KR101223615B1 - Inverted organic light-emitting diode and flat display device comprising the same - Google Patents

Abstract

Cathode; A first electron transport layer formed on the cathode and including a first electron transport material and an n-type dopant; A second electron transport layer formed on the first electron transport layer and including a second electron transport material; An emission layer formed on the second electron transport layer; A hole transport layer formed on the light emitting layer; And an anode formed on the hole transport layer, wherein the absolute value of the lowest unoccupied molecular orbial (LUMO) of the second electron transport layer and the lowest unoccupied molecular orbital (LUMO) of the first electron transport layer are included. An inverted organic light emitting device is provided in which the difference in absolute values is 0 to 0.2 eV.

Description

Inverted organic light-emitting diode and flat display device comprising the same

The present invention relates to an inverted organic light emitting diode and a flat panel display including the same. More specifically, the driving voltage is lowered and the external quantum efficiency is lowered by lowering an energy barrier between the n-doped first electron transport layer and the undoped second electron transport layer. The present invention relates to an inverted organic light emitting device having increased light emission efficiency and a flat panel display device including the same.

The present invention is derived from a study conducted as part of the industrial source technology development project of the Ministry of Knowledge Economy and Seoul National University Industry-University Cooperation Group.

[Task No .: 10035225, Title: Development of high quality plastic AMOLED source technology]

Organic light emitting diodes are self-luminous devices that have a wide viewing angle, excellent contrast, fast response time, excellent luminance, driving voltage and response speed, and are capable of multicoloring.

Inverted organic light emitting devices generally have a structure in which a cathode is formed on an upper substrate, and an electron transport layer, a light emitting layer, a hole transport layer, and an anode are sequentially formed on the cathode. Here, the electron transport layer, the light emitting layer, and the hole transport layer are organic layers containing organic compounds.

The driving principle of the inverted organic light emitting device is as follows. When a voltage is applied between the anode and the cathode, electrons injected from the cathode move to the light emitting layer via the electron transport layer, and holes injected from the anode move to the light emitting layer via the hole transport layer. Carriers such as holes and electrons recombine in the emission layer to generate excitons. The excitons change from excited state to ground state and light is generated.

Inverted organic light emitting devices developed to date do not sufficiently satisfy the required level of driving stability and luminous efficiency characteristics, and therefore, it is urgent to develop various technologies to solve them. Accordingly, there is a need to provide an inverted organic light emitting device having excellent driving voltage and luminous efficiency characteristics.

An inverted organic light emitting diode and a flat panel display including an n-doped first electron transport layer and an undoped second electron transport layer having a low energy barrier between the first electron transport layer and the second electron transport layer.

According to one aspect, a cathode; A first electron transport layer formed on the cathode and including a first electron transport material and an n-type dopant; A second electron transport layer formed on the first electron transport layer and including a second electron transport material; An emission layer formed on the second electron transport layer; A hole transport layer formed on the light emitting layer; And an anode formed on the hole transport layer, wherein the absolute value of the lowest unoccupied molecular orbial (LUMO) of the second electron transport layer and the lowest unoccupied molecular orbital (LUMO) of the first electron transport layer are included. An inverted organic light emitting device is provided in which the difference in absolute values is 0 to 0.2 eV.

The first electron transport material may include a 2-methylpyrimidine-based compound.

The first electron transport material may include one or more of the following compounds 1 to 3:

<Compound 1>

<Compound 2>

<Compound 3>

The n-type dopant is lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), Metals of at least one of lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy) and ytterbium (Yb); A nitride of the metal; A carbonate of the metal; And complexes of said metals; &Lt; / RTI &gt;

The n-type dopant may include one or more of Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Cs ₂ CO ₃ , Rb ₂ CO _3, and Ba ₂ CO ₃ .

The content of the n-type dopant may be 0.1 to 25% by weight based on the total weight of the first electron transport layer material.

The content of the n-type dopant may have a concentration gradient according to the thickness of the first electron transport layer.

The first electron transport layer may be a bilayer including a first layer containing the n-type dopant and a second layer formed on the first layer and containing the first electron transport material.

The sum of the thicknesses of the first electron transport layer and the second electron transport layer may be 200 to 1500 kPa.

The first electron transport layer may contact the cathode.

The energy barrier between the cathode and the first electron transport layer may be 0.05 to 2.5 eV.

The cathode may include at least one of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), Ag, and Al.

The cathode may be a transparent material, and the inverted organic light emitting diode may be a bottom emission type.

The anode is a transparent material, the inverted organic light emitting device may be a top emission type.

The inverted organic light emitting diode may further include a hole injection layer formed on the hole transport layer.

The hole injection layer is MoO ₃ , MoO ₂ , WO ₃ , V ₂ O ₅ , ReO _{3 ,} NiO, tetrafluoro-tetracyano-quinomethane (F4-TCNQ) based on the total weight of the hole injection layer material And, and at least one of tris [1,2-bis (trifluoromethyl) ethane-1,2-dithiene [Mo (tfd) ₃ ] in an amount of 0.1 to 25% by weight.

The emission layer may include a fluorescent host or a phosphorescent host.

The inverted organic light emitting diode may further include a hole blocking layer interposed between the light emitting layer and the second electron transport layer.

According to another aspect, forming a cathode on a substrate; Forming a first electron transport layer comprising a 2-methylpyrimidine-based compound and Rb ₂ CO ₃ on the cathode; Forming a second electron transport layer including the 2-methylpyrimidine-based compound on the first electron transport layer; Forming a light emitting layer on the second electron transport layer; Forming a hole transport layer on the light emitting layer; And forming an anode on the hole transport layer. A method of manufacturing an inverted organic light emitting device is provided.

According to another aspect, an n-type thin film transistor formed on the substrate and including a source electrode and a drain electrode, an oxide semiconductor layer, a gate electrode, and a gate insulating layer; A first insulating layer formed on the n-type thin film transistor; And an inverted organic light emitting diode as described above formed on the first insulating layer, and a cathode of the organic light emitting diode is electrically connected to one of the source electrode and the drain electrode.

The inverted organic light emitting diode described above provides an inverted organic light emitting diode and a flat panel display having excellent driving voltage and luminous efficiency due to a low energy barrier between the first electron transport layer and the second electron transport layer.

1 is a view schematically illustrating a structure of an inverted organic light emitting diode according to an embodiment.
2 is a view schematically illustrating a structure of an inverted organic light emitting diode according to an embodiment.
3 is a schematic view of an organic light emitting diode display including an inverted organic light emitting diode according to an embodiment.
4 is a graph showing a relationship between current density, voltage, and luminance of an inverted organic light emitting diode according to Example 1, Comparative Example 1, and Comparative Example 2. FIG.
FIG. 5 is a diagram illustrating energy levels of inverted organic light emitting diodes according to Example 1, Comparative Example 1, and Comparative Example 2. FIG.
6 is a graph showing external quantum efficiency of the inverted organic light emitting diode according to Example 1, Comparative Example 1, and Comparative Example 2. FIG.
7 is a graph illustrating a relationship between current density, voltage, and luminance of inverted organic light emitting diodes according to Example 1, Comparative Example 3, and Comparative Example 4. FIG.
8 is a graph showing luminous efficiency and power efficiency of inverted organic light emitting diodes according to Example 1, Comparative Example 3, and Comparative Example 4. FIG.

1 schematically illustrates a cross-sectional structure of an inverted organic light emitting diode 100 according to an embodiment.

Inverted organic light emitting device 100 according to the embodiment includes a cathode (21); A first electron transport layer 23 formed on the cathode 21 and including a first electron transport material and an n-type dopant; A second electron transport layer 24 formed on the first electron transport layer 23 and including a second electron transport material; An emission layer 26 formed on the second electron transport layer 24; A hole transport layer 27 formed on the light emitting layer 26; And an anode 29 formed on the hole transport layer 27. The difference between the absolute value of the lowest unoccupied molecular orbital (LUMO) of the second electron transport layer 24 of the inverted organic light emitting device 100 and the absolute value of the lowest unoccupied molecular orbital of the first electron transport layer 23 is 0 to 0.2 eV.

The cathode 21 is connected to one of a source electrode and a drain electrode of the n-type thin film transistor, and serves to receive a driving current applied from the n-type thin film transistor. The cathode 21 is formed of, for example, indium tin oxide (ITO), Ag, Al, or the like. In particular, in the case of back emission, a transparent electrode is required, and ITO can be used as a material.

The first electron transport layer 23 is provided on the cathode 21. The first electron transport layer 23 serves to move the electrons injected from the cathode 21 in the direction in which the light emitting layer 26 is located. The first electron transport layer 23 includes a first electron transport material and an n-type dopant. For example, the first electron transport layer 23 may have a structure in which an n-type dopant is doped into the first electron transport material.

The second electron transport layer 24 is provided on the first electron transport layer 23. The second electron transport layer 24 serves to move the electrons transferred from the first electron transport layer 23 to the light emitting layer 26. The second electron transport layer 24 includes the second electron transport material but does not include the n-type dopant. The second electron transport material may be the same as or different from the first electron transport material. The difference between the first electron transport layer 23 and the second electron transport layer 24 is whether it is doped with an n-type dopant. The difference is that the first electron transport layer 23 is an n-doped electron transport layer and the second electron transport layer 24 is an electron transport layer that does not contain an n-type dopant.

The n-doped first electron transport layer 23 and the n-doped second electron transport layer 24 have a relationship with a constant energy level difference. The difference between the absolute value of the lowest unoccupied molecular orbital LUMO of the second electron transport layer 24 and the absolute value of the lowest unoccupied molecular orbit of the first electron transport layer 23 is about 0 to about 0.2 eV. Since the second electron transport layer 24 does not include an n-type dopant, the lowest unoccupied molecular orbital (LUMO) value is determined by the first electron transport material, and the first electron transport layer 23 includes an n-type dopant. It is thought to bring about vacuum energy transfer at the junction. Although the first electron transport layer 23 includes an n-type dopant, the lowest unoccupied molecular orbital (LUMO) value of the first electron transport layer 23 and the lowest unoccupied molecular orbital (LUMO) value of the second electron transport layer 24 are They may be arranged identically to each other. For example, the absolute value of the lowest unoccupied molecular orbital LUUM of the second electron transport layer 24 that does not include the n-type dopant and the lowest unoccupied molecular orbital LUUM of the n-doped first electron transport layer 23. The difference between the absolute values of can be zero.

The light emitting layer 26 is provided on the second electron transport layer 24. The light emitting layer 26 is injected from the cathode 21 and injected from the anode 29 and the electrons via the first electron transport layer 23 and the second electron transport layer 24 to recombine holes through the hole transport layer 27. To generate excitons, and the generated excitons change from an excited state to a ground state and emit light.

The hole transport layer 27 is provided on the light emitting layer 26. The hole transport layer 27 serves to move electrons injected from the anode 29 or electrons injected from the anode 29 and moved through the hole injection layer (not shown) to the emission layer 26.

The anode 29 is provided on the hole transport layer 27. The anode 29 is commonly connected to a power supply voltage (not shown) to inject holes into the hole injection layer (not shown) or the hole transport layer 27.

The first electron transport material may include a 2-methylpyrimidine-based compound. The second electron transport layer 24 may use the same electron transport material as the first electron transport layer 23 or use another electron transport material. For example, both the first electron transport layer 23 and the second electron transport layer 24 may include a 2-methylpyrimidine-based compound. The 2-methylpyrimidine-based compound includes a pyrimidinyl group and the pyrimidinyl group is considered to have excellent electron transport ability.

For example, the first electron transport material may include one or more of the following compounds 1 to 3:

<Compound 1>

<Compound 2>

<Compound 3>

The 2-methylpyrimidine-based compound of Compounds 1 to 3 has a structure in which one dipyridylphenyl group is connected to both sides of a 2-methylpyrimidine moiety forming a basic skeleton. The 2-methylpyrimidine-based compound of Compounds 1 to 3 has excellent electron transport ability. The first electron transport layer 23 is composed of the n-type dopant doped with the 2-methylpyrimidine-based compound of the compounds 1 to 3 and the second electron transport layer 24 is the 2-methylpyridine of the compounds 1 to 3 In the case of a midine compound, the absolute value of the lowest unoccupied molecular orbital LUMO of the second electron transport layer 24 is 0 to more than the absolute value of the lowest unoccupied molecular orbital LUMO of the first electron transport layer 23. It is about 0.2 eV high and the energy barrier between the first electron transport layer 23 and the second electron transport layer 24 is low.

The n-type dopants doped in the first electron transport layer 23 include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), Among strontium (Sr), barium (Ba), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy) and ytterbium (Yb) One or more metals; A nitride of the metal; Carbonates of the metals; Or complexes of the metals; And the like, but are not limited thereto. Lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), lanthanum (La), Cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy) and ytterbium (Yb) are metals having a relatively low work function, and thus the metal, the metal Nitride, the carbonate of the metal, or the complex of metal lowers the energy barrier at the interface between the first electron transport layer 23 and the cathode 21 and reduces the lowest unoccupied molecular orbital (LUMO) value of the first electron transport layer 23. It is maintained at a level almost similar to the lowest unoccupied molecular orbital (LUMO) value of the second electron transport layer 24. For example, the difference between the absolute value of the lowest unoccupied molecular orbital LUMO of the second electron transport layer 24 and the absolute value of the lowest unoccupied molecular orbital LUMO of the first electron transport layer 24 is 0 to 0.2 eV. appear.

The n-type dopant may include, for example, one or more of Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Cs ₂ CO ₃ , Rb ₂ CO _3, and Ba ₂ CO ₃ , but is limited to the metal carbonate. It is not.

The content of the n-type dopant may be 0.1 to 25% by weight based on the total weight of the first electron transport layer material. When the doping concentration of the n-type dopant satisfies the above range, the inverted organic light emitting device can obtain a satisfactory driving voltage drop and no side leakage current is generated.

delete

The n-type dopant may be included only in a thickness of a portion of the entire thickness of the first electron transport layer 23. In this case, a layer having a thickness of a part of the total thickness of the first electron transport layer 23 including the n-type dopant is called the first layer, and the n-type dopant is not included in the entire thickness of the first electron transport layer 23. When the layer having the thickness of the remaining portion is called the second layer, the first electron transport layer 23 is formed on the first layer containing the n-type dopant and on the first layer and does not contain the n-type dopant. It may be a bilayer comprising a layer. Since the first layer contains the n-type dopant, the first layer may be located closer to the cathode 21, and the second layer may be relatively closer to the second electron transport layer 24.

The sum of the thicknesses of the first electron transport layer 23 and the second electron transport layer 24 may be 200 to 1500 kPa. When the sum of the thicknesses of the first electron transport layer 23 and the second electron transport layer 24 satisfies the above range, satisfactory electron transport characteristics can be obtained without a substantial increase in driving voltage.

The first electron transport layer 23 and the cathode 21 may be in contact with each other. A hole injection layer may be interposed between the first electron transport layer 23 and the cathode 21, but may be omitted in order to have a beneficial effect on cost reduction in mass production. Since the first electron transport layer 23 includes the n-doped first electron transport material, the hole injection characteristic is improved when contacted with the cathode 21.

The energy barrier of electron injection between the cathode 21 and the first electron transport layer 23 may be 0.5 to 2.5 eV. The cathode 21 of the inverted organic light emitting diode 100 may use a transparent electrode, and most of the transparent electrodes have a high work function of 4.3 eV or more. Such a high work function can create a significantly higher injection barrier in electron injection in conventional inverted organic light emitting devices. In the inverted organic light emitting diode 100, the first electron transport layer 23 is n-doped, so that an energy barrier between the cathode 21 and the first electron transport layer 23, which is a transparent electrode, is about 0.05 to about 2.5 eV. Can be lowered. When the energy barrier satisfies the above range, the injection of electrons from the cathode 21 into the first electron transport layer 23 can be made quite easy. For example, the energy barrier between the cathode 21 and the first electron transport layer 23 may be lowered to about 0.1 eV.

In addition, the inverted organic light emitting diode 100 has the first electron transport layer 23 n-doped, so that the energy barrier between the cathode 21 and the first electron transport layer 23 is not only low in the above range but also excellent external quantum efficiency. Has a value.

The cathode 21 of the inverted organic light emitting device 100 may use a transparent electrode. For example, the cathode 21 may be formed of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), It may include one or more of the thin film Ag and Al. In particular, when the inverted organic light emitting diode 100 is a bottom emission type, a transparent electrode may be used as the cathode 21. If the inverted organic light emitting device is a top emission type, the cathode need not be limited to the transparent electrode, but a transparent material is used for the anode. In this case, at least one of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), thin film Ag or Al may be used as the anode.

2 schematically illustrates a cross-sectional structure of an inverted organic light emitting device 200 according to an embodiment.

The inverted organic light emitting diode 200 includes a cathode 31; A first electron transport layer 33 formed on the cathode 31 and including a first electron transport material and an n-type dopant; A second electron transport layer 34 formed on the first electron transport layer 33; An emission layer 36 formed on the second electron transport layer 34; A hole transport layer 37 formed on the light emitting layer 36; A hole injection layer 38 formed on the hole transport layer 37; And an anode 39 formed on the hole injection layer 38. The difference between the absolute value of the lowest unoccupied molecular orbital (LUMO) of the second electron transport layer 34 of the inverted organic light emitting device 200 and the absolute value of the lowest unoccupied molecular orbit of the first electron transport layer 33 is 0 to 0.2 eV.

The cathode 31, the first electron transport layer 33, the second electron transport layer 34, the light emitting layer 36, the hole transport layer 37, and the anode 39 of the inverted organic light emitting device 200 are illustrated in FIG. 1. The cathode 21, the first electron transport layer 23, the second electron transport layer 24, the light emitting layer 26, the hole transport layer 27, and the anode 29 of the inverted organic light-emitting device 100 described in the foregoing description. It may be the same, so refer to it.

The inverted organic light emitting diode 200 includes a hole injection layer 38 on the hole transport layer 37. The hole injection layer 38 moves the holes injected from the anode 31 in the direction in which the light emitting layer 36 is positioned and assists the injection of holes.

The hole injection layer 38 may include a hole injection material and a metal oxide or organic p-type dopant. The metal oxide may be an oxide containing a transition metal. Examples of transition metals include molybdenum (Mo), tungsten (W), vanadium (V), rhenium (Re), ruthenium (Ru), chromium (Cr), manganese (Mn), nickel (Ni), iridium (Ir), APC (silver-palladium-copper alloy), combinations thereof, and the like. The metal oxides may include, for example, MoO ₃ , MoO ₂ , WO ₃ , V ₂ O ₅ , ReO ₃ or NiO. As the organic p-type dopant, for example, tetrafluoro-tetracyano-quinodimethane (F4-TCNQ) or tris [1,2-bis (trifluoromethyl) ethane-1,2-dithiene [Mo (tfd) ₃ ], etc. may be mentioned.

The hole injection layer 38 may include 0.1 to 25% by weight of the metal oxide or organic p-type dopant based on the total weight of the hole injection layer material. When the content of the metal oxide or organic p-type dopant satisfies the above range, the inverted organic light emitting diode may obtain a satisfactory driving voltage drop and no side leakage current may be generated.

3 is a diagram schematically illustrating a structure of an organic light emitting diode display including an inverted organic light emitting diode according to an embodiment.

The inverted organic light emitting display device is formed on a substrate 101, and includes a source electrode 109a and a drain electrode 109b, an oxide semiconductor layer 107, a gate electrode 103, and the gate electrode 103. And an n-type thin film transistor including a gate insulating layer 105 that insulates the source electrode 109a and the drain electrode 109b. The first insulating layer 110 is formed on the n-type thin film transistor. In addition, a cathode 121 is formed on the first insulating layer 110 and connected to the drain electrode 109b of the thin film transistor, and the pixel region is defined by the pixel defining layer 122. The first electron transport layer 123, the second electron transport layer 124, the light emitting layer 126, the hole transport layer 127, the hole injection layer 128, and the anode 129 are sequentially stacked on the cathode 121. .

As the substrate 101, a substrate used in a conventional organic light emitting device can be used, but a glass substrate or a transparent plastic substrate excellent in mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and waterproofness can be used. For example, the substrate 101 may be made of a transparent glass material mainly containing SiO ₂ .

The gate electrode 103 may be formed of a general electrode material (eg, metal). For example, the gate electrode 103 may include aluminum (Al), hafnium (Hf), zirconium (Zr), zinc (Zn), tungsten (W), cobalt (Co), gold (Au), and platinum (Pt). ), Ruthenium (Ru), Iridium (Ir), Titanium (Ti), Tantalum (Ta), Nickel (Ni), Silver (Ag), Molybdenum (Mo), Copper (Cu), Palladium (Pd), Indium (In ), Tin (Sn), combinations of two or more of these (including alloys, simple mixtures, etc.), oxides containing one or more of these elements (eg, indium tin oxide (ITO), indium zinc oxide (IZO) Etc.), but is not limited thereto.

The gate insulating layer 105 may cover the gate electrode 103 to insulate the gate electrode 103 from the source electrode 109a and the drain electrode 109b. The gate insulating layer 105 may be a silicon oxide layer or a silicon nitride layer, but may be a high dielectric material layer having a higher dielectric constant than another material layer, for example, a silicon nitride layer. The gate insulating layer 105 may have a structure in which at least two layers of a silicon oxide layer, a silicon nitride layer, and a high dielectric material layer are stacked.

The oxide semiconductor of the oxide semiconductor layer 107 has a band gap greater than the light energy of the visible light region, and thus may not substantially absorb visible light. Therefore, the n-type thin film transistor including the oxide semiconductor layer 107 may not substantially increase leakage current due to absorption of visible light.

The oxide semiconductor layer 107 may be formed of, for example, a Zn-O-based material, a Zn-Ga-O-based material, a Zn-In-O-based material, a Zn-In-Ga-O-based material, or Zn-Sn-O. It may be one of the material, and Hf-In-Zn-O-based material, but is not limited thereto.

The source electrode 109a and the drain electrode 109b are provided on the gate insulating layer 105 in contact with both ends of the oxide semiconductor layer 107, respectively. The source electrode 109a and the drain electrode 109b may be a single metal layer or multiple metal layers. The material for forming the source electrode 109a and the drain electrode 109b may refer to the material for forming the gate electrode 103.

The first insulating layer 110 may be formed to cover the n-type thin film transistor. The first insulating layer 110 may serve as a passivation layer and / or a planarization layer. The first insulating layer 110 may be a silicon oxide layer or a silicon nitride layer, but may be a high dielectric material layer having a higher dielectric constant than another material layer, for example, a silicon nitride layer. The first insulating layer 110 may have a structure in which at least two layers of a silicon oxide layer, a silicon nitride layer, and a high dielectric material layer are stacked. The first insulating layer 110 may be formed using various known methods such as a coating method, a deposition method, a sputtering method, and the like.

The cathode 121 is provided on the first insulating layer 110. The cathode 121 is electrically connected to the drain electrode 109b through a via hole. The cathode 121 injects electrons into the first electron transport layer 123.

The cathode 121 is, for example, an alkali metal such as lithium, sodium, potassium, rubidium, cesium, alkaline earth metal such as beryllium, magnesium, calcium, strontium, barium; Metals such as aluminum, scandium, vanadium, zinc, yttrium, indium, cerium, samarium, europium, terbium and ytterbium; Two or more of these alloys; Or an alloy of at least one of these with at least one of gold, silver, platinum, copper, manganese, titanium, cobalt, nickel, tungsten and tin; And combinations of two or more thereof. The combination includes an alloy including two or more of the elements as described above, a multilayer structure each including the elements as described above, and the like. Examples of the alloys include magnesium-silver alloys, magnesium-indium alloys, magnesium-aluminum alloys, indium-silver alloys, lithium-aluminum alloys, lithium-magnesium alloys, lithium-indium alloys, calcium-aluminum alloys, and the like. . For example, the cathode 121 may include a material selected from the group consisting of Mg, Al, Ca, In, Ag, and combinations of two or more thereof, but is not limited thereto. For back emission, the cathode 121 is a transparent oxide such as ITO, IZO, ZnO or In ₂ O ₃ ; Thin film Ag; Or Al. The cathode 121 may be formed using various known methods, for example, a deposition method, a sputtering method, or the like.

The pixel defining layer 122 defining the pixel area is formed at both ends of the cathode 121. The pixel defining layer 122 may be formed of a conventional organic insulator or the like.

On the cathode 121, injection and transport of electrons from the cathode 121 are facilitated, and a first electron transport layer 123 is provided. The first electron transport layer 123 may be formed by doping the n-type dopant to the first electron transport material. As the material for forming the first electron transport layer 123, for example, a 2-methylpyrimidine compound as the first electron transport material and a metal carbonate (for example, Rb ₂ CO ₃ ) may be used as the n-type dopant. have. The thickness of the first electron transport layer 123 may be about 50 to about 1000 mm. When the thickness of the first electron transport layer 123 satisfies the above range, satisfactory electron injection and transport characteristics may be obtained without a substantial increase in driving voltage. For a detailed description of the first electron transport layer 123, refer to the description of FIG.

The second electron transport layer 124 is provided on the first electron transport layer 123. The second electron transport layer 124 may include the same first electron transport material as the first electron transport layer 123 or may include a second electron transport material which is a known electron transport material different from the first electron transport material. n-doped features. The thickness of the second electron transport layer 124 may be about 150 to about 500 mm 3. When the thickness of the second electron transport layer 124 satisfies the above range, satisfactory electron injection and transport characteristics may be obtained without a substantial increase in driving voltage. For a detailed description of the second electron transport layer 124, refer to the description of FIG.

The light emitting layer 126 is provided on the second electron transport layer 124. The light emitting layer 126 may include a known phosphorescent host, a fluorescent host, a phosphorescent dopant, or a fluorescent dopant.

As the known host, CBP (4,4'-N, N'-dicarbazole-biphenyl), ADN (9, 10-di-naphthalen-2-yl-anthracene), TPBI, TBADN, E3, or the like can be used. It may be, but is not limited thereto. PtOEP, Ir (piq) ₃ , or Btp ₂ Ir (acac) may be used as the red dopant, but is not limited thereto. In addition, as the green dopant, Ir (ppy) ₃ (ppy = phenylpyridine), Ir (ppy) ₂ (acac), Ir (mpyp) ₃ , or the like may be used, but is not limited thereto. As a blue dopant, F ₂ Irpic, (F ₂ ppy) ₂ Ir (tmd), Ir (dfppz) ₃ , DPVBi, DPAVBi (4,4′-bis (4-diphenylaminostaryl) biphenyl), or 2 , 5,8,11-tetra- tert -butyl perylene (TBPe) may be used, but is not limited thereto.

When the light emitting layer 126 includes a host and a dopant, the content of the dopant may be generally selected from about 0.01 to about 15 parts by weight based on about 100 parts by weight of the host, but is not limited thereto.

The light emitting layer 126 may have a thickness of about 100 kPa to about 1000 kPa. When the thickness of the light emitting layer 126 satisfies the above range, it is possible to exhibit excellent luminescence characteristics without increasing the driving voltage substantially.

When the phosphorescent dopant is included in the emission layer 126, the hole blocking is performed between the emission layer 126 and the second electron transport layer 124 to prevent the triplet exciton or hole from being diffused into the second electron transport layer 124. The layer HBL (not shown in FIG. 3) may be formed.

The hole transport layer 127 is provided on the light emitting layer 126. The hole transport layer 127 may use a well-known hole transport material, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPB); 4,4'-bis [N- (3-methylphenyl) -N-phenylamino] biphenyl (TPD); 4,4 ′, 4′-tris [(3-methylphenyl) phenylamino] triphenylamine (MTDATA); 1,1-bis (4- (N, N-di-p-tolylamino) phenyl) cyclohexane (TAPC); 4- (9H-carbazol-9-yl) -N, N-bis [4- (9H-carbazol-9-yl) phenyl] -benzeneamine (TCTA); 9,9 '-[1,1'-biphenyl] -4,4'-diylbis-9H-carbazole (CBP); 9,9 ′-(1,3-phenylene) bis-9H-carbazole (mCP); 4,7-diphenyl-1,10-phenanthroline (Bphen) or 2,2 ′, 2 ′-(1,3,5-benzenetriyl) tris- [1-phenyl-1H-benzimidazole] (TPBi) may be used, but is not limited thereto. The hole transport layer 127 may have a thickness of about 20 kPa to about 1000 kPa. When the thickness of the hole transport layer 127 satisfies the above range, satisfactory hole transport characteristics may be obtained without a substantial increase in driving voltage.

The hole injection layer 128 is provided on the hole transport layer 127. The hole injection layer 128 may be formed by doping transition metal oxide (for example, ReO ₃ ) to the same material as the hole transport material used in the hole transport layer 127. The hole injection layer 127 may have a thickness of about 50 kPa to about 10000 kPa. When the thickness of the hole injection layer 127 satisfies the above range, satisfactory hole injection characteristics may be obtained without a substantial increase in driving voltage.

An anode 129 is provided on the hole injection layer 128. The anode 129 may be formed as a transparent electrode or a reflective electrode. When formed as a transparent electrode can be formed of ITO, IZO, ZnO, In ₂ O ₃ , thin film Ag or Al, when formed as a reflective electrode Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir , Cr, and after forming the reflective film as combinations thereof, etc., it can be formed by forming a film with ITO, IZO, ZnO or in ₂ O ₃ thereon.

According to an embodiment, the method of manufacturing the organic light emitting device may include forming a cathode on a substrate; Forming a first electron transport layer comprising a 2-methylpyrimidine-based compound and Rb ₂ CO ₃ on the cathode; Forming a second electron transport layer including the 2-methylpyrimidine-based compound on the first electron transport layer; Forming a light emitting layer on the second electron transport layer; Forming a hole transport layer on the light emitting layer; And forming an anode on the hole transport layer.

According to another aspect, an n-type thin film transistor formed on the substrate and including a source electrode and a drain electrode, an oxide semiconductor layer, a gate electrode, and a gate insulating layer; A first insulating layer formed on the n-type thin film transistor; And an inverted organic light emitting diode as described above formed on the first insulating layer, and a cathode of the inverted organic light emitting diode is electrically connected to one of the source electrode and the drain electrode.

Hereinafter, the inverted organic light emitting diode according to the exemplary embodiment will be described in more detail with reference to non-limiting examples, but the present invention is not limited to the following examples.

Example  One

As a cathode, an ITO glass substrate having a thickness of 1500 mm 3 was used. Doping 15% by weight of Rb ₂ CO ₃ to 85% by weight of bis-4,6- (3,5-di-3-pyridylphenyl) -2-methylpyrimidine (see Compound 1 below) on the ITO glass substrate To form a 300 nm thick first electron transport layer:

<Compound 1>

A bis-4,6- (3,5-di-3-pyridylphenyl) -2-methylpyrimidine was formed on the first electron transport layer to form a 300 nm thick second electron transport layer. A light emitting layer having a thickness of 150 μs was formed on the second electron transport layer by using 92 wt% of 4,4-N, N′-dicarbazole-biphenyl (CBP) as a host and 8 wt% Ir (ppy) ₃ as a dopant. . 1,1-bis- (4-bis (4-methyl-phenyl) -amino-phenyl) -cyclohexane (TAPC) was vacuum deposited on the emission layer to form a hole transport layer having a thickness of 300 Å. The hole injection layer was doped with 85 wt% of TAPC and 15 wt% of ReO ₃ to form a hole injection layer having a thickness of 200 μs, followed by vacuum deposition of Al to form an anode having a thickness of 200 μs, thereby completing an inverted organic light emitting device.

Comparative example  One

4,7-diphenyl instead of bis-4,6- (3,5-di-3-pyridylphenyl) -2-methylpyrimidine in the process of forming the first electron transport layer and the second electron transport layer of Example 1 Except for using -1,10-phenanthroline (Bphen), the inverted organic light emitting device was completed in the same manner as in Example 1.

Comparative example  2

2,2 ′, 2 instead of bis-4,6- (3,5-di-3-pyridylphenyl) -2-methylpyrimidine in the formation of the first electron transport layer and the second electron transport layer of Example 1 Inverter was prepared in the same manner as in Example 1, except that X- (1,3,5-benzenetriyl) tris- [1-phenyl-1H-benzimidazole] (TPBi) was used. The tide organic light emitting device was completed.

Comparative example  3

Except for using Bphen instead of bis-4,6- (3,5-di-3-pyridylphenyl) -2-methylpyrimidine in the formation of the second electron transport layer of Example 1, An inverted organic light emitting device was completed in the same manner as in Example 1.

Comparative example  4

Except for using TPBi instead of bis-4,6- (3,5-di-3-pyridylphenyl) -2-methylpyrimidine in the formation of the second electron transport layer of Example 1, An inverted organic light emitting device was completed in the same manner as in Example 1.

evaluation

For the inverted organic light emitting diodes of Example 1, Comparative Example 1 and Comparative Example 2, the relationship between the current density-voltage-luminance using a photo research spectrophotometer (PR-650) and a power supply (Keithley 237) Was measured and the results are shown in FIG.

Referring to FIG. 4, the inverted organic light emitting diode according to the first embodiment has a charge injection voltage of 1.9 V and a 2.4 V turn-on voltage, and thus, the inverted organic light emitting diode according to the first embodiment is the most inverted organic light emitting diode. It can be seen that it has a low value. Here, the charge injection voltage means a voltage at which charge injection starts to rise. The difference between the charge injection voltage and the threshold voltage of the inverted organic light emitting device of Example 1 is only 0.5V, whereas the difference is greater than 1.5V in the inverted organic light emitting devices of Comparative Examples 1 and 2. This fact suggests that the inverted organic light emitting device of Example 1 has a better balance of electron and hole injection than the inverted organic light emitting devices of Comparative Examples 1 and 2.

For the inverted organic light emitting diodes of Example 1, Comparative Example 1 and Comparative Example 2, the electron injection characteristics were measured by using an ultraviolet spectroscopy (UPS) and the results are shown in FIG. 5. Ultraviolet spectroscopy measurements were performed with HeI (21.2 eV) and HeII (40.8 eV) as exciton sources at a base pressure of 10 ⁻¹⁰ Torr.

Referring to FIG. 5, in the case of the inverted organic light emitting device of Example 1, the electron injection energy barrier between the cathode and the first electron transport layer is 0.1 eV, and in the case of the inverted organic light emitting device of Comparative Example 2, the cathode and the first The electron injection energy barrier between the electron transport layers is 0.1 eV, and in the inverted organic light emitting device of Comparative Example 2, the electron injection energy barrier between the cathode and the first electron transport layer is 0.25 eV. This is considered to be the same result obtained because all of the first electron transport layers of the three inverted organic light emitting devices are n-doped with Rb ₂ CO ₃ . However, the electron injection energy barrier between the first electron transport layer and the second electron transport layer shows a relatively large difference between the three inverted organic light emitting devices. That is, in the inverted organic light emitting device of Example 1, the electron injection energy barrier between the first electron transport layer and the second electron transport layer was almost zero, but in the case of the inverted organic light emitting devices of Comparative Examples 1 and 2, the first The electron injection energy barriers of 0.2 eV and 0.25 eV were shown between the electron transport layer and the second electron transport layer, respectively. This shows the same tendency that the inverted organic light emitting diode according to Example 1 shows the lowest charge injection voltage and threshold voltage in FIG. 4.

For the inverted organic light emitting diodes of Example 1, Comparative Example 1, and Comparative Example 2, external quantum efficiency is measured.

Referring to FIG. 6, it can be seen that the inverted organic light emitting diode of Example 1 exhibits a maximum external light emission efficiency of 19.8%. This is the highest inverted organic light emitting device known to date.

The drive voltage, maximum external quantum efficiency, external quantum efficiency, maximum power efficiency, and power efficiency of the inverted organic light emitting diodes of Example 1, Comparative Example 1, and Comparative Example 2 are summarized in Table 1 below.

Driving voltage (V; @ 1000 mA / ㎡) Maximum external quantum efficiency (%) External quantum efficiency (%; @ 100㏅ / ㎡) External quantum efficiency (%; @ 1000㏅ / ㎡) Maximum power efficiency (㏐ / W) Power efficiency (㏐ / W; @ 1000㏅ / ㎡) Example 1 4.3 19.8 19.2 13.5 79.8 33.3 Comparative Example 1 5.4 14.2 14.5 13.6 37.3 27.2 Comparative Example 2 7.4 17.1 16.1 14.3 42.7 21.2

Referring to Table 1, the inverted organic light emitting diode of Example 1 has a driving voltage of 4.3 V at a luminance of 1000 mA / m 2, an inverted organic light emitting diode of Comparative Example 1 and an inverted organic light emitting diode of Comparative Example 2 Has driving voltages of 5.4V and 7.4V, respectively. From these results, it can be seen that the inverted organic light emitting device of Example 1 more easily injects and transports electrons from the cathode to the light emitting layer than the inverted organic light emitting devices of Comparative Examples 1 and 2. This feature can be expected to be due to the first electron transport layer and the second electron transport layer material of the inverted organic light emitting device of Example 1. Also. The inverted organic light emitting device of Example 1 has a very high maximum power efficiency of 79.8 ㏐ / W, and the inverted organic light emitting devices of Comparative Examples 1 and 2 have a maximum power efficiency of 37.3 ㏐ / W and 42.7 ㏐ / W, respectively. It can be seen that it has.

For the inverted organic light emitting diodes of Example 1, Comparative Example 3, and Comparative Example 4, the relationship between the current density, the voltage, and the luminance was measured using a colorimeter (PR-650) and a power supply (Keithley 237). Is shown in FIG. 7.

Referring to FIG. 7, it can be seen that the inverted organic light emitting diode of Example 1 has a lower driving voltage than the inverted organic light emitting diodes of Comparative Examples 3 and 4 under a luminance of 1 mA / m 2. Also, in terms of luminance, it can be seen that the inverted organic light emitting diode of Example 1 has an excellent luminance value compared to the inverted organic light emitting diodes of Comparative Examples 3 and 4. That is, it can be seen that the case where the electron transporting material of the first electron transporting layer and the electron transporting material of the second electron transporting layer of the inverted organic light emitting device are identical to each other shows better performance than the case where they are different from each other.

For the inverted organic light emitting diodes of Example 1, Comparative Example 3, and Comparative Example 4, the luminous efficiency and power efficiency were measured using a colorimeter (PR-650) and a power supply (Keithley 237), and the results are shown below. 8 is shown.

Referring to FIG. 8, it can be seen that the inverted organic light emitting diodes of Example 1 exhibit higher emission efficiency and power efficiency than the inverted organic light emitting diodes of Comparative Examples 3 and 4. From this, when the electron transport material of the first electron transport layer and the electron transport material of the second electron transport layer of the inverted organic light emitting device are the same, the electron transport material of the first electron transport layer and the electron transport material of the second electron transport layer are different from each other. It can be seen that better performance than the case. This includes the layer containing the first electron transport material and the first electron transport material n-doped due to the difference in energy level between the electron transport material of the first electron transport layer and the electron transport material of the second electron transport layer of the inverted organic light emitting device. It can be explained that it is more advantageous to be composed of layers.

Although the present invention has been described with reference to the above embodiments, it is merely illustrative, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. . Therefore, the true technical protection scope of the present invention will be defined by the technical details of the appended claims.

21, 31: cathode
23, 33, 123: first electron transport layer
24, 34, 124: second electron transport layer
26, 36, 126: light emitting layer
27, 37, 127: hole transport layer
29, 39, 129: anode
38, 128: hole injection layer
100 and 200: organic light emitting element
101: substrate
103: gate electrode
105: gate insulating layer
107: oxide semiconductor layer
109a: source electrode
109b: drain electrode
110: first insulating layer
122: pixel defining layer

Claims (20)

Cathode; A first electron transport layer formed on the cathode and including a first electron transport material and an n-type dopant; A second electron transport layer formed on the first electron transport layer and including a second electron transport material; An emission layer formed on the second electron transport layer; A hole transport layer formed on the light emitting layer; And an anode formed on the hole transport layer.
The difference between the absolute value of the lowest unoccupied molecular orbial (LUMO) of the second electron transport layer and the absolute value of the lowest unoccupied molecular orbital (LUMO) of the first electron transport layer is 0 to 0.2 eV,
Wherein the first electron transport material comprises a 2-methylpyrimidine-based compound,
Inverted organic light emitting device. delete The method of claim 1,
Inverted organic light emitting device, characterized in that the first electron transport material comprises at least one of the following compounds 1 to 3:
<Compound 1>

<Compound 2>

<Compound 3>

The method of claim 1,
The n-type dopant is lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), Metals of at least one of lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy) and ytterbium (Yb); Nitrides of the metals; A carbonate of the metal; And complexes of the metals; An inverted organic light emitting device comprising at least one of. The method of claim 1,
Inverted organic light emitting device, characterized in that the n-type dopant comprises at least one of Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Cs ₂ CO ₃ , Rb ₂ CO ₃ and Ba ₂ CO ₃ . The method of claim 1,
Inverted organic light emitting device, characterized in that the content of the n-type dopant is 0.1 to 25% by weight based on the total weight of the first electron transport layer material. delete The method of claim 1,
The first electron transport layer is a bilayer comprising a first layer containing the n-type dopant and a second layer formed on the first layer and containing the first electron transport material. Tied organic light emitting device. The method of claim 1,
Inverted organic light-emitting device, characterized in that the sum of the thickness of the first electron transport layer and the second electron transport layer is 200 to 1500 200. The method of claim 1,
The inverted organic light emitting device of claim 1, wherein the first electron transport layer is in contact with the cathode. The method of claim 1,
Inverted organic light emitting device, characterized in that the energy barrier between the cathode and the first electron transport layer is 0.05 to 2.5eV. The method of claim 1,
Inverted organic light-emitting device, characterized in that the cathode comprises at least one of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), Ag and Al. The method of claim 1,
Inverted organic light-emitting device, characterized in that the cathode is a transparent material, the bottom emission type. The method of claim 1,
Inverted organic light emitting device, characterized in that the anode is a transparent material, the top emission type. The method of claim 1,
Inverted organic light emitting device further comprises a hole injection layer formed on the hole transport layer. 16. The method of claim 15,
The hole injection layer is MoO ₃ , MoO ₂ , WO ₃ , V ₂ O ₅ , ReO _{3 ,} NiO, tetrafluoro-tetracyano-quinomethane (F4-TCNQ) based on the total weight of the hole injection layer material And 0.1% to 25% by weight of at least one of tris [1,2-bis (trifluoromethyl) ethane-1,2-dithiolene [Mo (tfd) ₃ ]. device. The method of claim 1,
Inverted organic light emitting device, characterized in that the light emitting layer comprises a fluorescent host or a phosphorescent host. The method of claim 1,
Inverted organic light emitting device further comprises a hole blocking layer interposed between the light emitting layer and the second electron transport layer. Forming a cathode on the substrate;
Forming a first electron transport layer comprising a 2-methylpyrimidine-based compound and Rb ₂ CO ₃ on the cathode;
Forming a second electron transport layer including the 2-methylpyrimidine-based compound on the first electron transport layer;
Forming a light emitting layer on the second electron transport layer;
Forming a hole transport layer on the light emitting layer; And
Forming an anode on the hole transport layer; Method of manufacturing an inverted organic light emitting device comprising a. An n-type thin film transistor formed on the substrate and including a source electrode and a drain electrode, an oxide semiconductor layer, a gate electrode, and a gate insulating layer; A first insulating layer formed on the n-type thin film transistor; And an inverted organic light emitting device according to any one of claims 1, 3 to 6, and 8 to 18, formed on the first insulating layer.
And a cathode of the inverted organic light emitting diode is electrically connected to one of the source electrode and the drain electrode.

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