JP5945834B2 - Manufacturing method of reverse structure OLED - Google Patents

Description

The present invention relates to an OLED display technology, and more particularly to a method for manufacturing an inverted OLED.

With the continuous development of science and technology, in the field of display technology, an OLED element having an element structure opposite to that of a normal element, that is, “inverted OLED (iOLED)” has already been developed and attracts wide attention. The full name of iOLED is Inverted Organic Light-Emitting Diode.

As shown in FIG. 1, a general ordinary OLED structure is formed by first forming a transparent anode ITO film 92 (Indium Tin Oxide) on a substrate 91, and then forming holes on it. Various organic layers such as a transport layer 93 (HTL), a light-emitting layer 94, and an electron transport layer 95 (ETL) are sequentially formed, and finally an electron injection layer 96 (EIL) and a cathode 97 are formed. is there. By applying a voltage to the element from the outside, electrons are injected from the cathode, holes are injected from the anode ITO, are combined with the light emitting layer, and organic molecules are excited by complex excitation. The EIL and cathode materials adopted by ordinary OLEDs are low work function, high air activity materials such as alkali metals (lithium, cesium, barium) and aluminum, so they were affected by oxygen gas and moisture in the atmosphere. Thereafter, the cathode part is oxidized and deteriorated. Therefore, adopting ordinary OLED products, it is necessary to seal the electron injection layer and cathode of ordinary OLED in the display with the influence of moisture and oxygen gas in the atmosphere with glass and binder, Furthermore, even some hard barrier materials with high barrier properties are used. This is one of the reasons for the high cost of OLED displays and OLED illuminators, and a major obstacle to realizing flexible displays and illuminators.

As shown in FIG. 2, the structure of the reverse structure OLED is exactly the reverse of the structure of a normal OLED. Using ITO as the cathode, first, a cathode ITO film 98 is formed on the substrate 91. Then, an electron injection layer 96, an electron transport layer 95, a light emitting layer 94, and a hole transport layer 93 are sequentially formed thereon, and an anode 99 is finally formed. iOLED's electron injection layer (EIL) material improves luminous efficiency compared to conventional OLED devices, and iOLED's resistance to oxygen gas and moisture is much higher than the characteristics of ordinary OLED devices It was also confirmed that it was expensive. This is because bottom emission type iOLEDs use ITO as the cathode, so if the EIL stacked on the ITO cathode can use an inert material, an OLED element with oxygen resistance and water resistance can be realized, and a high barrier This is because it is possible to reduce the necessity of using a hard package material. Therefore, iOLED greatly improved the atmospheric stability and luminous efficiency of the cathode compared to ordinary OLED.

In an OLED device, electrons are injected from the cathode into the organic material, and the electron injection efficiency is determined by the work function of the cathode and the energy level of the organic material minus the lowest unoccupied molecular orbital (LUMO), that is, the work function of the cathode. However, the closer to the LUMO energy level, the higher the electron injection efficiency, and the higher the electron injection efficiency, the lower the required drive voltage and the more power-saving the device. In a general situation, the LUMO energy level of organic materials is much lower than the work function of the cathode, and now the normal method in the industry matches the cathode looking for some high LUMO organic materials Yes, but the cost of such a scheme is too high.

Currently, the biggest challenge in iOLED research is how to reduce the work function of ITO used for the cathode of iOLEDs. This is because when ITO is used as a transparent cathode, it is generally very difficult to inject electrons directly from the ITO into the organic layer. This is because the energy difference between the work function value of ITO and the energy level of LUMO receiving electrons in the organic layer is large. Although the work function of ITO is about 5 eV, since the LUMO energy of an electron transport material for ordinary OLED devices is about 3 eV, an electron injection barrier of about 2 eV exists on the surface.

When conventional ITO is used as a cathode, the electron injection efficiency cannot often be improved effectively with a multilayer electron injection layer, but such a method is complicated and expensive. Therefore, it is necessary to reduce the work function of ITO as much as possible in order to reduce the use of the electron injection layer. Currently, the method for reducing the work function of the ITO surface is to reduce the work function of the ITO surface by improving the oxygen vacancies on the ITO surface using the hydrogen plasma surface treatment method. The method only improves on the ITO surface, so it is easy to expire and the device becomes unstable. Another method is to dope some highly active metals such as Cs element during the ITO manufacturing process, and this method can also reduce the work function of ITO, but because it incorporated Cs element, ITO Other good performances, such as transparency, are severely affected and are therefore also disadvantageous for light output.

Therefore, how to effectively reduce the work function of ITO used for the cathode in the reverse structure OLED is a new problem in this field.

In view of the above problems, an object of the present invention is to provide a method for manufacturing an inverted OLED capable of effectively reducing the work function of an ITO cathode.

In order to achieve the above object, the present invention provides:
Providing a substrate and producing an ITO thin film as a cathode on the substrate;
Performing plasma intrusion ion implantation on the ITO thin film and applying a negative pulse bias to the ITO thin film to inject the plasma into the ITO thin film at a set implantation depth; and
Forming and sequentially forming an organic layer including an electron injection layer, an electron transport layer, a light emitting layer and a hole transport layer on the ITO thin film;
Forming and forming an anode on the organic layer;
A method of manufacturing an inverted OLED comprising:

According to another aspect of the present invention, there is provided a method for manufacturing a reverse structure OLED, wherein the plasma injection depth is controlled by adjusting the magnitude of the negative pulse bias, and the plasma intensity is adjusted by adjusting the plasma intensity. The purpose of this is to control the implantation concentration.

A further improvement to the manufacturing method of the inverse structure OLED according to the present invention is that the plasma injection depth is 1 to 2 nm.

A further improvement to the method for manufacturing an inversely structured OLED according to the present invention is that the plasma is generated by hydrogen atoms or by metal atoms having a low work function.

The further improvement with respect to the manufacturing method of the reverse structure OLED which concerns on this invention exists in the said low work function metal atom being a lithium atom, a magnesium atom, or a cesium atom.

であり、即ち酸素空孔の濃度が大きいほど、該算出公式の比の値が小さくなり、その仕事関数が小さくなる。 The manufacturing method of the inverse structure OLED according to the present invention performs plasma intrusion ion implantation at a certain depth below the surface of the ITO thin film and below the surface, and the implanted plasma is generated by hydrogen atoms, or has a low work function. It is produced by the metal atom. The work function of ITO is calculated according to the concentration of oxygen vacancies inside it.

That is, the greater the concentration of oxygen vacancies, the smaller the ratio value of the calculation formula and the smaller the work function.

Therefore, the present invention injects plasma generated by hydrogen atoms into the ITO thin film to form a large amount of HO bonds in the ITO thin film, thereby improving the oxygen vacancy concentration on the ITO surface and The function can be effectively reduced. The plasma generated by hydrogen atoms is relatively easy to desorb when injected only on the ITO surface. Therefore, the plasma generated by hydrogen atoms is injected at a certain depth below the ITO surface and the surface. Thus, the plasma can be constrained within the ITO surface, and is more difficult to desorb than the surface alone, making it more stable and less effective to improve the oxygen vacancies. On the other hand, injecting plasma generated by low work function metal atoms into the ITO thin film also reduces the ITO work function, improves the electron concentration on the cathode surface, and effectively increases the electron injection efficiency. Can be improved. In addition, if the entire ITO is doped with metal atoms having a low work function, the transparency of the entire ITO thin film is reduced. Therefore, the plasma generated by the metal atoms having a low work function is reduced to a certain depth below the ITO surface and the surface. By injecting, the conductivity of the ITO thin film can be increased, and the transparency of the ITO thin film is not affected.

A good effect of the manufacturing method of the inverted structure OLED according to the present invention is as follows.

1) PIII technology is a low-cost, easy-to-operate, large-area processing technology that is very suitable for industrial applications.

2) By using the method of the present invention, an ITO thin film having a low work function can be obtained, and transparency and conductivity of the ITO thin film can be maintained.

3) Since the plasma is injected into the ITO thin film, the stability of the modification effect can be improved.

4) Manufacturing an OLED device using ITO treated by the method of the present invention as a cathode can effectively improve the light extraction efficiency and the stability of the device.

It is a structural schematic diagram of a conventional OLED. It is a structure schematic diagram of the conventional reverse structure OLED. It is a flowchart of the manufacturing method of the reverse structure OLED which concerns on this invention. FIG. 3 is a structural schematic diagram of an inverted OLED manufactured by the method of the present invention. FIG. 6 is an exemplary view showing that a plasma is injected to an ITO surface and to a certain depth below the surface in the method for manufacturing an inverted OLED according to the present invention.

To make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below in conjunction with the drawings and examples. It will be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

3 and 4 are flowcharts of a method for manufacturing an inverted OLED according to the present invention.
Providing a substrate 10 and producing an ITO thin film 20 as a cathode on the substrate (S101);
Plasma intrusion ion implantation (Plasma Immersion Ion Implantation; simply referred to as “PIII”) is applied to the ITO thin film 20, and a negative pulse bias is applied to the ITO thin film 20, thereby setting the plasma implantation depth. Injecting into the ITO thin film 20 (S102),
Forming an organic layer including the electron injection layer 30, the electron transport layer 40, the light emitting layer 50, and the hole transport layer 60 in order on the ITO thin film 20 (S103);
Forming an anode 70 on the organic layer (S104).

Hereinafter, the present invention will be further described by combining specific examples.

であり、即ち酸素空孔の濃度が大きいほど、該算出公式の比の値が小さくなり、その仕事関数が小さくなる。したがって、プラズマ浸入イオン注入方式を利用して水素原子により生成されたプラズマをITO表面及び表面以下の一定の深さ（注入深さは、1〜2 nmであることが好ましい。）に注入することで、ITO表面及び表面以下の一定の深さに大量のH-O結合を形成して、ITO表面の酸素空孔濃度を向上させ、ITOの表面仕事関数を有効に低下させることができる。該方法の注入深さがITO表面以下の一定の深さであるが、ITO薄膜全体の厚さが数百ナノメートルであるので、ITO薄膜の透明性と導電性に影響することがない。なお、前記負パルスバイアスの大きさを調節することで前記プラズマの注入深さを制御して、前記プラズマの強度を調節することで前記プラズマの注入濃度を制御する。 Example 1
As shown in Figure 4, the work function of ITO (In ₂ O ₃ / SnO ₂ ) is closely related to the oxygen vacancy concentration inside it, and the calculation formula is

That is, the greater the concentration of oxygen vacancies, the smaller the ratio value of the calculation formula and the smaller the work function. Therefore, plasma generated by hydrogen atoms using a plasma intrusion ion implantation method is implanted at an ITO surface and a certain depth below the surface (the implantation depth is preferably 1 to 2 nm). Thus, a large amount of HO bonds can be formed at a certain depth below the ITO surface and below the surface, thereby improving the oxygen vacancy concentration on the ITO surface and effectively reducing the surface work function of the ITO. Although the implantation depth of this method is a constant depth below the ITO surface, the thickness of the entire ITO thin film is several hundred nanometers, so that the transparency and conductivity of the ITO thin film are not affected. The plasma injection concentration is controlled by adjusting the magnitude of the negative pulse bias to control the plasma injection depth, and the plasma intensity is controlled.

Example 2
As shown in FIG. 4, plasma (for example, Li, Mg, Cs, etc.) generated by metal atoms with a low work function is implanted at a certain depth below the ITO surface and below using the plasma immersion ion implantation method. Thus, the electron concentration on the cathode surface can be improved, the Fermi energy level on the cathode surface can be improved, the work function of the ITO thin film can be lowered, and the electron injection efficiency can be effectively improved. Similarly, since these metal elements are implanted at a certain depth below the ITO surface, the transparency and conductivity inherent in the ITO thin film are not degraded. The plasma injection concentration is controlled by adjusting the magnitude of the negative pulse bias to control the plasma injection depth, and the plasma intensity is controlled.

Therefore, the present invention injects plasma generated by hydrogen atoms into the ITO thin film to form a large amount of HO bonds in the ITO thin film, thereby improving the oxygen vacancy concentration on the ITO surface and The function can be effectively reduced. And if the plasma generated by hydrogen atoms is injected only to the ITO surface, it is relatively easy to desorb. By injecting the plasma generated by hydrogen atoms to a certain depth below the ITO surface and the surface, The plasma can be constrained within the ITO surface, and is more difficult to desorb than the surface alone, making it more stable and less effective for improving oxygen vacancies. On the other hand, injecting plasma generated by low work function metal atoms into the ITO thin film also reduces the ITO work function, improves the electron concentration on the cathode surface, and effectively increases the electron injection efficiency. Can be improved. In addition, if the entire ITO is doped with metal atoms having a low work function, the transparency of the entire ITO thin film is reduced. Therefore, the plasma generated by the metal atoms having a low work function is reduced to a certain depth below the ITO surface and the surface. By injecting, the conductivity of the ITO thin film can be increased, and the transparency of the ITO thin film is not affected.

Therefore, the ITO cathode having a low work function can be obtained by the method for manufacturing an inverted OLED according to the present invention, and the transparency and conductivity of the ITO thin film can be maintained. Manufacturing an OLED device using ITO treated by the method of the present invention as a cathode can effectively improve the light extraction efficiency and the stability of the device.

The above are only preferred embodiments of the present invention and there are no formal limitations to the present invention. Although the present invention has been disclosed in the preferred embodiment as described above, it is not intended to limit the present invention, and those skilled in the art will recognize the technical contents disclosed above without departing from the technical solution of the present invention. It should be possible to modify the equivalent embodiment with some changes using the same, but all the contents without departing from the technical solution of the present invention are more than the technical substance of the present invention. All simple corrections, identical changes and modifications made to the embodiments are within the scope of the technical solution of the present invention.

Claims (3)

Providing a substrate and producing an ITO thin film as a cathode on the substrate;
Plasma intrusion ion implantation is performed on the ITO thin film, and a negative pulse bias is applied to the ITO thin film, which is generated by hydrogen atoms or by lithium atoms, magnesium atoms, or cesium atoms, which are metal atoms having a low work function. Injecting the generated plasma into the ITO thin film at a set implantation depth not affected by the transparency of the set ITO thin film ;
Forming and sequentially forming an organic layer including an electron injection layer, an electron transport layer, a light emitting layer and a hole transport layer on the ITO thin film;
Forming and forming an anode on the organic layer;
A method for manufacturing an inverted OLED, comprising: 2. The plasma injection concentration is controlled by adjusting the magnitude of the negative pulse bias to control the plasma injection depth, and the plasma intensity is adjusted. The manufacturing method of the reverse structure OLED of description. 2. The method for manufacturing an inverted OLED according to claim 1, wherein the plasma implantation depth is 1 to 2 nm.

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