KR20020092558A - Preparation of organic and inorganic layers-structured electronic device having improved thermal stability - Google Patents

Abstract

PURPOSE: A method for fabricating an element having an inorganic layer and an organic layer is provided to improve thermal stability by performing a thermal process for the organic layer having the lowest thermal stability. CONSTITUTION: A substrate including ITO(Indium Tin Oxide) is cleaned. A PEDT-PSS layer of 15 weight percent is coated on an upper surface of the substrate including ITO(Indium Tin Oxide) by using a spin coating method. The PEDT-PSS layer is dried under temperature of 200 degrees centigrade during 10 minutes. An NPB layer is formed on the substrate including the PEDT-PSS layer under normal temperature by using a vapor deposition method. The deposited NPB layer has thickness of 500 angstrom. A thermal process for the NPB layer is performed under the temperature of 110 degrees centigrade during 30 minutes. A BCzVBi layer and an Al/LiF layer are deposited sequentially thereon.

Description

A method for manufacturing an element having an inorganic layer and an organic layer having excellent thermal stability {PREPARATION OF ORGANIC AND INORGANIC LAYERS-STRUCTURED ELECTRONIC DEVICE HAVING IMPROVED THERMAL STABILITY}

The present invention relates to a device composed of at least one inorganic material layer and at least one organic material layer and a method for manufacturing the same, and more particularly, a device having excellent thermal stability and a method of manufacturing the same, which is manufactured by heat-treating the organic material layer having the lowest thermal stability It is about.

In a device having an inorganic layer and an organic layer, there is a problem in that the organic layer has low thermal stability, leading to failure of device operation due to joule heat and external heating generated during operation of the device. That is, when the temperature of the device rises above the glass transition temperature of the organic material from Joule heat or external heating, the fluidity of these organic material layers is induced, and thus, the organic material layer or the metal layer deposited thereon is subjected to compressive stress. The surface bends or splits to occur.

For example, in the organic light emitting device, the organic substance used in the hole transport layer is N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-diphenyl-4,4'-diamine (TPD), α-naphthylphenylbiphenyl diamine (NPB), and the like, all of which have a glass transition temperature of 100 ° C. or lower. Therefore, when the temperature of the device is 100 ° C. or more, performance degradation of the device as described above is caused. In order to prevent this phenomenon, materials with high glass transition temperature have been developed as organic materials used as the hole transport layer. However, it is not easy to develop a material with high glass transition temperature that is suitable for the device, such as to balance the energy of the entire device having a multilayer structure.

On the other hand, when the hole transport layer is heated, crystallization occurs. Such crystallization, which occurs during device operation, causes current leakage in the device and should be suppressed as much as possible. However, when a predetermined hole transport layer is used in the device, the mobility of the holes may be increased and the interdiffusion with the light emitting layer may be reduced, thereby improving the performance of the device. However, when the crystallized hole transport layer is formed by depositing the hole transport material while raising the temperature of the substrate as in the conventional deposition method above the crystallization temperature, the hole transport material is fluidized to dewetting. As a result, the surface of the hole transport layer may be deteriorated, resulting in deterioration of device performance.

Therefore, in the method of manufacturing a device having at least one inorganic material layer and at least one organic material layer, the present inventors have formed the organic material layer having the lowest thermal stability into a thin film, and then heat-treated at a temperature below the sublimation point of the organic material layer. Deterioration of the device, such as wrinkles, splitting, etc. caused by heat from the inside and outside can be prevented, and when the organic material is a hole transport material, crystallization thereof is induced to improve the performance of the device. It is finished.

An object of the present invention is to provide a device having at least one inorganic material layer and at least one organic material layer having excellent thermal stability by heat-treating an organic material layer having the lowest thermal property, that is, having the lowest glass transition temperature, under appropriate conditions.

1 is a schematic diagram showing the structure of an organic light emitting device manufactured in an embodiment of the present invention,

2A and 2B illustrate Al cathode surfaces after device driving of a device (Example 1) and an unheated device (Comparative Example 1) prepared by heat-treating the hole transport layer (NPB layer) at 110 ° C. for 30 minutes according to the present invention, respectively. Optical micrograph for,

3A and 3B illustrate an Al cathode after heating at 160 ° C. of a device (Example 1) and an unheated device (Comparative Example 1), which were manufactured by heat treatment at 110 ° C. for 30 minutes after deposition of a hole transport layer (NPB layer), respectively. Optical micrograph of the surface,

4A and 4B are optical micrographs of the surface of the NPB layer of the specimen prepared by heat treatment at 180 ° C. (Example 2) and 130 ° C. (Example 4) after deposition of the hole transport layer (NPB layer), respectively, for 30 minutes;

5A, 5B, and 5C show voltages of devices (Examples 1, 2, and 4) and non-heat-treated devices (Comparative Example 1) prepared by heat treatment at various temperatures for 30 minutes after deposition of the hole transport layer (NPB layer), respectively. Is a graph of the current characteristics, the light emission characteristics according to the current and the electrical efficiency characteristics according to the current,

6A and 6B illustrate light emission characteristics of devices manufactured by heat treatment at 130 ° C. (Example 3-5) and 190 ° C. (Example 6-8) for various times after deposition of the hole transport layer (NPB layer), respectively. It is a graph.

In order to achieve the above object, in the present invention, in the method of manufacturing an organic light emitting device having at least one inorganic layer and at least one organic material layer, the organic material layer having the lowest thermal property after the thin film is formed at a sublimation point or less before the post-process thin film formation. Provided is a method of manufacturing a device, characterized in that the step of heat treatment in a vacuum or inert atmosphere at a temperature.

The present invention also provides a device excellent in thermal stability produced by the method of the present invention.

Hereinafter, the present invention will be described in detail.

According to the present invention, in the device having at least one inorganic layer and at least one organic material layer, a thin film of a layer having the lowest thermal property among the organic material layers is formed at room temperature and then heat-treated. When the heat treatment is performed after the formation of the thin film, the thin film is subjected to tensile stress due to the difference in the coefficient of thermal expansion between the adjacent layers. The tensile stress is generated by Joule heat generated from driving the device and heat from the outside. By compensating for the compressive stress, it is possible to prevent the neighboring organic material layer or the metal layer from bending or splitting due to the compressive stress.

In the method of the present invention, the formation of the thin film may be performed by any method performed at room temperature, for example, evaporation deposition, spin coating, sputtering, and the like, and the heat treatment may be performed in a vacuum or inert state within a temperature range in which the organic layer is not sublimated. Carried out under atmosphere. In the surface modification or electrical properties, the heat treatment process has little temperature and time dependence, but may be performed for 5 minutes to 120 minutes within the temperature range.

In addition, according to the present invention, it is possible to provide additional effects when the heat treated layer as described above is a hole transport layer of the organic light emitting device. That is, in manufacturing the device, if the hole transport layer is pre-annealed after the thin film is formed before the thin film is formed in the post process, crystallization of the hole transport layer may be induced. As such, when the thin film layer is first formed at room temperature without raising the temperature of the substrate and then crystallized by heat treatment, aggregation of the hole transport material may not occur, thereby preventing deterioration of device performance.

The characteristic heat treatment process of the present invention is applicable to all devices having at least one inorganic layer and at least one organic material layer, regardless of the type of organic layer component, for example, an organic transistor, an LCD backlight unit or a reflector, an organic light emitting device, or the like. Can be.

Specific examples of the method of the present invention include poly (3,4-ethylenedioxythiophene) -poly (4-styrene sulfonate) [PEDT-PSS] as the hole injection layer, and α-naphthylphenylbiphenyl as the hole transport layer. In the case of an organic light emitting element comprising diamine (NPB) and 4,4'-bis (2- (9-ethylcarbazolyl) -ethen-1-yl) -biphenyl [BCzVBi] as an organic layer, in an organic layer Since NPB is the lowest material having a glass transition temperature of 100 ° C. or lower, the NPB is heat-treated at the manufacturing stage of the device.

The device manufactured by the method of the present invention can prevent wrinkles or splitting of the surface of the cathode and can overcome the compressive stress due to Joule heat or external heating generated when the device is driven, thereby improving thermal stability and performance. have.

The invention can be better understood by the following examples, which are intended for the purpose of illustration of the invention and are not intended to limit the scope of protection defined by the appended claims.

Example

Example 1

After washing the glass substrate containing ITO (Indium-tin-oxide) (anode layer, thickness: 1000 GPa) by a conventional method, a poly (3,4-ethylenedioxythiophene) having a concentration of 15% by weight on the ITO- Poly (4-styrene sulfonate) (PEDT-PSS) (hole injection layer) was spin coated at 7000 rpm to form a film. The PEDT-PSS layer was heat-treated at 200 ° C. for 10 minutes to dry. An α-naphthylphenylbiphenyl diamine (NPB) layer (hole transport layer) was formed on the heat-treated specimen at a thickness of 500 kPa by evaporation at room temperature, followed by annealing at 110 ° C. for 30 minutes. 4,4'-bis (2- (9-ethylcarbazolyl) -ethen-1-yl) -biphenyl (BCzVBi) (light emitting layer) and LiF (energy barrier layer) / Al (cathode layer) were sequentially vacuumed The organic light emitting device was fabricated by forming a light emitting layer having a thickness of 500 mV and an energy barrier layer / cathode electrode layer having a thickness of 7 mV / 1000 mV respectively. The structure of the device manufactured as described above is as shown in FIG.

Example 2-8 and Comparative Example 1

An organic light-emitting device was manufactured in the same manner as in Example 1, except that the deposited NPB layer was heat-treated at the temperature and time shown in Table 1 below (Comparative Example 1 was not heat-treated).

division Heat treatment temperature (℃) Heat treatment time (minutes) Example 2 180 30 3 130 10 4 30 5 60 6 190 10 7 30 8 60 Comparative Example 1 Unannealed

Surface property evaluation

Optical microscopic observation photographs of the negative electrode surface and the NPB layer (hole transport layer) after driving the devices manufactured in Examples and Comparative Examples are shown in FIGS. 2 to 4.

From FIG. 2, the device manufactured by heat treatment at 110 ° C. for 30 minutes after deposition of the NPB layer (Example 1) did not generate wrinkles or cracks on the surface of the Al electrode as the cathode after Joule heat was generated at 15 V for 40 seconds ( Fig. 2a), it can be seen that the surface of the Al electrode of the non-heat treatment element (Comparative Example 1) had a thin wrinkle (Fig. 2b).

From FIG. 3, the surface after the heat-treated device (Example 1) was heated at 160 ° C. was uniform and clean (FIG. 3A), but in the case of the unheated device (Comparative Example 1), wrinkles occurred (FIG. 3b) can be seen.

From the optical micrograph of the NPB surface of the specimen prepared by heat treatment for 30 minutes at 180 ° C. (Example 2) (FIG. 4 a) and 130 ° C. (Example 4) (FIG. 4 b) after deposition of the NPB layer shown in FIG. 4. It can be seen that the surface of the NPB layer heat treated at 180 ° C. and 130 ° C. all crystallized.

2 and 3 show the thermal stability of the device heat-treated according to the present invention, Figure 4 shows the crystallization caused by the heat treatment of the hole transport layer.

Evaluation of Electrical Characteristics of Devices

5 and 6 show graphs showing electrical characteristics, that is, voltage-current characteristics, current-emitting characteristics, and current-electricity efficiency characteristics of devices manufactured in Examples and Comparative Examples according to the organic material layer heat treatment conditions.

5A, 5B, and 5C, the current characteristics according to the rated voltage of the device (Comparative Example 1), in which the organic material layer was not heat-treated, were compared with the devices (Examples 1, 2, and 4) heat-treated at 110 ° C, 130 ° C, and 180 ° C, respectively. It can be seen that the light emission characteristics according to the current and the electrical efficiency characteristics according to the current are low, and for the same heat treatment time, the electrical characteristics of the device increase as the heat treatment temperature increases. In addition, when the heat treatment time (10 minutes, 30 minutes, 60 minutes) was variously changed at the same heat treatment temperature of 130 ℃, there was almost no difference in the light emission and electrical efficiency with time (Fig. 6a), There was no difference in electrical characteristics with treatment time even at the heat treatment temperature (FIG. 6B). 6A and 6B, it can be seen that there is almost no difference in the light emission characteristics according to the heat treatment temperatures (130 ° C. and 190 ° C.).

Therefore, it can be seen that the heat treatment of the organic material layer is superior to the efficiency of the electrical characteristics of the device rather than the heat treatment in the device manufacturing process.

According to the present invention, the device having at least one inorganic material layer and at least one organic material layer is manufactured by heat-treating the organic material layer having the lowest thermal property to suppress the occurrence of wrinkles or cracks on the surface of the cathode, and in particular, the organic material layer is a hole transport layer. In this case, crystallization of the organic material may be induced by heat treatment after the thin film is formed, thereby greatly improving thermal stability and performance of the device.

Simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (5)

In the method for manufacturing a device composed of at least one inorganic layer and at least one organic layer, annealing the organic material layer having the lowest thermal properties in a vacuum or inert atmosphere at a temperature below the sublimation point after the thin film is formed before the thin film is formed in the post-process Method for manufacturing a device, characterized in that it comprises a step. The method of claim 1, The device is an organic light emitting device. The method of claim 2, The organic material layer to be heat-treated is characterized in that the hole transport layer. The method of claim 3, Crystallization of the organic material layer in the heat treatment step characterized in that the. A device manufactured by the method of claim 1.