JPH11121180A - Organic photoelectron device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve carrier implanting efficiency, and enhance reproducibility and stability by sloping the relative rate of first and second components in the direction extending laterally to a boundary face inside an electrode substance. SOLUTION: The composition of a negative electrode 9 proceeding to a boundary face between the negative electrode 9 and an organic substance 10 from an electrode surface 11 contains LiAl alloy. This component mainly comprises A1 of" high work function on its outer surface, is sloped toward the component, and comprises Li of low work function at the highest portion 14 of a curve 15. The slope is for Lix Al1-x , it starts at a distance of 1500 to 2000 Å from the boundary face 11, and continues in an arrow sign 12 direction as increasing (x). The slope is reversed at an average free path distance of 70 to 150 Å, the component reduces (x) in an arrow sigh 13 direction, and is gradually sloped from the component comprising mainly Li at the highest portion 14 to the composition comprising mainly Al at the boundary face 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to organic optoelectronic devices, such as electroluminescent (EL) devices and organic photoresponsive devices.

[0002]

2. Description of the Related Art As shown in FIG. 7, an organic EL device 100 includes an organic light emitting layer 102 disposed between a positive electrode 103 and a negative electrode 104, and the organic light emitting layer 102 is provided between the electrodes. Applies to emit light when a voltage is applied. This layer 102 comprises a hole transport layer 105 adjacent to the positive electrode 103 and an electron transport layer 10 adjacent to the negative electrode 104.
6 is included. In such devices, the positive and negative electrodes are usually made of inorganic materials. The positive electrode is typically made of a transparent metal material such as indium tin oxide (ITO), and the negative electrode is typically made of a reactive metal such as lithium or magnesium. However, it has also been proposed to make the positive electrode from an organic material such as polyaniline.

[0003] As is well known, the emission of light from an organic light emitting layer includes the injection of vacancies (positive charge carriers) from the positive electrode under the influence of a voltage applied between the electrodes by an external power source; The injection of electrons (negative charge carriers) from the negative electrode results from the fact that the vacancy-electron recombination obtained inside the organic light-emitting layer results in the emission of energy from this layer in the form of light. Furthermore, the amount of electrons and vacancies injected into this organic layer depends on the energy band offset between the organic layer material and the electrode material. These offsets are determined by material parameters. The energy band offset between the organic layer and the positive electrode is ideally
In order to equalize the injection of electrons and vacancies into the organic layer, it should be as large as the energy band offset between the organic layer and the cathode (electrons inside the organic layer material and It is assumed that the transport properties with vacancies are equal).

It is known to adjust the energy band offset by appropriately selecting the electrode material.
Furthermore, the low work function or low electron affinity materials required to be suitable for the positive electrode are often reactive. It is known to alloy such materials with less reactive materials having high work functions and electron affinities in order to make stable electron injectors. U.S. Pat. No. 4,885,111 discloses making a negative electrode from an alloy of magnesium (Mg) and silver (Ag).
In contrast, U.S. Pat.
The production of a negative electrode from an alloy of (Al) and lithium (Li) is disclosed. In both cases, small amounts of less reactive metals (eg, Ag or A
l) is required. FIG. 8 is an energy band diagram showing the energy band offset of different cathode materials with respect to the organic light emitting layer material at the interface 115 between the organic light emitting layer and the cathode in a typical organic EL device. Here, the energy level E is plotted in the z direction orthogonal to both electrodes. Ca and Mg: Ag materials (reactive metals) with low work function or electron affinity have positive energy band offsets 111 and 112. On the other hand, Al and Au substances (stable metals) having a high work function or electron affinity have negative energy band offsets 113 and 114. Further, these substances, as shown in FIG.
Work functions 111a, 112a, 113 for vacuum levels
a, and 114a. Substances with low electron affinity readily emit electrons. On the other hand, a substance having a high electron affinity does not easily emit electrons.

In the case of a negative electrode (which includes an alloy of a material having a low work function or an electron affinity and a material having a high work function or an electron affinity), the composition of the alloy includes a material having a high work function. From a composition containing a substance having a low work function at a low concentration to a composition containing a substance having a low work function at a high concentration and containing a substance having a high work function at a low concentration. , It is possible to make a linear gradient. The former composition, which contains a relatively high concentration of a high work function material, is a negative electrode, which also acts to stabilize or encapsulate the device.
To make a stable alloy on the surface. In contrast, the latter composition, which contains a relatively high concentration of a low work function material, provides for efficient injection of electrons at the interface of the cathode with the organic luminescent material.

The positive electrode (which is a vacancy (positive charge carrier)
Is injected into an organic substance in the energy range (HOMO level, or valence band) appropriate for the transport of vacancies inside the organic substance), the work function of this electrode is usually Should be high. Therefore, this means that the composition of the positive electrode alloy contains a high work function material at a high concentration and a high work function material at a low concentration. It is convenient to have a linear gradient (contrary to the negative electrode configuration described above) to a composition containing a low concentration of a substance with a low work function at a low concentration.

[0007]

FIG. 9 is an energy band diagram of the energy E along the z direction at the interface 115 between the organic luminescent material 110 and the negative electrode 116 of the organic EL device. Here, the composition of the negative electrode 116 is graded as described above. Curve 117 indicates that the composition has a low work function material (a more reactive material, such as L
From the region 118 close to the interface containing a relatively high concentration of (i or Mg), the composition contains a relatively high concentration of a high work function material (a less reactive material, such as Al or Ag). 5 shows the change in the energy band of the negative electrode in a direction that allows the composition of the cathodic material to be linearly graded, up to a region 119 close to the surface of the negative electrode 116. In such a device, the organic luminescent material 110
The injection of carriers (electrons) into it can occur via thermionic emission, as indicated by arrow 120, or by tunneling through the energy barrier, as indicated by wave arrow 121. Both of these implantation processes are highly dependent on the height and shape of the energy barrier and are therefore very susceptible to interface effects, which are surface energy levels and potential effects.

FIG. 10 is an energy band diagram showing the manner in which the height of the energy barrier in such a device is affected by the surface energy level. If the impurity energy level at the interface 115 exceeds the Fermi level as indicated by the level 124, the barrier height increases as indicated by the curve 122. On the other hand, when the impurity energy level is lower than the Fermi level, the barrier height decreases as indicated by the dotted curve 125. Therefore, the Fermi level is effectively fixed at the impurity energy level. Referring again to FIG. 10, a curve 123 indicates that the energy level changes inside the organic material due to the surface energy level. Of particular importance is the manner in which the shape of the barrier top changes as charge transfer is encapsulated. This is because it changes the contribution to carrier injection due to thermionic emission 120 and tunneling 121 (the latter is preferred over the former). Tunneling is particularly dependent on the shape of the barrier and is very susceptible to such surface effects. As a result, electron injection into the organic light emitting layer is very difficult to reproduce and even if the exact same composition material is used for the organic light emitting layer and the adjacent negative electrode, it varies greatly between different EL devices. .

Although metal contact using the above-described alloy materials is frequently used in semiconductor devices, the problem experienced at the metal / semiconductor interface in such devices is that the energy band offset can cause the electrode to become a stable metal. When made in, they are usually large enough and differ from those described above in that the interface has a higher quality than usual. As a result, in such a semiconductor device, the electrodes are usually made of aluminum. Schottky barriers at the aluminum / silicon interface of semiconductors have been actively studied. In particular, Arizumi et al., Jap. J. Appl. Phys., 7,870, 1968.
Discloses controlling barrier height by alloying different metals, and Archer and Atalla, Ann.N.
Y. Acad. Sci., 101, 697, 1963 discloses controlling the barrier height by introducing an oxide interface layer. Furthermore, Shannon, Solid State Electronics, 19,537,1976
Proposes to vary the barrier height by introducing a highly doped surface layer fabricated by ion implantation. U.S. Pat. No. 5,471,067 discloses the use of a layered (multi-quantum well) p-type semiconductor (ZnTe / ZnSe) for the contact region of a II-VI laser diode to control the barrier height. FIG. 11 shows the p-type Z of the laser diode.
FIG. 5 is an energy band diagram near the interface between the nSe electrode layer 125 and the p-type ZnTe electrode layer 126, where the limiting levels resonate across the structure, allowing good transport of vacancies through the structure. The effect of the intermediate multiple quantum layer 127 including the arrangement of the quantum wells 128 whose design width is changed to obtain is shown.

If the injection mechanism is thermionic,
The fact that the energy band offset between the electrode and the semiconductor material allows the carrier to gain substantially forward momentum into the semiconductor is also from semiconductor contact theory, for example, Rh
oderick et al., Metal-Semiconductor Contacts, Clarendon
Press, Oxford, 1988. In this phenomenon, known as the jet effect, the carrier trajectories occur mainly in the forward direction, but this effect is only obtained if the interface between the electrode of the device and the active area is very good. Therefore, the same effect cannot be obtained at the interface between the metal electrode and the organic light emitting substance.

It is an object of the present invention to provide an improved organic optoelectronic device. More specifically, it is an object of the present invention to provide a stable organic optoelectronic device that can obtain good carrier injection efficiency and has reproducibility.

[0012]

The organic optoelectronic device of the present invention comprises an organic layer disposed between a positive electrode and a negative electrode, wherein at least one of the electrodes comprises a cathode. A first component, which has a relatively high work function in some cases, or has a relatively low work function when the electrode comprises an anode; and a relatively low work function when the electrode comprises a cathode. Or a material having a second composition, wherein the material has a relatively high work function when the electrode constitutes the anode, and wherein the material comprises: at the interface between the electrode and the organic layer A relatively high percentage of the first component and a relatively low percentage of the second component in the adjacent first region; a second region at a first distance into the electrode from the interface. A relatively high proportion of the second construct and the comparative A lower proportion of the first composition; and a relatively higher proportion of the first composition in a third region at a second distance greater than the first distance from the interface into the electrode. The relative proportion of the first and second components is graded in a direction extending laterally to the interface within the material of the electrode so as to have a relatively low proportion of the second component. Can be

In a preferred embodiment, the relative proportions of the first and second components are substantially linearly sloped between the first region and the second region. Can be

[0014] In a preferred embodiment, the first and second components include a first region and an intermediate region between the first region and the second region. A gradient of one and a gradient between the intermediate region and the second region at a second ratio less than the first ratio.

In a preferred embodiment, the relative proportions of the first and second components are substantially linearly sloped between the second region and the third region. Can be

In a preferred embodiment, the electrode comprises a thin layer with a high work function to prevent carriers from passing from the organic layer into the electrode.

In a preferred embodiment, the thin layer is made of a material having a wide band gap so that carriers passing from the electrode into the organic layer form a barrier for tunneling.

In a preferred embodiment, the electrode includes at least one barrier layer to limit the diffusion of mobile atoms inside the electrode.

In a preferred embodiment, the electrodes are 2
One barrier layer.

In a preferred embodiment, the barrier layer is formed of a material effective to prevent diffusion, the material comprising:
It is selected from the group consisting of titanium, molybdenum, nickel, palladium, and mixtures thereof.

In a preferred embodiment, the barrier layer is an inorganic layer through which electric charges can pass through by tunneling, and the inorganic layer is selected from the group consisting of SiO ₂ , Si ₃ N ₄ , LiF, and Al ₂ O _3. Selected.

In a preferred embodiment, the thickness of the barrier layer is approximately equal to the mean free path of the material forming the barrier layer.

In a preferred embodiment, the thickness of the barrier layer is 1 nm to 10 nm.

[0024] In a preferred embodiment, the first component is aluminum and the second component is lithium.

In a preferred embodiment, the first component is silver and the second component is magnesium.

The method for producing an organic optoelectronic device of the present invention is a method for producing an organic optoelectronic device containing an organic layer disposed between a positive electrode and a negative electrode, wherein at least one of the electrodes is provided. A: a first component, wherein the electrode has a relatively high work function when forming an anode, and has a relatively low work function when forming an anode; and Forming by depositing a material having a second composition having a relatively low work function when configured and having a relatively high work function when the electrode comprises an anode. Wherein the material comprises: in a first region proximate the interface between the electrode and the organic layer, a relatively high proportion of the first composition and a relatively low proportion of the second composition; Object; a first distance from the interface into the electrode. A relatively high proportion of the second composition and a relatively low proportion of the first composition; and a second greater than a first distance from the interface into the electrode. In a third region at a distance of the first and second components relative to each other so as to have a relatively high percentage of the first component and a relatively low percentage of the second component. A percentage is formed inside the electrode,
A gradient can be provided in a direction extending laterally to the interface.

In a preferred embodiment, in the step of forming at least one of the electrodes, the electrode is connected to the first and second components while simultaneously depositing the first and second components. Is formed by changing the relative ratio of the above.

In a preferred embodiment, the step of forming at least one of the electrodes includes the step of forming the first electrodes having different thicknesses.
Alternately depositing a sub-layer of the second component having a thickness different from that of the second component, and annealing the deposited sub-layer, whereby the first sub-layer is formed. And the second component are alloyed together, and the relative proportions of the first and second components are graded in the required manner.

In a preferred embodiment, the step of forming at least one of the electrodes further includes the step of forming at least one barrier layer, whereby the transfer of atoms capable of migrating atoms inside the electrode is performed. Limit spread.

The operation of the present invention will be described below.

In the organic optoelectronic device of the present invention, at least one electrode is made of a substance having the above-described first and second components, and the substance comprises: A relatively high percentage of the first component and a relatively low percentage of the second component in a first region proximate the interface; a second region at a first distance into the electrode from the interface. A relatively high proportion of the second composition and a relatively low proportion of the first composition; and in a third region at a second distance greater than the first distance into the electrode from the interface, The relative proportions of the first and second constituents are within the material of the electrode to the interface so as to have a relatively high proportion of the first constituent and a relatively low proportion of the second constituent. Gradient can be applied in the lateral direction, so good carrier injection effect It is obtained, and is reproducible,
And a stable device is provided.

The reason for this is that, as described above, the alloy composition of the composition is converted from a composition containing a substance having a high work function at a high concentration on the electrode surface and a substance containing a low work function at a low concentration on the electrode surface. Since the composition containing a substance having a high function at a low concentration and a substance having a low work function at a high concentration is gradually changed, an energy band offset required for carrier injection can be created. further,
Towards the interface with the organic material, the composition is inversely graded to increase the concentration of high work function materials and decrease the concentration of low work function materials, thereby creating a potential gradient across the electrode. Can be made. In this way, by controlling the energy band offset height and the potential gradient across the negative electrode of this type of device, it is possible to increase the velocity of the injected carriers passing through the electrode. Thus, the carriers are strongly deflected from the electrode with the momentum of the forward component, which is preferred for transporting carriers across the organic layer, rather than simply diffusing and transporting inside the charge transport layer. Leave. This effect is similar to the conventional organic E
It does not occur for L devices. This is because in such devices, the quality of the interface between the cathode and the organic material is poor, as already described herein.
Further, according to the organic optoelectronic device of the present invention, such a gradient at the interface can reduce the quantum mechanical reflection of carriers.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention are shown in FIGS.
This will be described with reference to FIG.

Each of these embodiments includes an organic EL device of the type that includes a layer of an organic luminescent material disposed between a positive electrode and a negative electrode. As shown in FIG. 1, these organic EL devices 1 include an organic light emitting layer 2 disposed between a positive electrode 3 and a negative electrode 4, and a voltage is applied to the organic light emitting layer 2 between the electrodes. Applies to emit light if
This layer 2 includes a hole transport layer 5 adjacent to the positive electrode 3 and an electron transport layer 6 adjacent to the negative electrode 104. This organic E
The basic configuration of the L device is substantially the same as that described with reference to FIG. Further, one of the electrodes of each embodiment,
Or each has a graded composition to obtain good carrier injection efficiency as well as to be reproducible and stable. In principle, such a gradient can be applied to either the positive or negative electrode,
The description below relates to the application of such a gradient to the negative electrode. This is because the negative electrode is an electrode that experiences major contact problems in conventional organic EL devices. The required gradient is the alloy composition of the composition,
From a composition containing a high work function substance at a high concentration on the electrode surface and a low work function substance at a low concentration, a composition containing a high work function substance at a low concentration and a low work function substance is used. Increasingly increasing the composition containing the high concentration to create the offset required for carrier injection, then increasing the concentration of the high work function material toward the interface with the organic material, It can be obtained by applying a reverse gradient to reduce the concentration of the substance. Conversely, the grading can also be applied in the case of the positive electrode.

By controlling the energy band offset height and the potential gradient across the negative electrode of this type of device, it is possible to increase the velocity of the injected carriers passing through the electrode. Thus, the carriers are strongly deflected from the electrode with the momentum of the forward component, which is preferred for transporting carriers across the organic layer, rather than simply diffusing and transporting inside the charge transport layer. Leave. This effect is similar to the conventional organic E
It does not occur for L devices. This is because in such devices, the quality of the interface between the cathode and the organic material is poor, as already described herein.
In addition, the quantum mechanical reflection of the carriers is reduced by such a gradient at the interface.

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

FIG. 2 is an energy band diagram of a general embodiment of the present invention. In this embodiment, the composition of the negative electrode 9 from the electrode surface in the z direction toward the interface 11 between the negative electrode 9 and the organic substance 10 will be considered. This material contains an alloy such as LiAl, which on the outer surface consists mainly of the high work function material (Al), but is graded towards the composition and the curve 15
In the highest part 14 of the material, mainly the material (Li)
Consists of The gradient starts at a distance of 1500-2000 ° from the interface 11 and continues with increasing x in the direction of arrow 12. Here, the gradient is that of Li _x Al _{1 -x} . This creates an energy offset required for carrier injection. Distance of mean free path from interface 11 (about 70
At a distance of Å150 °), the gradient is reversed. Therefore,
The composition has a decreasing x, as indicated by arrow 13, gradually increasing from a composition consisting mainly of low work function material at the top 14 to a composition consisting mainly of high work function material at the interface 11. Can be attached. The cathode is MgA
A similar configuration can usually be provided for a g alloy.

In the first embodiment of the method for manufacturing an organic EL device according to the present invention, a glass substrate is made of ITO.
Layer (which constitutes the positive electrode), and then a Å1Å-thick hole transport layer of 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane, with Evaporated with a filament and vacuum deposited on ITO. Next, an electron transport layer having a thickness of about 750 ° was deposited on the hole transport layer by vacuum deposition of aluminum trisoxine, again evaporating the material from a quartz boat with a tungsten filament. A negative electrode, approximately 4000 ° thick, was made from a MgAg alloy and then deposited through a shadow mask with 0.1 cm ² openings defining the active area of the device over the electron transport layer. The components of the alloy were deposited using two separate boats: a tantalum boat with a perforated cover for Mg evaporation and an open tantalum boat for Ag evaporation. The relative rates of evaporation were independently controlled using current and temperature so that the relative composition of the constituents gradually changed as the cathode grew from the two boats, and Mg and Ag were evaporated together. I let it.

In a second embodiment of the method of manufacturing an organic EL device of the present invention, a positive electrode formed of ITO is deposited on a glass substrate, and then a hole transporting organic layer formed of aluminum trisoxine is formed. Was deposited on the ITO layer, followed by an electron transporting organic layer of N, N'-bis (3-methylphenyl) -1,1'biphenyl-4,4'-dimine (TPD). Next, the previously prepared AlLi alloy matrix (L
Prepare the first evaporation boat and another evaporation boat by itself for i or Al, and change the current and temperature to control the evaporation rate so as to gradient the relative composition of Al and Li across the negative electrode The negative electrode was deposited on the electron transport layer.

FIG. 3 is an energy band diagram showing two stages in the manufacturing method of the present invention in which the embodiment of FIG. 2 is modified. The energy level is represented by a solid line 16 before the annealing step and a broken line 17 after the annealing step.
In this case, the negative electrode 9 ′ comprises a sub-layer 18 of a material having a high work function (for example, Al or Ag) and a sub-layer 19 of a material having a low work function (for example, Li or Mg), which corresponds to FIG. It is made by depositing a number of distinct layers of alternating materials, as shown by an energy level diagram. In each case, the width 20 of each sub-layer 18 or 19
Or 21 changes such that the width 20 first decreases in the direction toward the interface 11 and then increases, whereas the width 21 increases first in the direction toward the interface 11 and then decreases.
Subsequently, this is annealed. In this annealing step, the material of sublayers 18 and 19 has been alloyed and effectively graded, as shown by the dashed line 17 having a profile similar to the energy band profile of the embodiment of FIG. Make potential. Each of the sub-layers 18 and 19 may be formed of a pure construction of a low or high work function metal, or an alloy of such a metal. This embodiment can be applied to negative electrodes made of constituents that do not alloy well but alloy only at certain concentrations. If the sublayers 18 and 19 are sufficiently thin, they act as quantum wells and barriers (where the limiting levels of the quantum wells follow the gradient profile required for electrons to jump from well to well). It may be possible to design them.

FIG. 4 is an energy band diagram according to another embodiment of the present invention. In this embodiment, the composition gradient of the negative electrode is more complex, changing the potential near the interface 11 non-linearly. This is the area of the negative electrode (where the composition is graded at the interface 11 from a concentration consisting mainly of low work function constituents to a concentration mainly consisting of high work function constituents).
Affect. In this region, the composition is represented by curve 26
From the distance of 100-400 ° from the interface 11, x is reduced at a first rate, as shown by the portion 25 of the interface 11, and then the first x By decreasing x at a second rate that is greater than the rate of Because the energy and momentum relaxation paths are different,
To increase the efficiency of electron injection into the organic material 10, such a two-step gradient can be used. Organic substance 1
The injection of high-energy electrons into zero is performed by the arrow 24 in FIG.
Indicated by

At this point, the total energy of the incident electrons can be controlled by the width of the composition gradient. If the width of the composition gradient is short, electrons can be injected with an energy that matches the energy peak of the barrier because the electrons scatter and do not have enough time to equilibrate with the lattice. on the other hand,
If the gradient extends over a greater distance, the incident electrons are equilibrated with the lattice and their energy becomes the energy of the energy profile of the electrode. Further, by changing the composition during the growth of the cathode to provide different energy and momentum distributions to the injected electrons due to the non-equilibrium effect, for example, two gradients may be used.
Like a profile containing two parts 25 and 27,
Profiles with different slopes can be obtained.

Any embodiment in which the gradient profile includes an interface inside the material to be gradient (eg, portion 25)
In the embodiment of FIG. 4 with an interface between the interface and 27), if the dopant is needed for any purpose, this is also advantageous for incorporating the dopant into the interface. In n-type and p-type semiconductor devices, dopants are incorporated to determine charge carriers. Dopants are more easily incorporated at the interface where size changes and the like are better applied.

The distance that electrons can travel before they scatter and move to equilibrium with the lattice is estimated from the mean free path.
For example, MWAshcroft and NDMermin, Solid State P
hysics HRW International Edition, Holt, Rinehart and Winston, 1976, p. 52. The energy and momentum relaxation paths may be associated with a mean free path. For metals, the mean free path is defined as a result of the Fermi velocity and the scattering velocity. At a temperature of 273 K, the following mean free path is obtained for the following metals: Li 114 {Ag 556} Mg 167} Al 161}.

FIG. 5 is an energy band diagram in still another embodiment of the present invention. In this embodiment, a thin layer of a high work function material, or a material that creates a barrier for vacancy transport, is introduced near the interface 11, as shown by the corresponding energy level 30 in FIG. . This thin layer creates a potential barrier to injected electrons and tunnels as indicated by arrow 31. The thin layer then prevents the passage of holes from the organic material 10 into the negative electrode, as shown by arrow 32, by creating an energy barrier for such holes. If layer 30 is a high work function metal, this forms an effective quantum well in the conduction band of the electrons. If layer 30 is sufficiently thin (eg, 10-30 °), few electrons will be trapped in layer 30. If layer 30 is formed of a wide bandgap semiconductor, this forms a thin tunneling barrier for electrons, which balances the energy of the injected electrons but reduces the injection efficiency. I will.

FIG. 6 is an energy band diagram of still another embodiment of the present invention. In this embodiment, FIG.
As indicated by the corresponding energy levels 35 and 36 therein, two barrier layers are added to reduce the diffusion of mobile species (eg, lithium atoms). The barrier layer is
It may be formed of any material effective to prevent such diffusion. Such materials include, for example, titanium,
Molybdenum, nickel, palladium and the like can be mentioned. Further, the barrier layer may be any suitable layer through which charges can tunnel through. For example, S
_{iO 2, Si 3 N 4,} LiF, include Al ₂ O ₃ or the like
(Hung, LS, Tang, CW and Mason, MG, Appl.Phys.Let
t., 70, 152-155, (1997)). Each layer typically has the essential features of the potential profile to be retained, while still obtaining the required interference,
It has a width between 10 and 100 °, preferably between 50 and 100 °.
The work function of the barrier layer is not particularly important because the layer is thin.
It is possible to configure in each layer a barrier for electrons to tunnel, or alternatively to configure a quantum well in each layer that has a high limiting level, so that electrons are hardly trapped in the quantum well.

Such an organic EL device according to the present invention controls the forward momentum of electrons injected into the organic luminescent material from the negative electrode in a manner favorable for the transport of electrons across the organic material, and thereby, There is an advantage in providing good injection efficiency while providing a stable and reproducible interface between the electrode and the organic material. The barrier height is effectively determined only by the composition of the cathode electrode material and the smoothness of the composition gradient, since the barrier height is displaced from the interface and is not affected by physics such as interface surface states and impurities. . If the gradient is shallow near the barrier to create a thick triangular barrier, electrons are injected by a thermionic emission process. This process must be more reproducible in the current-voltage plot. In addition to this, the quantum mechanical considerations of the electrons are reduced by gradients at the interface.

Since the peak potential is not subject to the interference scattering effect, the electrons undergo the jet effect described above, and their forward momentum exceeds the barrier, which acts like an electric field that projects the electrons forward. Increase by passing through. Ignoring the electric field provided by the gradient, the electrons in the negative electrode will have energy and average velocity √ (3
It has an isotropic distribution of momentum with kT / m ^* ). As the electrons pass through the barrier, they gain an amount of energy that corresponds to the energy difference between the top of the barrier and the organic conductor. Since momentum parallel to the interface is preserved, the momentum change of the electron occurs only in the z direction. Therefore, the electron orbit in an organic substance has a forward peak, and the half-angle tan ^-1 [(3 kT / m ^* )
/ vf] cones or jets.
Here, k is the Boltzmann constant, T is the temperature, m ^* is the effective mass of the carrier, and vf is the Fermi velocity.

When the electron injection energy is adjusted to correspond to the narrow transport band of the organic substance, the transport of electrons in the organic substance is promoted. However, if the organic material is so disordered that such a transport band does not exist, the electron injection energy can be further adjusted to optimize the transport of electrons through the organic material. However, in this case, the advantage of the forward momentum of the electrons becomes less clear.

The Li: Al and Mg: Ag alloy materials described above are a preferred combination of low work function and high work function materials for use in the devices of the present invention. However, SMSze, Physics of Semiconductor Dev
As referenced in the work function table provided by ices, John Wiley & Sons, 1981, there can be many other combinations of such materials that can be used in the devices of the present invention. However, the alloy material chosen needs to be able to maintain a graded profile across the contact area. Cathode performance is degraded if the constituents of the alloy material involved mix or diffuse after manufacture or under operating conditions (perhaps under the influence of high electric fields across the device). This is a problem when Li is used for the cathode material. However, when the cathode material contains Mg, such a problem is not expected to occur. In certain applications, it may be preferred that lightweight, mobile, diffusible atoms be included in the cathodic material.
In such cases, this may be advantageous to incorporate means for stopping diffusion of the mobile species, such as the incorporation of a barrier layer as described above.

A further advantage of the present invention is that the total carrier injection energy into the organic material is controlled by controlling the magnitude of the energy band offset at the interface between the organic material and the negative electrode, thereby reducing the material used. It can be optimally prepared. Because, excessive implantation energy can activate external processes that reduce carrier transport and / or reduce materials. On the other hand, when the carrier injection energy is too small, the carriers are localized. Because the career,
This is because they do not have enough energy to escape the local minimum or to exceed the activation energy.

A further advantage of the present invention is that the energy barrier is removed from the interface. This makes the barrier height less sensitive to interface and potential effects. As a result, carrier injection is reproducible between different devices. In addition, the highly reactive material of the cathode, which creates a high energy barrier, is effectively completely encapsulated by the area of the cathode that is largely composed of less reactive components. A less reactive substance is typically more reactive than a configuration in which a region of predominantly reactive material contacts, on one side, a region of predominantly less reactive material.

[0053]

According to the present invention, it is possible to provide a stable organic optoelectronic device having good carrier injection efficiency, reproducibility, and a method for manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a schematic view of an organic EL device of the present invention.

FIG. 2 is an energy band diagram at an interface between a negative electrode and an organic material of the EL device according to one embodiment of the present invention.

FIG. 3 is an energy band diagram at an interface between a cathode and an organic material of an EL device according to another embodiment of the present invention.

FIG. 4 is an energy band diagram at an interface between a negative electrode and an organic material of an EL device according to another embodiment of the present invention.

FIG. 5 is an energy band diagram at an interface between a negative electrode and an organic material of an EL device according to another embodiment of the present invention.

FIG. 6 is an energy band diagram at an interface between a negative electrode and an organic substance of an EL device according to another embodiment of the present invention.

FIG. 7 is a schematic view of a conventional organic EL device.

FIG. 8 is an energy band diagram showing energy band offsets for different cathode materials.

FIG. 9 is an energy band diagram at an interface between a cathode and an organic material of an EL device.

FIG. 10 is an energy band diagram at an interface between a cathode and an organic material of an EL device.

FIG. 11 is an energy band diagram of a metal / semiconductor interface of a semiconductor laser diode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic EL device 2 Organic light emitting layer 3 Positive electrode 4 Negative electrode 5 Vacancy transport layer 6 Electron transport layer 9 Electrode (negative electrode) 10 Organic substance 11 Interface

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Harald Reinhard Bock UK 4 Ox4 3B Oxford, Howard Street 54

Claims (18)

[Claims] An organic optoelectronic device comprising an organic layer disposed between a positive electrode and a negative electrode, wherein at least one of the electrodes comprises: a relatively high work when the electrode comprises a cathode. A first composition having a function or having a relatively low work function when the electrode comprises the anode;
And a material having a second composition, wherein the electrode has a relatively low work function when forming an anode, or has a relatively high work function when forming an anode. A substance: in a first region proximate an interface between the electrode and the organic layer, a relatively high proportion of the first composition and a relatively low proportion of the second composition; A relatively high percentage of the second composition and a relatively low percentage of the first composition in a second region at a first distance from the interface; and from the interface into the electrode. A third at a second distance greater than the first distance
In the region of the above, so as to have a relatively high proportion of the first constituent and a relatively low proportion of the second constituent,
An organic optoelectronic device wherein a relative proportion of the first and second components is graded in a direction extending laterally to the interface within the material of the electrode. 2. The method of claim 1, wherein the relative proportions of the first and second components are ramped substantially linearly between the first region and the second region. A device as described in. 3. The method according to claim 1, wherein the first and second components are sloped at a first ratio between the first region and an intermediate region between the first region and the second region. The device of claim 1, wherein the device is graded and is ramped between the intermediate region and the second region at a second ratio that is less than a first ratio. 4. The method of claim 1, wherein the relative proportions of the first and second components are ramped substantially linearly between the second region and the third region. A device according to any of claims 1 to 3. 5. The device according to claim 1, wherein the electrode comprises a thin layer with a high work function to prevent carriers from passing from the organic layer into the electrode. 6. The thin layer is made of a wide bandgap material to form a barrier through which carriers passing from the electrode into the organic layer tunnel.
A device as described in. 7. The device according to claim 1, wherein the electrode comprises at least one barrier layer to limit the diffusion of mobile atoms inside the electrode. 8. The device according to claim 7, wherein said electrode comprises two barrier layers. 9. The barrier layer of claim 7, wherein the barrier layer is formed of a material effective to prevent diffusion, wherein the material is selected from the group consisting of titanium, molybdenum, nickel, palladium, and mixtures thereof. 9. The device according to 8. 10. The barrier layer is an inorganic layer through which charges can pass by tunneling, and the inorganic layer is made of SiO ₂ , Si ₃ N.
_4, LiF, and Al ₂ is selected from the group consisting of O _3, device according to claim 7 or 8. 11. The barrier layer according to claim 7, wherein the thickness of the barrier layer is approximately equal to the mean free path of the material forming the barrier layer.
0. The device according to any of 0. 12. The device according to claim 7, wherein the thickness of the barrier layer is 1 nm to 10 nm. 13. The method according to claim 1, wherein the first component is aluminum and the second component is lithium.
A device according to any of claims 1 to 12. 14. The method according to claim 1, wherein the first constituent is silver and the second constituent is magnesium.
3. The device according to any one of 2. 15. A method of manufacturing an organic optoelectronic device comprising an organic layer disposed between a positive electrode and a negative electrode, wherein at least one of said electrodes comprises: a cathode. A first component having a relatively high work function when the electrode comprises an anode, and a relatively low work function when the electrode comprises a cathode; And forming by depositing a material having a second composition, wherein the electrode has a relatively high work function when composing the anode.
This allows the substance to: in a first region close to the interface between the electrode and the organic layer, a relatively high proportion of the first composition and a relatively low proportion of the second composition A relatively high percentage of the second component and a relatively low percentage of the first component in a second region at a first distance into the electrode from the interface; In a third region at a second distance greater than the first distance in the electrode, having a relatively high percentage of the first component and a relatively low percentage of the second component. , The first
And a relative proportion of the second component is graded in a direction extending laterally to the interface within the formed electrode. 16. The step of forming at least one of said electrodes, wherein said electrode is configured to adjust said relative proportion of said first and second components while simultaneously depositing said first and second components. 2. The method according to claim 1, wherein the first member is formed by changing.
5. The method according to 5. 17. The method of forming at least one of the electrodes, comprising alternately depositing sublayers of the first component having different thicknesses and sublayers of the second component having different thicknesses. And annealing the deposited sub-layer, whereby the first and second components are alloyed together and the relative proportions of the first and second components are Is graded in the required manner.
The method described in. 18. The method of claim 18, wherein forming at least one of the electrodes further comprises forming at least one barrier layer, thereby limiting diffusion of mobile atoms within the electrode. The method according to claim 15.