KR20070119171A - Organic electroluminescent device - Google Patents

Abstract

An organic EL(electro-luminescence) device is provided to increase brightness of the EL device by increasing a critical angle for a total reflection using a first buffer layer. An organic EL(electro-luminescence) device includes first and second substrates(101,131), a first buffer layer(105), a first electrode(112), an organic light emitting layer(114), and a second electrode(116). The first and second substrates face each other. The first buffer layer is formed on the first substrate and has a first refractive index. The first electrode is formed on the first buffer layer. The organic light emitting layer is formed on the first electrode. The second electrode is formed on the organic light emitting layer. The first refractive index is smaller than that of the material of the first electrode and greater than that of a material of first substrate.

Description

Organic Electroluminescent Device

1 is a circuit diagram of one pixel of a typical active matrix organic electroluminescent device.

Figure 2 is a schematic cross-sectional view of a conventional bottom emission organic electroluminescent device.

3 is a view showing a progress state according to the change in the incident angle upon incidence of the light medium in the dense medium.

4 is a cross-sectional view showing a part of a bottom emission type active matrix type organic light emitting display device according to a first embodiment of the present invention;

5 is a cross-sectional view showing a part of a bottom emission type active matrix type organic light emitting display device according to a second embodiment of the present invention;

6 is a cross-sectional view showing a part of a bottom emission type active matrix type organic light emitting display device according to a third embodiment of the present invention;

<Explanation of symbols for main parts of the drawings>

101: first substrate 105: buffer layer having a specific refractive index

112: first electrode 114: organic light emitting layer

116: second electrode 131: second substrate

132: absorbent

DTr: Drive element

The present invention relates to an organic electroluminescent device, and more particularly to an organic electroluminescent device, characterized in that the luminous efficiency is maximized.

One of flat panel displays (FPDs), an organic light emitting display device has high luminance and low operating voltage characteristics. In addition, the self-luminous self-illuminating type provides high contrast ratio, enables ultra-thin display, easy response time with several microsecond response time, no restriction on viewing angle, and stable at low temperatures. Since it is driven at a low voltage of 5 to 15V DC, it is easy to manufacture and design a driving circuit.

In addition, the manufacturing process of the organic electroluminescent device is very simple because the deposition (deposition) and encapsulation (encapsulation) equipment is all.

The organic light emitting display device having such a characteristic is largely divided into a passive matrix type and an active matrix type. In the passive matrix method, since the scan line and the signal line cross each other and configure the device in a matrix form, Since the scanning lines are sequentially driven in time to drive the pixels, in order to represent the required average luminance, the instantaneous luminance must be equal to the average luminance multiplied by the number of lines.

However, in the active matrix method, a thin film transistor, which is a switching element that turns a pixel on and off, is positioned for each pixel, and the first electrode connected to the thin film transistor is a pixel unit. It turns on / off and the 2nd electrode which opposes this 1st electrode becomes a common electrode.

In the active matrix method, a voltage applied to a pixel is charged in a storage capacitor (C _ST ), and the power is applied until the next frame signal is applied, thereby relating to the number of scan lines. Run continuously for one screen without Accordingly, since low luminance, high definition, and large size can be obtained even when a low current is applied, an active matrix type organic light emitting display device has been mainly used in recent years.

Hereinafter, the basic structure and operation characteristics of the active matrix organic light emitting display device will be described in detail with reference to the accompanying drawings.

1 is a circuit diagram of one pixel of a typical active matrix organic electroluminescent device.

As illustrated, one pixel of the active matrix organic light emitting diode is a switching thin film transistor STr, a driving thin film transistor DTr, a storage capacitor StgC, and an organic light emitting diode E. Is made of.

That is, the gate line GL is formed in the first direction, is formed in the second direction crossing the first direction to define the pixel region P, and the data line DL is formed. A power supply line PL is formed to be spaced apart from the DL and to apply a power supply voltage.

In addition, a switching thin film transistor STr is formed at a portion where the data line DL and the gate wiring GL cross, and a driving thin film transistor DTr electrically connected to the switching thin film transistor STr is formed. have.

In this case, the driving thin film transistor DTr is electrically connected to the organic light emitting diode E. That is, the first electrode, which is one terminal of the organic light emitting diode E, is connected to the drain electrode of the driving thin film transistor DTr, and the second electrode, which is the other terminal, is connected to the power line PL. In this case, the power line PL transfers a power supply voltage to the organic light emitting diode E.

In addition, a storage capacitor StgC is formed between the gate electrode and the source electrode of the driving thin film transistor DTr.

Therefore, when a signal is applied through the gate line GL, the switching thin film transistor STr is turned on, and the signal of the data line DL is transferred to the gate electrode of the driving thin film transistor DTr to drive the driving signal. Since the thin film transistor DTr is turned on, light is output through the organic electroluminescent diode E. At this time, when the driving thin film transistor DTr is in an on state, the level of the current flowing from the power supply line PL to the organic light emitting diode E is determined, and thus the organic light emitting diode E is The gray scale may be implemented, and the storage capacitor StgC maintains the gate voltage of the driving thin film transistor DTr constant when the switching thin film transistor STr is turned off. As a result, even when the switching thin film transistor STr is turned off, the level of the current flowing through the organic light emitting diode E may be maintained until the next frame.

The organic light emitting diode which drives such a light is classified into a top emission type and a bottom emission type according to a transmission direction of light emitted through the organic light emitting diode.

2 is a schematic cross-sectional view of a conventional bottom emission type organic electroluminescent device.

As shown, the first substrate 1, which is usually made of glass, and the second substrate 31 facing the first substrate 1 and merely for encapsulation are arranged opposite each other.

In addition, edge portions of the first and second substrates 1 and 31 are sealed by a seal pattern 40, and each pixel region driving thin film transistor DTr is formed on the first substrate 1. The first electrode 12 is connected to each of the driving thin film transistors DTr, and a red, green, and blue color is formed on the first electrode 12. The organic light emitting layer 14 including the light emitting material patterns 14a, 14b, and 14c emitting light may be formed, and the second electrode 16 is formed on the entire surface of the organic light emitting layer 14. In this case, the first and second electrodes 12 and 16 serve to apply an electric field to the organic light emitting layer 14.

In addition, the first and second substrates are bonded to each other by the seal pattern 40 described above, and spaced apart from each other, that is, the second electrode 16 and the second substrate formed on the first substrate 1. 31 is spaced apart from each other, the inner surface of the second substrate 31, the moisture absorbent 32 to block moisture to the outside and the semi-permeable for adhesion between the moisture absorbent 32 and the second substrate 31 Tape is included.

In the organic electroluminescent device having such a structure, when the first electrode 12 is formed of an anode and the second electrode 16 is formed of a cathode, the first electrode 12 is made of a transparent conductive material. It is formed of indium tin oxide (ITO), a material having a high work function, and the second electrode 16 is selected from a metal material having a low work function, and the organic light emitting layer 14 is formed in multiple layers to maximize luminous efficiency. It may also form.

In the organic light emitting device having such a configuration, the light felt by the user looking at the organic light emitting device is emitted from the organic light emitting layer and passes through the anode, the substrate and the air layer, or is emitted from the organic light emitting layer, and thus the cathode. It is seen that the light is reflected by the cathode and passes through the organic light emitting layer, the anode, the substrate, and the air layer.

In this case, the refractive index of each material layer through which the emitted light passes is typically 1.7 to 1.8, and the first electrode, which is the anode, is made of indium tin oxide (ITO), and has a refractive index of about 2 degrees. The first substrate of glass has a refractive index of 1.5 and the air has a refractive index of 1.

Therefore, the light emitted from the organic light emitting layer recognizes the difference in refractive index by advancing the multi-layered material layer, and it can be seen that the light is mainly progressed from the dense medium to the medium. For example, in a dense medium (relatively high refractive index medium), the first electrode having a refractive index of 2 passes through a first substrate having a refractive index of 1.5 and the air layer having a refractive index of 1 has a refractive index of 1 in the first substrate having a refractive index of 2. It can be seen that the medium passes through a medium (relatively small refractive index).

In this case, referring to FIG. 3, which shows a progress state according to a change in the incident angle of light from the dense medium n1 to the small medium n2, the normal line Lp for the interface between two material layers having different refractive indices (n1> n2). ), The angles of incidence (θc, θ1, θ3), defined as the angles between the two sides, are the angles of incidence (θc, θ1, θ3) when light travels from a medium with a high refractive index (dense medium, n1) to a medium with a small refractive index (small medium, n2) When the angle of refraction (θ2, θ4) is larger than this, when the angle of refraction becomes larger than the critical angle (θc), which is defined as an angle of incidence of 90 degrees, the light does not cross the interface of the medium and total reflection occurs, thereby causing waveguide at the interface of these two mediums. The problem arises that the luminance is lowered by the formation of a wave guide (a phenomenon in which light flows along the interface).

The present invention has been made to solve the above problems, and an object of the present invention is to suppress the total reflection phenomenon to reduce the loss of light caused by the wave guide phenomenon.

In order to achieve the above object, the organic light emitting device according to the first aspect of the present invention, the first substrate and the second substrate facing each other; A first buffer layer having a first refractive index formed on said first substrate; A first electrode formed on the first buffer layer; An organic light emitting layer formed on the first electrode; And a second electrode formed on the organic emission layer, wherein the first refractive index is smaller than the refractive index of the material constituting the first electrode and larger than the refractive index of the material constituting the first substrate.

In this case, a second buffer layer having a second refractive index that is larger than the refractive index of air and smaller than the refractive index of the material forming the first substrate is further formed on a surface exposed to the outside of the first substrate.

An organic electroluminescent device according to a second aspect of the present invention comprises: a first substrate and a second substrate facing each other; A first electrode formed on the first substrate; An organic light emitting layer formed on the first electrode; A second electrode formed on the organic emission layer; A second buffer layer formed on the exposed surface of the first substrate, the second buffer layer being formed of a material having a second refractive index value, wherein the second refractive index value is greater than the refractive index of air and the refractive index of the material forming the first substrate. It is characterized by a small one.

In the organic electroluminescent device according to the first and second features, the first substrate is made of glass, and the first electrode is indium-tin oxide (ITO), wherein the first refractive index is 1.6 to 1.9. In this case, the first buffer layer is preferably made of one of Al ₂ O ₃ , CeF ₃ , MgO, PbF ₂ .

In addition, the second refractive index is characterized in that 1.1 to 1.4, wherein the second buffer layer is preferably made of one material of PTFE, PFA, Teflon, Cytop.

In addition, the organic light emitting layer is a multilayer of the hole injection layer, a hole transporting layer, a hole transporting layer, an emitting material layer, an electron transporting layer and an electron injection layer. The organic electroluminescent device further includes a driving device and a switching device.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

<First Embodiment>

4 is a cross-sectional view illustrating a part of a bottom emission type active matrix type organic light emitting display device according to a first embodiment of the present invention.

As shown, an organic electric field composed of a first substrate 101 made of glass and a first electrode 112, an organic emission layer 114, and a second electrode 116 facing the first substrate 101. The second substrate 131 for encapsulation for protecting the light emitting diode from the outside air is disposed to face each other.

A seal pattern 140 is formed along the edges of the first and second substrates 101 and 131 as a means for blocking external air and adhering the first and second substrates 101 and 131. The first and second substrates 101 and 131 are bonded to each other by the seal pattern 140.

On the other hand, the most characteristic of the present invention on the front surface of the first substrate 101 is a transparent material having a refractive index value of more preferably about 1.6 to 1.8, the refractive index in the visible light band is more than 1.5 2.0min, for example Al ₂ O ₃ (refractive index 1.63), CeF ₃ (refractive index 1.63), MgO (refractive index 1.7), PbF ₂ (refractive index 1.7) The buffer layer 105 is formed as a material selected from among them.

In addition, a driving thin film transistor DTr is formed in each pixel area over the buffer layer 105, and is connected to each of the driving thin film transistors DTr and has a relatively high work function value. Indium-tin-oxide (ITO) As a result, the first electrode 112 is formed.

In addition, an organic emission layer 114 including red, green, and blue organic light emitting patterns 114a, 114b, and 114c formed of a material emitting red, green, and blue light in each pixel area is formed on the first electrode 112. A second electrode 116 is formed on the organic emission layer 114 on the entire surface of the metal material, for example, aluminum (Al) or aluminum alloy (AlNd), having a relatively low work function value.

Meanwhile, an inner surface of the second substrate 131 formed for encapsulation, that is, a surface of the second substrate 131 facing the second electrode 116 may be formed on the first and second substrates 101 and 131. A moisture absorbent 132 is attached to absorb moisture present in the space.

In the organic electroluminescent device having the structure according to the first embodiment of the present invention described above, the organic light emitting layer 114, although shown as a single layer in the drawing, in order to increase the luminous efficiency from the bottom of the hole injection layer ( It may be composed of multiple layers of a hole injection layer, a hole transporting layer, an emitting material layer, an electron transporting layer and an electron injection layer. In this case, each material layer having the multilayer structure is made of a material having a refractive index of about 1.7 to about 1.8.

In this structure, when looking at the path of the light emitted from the organic light emitting layer 114 of the single or multi-layer structure, first of all, the light emitted from the organic light emitting layer 114 is lowered to the first electrode 112-> And a first path through the buffer layer 105-> first substrate 101-> air layer, and secondly, the organic light emitting layer 114 emits light upward and is reflected by the second electrode 116. As a result, the organic light emitting layer 114 may pass through the inside of the organic light emitting layer 114 again, and then may have a second path through the first electrode 112-> buffer layer 105-> first substrate 101-> air layer. .

In this case, looking at the refractive index of each material layer through which the light emitted from the organic light emitting layer 114 passes, the organic light emitting layer 114 itself is 1.7 to 1.8, the first electrode 112 made of indium tin oxide (ITO) 2.0, the buffer layer 105 is 1.6 to 1.9, and the air layer is 1.0.

Therefore, when light passes from the small medium to the dense medium only when the organic light emitting layer 114 passes through the first electrode 112, total reflection does not occur at the interface, and the buffer layer 105 is formed at the first electrode 112. ), When light passes through the first substrate 101 made of glass in the buffer layer 105 and the air layer in the first substrate 101, the state is a structure in which all of the states are incident on the dense medium into the small medium, and thus the critical angle is greater than or equal to This results in total reflection.

In this case, Snell's law used to calculate the critical angle will be briefly described. Snell's law is,

n ₁ sinθ ₁ = n ₂ sinθ ₂ --- ①

It can be represented as.

In this case, referring to FIG. 3, n1 and n2 represent refractive indices of two materials, and θ ₁ and θ ₂ are incident angles θ ₁ and refractive angles θ ₂ formed by a line perpendicular to the interface, that is, normal Lp.

Since the ratio of n1 / n2 is constant for a given wavelength of light, the ratio of the two sin values is also constant regardless of the angle. Therefore, when light is incident on a material having a refractive index larger than that of the past material, the light path is bent in the normal direction. On the contrary, when entering a material having a high refractive index (density medium) from a material having a small refractive index (small medium), the light path is reversible, so the refracted light is bent away from the normal.

Based on this Snell's law, when the light enters the dense medium from the dense medium, the critical angle θc that causes total reflection refers to the incident angle θ ₁ of the light when the refraction angle θ ₂ is 90 °. If θ ₁ is greater than the critical angle θ c (θ ₁ > θ c), the light is totally reflected.

Thus, the critical angle (θc) From this fact may be seen that this point is 90 ㅀil value of θ ₂ in the above-mentioned formula ① (θ ₂ = 90 DEG), the value of θ ₁ of (θ ₁ = θc), the following equation It can be expressed as.

θ ₁ = sin ^-1 (n2 / n1) --- ②

Therefore, in the first embodiment according to Equation (2), when the light emitted from the organic light emitting layer 114 is incident from the first electrode (refractive index 2.0) 112 to the buffer layer (when refractive index is 1.7) 105, the critical angle θ ₁ ) becomes 58.2 占, and the critical angle θ ₁ when incident on the first substrate (refractive index 1.5) 101 from the buffer layer (when the refractive index is 1.7) 105 is 61.9 占.

In the conventional case in which a transparent buffer layer having a refractive index of about 1.51 to 1.73 is not present between the first electrode and the substrate, light that can pass through the first substrate without total reflection of light from the first electrode toward the substrate is expressed by the above equation. According to (2), since the critical angle is 48.5 μs, only light incident at an angle smaller than the critical angle of 48.5 μs passes, but in the case of the present invention, it is preferably 1.6 between the first electrode 112 and the first substrate 101. Since the presence of the buffer layer 105 having a refractive index of about 1.9 to 1.9, the critical angle of the light passing through the buffer layer 105 at the first electrode 112 is 49 kV to 59.9 kV, and the first layer of the buffer layer 105 has a first refractive index. Since the critical angle of light passing through the substrate 101 is 83.4 kW to 60.1 kW, the critical angle of total reflection at the boundary of each material layer is increased, thereby reducing the loss of light due to the wave guide.

In other words, the buffer layer 105 is characterized by improving the luminance by reducing the total reflection and finally disappears along the interface between the media.

In this case, the amount of light absorbed by the buffer layer 105 is also generated by the addition of the buffer layer 105, but the amount absorbed by the buffer layer 105 is very small and the buffer layer 105 is not formed even in consideration of the amount of absorbed light. The amount of light that disappears due to the loss caused by the wave guide generated at the interface between the first electrode and the second substrate is much higher, so it is not a problem.

Second Embodiment

5 is a schematic cross-sectional view of a portion of a bottom emission type active matrix type organic light emitting display device according to a second embodiment of the present invention.

Since the second embodiment of the present invention differs only in the position where the buffer layer is formed, and all other components are the same as in the first embodiment, the description of the same parts will be omitted.

The most characteristic part of the second embodiment is transparent and the material having a refractive index value of visible band of greater than 1.0 and less than 1.5 is more preferably 1.1 to 1.4, for example PTFE (refractive index 1.35), PFA (refractive index 1.35). ), A buffer layer 250 made of one of Teflon (refractive index 1.29-1.31) and Cytop (refractive index 1.34) is formed on the outer surface of the first substrate 201.

In this case, looking at the path of the light emitted from the organic light emitting layer 214, except for the case where the light is reflected from the second electrode 216, the organic light emitting layer 214-> first electrode 212-> first 1 It can be seen that the substrate 201-> buffer layer 250-> air layer.

Therefore, a path different from the conventional one is the first substrate 201-> buffer layer 250-> air layer, in which case the light has a refractive index of 1.3 on the first substrate 201 of glass material having a refractive index of 1.5. When the incident to the buffer layer 250 made of a Teflon having a total reflection, the critical angle is 60.1 ㅀ, the critical angle is 50.3 ㅀ when incident to the air layer having a refractive index of 1 in the buffer layer 250, the conventional first substrate (Fig. In (1), the loss of light due to wave guide generation at each boundary is improved since it is larger than 46.5 mm, which is a critical angle at the time of entering the air layer.

Third Embodiment

6 is a cross-sectional view briefly illustrating a part of a bottom emission type active matrix type organic light emitting display device according to a third embodiment of the present invention.

In this case, the third embodiment of the present invention also has a buffer layer having a different refractive index than that of the first embodiment, and only the formation position of the buffer layer is different, and all other components are the same as the first embodiment. Omit.

The most characteristic part of the third embodiment of the present invention is a transparent material having a refractive index value greater than 1.5 and smaller than 2.0, more preferably a refractive index value of 1.6 to 1.9, for example Al ₂ O ₃ , CeF ₃ , A first buffer layer 305 formed of a material selected from MgO and PbF ₂ is formed between the first electrode 312 and the first substrate 301, and is outside the first substrate 301 in contact with the air layer. A second buffer layer 350 formed of a material having a refractive index value of 1.1 to 1.4, for example, one of PTFE, PFA, Teflon, and Cytop, is formed on a side surface thereof.

Therefore, the first buffer layer 305 is formed by the wave guide (1) by increasing the critical angle between the first electrode 312 made of indium-tin-oxide (ITO) and the first substrate 301 as described in the first embodiment. The loss of light due to wave guide generation is reduced, and the second buffer layer 350 increases the critical angle between the first substrate 301 and the air layer as described in the second embodiment. It will reduce the loss of light.

On the other hand, the first, second and third embodiments described above have been described with respect to the active matrix organic light emitting device of the bottom emission type including the switching element, the present invention is active matrix type of the above-described bottom emission type It is obvious that the present invention can be applied to a passive matrix organic light emitting display device, which is not limited to an organic light emitting display device, and forms a first electrode and a second electrode by crossing a scan line and a signal line without a switching device. Various modifications and variations are possible without departing from the invention.

The organic electroluminescent device according to the present invention is a transparent material having a specific range of refractive index, and a buffer layer is formed between the first electrode and the substrate forming the anode or on the outer surface of the substrate to increase the critical angle size of the total reflection at the boundary between the material layers. There is an effect of reducing the loss of light by the generated wave guide (wave guide).

Claims (10)

A first substrate and a second substrate facing each other; A first buffer layer having a first refractive index formed on said first substrate; A first electrode formed on the first buffer layer; An organic light emitting layer formed on the first electrode; A second electrode formed on the organic emission layer And the first refractive index is smaller than the refractive index of the material constituting the first electrode and greater than the refractive index of the material constituting the first substrate. The method of claim 1, And a second buffer layer having a second refractive index on the surface exposed to the outside of the first substrate, the second buffer layer having a second refractive index larger than that of air and smaller than the refractive index of the material forming the first substrate. A first substrate and a second substrate facing each other; A first electrode formed on the first substrate; An organic light emitting layer formed on the first electrode; A second electrode formed on the organic emission layer; A second buffer layer formed on the exposed surface of the first substrate and made of a material having a second refractive index value Wherein the second refractive index value is larger than the refractive index of air and smaller than the refractive index of the material of the first substrate. The method according to any one of claims 1 to 3, The first substrate is made of glass, and the first electrode is indium tin oxide (ITO). The method of claim 4, wherein The first refractive index is an organic light emitting device, characterized in that 1.6 to 1.9. The method of claim 5, The first buffer layer is an organic electroluminescent device consisting of one of Al ₂ O ₃ , CeF ₃ , MgO, PbF ₂ . The method of claim 4, wherein The second refractive index is an organic electroluminescent device, characterized in that 1.1 to 1.4. The method of claim 7, wherein The second buffer layer is an organic light emitting display device made of one of PTFE, PFA, Teflon, Cytop. The method according to any one of claims 1 to 3, The organic light emitting layer is composed of multiple layers of the hole injection layer, the hole transporting layer, the emitting material layer, the electron transporting layer, and the electron injection layer. An organic light emitting display device characterized in that. The method according to any one of claims 1 to 3, The organic light emitting diode is an organic matrix light emitting device of the active matrix type further comprising a driving device and a switching device.

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