CN101226993A - Transparent electrode and organic electroluminescent element comprising same - Google Patents

Abstract

The present invention provides a transparent electrode and an organic electroluminescent element including the transparent electrode. The transparent electrode includes an electrode layer, which is formed by co-evaporation of a metal material and a metal oxide. The transparent electrode of the present invention has good conductivity, transmittance and flexibility, and can be used as an anode or cathode of an organic electroluminescent element. In addition, an additional light extraction layer is formed on the transparent electrode to increase the transmittance of the transparent electrode.

Description

Transparent electrode and organic electroluminescent element comprising the transparent electrode

technical field

The invention relates to an organic electroluminescent element, in particular to an improved electrode structure of the organic electroluminescent element.

Background technique

In recent years, with the advancement of electronic product development technology and its increasingly wide application, such as the advent of mobile phones, PDAs and notebook computers, the demand for flat-panel displays with smaller volume and power consumption characteristics compared with traditional displays Increasing day by day, become one of the most important electronic application products at present. Among flat-panel displays, organic electroluminescent elements will undoubtedly become the best choice for next-generation flat-panel displays due to their characteristics such as self-luminescence, high brightness, wide viewing angle, high response speed, and easy process.

The organic electroluminescent element is mainly composed of a multi-layer organic material layer sandwiched between two cathode and anode electrodes, including a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer. The electrodes need to have a high transmittance to facilitate the extraction of light generated by the material of the light-emitting layer. The preparation method of the transparent electrode is usually sputtering to form a transparent and highly conductive metal oxide, such as indium tin oxide (ITO) or indium zinc oxide (IZO). However, the relationship between the work function of ITO itself makes it only suitable for the anode of hole injection; if it is used as the cathode of electron injection, the operating voltage of the device will be too high, and the sputtering process on the organic layer will destroy the organic material. cause a decrease in component efficiency. In addition, the surface resistance of ITO will increase with time and flexing times, so ITO has poor flex resistance and is not suitable for flex organic electroluminescent devices.

To replace the ITO electrode, a metal material with high conductivity and ductility can be used; however, the metal has a large absorption number and can only have good transmittance at a thinner thickness. In the previous case, US5739545 disclosed semiconductor materials covering a large potential barrier on thin metals, such as ZnSe, ZnS or GaN; or EP1076368, JP2003-288993 and JP2004-006249 covered metal oxides or organic materials on thin metals, such as MgO , NPB or Alq ₃ , to increase the transmittance of the metal material; but the previous proposals are all double-layer metal electrodes, and the process is relatively complicated.

Therefore, how to develop a transparent electrode with high conductivity, transmittance and resistance to flexure is one of the key research points in the current organic electroluminescent device technology.

Contents of the invention

The object of the present invention is to provide a transparent electrode with high conductivity, transmittance and flexibility, which can be applied to organic electroluminescent elements.

To achieve the above purpose, the present invention provides a transparent electrode, including a conductive layer formed by co-evaporating metal materials and metal oxides.

In order to achieve the above object, the present invention provides an organic electroluminescent element, including a substrate, a first electrode formed on the substrate, a multilayer organic material layer, including a hole injection layer, a hole transport layer, and a light emitting layer. , an electron transport layer, and an electron injection layer are formed on the first electrode, and a second electrode is formed on the multilayer organic material layer, wherein the first and/or second electrode includes a conductive layer, by The metal material and the metal oxide are co-evaporated.

In order to make the above and other objects, features, and advantages of the present invention more comprehensible, preferred embodiments are specifically cited below, together with accompanying drawings, and are described in detail as follows.

Description of drawings

FIG. 1 shows a cross-sectional view of the organic electroluminescence device of the present invention.

FIG. 2 shows the formation of a light extraction layer on the transparent electrode of the present invention.

Figure 3 shows the transmittance of silver-doped _MoO3 .

Figure 4 shows the resistance values of silver-doped _MoO3 .

FIG. 5 shows the transmittance of a light extraction layer formed on a silver metal layer.

Explanation of reference signs

10a, 10b Organic electroluminescence element 12 Substrate

14 first electrode 16a hole injection layer

16b Hole transport layer 16c Light emitting layer

16d Electron transport layer           16e Electron injection layer

18 Second electrode 20 Light extraction layer

Detailed ways

The invention provides a transparent electrode, including an electrode layer formed by co-evaporating metal materials and metal oxides. The metal material can be calcium, magnesium, indium, molybdenum, aluminum or silver, etc., and its work function is between 2.6eV and 5.3eV, and a suitable metal material can be selected according to the required electrode work function. The metal oxide can be MoO ₃ , SnO ₂ , TeO ₂ , TiO ₂ or Ta ₂ O ₃ , etc., and the refractive index of the metal oxide is greater than 1.7, preferably greater than 2.0, and the doping ratio of the metal oxide is between 10% and 90%. (wt%), preferably between 30% and 70%. The resistance of the transparent electrode of the present invention is less than 50Ω/sq, preferably less than 20Ω/sq, and in the range of visible light, the transmittance is greater than 50%, preferably greater than 70%. In addition, the transparent electrode of the present invention can be used as an anode and/or a cathode in an organic electroluminescence element as needed.

In another embodiment, a light extraction layer is further formed on the transparent electrode. The material of the light extraction layer can be MoO ₃ , SnO ₂ , TeO ₂ , TiO ₂ or Ta ₂ O ₃ , etc., and the refractive index is greater than 1.7, preferably greater than 2.0. The additional light-accepting layer can increase the transmittance of the electrode, so that the transmittance of the transparent electrode of the present invention is greater than 60%, preferably greater than 80%, in the range of visible light.

The transparent electrode of the present invention can be applied to displays or elements requiring transparent electrodes, such as liquid crystal display elements (LCD), light emitting diodes (LED) or organic electroluminescence elements (OLED), etc., but not limited thereto.

The invention further provides an organic electroluminescence element. The organic electroluminescence element of the present invention is characterized in that it has the above-mentioned transparent metal electrode doped with metal oxide. The organic electroluminescence device of the present invention at least includes a substrate, a cathode, an anode, and multiple organic material layers. Wherein, one of the cathode and the anode is the transparent electrode provided above.

Below, the embodiment of the organic electroluminescent element according to the present invention is shown, and the detailed description is as follows in conjunction with the accompanying drawings:

Referring to FIG. 1 , the organic electroluminescent device 10 includes a substrate 12 , such as glass, ceramic, plastic substrate, flexible substrate or semiconductor substrate. The substrate can be selected as required, that is, if it is desired to form a top-emission organic electroluminescent element, then the substrate can be an opaque substrate; in addition, if it is desired to form a double-sided emission type organic electroluminescent element, then The substrate can be a transparent substrate.

Next, the first electrode 14 is formed on the upper surface of the substrate 12 . The first electrode is an anode, which can be a transparent electrode, a metal electrode or a composite electrode, and its material can be selected from, for example, free, magnesium, calcium, aluminum, silver, indium, gold, tungsten, nickel, platinum, molybdenum , alloys formed by the above elements, indium tin oxide (ITO), indium zinc oxide (IZO), zinc aluminum oxide (AZO), zinc oxide (ZnO) or a combination thereof, and the formation method can be thermal evaporation , sputtering or plasma enhanced chemical vapor deposition.

Next, a multi-layer organic material layer 16 is formed on the first electrode 14 . The multi-layer organic material layer 16 at least includes a light emitting layer 16c, and may further include a hole injection layer 16a, a hole transport layer 16b, an electron transport layer 16d, and an electron injection layer 16e, please refer to FIG. 1 . Each film layer of this multi-layer organic material layer 16 can be respectively small molecule organic material or macromolecule material, if it is small molecule organic material, can utilize vacuum evaporation method to form multilayer organic material layer; If it is macromolecule material, then Multiple organic material layers can be formed by spin coating, inkjet or screen printing. In addition, the light-emitting layer 16c may include a host material and a dopant. The doping amount of the dopant is not related to the characteristics of the present invention, and is not a basis for limiting the scope of the present invention. The dopant can be an energy transfer type doping material or a carrier trapping type doping material, and enables the device to obtain high efficiency and high brightness.

Finally, a second electrode 18 is formed on the multi-layer organic material layer 16, the second electrode 18 is a cathode, and it is worth noting that the second electrode 18 is a transparent metal electrode. The metal material of the transparent metal electrode can be a common metal material, such as calcium, magnesium, indium, molybdenum, aluminum or silver, and the work function is between 2.6eV and 5.3eV. In the present invention, the metal material is doped with metal oxide to increase the transmittance, and the doping method can be a general prior art, such as co-evaporation. The metal oxide can be MoO ₃ , SnO ₂ , TeO ₂ , TiO ₂ or Ta ₂ O ₃ , etc., and the refractive index of the metal oxide is greater than 1.7, preferably greater than 2.0. The doping ratio of the metal oxide is between 10% and 90% (wt%), preferably between 30% and 70%. The resistance of the transparent metal electrode of the present invention is less than 50Ω/sq, preferably less than 20Ω/sq, and in the range of visible light, the transmittance is greater than 50%, preferably greater than 70%.

Referring to FIG. 2 , in another embodiment of the present invention, it further includes forming a light extraction layer 20 on the transparent metal electrode 18 of the present invention. The light extraction layer can be a metal oxide, such as MoO ₃ , SnO ₂ , TeO ₂ , TiO ₂ or Ta ₂ O ₃ , etc., with a refractive index greater than 1.7, preferably greater than 2.0. The additional light-absorbing layer can increase the transmittance of the electrode, so that the transparent electrode of the present invention can have a transmittance greater than 60%, preferably greater than 80%, in the range of visible light.

In another embodiment, the transparent metal electrode of the present invention is the first electrode 14 and is formed on the upper surface of the substrate 12 . The rest of the steps are similar to the above embodiment, and the same procedure will not be repeated.

Please refer to Figure 3, which shows the transmittance of silver doped with different proportions of MoO ₃ . The doping ratios of MoO ₃ are 0wt%, 33wt%, 50wt% and 66wt%, respectively. It can be seen from the figure that doping MoO ₃ can increase the transmittance of the electrode, from 20%@λ=550nm of pure silver to 70%@λ=550nm when 66wt% MoO ₃ is doped in silver.

Please refer to Figure 4, which shows the resistance of silver doped with different proportions of MoO ₃ . The doping ratios of MoO ₃ are 0wt%, 33wt%, 50wt%, 66wt% and 80wt%, respectively. It can be seen from the figure that doping MoO ₃ will increase the resistance of the electrode, but it can still be maintained below 20Ω/sq, so the preferred doping ratio of MoO ₃ is between 30wt% and 70wt%.

Please refer to FIG. 5 , which shows that a light extraction layer is formed on the silver metal electrode. The material of the light extraction layer is MoO ₃ , and the thicknesses are 0nm, 15nm, 30nm and 50nm respectively. It can be seen from the figure that the light extraction layer can increase the transmittance of the electrode, from 20%@λ=550nm of pure silver to 80%@λ=550nm when the silver is covered with 30nm thick MoO ₃ .

Although the present invention is disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection should be defined by the claims.

Claims (13)

1. a transparency electrode comprises conductive layer, is total to evaporation by metal material and metal oxide and forms.

2. transparency electrode as claimed in claim 1 comprises that more the light removing layer is formed on this transparency electrode.

3. transparency electrode as claimed in claim 2, wherein the refractive index of this light removing layer is greater than 1.7.

4. transparency electrode as claimed in claim 2, wherein this light removing layer is MoO ₃, SnO ₂, TeO ₂, TiO ₂Or Ta ₂O ₃

5. transparency electrode as claimed in claim 2, wherein this metal oxide is identical with the material of light removing layer.

6. transparency electrode as claimed in claim 1, wherein the work function of this metal material is between 2.6eV to 5.3eV.

7. transparency electrode as claimed in claim 1, wherein this metal material is calcium, magnesium, indium, molybdenum, aluminium or silver.

8. transparency electrode as claimed in claim 1, wherein the refractive index of this metal oxide is greater than 1.7.

9. transparency electrode as claimed in claim 1, wherein this metal oxide is MoO ₃, SnO ₂, TeO ₂, TiO ₂Or Ta ₂O ₃

10. transparency electrode as claimed in claim 1, wherein the doping ratio of this metal oxide is between 30% to 70%.

11. transparency electrode as claimed in claim 1, wherein the resistance of this transparency electrode is less than 50 Ω/sq.

12. transparency electrode as claimed in claim 1, wherein this transparency electrode is under the scope of visible light, and transmissivity is greater than 50%.

13. an organic electroluminescent device comprises:

Substrate;

First electrode is formed on this substrate;

The multilayer organic material layer is formed on this first electrode; And

Second electrode is formed on this multilayer organic material layer,

Wherein this first and second electrode is the described transparency electrode of claim 1.

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