KR20070035758A - Organic electroluminescence device with photonic crystal and method of making the same - Google Patents

Abstract

The present invention relates to a photonic crystal organic light emitting device and a method of manufacturing the same, the photonic crystal organic light emitting device of the present invention comprises a substrate including a photonic crystal, an anode formed on the substrate, a light emitting layer formed on the anode and a cathode formed on the light emitting layer The manufacturing method includes forming a photonic crystal in a substrate, forming an anode on the substrate, forming a light emitting layer on the anode, and forming a cathode on the light emitting layer.

Due to this feature, the present invention can effectively increase the light efficiency of the organic light emitting device and can be manufactured in a simple process, thereby reducing the risk of device contamination and economically advantageous.

Photonic crystal, laser, organic light emitting device

Description

Photonic organic light emitting device and its manufacturing method {Organic Electroluminescence Device With Photonic Crystal And Method Of Making The Same}

1 is a cross-sectional view showing a schematic structure of a general organic light emitting device;

2 is a cross-sectional view showing a schematic structure of a conventional photonic crystal organic light emitting device;

3A to 3D are flowcharts illustrating a method of manufacturing a photonic crystal organic light emitting diode according to the present invention;

4A to 4D are plan views showing the two-dimensional arrangement of the photonic crystal constituting the present invention;

5 is a cross-sectional view showing another embodiment of a photonic crystal organic light emitting device according to the present invention;

6 is a cross-sectional view showing still another embodiment of the photonic crystal organic light emitting diode according to the present invention.

*** Explanation of the Major Symbols in the Drawings ***

10 substrate 11 anode

12 emitting layer 13 cathode

14: hole transport layer 15: electron transport layer

16: hole injection layer 17: electron injection layer

20: photonic crystal 21: objective lens

22: laser device

The present invention relates to a photonic crystal organic light emitting device and a method of manufacturing the same, and more particularly, it is possible to prevent the light efficiency from being lowered due to total reflection of the light emitted from the light emitting layer of the organic light emitting device, and to provide a simpler method as compared to the conventional technology. An object of the present invention is to provide a photonic crystal organic light emitting device that can be manufactured by a step, and a method of manufacturing the same.

      Electroluminescence devices (EL devices) are attracting attention as next-generation display devices because of their advantages such as wide viewing angle, excellent contrast, and fast response speed. Such electroluminescent devices are classified into inorganic electroluminescent devices and organic electroluminescent devices according to materials for forming an emitting layer.

      Firstly, an inorganic electroluminescent element is a device that emits light by applying a high electric field to a light emitting part and accelerating an electron in this high electric field to impinge on the light emitting center thereby exciting the light emitting center. The inorganic electroluminescent device having the above operation principle requires a high voltage of about 100 to 200 V as a driving voltage because a high electric field is required, whereas the organic electroluminescent device is driven at a low voltage of about 5 to 20 V. It has the advantage of being able to be used, and it has excellent features such as wide viewing angle, high speed response and high contrast, so it can be used as pixel of graphic display, pixel of TV image display or surface light source. It is thin, light and easy to implement three colors of green, blue, and red, making it suitable for next-generation flat panel displays.

      1 is a cross-sectional view showing an organic light emitting device according to the prior art. As illustrated, the organic light emitting diode has a structure in which a light emitting layer 120 made of a light emitting material is inserted between a metal having a high work function and a low metal electrode on the substrate 100. The metal electrode having a high work function is used as the anode 110 for injecting holes and the metal electrode having low work function is used as the cathode 130 for injecting electrons. In order to emit the emitted light to the outside of the light emitting device, the substrate and one electrode are made of a transparent material having almost no light absorption in the light emitting wavelength region. Indium Tin Oxide (ITO) is most commonly used as a transparent electrode, and this metal is usually used as an anode into which holes are injected. As the cathode, a metal having a low work function is generally used to facilitate the injection of electrons.

      The emission principle of the organic light emitting device is as follows. When holes and electrons are injected into the light emitting layer, respectively, in the anode and the cathode having a high work function, excitons are generated in the light emitting layer. ) And light corresponding to the energy difference between HOMO (Highest Occupied Molecular Orbital).

      Light emitted from the light emitting layer is emitted to the outside through an electrode and a substrate, and at this time, due to the difference in refractive index between the interface between the electrode and the substrate or the interface between the substrate and the outside, the light incident at an angle greater than the critical angle is totally reflected to the organic light emitting device. Emission in the lateral direction or absorbed or attenuated in the interior is an important cause of the luminous efficiency degradation. When the luminous efficiency is low, the power consumption of the device is increased, and the lifespan of the organic light emitting elements in the array is shortened, which adversely affects the performance of the device.

     As a conventional technique for reducing such total reflection, a photonic crystal organic light emitting diode is disclosed in Korean Patent No. 10-2003-0059278. FIG. 2 is a cross-sectional view illustrating a schematic configuration of the photonic crystal organic light emitting diode, and includes a substrate 101, an anode 111, a light emitting layer 121, and a cathode 131, and has an uneven shape at an interface between the substrate and the anode. Photonic crystal 200 is formed. The photonic crystal reduces the total reflection of the light emitted from the light emitting layer at the interface between the substrate and the anode, thereby increasing the luminous efficiency of the device. However, when the above-described photonic crystal structure is included, the surface of the substrate may not be flat and the characteristics of the organic thin film formed thereon may be deteriorated.

      Therefore, there is a need for an organic light emitting device that can effectively reduce the total reflection occurring at the substrate interface while solving the problems of the prior art.

The present invention is to solve the above problems, to provide a photonic crystal organic light emitting device and a method for manufacturing the same that can prevent the light efficiency is lowered due to total reflection of the light emitted from the light emitting layer of the organic light emitting device.

Another object of the present invention is to provide a photonic crystal organic light emitting device and a method of manufacturing the same, which can be manufactured by a simple process as compared with the conventional art.

The present invention is a photonic crystal organic light emitting device comprising a substrate including a photonic crystal, an anode formed on the substrate, a light emitting layer formed on the anode and a cathode formed on the light emitting layer.

A method of manufacturing a photonic crystal organic light emitting device includes forming a photonic crystal in a substrate, forming an anode on the substrate, forming a light emitting layer on the anode, and forming a cathode on the light emitting layer.

The organic light emitting device of the present invention is characterized by including a photonic crystal inside the substrate. Photonic crystal refers to an optical structure that exhibits photonic band gap, localization of light, nonlinearity of light, and strong dispersion characteristics, and particularly refers to a shape and pattern having a lattice period of a length similar to that of light. The use of such a photonic crystal can not only control the propagation of light, but also control the spontaneous emission, which can greatly contribute to the improvement and miniaturization of the optical device.

The periodic structure of the photonic crystal can be divided into 1, 2, and 3 dimensional structures. The method of making each photonic crystal structure depends on the dimension of the photonic crystal to be made. In the simplest one-dimensional photonic crystal structure, different materials can be formed simply by layering them. In the case of two-dimensional photonic crystal, there is no change in the z-axis, and different materials are arranged periodically on the x-y plane. In the case of a two-dimensional photonic crystal structure, air may be used as a material that inserts other materials into the material in the form of a rod. In other words, two-dimensional photonic crystal structures can be created by simply drilling holes in the material. In the case of the three-dimensional photonic crystal structure is not easy to manufacture, but has the advantage of forming the optical band gap in all directions.

In the organic light emitting device of the present invention, by introducing a photonic crystal structure having a two-dimensional or three-dimensional periodic arrangement inside the substrate, the light emitted from the light emitting layer is emitted to the side of the device due to total reflection occurring at the interface of the substrate, Light loss caused by absorption and attenuation can be reduced. In addition, due to the structural characteristics in which the photonic crystal is formed inside the substrate, the growth of the organic thin film formed on the substrate is performed on the flat surface of the substrate to improve the characteristics of the thin film. The inconvenience to be controlled can be eliminated.

The present invention uses a method of focusing a laser beam at a certain point in the substrate through a lens to form a photonic crystal inside the substrate. In more detail, a glass substrate made of aluminum oxide, silicon oxide, or the like is prepared, and a focal point is formed inside the substrate through an objective lens to irradiate a laser beam. At this time, the laser beam uses a femto-second laser beam.

In response to the absorption of light by electron excitation, the tip of the material absorbs light corresponds to the optical band gap, so light having a lower photon energy than the optical band gap is not absorbed by the material. However, when a high density photon is incident in a very short time such as a femtosecond laser, multiphoton absorption by multiple photons occurs. Since multiphoton absorption does not occur if the laser intensity is not above a certain threshold, when the laser beam is focused on a point using a lens and energy is adjusted, multiphoton absorption occurs only at that point, and the microstructure changes due to heat. The modified portion may have an increased refractive index than other portions, and may be arranged and arranged to obtain a photonic crystal structure.

The method of forming the photonic crystal using the laser beam is simpler and more economically advantageous than the photolithography process, which is a conventional photonic crystal forming technique, and can reduce problems such as contamination of the organic light emitting device generated during manufacturing.

Hereinafter, with reference to the accompanying drawings will be described in detail the technical features of the present invention. The invention can be better understood by the examples, the following examples are for illustrative purposes of the invention and are not intended to limit the scope of protection defined by the appended claims.

3A to 3D are flowcharts illustrating one embodiment of a method for manufacturing a photonic crystal organic light emitting diode according to the present invention. First, a photonic crystal 20 is formed inside a substrate 10 (FIG. 3A).

In the forming of the photonic crystal, as described above, a glass substrate made of aluminum oxide, silicon oxide, or the like is prepared, and then a focal point is formed inside the substrate through the objective lens 22 and the femtosecond laser is formed using the laser device 21. Photonic crystals are formed by irradiating the beams.

The period of the photonic crystal is preferably about? / Sin? (?: Wavelength of light emitted from the light emitting layer,?: Critical angle at the substrate interface). The organic light emitting device may emit light of various wavelengths depending on the composition of the active layer. Therefore, the period of the photonic crystal varies depending on the wavelength of light.

The photonic crystal is formed directly inside the interface of the substrate and the anode, i.e., adjacent to the top of the substrate, or within the interface of the substrate and the air layer, i.e., near the bottom of the substrate, considering the diffraction and scattering of light passing through the photonic crystal. Good to do. In addition, it may be formed on both sides, and in order to maximize the light extraction efficiency, the photonic crystal may be formed over the entire inside of the substrate.

Next, an anode 11 is formed on the substrate 10 (FIG. 3B). The anode is formed of a transparent electrode. The material for forming the transparent electrode is indium tin oxide (ITO) or indium zinc oxide (IZO).

Next, the light emitting layer 12 is formed on the anode 11 (FIG. 3C). The light emitting layer is made of an organic light emitting material, and the organic light emitting material is HP (Para-Hexaphenyl) or DPVBi (4,4'-bis (2,2-diphenylvinyl) -1,1'-iphenyl), or BCzVBi ( 4,4'-bis [2- (3-N-ethylcarbazoryl) vinyl] biphenyl) may be used. In addition to this, all light emitting materials used in general organic light emitting devices may be used.

A hole transport layer or a hole injection layer may be formed between the anode 11 and the light emitting layer 13 to improve the injection of holes into the light emitting layer.

      The movement of carriers in organic material generally moves holes more easily than electrons due to reasons such as ionization potential and electron affinity. That is, excitons are generated near the cathode because electrons are not easily moved within the organic material, but the quantum efficiency of the organic light emitting device is deteriorated because the specific gravity of the non-light-emitting extinction is larger than the light-emitting extinction.

      In order to solve such a problem and to accelerate the movement of electrons and holes, it is preferable to form a heterostructure of light emitting devices using two or more organic materials having different band gaps. This structure increases the local charge density by inhibiting the movement of holes, facilitating the injection of electrons by the space charge field, and rapidly transfers the electrons into the collision radius that can recombine with holes using a material having good electron transport ability. The luminous efficiency is increased by letting in.

      The heterojunction structure can be made by forming a charge transport layer between the light emitting layer and the electrode. The charge transport layer includes an electron transport layer and a hole transport layer.

      The charge transport layer efficiently transports the carriers to the light emitting material, thereby increasing the probability of light emitting coupling in the light emitting layer. In addition, the HOMO and LUMO levels of the charge transport material deviate to some extent from that of the luminescent material, thereby suppressing the transport of the carriers. For example, the electron transport layer improves the electron injection from the cathode because the electron transport layer increases the electric field in the electron transport layer by suppressing the flow of holes at the interface with the light emitting layer. In addition, when the hole mobility is higher than the electron mobility in the light emitting layer, luminescence recombination mainly occurs near the cathode to form a single exciton, and the metal defect diffused from the metal electrode near the cathode is a source of non-light emission. Although the probability of luminescence recombination decreases as a result of the formation of the electron-carrying layer, since the luminescence recombination occurs at the interface between the luminescent layer and the transport layer, there is a certain distance from the metal electrode and the suppression of excitons is reduced.

 The heterojunction structure may include a charge injection layer divided into an electron injection layer and a hole injection layer in addition to the above-described charge transport layer.

As the hole transport layer, PVK (Poly (N-vinylcarbazole)) or TPD (N, N'-diphenyl-N, N'-bis (3-methylphenyl)-(1,1'-biphenyl) -4,4'- diamine) and copper phthalocyanine (CuPc) is used as the hole injection layer. In the case where both the hole transport layer and the hole injection layer are formed, it is preferable to form an anode-hole injection layer-hole transport layer-light emitting layer.

Next, a cathode 13 is formed on the light emitting layer 12 (FIG. 3D). As the cathode, a metal having a small work function such as calcium, magnesium, lithium, or the like may be used. However, such metals are not only easily oxidized in the air due to their strong reactivity, but also may diffuse into the light emitting layer, thereby degrading the performance of the device. Therefore, in the present invention, the cathode is formed by using silver or aluminum having high stability. As a method of forming a cathode on the light emitting layer, vacuum deposition or sputtering is used.

Since the light emitted from the light emitting layer proceeds not only in the direction of the substrate but also in the direction of the cathode, the organic light emitting device needs to include a reflective layer in order to control the traveling direction of the light. Since the silver or aluminum is a metal having high reflectance, the silver or aluminum may be formed to cover the entire light emitting layer to serve as a reflective layer.

As described above, an electron transport layer or an electron injection layer may be formed between the emission layer 12 and the cathode 13 to improve injection of electrons.

As the electron transport layer, polymer materials such as PBD (1,3,4-oxadiazole dreivertive) and spiro-PBD and low molecular materials such as Alq3 (Aluminum tris (8-quinolinolate)) can be used.For electron injection layers, PBD, LiF, gallium mixtures, Alq3 and the like can be used.

4A to 4D show a two-dimensional array of photonic crystals formed inside the substrate as viewed from an upper surface of the substrate. As shown in FIG. 4A to FIG. 4D, a square lattice (FIG. It may also be formed in the shape of a honeycomb lattice (Honeycomb Lattice (FIG. 3C), random lattice (FIG. 3D)). Arranging the photonic crystal lattice in a random lattice and having a predetermined average period eliminates the direction dependence according to the wavelength of light passing through the photonic crystal, thereby eliminating the color deflection phenomenon in which light of a specific wavelength is concentrated in a specific direction.

Since the present invention is to form a photonic crystal by intensively irradiating a laser beam inside the photonic crystal, the photonic crystal can be arranged in three dimensions to form a three-dimensional photonic crystal structure. In the three-dimensional photonic crystal structure, light diffraction and scattering may be further increased to further increase light extraction efficiency. For example, it is a method of arranging or zigzag in a row in the z-axis direction, that is, the direction perpendicular to the interface between the substrate and the anode, following the two-dimensional arrangement described above.

FIG. 5 shows another embodiment of the photonic crystal organic light emitting diode according to the present invention, in which a photonic crystal 20 is formed adjacent to an upper end of the substrate 10, and an anode 11, a hole transport layer 14, and a light emitting layer ( 12), the electron transport layer 15 is formed in order, the cathode 13 is formed to cover the entire upper portion of the electron transport layer, made of aluminum or silver serves as a reflective layer.

FIG. 6 shows another embodiment of the photonic crystal organic light emitting diode according to the present invention, in which photonic crystals 20 are formed adjacent to upper and lower ends of the substrate 10, respectively. 16, the hole transport layer 14, the light emitting layer 12, the electron transport layer 15, the electron injection layer 17 is formed in order, the cathode 13 is formed to cover the entire upper portion of the electron injection layer, aluminum Or silver to serve as a reflective layer.

As described above, according to the present invention, by using the photonic crystal structure, the light emitted from the light emitting layer is totally reflected to escape to the side of the light emitting device, or the absorption and attenuation in the light emitting device is reduced, thereby effectively reducing the light efficiency of the organic light emitting device. Increase.

In addition, the present invention can further increase the light efficiency of the organic light emitting device by forming a three-dimensional photonic crystal structure.

In addition, the present invention forms the photonic crystal structure inside the substrate rather than at the interface between the substrate and the anode, so that the characteristics of the organic thin film formed on the substrate are not deteriorated, thereby increasing the efficiency of the organic light emitting device.

In addition, the present invention has an advantageous effect of forming a photonic crystal by using a method of irradiating a laser beam to the inside of a substrate in forming a photonic crystal structure in a simpler process than in the prior art.

Claims (13)

A substrate including a photonic crystal; An anode formed on the substrate; A light emitting layer formed on the anode; And A photonic crystal organic light emitting device comprising a cathode formed on the light emitting layer. The method of claim 1, A hole transport layer is further formed between the anode and the light emitting layer, and an electron transport layer is further formed between the light emitting layer and the cathode. The method of claim 1, A hole injection layer is further formed between the anode and the light emitting layer, and an electron injection layer is further formed between the light emitting layer and the cathode. The method of claim 1, And the photonic crystal is formed adjacent to the top surface of the substrate. The method of claim 1, And the photonic crystal is formed adjacent to the bottom surface of the substrate. The method of claim 1, The photonic crystal organic light emitting device of claim 2, wherein the photonic crystal is arranged in a two-dimensional period. The method of claim 1, The photonic crystal organic light emitting device of claim 3, wherein the photonic crystal is arranged in a three-dimensional period. The method of claim 1, The period of the photonic crystal is λ / sin θ (λ: wavelength of the light emitted from the light emitting layer, θ: the critical angle at the substrate interface) characterized in that the organic light emitting device. The method of claim 1, The anode is an organic light emitting device, characterized in that the transparent electrode made of ITO or IZO. The method of claim 1, The cathode is made of silver or aluminum and an organic light emitting device, characterized in that formed to cover the entire upper surface of the light emitting layer. Forming a photonic crystal inside the substrate; Forming an anode on the substrate; Forming a light emitting layer on the anode; And A method of manufacturing a photonic crystal organic light emitting device comprising the step of forming a cathode on the light emitting layer. The method of claim 11, The forming of the photonic crystal is a method of manufacturing a photonic crystal organic light emitting device, characterized in that formed by irradiating a laser beam to a predetermined point inside the substrate. The method of claim 12, And the laser beam is a femtosecond laser beam.

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