figure 7;

Figure 9: Schematic diagram of an organic light emitting device fabricated on the other side of the organic light emitting device substrate;

Figure 10: Curves of luminance efficiency in the normal direction of organic electroluminescent devices with and without silica microspheres as a function of current;

Fig. 11: The electroluminescent spectrum of the organic electroluminescent device with silica microspheres as a function of the observation angle, where the normal direction is 0 degree angle.

In the above-mentioned Figures 1 to 11, 1 is a silica microsphere, 2 is a silicon substrate, 3 is a polymer PDMS, 4 is tin indium oxide, 5 is a substrate of an organic light-emitting device, 6 is a polymer PVA, 7 is an organic light-emitting polymer layer or a small molecule layer, 8 is a cathode layer, and 9 is a power supply.

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the present invention is not limited to the following preferred embodiments, which are merely illustrative embodiments of the present invention.

Detailed ways

Example 1:

Monodisperse silica microspheres of various diameters were prepared in ethanol. For narrowly dispersed silica microspheres with a diameter below 500nm, the following method is used: 14ml tetraethyl orthosilicate is dissolved in 100ml ethanol, 27.5ml water, 9.5ml ammonia water are dissolved in 100ml ethanol, and then the two solutions are mixed and stirred at room temperature 6 hours. The emulsion was then centrifuged and washed three times with ethanol or water, and finally dried in an oven at 60°C. For silica microspheres with a diameter of 500nm to 1.4μm, the operation is similar to the above, only need to introduce a seed silica powder or emulsion with a size of 250nm to 500nm in the system (if it is a powder, it needs to be completely dispersed by ultrasonic before use. ). After the reaction is completed, wash and dry in the same way.

The microspheres with different diameters are classified by a centrifuge, and the silica microspheres with a diameter of 550 nanometers are selected here for the following steps.

Drop the colloidal liquid _{containing silicon} dioxide microspheres on the silicon substrate inclined at ₉ °, and the cleaning process of the silicon _substrate is as follows: 3 at 90°C for 5 hours, rinsed with distilled water, and finally dried with high-purity nitrogen. Then transfer the silicon substrate with silicon dioxide microsphere colloidal droplets on the surface to an oven that can control temperature and humidity, and form multilayer microsphere colloidal crystals that are closely packed on the silicon substrate by evaporating the solvent, as shown in Figure 1 Show.

Make a flat sheet (above 250nm) from a polymer with relatively good elasticity. Here, poly (dimethylsiloxane) is selected for short as PDMS, which is in close contact with the colloidal crystal of silica microspheres shown in Figure 1, and then heated at 100°C for 3 hours ,as shown in picture 2.

After the sample was cooled to room temperature, the PDMS was carefully lifted, and a layer of silica microspheres was adhered to the PDMS, as shown in Figure 3.

At this time, the PDMS bonded with silica microspheres can be directly pressed tightly with the polymer PVA pre-spin-coated on the substrate of the organic light-emitting device to form a dense packing of silica microspheres, as shown in FIG. 4 . It is also possible to stretch PDMS in two directions and then tightly compress it with PVA to form non-close packing of silica microspheres, as shown in Figure 5. Among them, the organic light-emitting device substrate selects glass with tin indium oxide (ITO for short) sputtered on the other side, and undergoes a process of acetone, ethanol ultrasonication, deionized water washing, and nitrogen blowing.

Then apply a pressure of 0.2×10 ⁵ Pa and heat at 100° C. for 1.5 hours to half-press the silica microspheres into the PVA, as shown in FIG. 6 .

After cooling to room temperature, after carefully peeling off the PDMS, the silica microspheres remained in the PVA because the adhesive force between the silica microspheres and PVA was greater than that of the silica microspheres and PDMS, forming a A microlens-like structure, as shown in Figure 7.

Fig. 8 is an electron micrograph of the structure shown in Fig. 7, and it can be seen that the silica microspheres are uniform in size and neatly arranged.

Fabricate an organic electroluminescence device on the other side of the substrate shown in Figure 7 afterwards, the structure is: ITO/N, N'-two-(1-naphthyl)-N, N'-diphenyl-1, 1-biphenyl-4,-4-diamine (abbreviated as NPB) (60nm)/aluminum octahydroxyquinoline (abbreviated as Alq ₃ ) (70nm)/LiF (0.5nm)/Al (100nm). At the same time, for comparison and illustration, an organic electroluminescent device with the same structure was fabricated on a substrate without silica microspheres. The above-mentioned organic electroluminescent device is manufactured by thermal evaporation in a vacuum chamber, and the pressure of the vacuum chamber is 6×10 ^-4 Pa. In this device structure, NPB is the hole transport layer, and Alq ₃ is the electron transport layer and also the light emitting layer.

Fig. 10 is the change curve of the luminance efficiency in the normal direction of the organic electroluminescent device with and without silicon dioxide microspheres as a function of current. It can be seen that the maximum brightness efficiency of the organic electroluminescent device with silica microspheres is 1.8 times that of the organic electroluminescent device without silica microspheres.

Fig. 11 is the change of the electroluminescent spectrum of the organic electroluminescent device with silica microspheres with the observation angle, wherein the normal direction is 0 degree angle, it can be seen that the electroluminescent spectrum of the device does not change with the angle, which means It shows that the mechanism of increasing the outcoupling light efficiency of the present invention is not the scattering mechanism, but the mechanism of increasing the critical angle of total reflection.

Although the present invention has been described in conjunction with preferred embodiments, the present invention is not limited to the above-mentioned embodiments, it should be understood that under the guidance of the present invention, those skilled in the art can make various modifications and improvements, and the appended claims summarize scope of the invention.

Claims (10)

1, a kind of method of improving coupling luminous efficiency of flat plate luminescent device, it may further comprise the steps:

(1) the preparation diameter is the inorganic material microballoon or the polymeric material microballoon colloidal liquid of nanometer or micron dimension;

(2) adopt centrifugal separator that the microballoon of different-diameter is separated, the microballoon of choosing a kind of diameter carries out following step;

(3) colloidal liquid that will contain microballoon drips on the substrate of the certain angle that tilts a little, forms the closelypacked microballoon colloidal crystal of multilayer by evaporating solvent on substrate;

(4) utilize the reasonable polymer 1 of elasticity the individual layer microballoon to be transferred on the organic luminescent device substrate of spin on polymers 2 in advance, form tightly packed or non-closelypacked micro-sphere structure, the bonding force of polymer 2 and microballoon is greater than the bonding force of polymer 1 with microballoon, and the refractive index of polymer 2, microballoon, organic luminescent device substrate is approaching or equates;

(5) heating organic luminescent device substrate makes its temperature surpass the vitrification point of polymer 2, and exerts pressure microballoon partly is pressed in the polymer 2, throws off polymer 1 then;

(6) the another side making at the organic luminescent device substrate comprises the organic polymer layers or the electroluminescent device of micromolecule layer, thereby prepares the improved flat plate luminescent device of coupling luminous efficiency.

2, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 1 is characterized in that: the preparation diameter is the silicon dioxide microsphere of 100nm～1400nm.

3, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 2 is characterized in that: choosing diameter by centrifugal separator is silicon dioxide microsphere between 400～700nm.

4, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 1 is characterized in that: polymer 1 is polysiloxanes, polyethylene, ethylene-propylene rubber or neoprene; Polymer 2 is polyvinyl alcohol, polyethylene glycol, polymethyl methacrylate or polyurethane.

5, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 3 is characterized in that: polymer 1 is PDMS, and polymer 2 is PVA.

6, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 1, it is characterized in that: be method by strained polymer 1, make the microballoon that partly is pressed in the polymer 2 form non-close-packed structure, the microballoon spacing is 100 nanometers～1000 nanometers.

7, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 1 is characterized in that: organic luminescent device comprises transparent substrate, first and second electrode layers and presss from both sides two organic polymer layers or micromolecule layers between the electrode layer.

8, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 7 is characterized in that: transparent substrate uses glass or flexiplast.

9, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 7 is characterized in that: first electrode is the big and transparent metal of work function, alloy or electrical conductivity compound, and second electrode is the low metal or alloy of work function.

10, the method for improving coupling luminous efficiency of flat plate luminescent device as claimed in claim 7 is characterized in that: organic polymer layers or micromolecule layer are one or more layers in hole injection layer, hole transmission layer, electronic barrier layer, luminescent layer, hole blocking layer, electron transfer layer or the electron injecting layer.

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