JP4842289B2 - Hole injection electrode and organic EL element using the electrode - Google Patents

Description

The present invention relates to a hole injection electrode capable of hole injection at a low voltage with a small hole injection barrier with respect to an organic semiconductor, and an organic EL device using the electrode.

Currently, research and development of electronic devices using organic semiconductors, in particular organic EL elements, are being actively conducted. Originally, organic semiconductors do not have carriers (electrons and holes) responsible for electrical conduction,
An electrical insulator with very low electrical conduction. By injecting electrons or holes into such an electrical insulator through electrodes, the characteristics of a semiconductor appear. Organic thin film transistor and organic E
In an L element or the like, an electrode for injecting electrons is called a cathode, and an electrode for injecting holes is called an anode.

Electrons injected from the cathode are the lowest energy orbits in the organic semiconductor (lowest orbital: L
The holes injected from the anode occupy the highest energy occupied orbit (highest occupied orbit: HOMO), and the electrons and holes move in the organic semiconductor material on the LUMO and HOMO.
Electrons are sequentially occupied from the lowest energy level in the material, and the occupied level with the largest energy is called the Fermi level.

As can be seen from the schematic diagram of the energy levels of the organic semiconductor and electrode shown in FIG. 10, in order to inject holes into the organic semiconductor at a low voltage, the Fermi level needs to be equal to or deeper than HOMO. It is. The energy level at which electrons leave the solid is called “vacuum level”, and the energy difference between “vacuum level” and “Fermi level” is called “work function”. Most organic semiconductor HOMOs used in practical devices are at an energy position that is 4.6 to 6.0 eV deep from the vacuum level. Therefore, it is desirable that the anode material for practical devices has a work function equivalent to or better than 4.6 to 6.0 eV. .

An organic EL element that is most practically used among electronic devices using an organic semiconductor has a structure (cathode / light-emitting layer / anode) in which an organic semiconductor to be a light-emitting layer is sandwiched between a cathode and an anode. In practical devices, a structure in which a hole injection layer (for example, CuPc; copper phthalocyanine) and a hole transport layer (for example, TPD: triphenyldiamine derivative) are sandwiched between the anode and the light emitting layer in order to increase carrier injection efficiency. Or a structure in which an electron injection layer and an electron transport layer are sandwiched between a cathode and a light emitting layer (cathode / electron injection layer / electron transport layer / light emitting layer / hole transport layer / hole injection layer / anode).
And often.

An organic EL element has a structure in which two or more light emitting layers are provided and an intermediate electrode layer is interposed therebetween (Patent Document 1). The hole transport layer facilitates hole injection into the light emitting layer,
It is a layer that stably transports holes from the hole injection electrode and blocks electrons, but as an inorganic hole transport layer, transition metals such as titanium, zirconium, hafnium, vanadium, tantalum, niobium, molybdenum, and tungsten, It is known to use dichalcogenides or monochalcogenides of non-transition metals such as tin (Patent Document 2).

In the organic EL element, since it is necessary to extract light to the outside, at least one of the anode and the cathode sandwiching the light emitting layer needs to be transparent to visible light. The element structure is divided into a “top emission type structure” shown in FIG. 8 and a “bottom emission type structure” shown in FIG. 9 depending on whether the light extraction surface is the element surface or the substrate surface.

Hole injection electrode (anode) materials such as aluminum, gold, silver, nickel, palladium, platinum, etc., high work function (4 eV or more) metals, conductive compounds, halogenated metals such as copper iodide, carbon black, etc. In any structure, In ₂ O ₃ : Sn (ITO) in which tin is added to indium oxide is used as a practical element. This is because ITO has high transmittance in the visible region and high electrical conductivity exceeding 10 ³ S / cm. ITO's work function is about 4.
The work function can be increased to 4.8 to 5.3 eV by performing surface oxidation treatment using oxygen plasma or UV ozone.

However, since ITO is an electron-conducting (n-type) semiconductor, if this surface oxidation treatment is performed, IT
The carrier (electron) concentration on the O outermost surface decreases, the electrical resistance increases, and the contact resistance between the anode and the hole injection layer increases.

Also, since the ITO surface layer has irregularities and the contact resistance at the interface with the organic semiconductor is large,
Metals such as gold, nickel, manganese, iridium, molybdenum, palladium, and platinum, and MoO ₃ , V ₂ O ₅ , NiO with a thickness of 1 to 3 nm so as not to impair the light transmittance at the interface between the ITO electrode and the organic semiconductor
Or insert a p-type conductive metal oxide ultrathin film (Patent Document 3), or a layer thickness of 3 to 100 nm
By applying a certain degree of organic polymer (Patent Document 4), the contact resistance is reduced and the hole injection efficiency is increased. Such an ultrathin film that reduces the contact resistance at the interface between the anode and the organic semiconductor and increases the hole injection efficiency is called an “anode buffer layer”.

On the other hand, if a p-type degenerate semiconductor is used as the hole injection electrode, it is considered that the hole concentration does not decrease even if the surface treatment is performed, and therefore it is expected that an increase in contact resistance can be avoided. The present inventors have compared the NPB that is a hole transport layer with LaCuOSe, which is a p-type semiconductor, to a ratio of 0.2.
It was reported that a low hole injection barrier of 3 eV can be realized (Non-patent Document 2).

In the “bottom emission type structure” organic EL element, a transparent anode ITO is formed on a substrate, and an organic element is formed thereon. In this structure, since the organic EL element driving thin film transistor formed on the substrate is opaque, there is a problem that an area where light can be extracted is limited.

In order to solve this problem, an organic EL element having a “top emission structure” in which light is extracted from a surface (front surface) opposite to the substrate has been developed. In the organic EL device having such a structure, the influence of the drive circuit can be eliminated by setting the light emitting surface to the front surface of the device, but it is necessary to use a transparent cathode on the front surface in order to efficiently extract light to the outside. Generally, ITO is used for the transparent cathode.

When the anode is formed on the substrate side in the top emission type structure, since the material used as the anode must have a high reflectance, Al, Ag, or an alloy thereof is used (Patent Documents 5 and 6). ). If a light reflective electrode such as Ag or Al is used for the anode, the light emission efficiency can be expected to be improved, but it is difficult to inject holes directly into the organic layer 13 from Ag or Al. Causes an increase in operating voltage.

As another method of the top emission type structure, a cathode can be produced on a substrate surface, and a transparent anode using a semiconductor material such as ITO can be used as a front electrode. However, when ITO is used as the front electrode as the anode, the ITO anode / organic semiconductor interface cannot be oxidized in principle, so that the hole injection barrier at the interface increases and the hole injection efficiency decreases. .

When ITO is used as the front electrode, the substrate temperature is preferably set to 200 ° C. or higher in order to obtain a good ITO film. However, the organic EL element is composed of an organic substance and is 200 ° C.
Then, due to a change in the layer structure or the like, the element deteriorates, and when the temperature exceeds 300 ° C., a component that easily volatilizes evaporates and the compound decomposes. Therefore, ITO as a front electrode
It is difficult to form a film on the organic semiconductor layer. In order to form the front electrode without damaging the organic semiconductor layer by heating, the temperature is low (from room temperature to about 300 ° C., preferably from room temperature to 200 ° C.
It is indispensable that the film can be formed within a range of less than ° C.

Y. Park, V. Choong, Y. Gao, B. R. Hsieh, and C. W. Tang, Appl. Phys. Lett. 1996, 68, 2699-2701 Hiroshi Yanagi et al., "Electron structure analysis of LaCuOSe interface and formation of low hole injection barrier by photoelectron spectroscopy", Proceedings of the 54th Joint Conference on Applied Physics, 28a-SK-3, March 27, 2007 WO2005 / 009087 Japanese translation of PCT publication No. 2004-527093 JP 2007-005784 A JP 2004-228002 A JP 2005-056848 A JP 2007-220351 A

As a hole injection electrode, a film can be formed on an organic semiconductor layer, and a good interface can be formed with the organic semiconductor layer without performing surface oxidation after film formation, and hole injection can be performed at a low voltage. There is a need for electrode materials. In the present invention, an object is to provide an electrode material having a large work function capable of hole injection at a low voltage.
It aims at providing the electrode material which can be formed into the following film. Furthermore, it is an object to provide a material particularly suitable as a front electrode of an organic EL element having a top emission type structure.

The inventor has used the formula Cu _2-x Ch (where Ch is S
, Se, or Te chalcogen element, at least one, having a composition represented by 0 <x <0.5),
It has been found that the above problem can be solved by using a p-type degenerate semiconductor made of a copper chalcogenide having a work function of 4.6 eV or more. This hole injection electrode material is suitable not only as an electrode body but also as a material for an intermediate electrode layer having a hole injection function and a material for an anode buffer layer.

Specifically, the present inventors have found that a copper chalcogenide thin film having a composition represented by the formula Cu _2-x Ch formed at a low temperature of room temperature to about 300 ° C. is a p-type semiconductor, and 10 ² S / cm It has been found that it exhibits super high electrical conductivity and has a large work function of about 4.6 to 5.0 eV.

Furthermore, the chalcogenide thin film can have a work function increased from 6.0 to 7.0 eV by surface oxidation treatment such as oxygen plasma treatment, and the hole injection voltage can be lowered. This oxidation treatment does not affect the hole transport properties, and high hole transport properties are maintained after the oxidation treatment.
Therefore, by forming this p-type semiconductor layer as a hole injection electrode layer on the substrate side, surface oxidizing treatment, and forming an organic semiconductor on this p-type semiconductor layer subjected to surface oxidation treatment, further lower hole An interface having an injection barrier can be formed, and holes can be injected into the organic semiconductor at a low voltage.

That is, the present invention relates to the formula (1) Cu _{2 -x} Ch (Ch is at least one of chalcogen elements of S, Se, Te), x indicates the amount of monovalent copper deficiency, 0.2-0. 4 ) A hole injection electrode for an organic semiconductor, characterized in that a semiconductor compound layer having a composition represented by 4 ) and having a work function of 4.6 eV or more and exhibiting p-type degenerate electrical conductivity is used as an electrode.
In addition, the present invention provides at least one of the chalcogen elements of formula (2): Cu _2-x Ch (Ch is S, Se, Te)
Species, x represents a deficiency of monovalent copper , has a composition represented by 0.2 to 0.4 ), and has a work function of
A hole injection electrode into an organic semiconductor, wherein a semiconductor compound layer having a p-type degenerate electrical conductivity at 4.6 eV or more is laminated as an anode buffer layer.

The present invention is also (3) the hole injection electrode described in (1) or (2) above, wherein the semiconductor compound layer is formed at room temperature.
In addition, the present invention provides (4) the semiconductor compound layer described above in (1) or (2), wherein the surface of the semiconductor compound layer is subjected to oxygen plasma treatment to have a work function of 6.0 or more. Electrodes.

Moreover, this invention is (5) the organic EL element using the hole injection electrode as described in any one of said (1)-(4).
The present invention also provides (6) using the hole injection electrode described in any of (1) to (4) above, and using [Ca ₂₄ Al ₂₈ O ₆₄ ] ⁴⁺ (e ⁻ ) ₄ electride as a cathode. It is a top emission type organic EL element characterized by being used.

The present invention provides a material capable of injecting holes at a low voltage into an organic element of an electronic device made of an organic semiconductor, and realizing a low-voltage driven organic semiconductor element. Further, the present invention provides a material suitable as a hole injection electrode capable of forming an organic EL element at room temperature, particularly as a hole injection electrode suitable as a front electrode of an organic EL element having a top emission type structure. Further, not only the material of the anode body, but also a material suitable as an intermediate electrode and an anode buffer layer that increase the hole injection efficiency is provided.

The material of the hole injection electrode to the organic semiconductor of the present invention is a composition represented by the formula Cu _2-x Ch (Ch is at least one of chalcogen elements of S, Se, Te, 0 <x <0.5). Have Copper chalcogenides include copper sulfide (I) (Cu ₂ S), copper sulfide (II) (CuS), copper selenide (I) (Cu ₂ Se), copper selenide (II) (CuSe), copper telluride (I) (Cu ₂ Te), copper telluride (II) (CuTe). That is, the copper chalcogenide may be monovalent or divalent in copper, but _{x in} the formula Cu _2-x Ch indicates the amount of monovalent copper deficiency. The hole concentration in Cu _2-x Ch increases with increasing x, but x is 0
. When it is 5 or more, the valence of Cu becomes divalent, and the decrease in mobility becomes remarkable. When x is 0, that is, Cu ₂ Ch, the hole concentration is small and the electric conductivity is small. A more preferable range of x is 0.2 to 0.4. Copper selenide or telluride is larger than equivalent copper sulfide
Cu ⁺ ion conductivity. The composition of Cu _2-x Ch may be a mixture of a plurality of types of chalcogenide copper selected from copper sulfide, copper selenide, and copper telluride, or a solid solution thereof to obtain desired characteristics.

In the organic EL element, the materials of the anode, the anode buffer layer, the cathode, the cathode buffer layer, and the substrate differ depending on which element is the top emission method shown in FIG. 8 or the bottom emission method shown in FIG. In the present invention, the structures and materials of the organic semiconductor element and the cathode may be those usually employed. As shown in FIG. 8, the top emission type organic EL element includes an insulating substrate 11, an anode 12, a cathode 14 made of a light transmissive electrode, and an anode 12 and a cathode 14 between the anode 12 and the anode 12. An organic layer (laminated body) 13 including a light emitting layer laminated in order of a hole transport layer and a light emitting layer is provided. Further, an anode buffer layer may be provided between the anode 12 and the hole transport layer. Further, there are cases where two or more light emitting layers are provided and an intermediate electrode layer is interposed between them.

The anode 12 is an electrode that injects holes into the hole transport layer. The material of the anode 12 needs to have a large work function, excellent conductivity, and translucency. Formula Cu _2-x Ch used for the hole injection electrode of the present invention (where Ch is at least one of the chalcogen elements of S, Se, or Te)
A copper chalcogenide having a composition represented by a species, 0 <x <0.5) is a p-type semiconductor, 10 ² S / c
It exhibits high electrical conductivity exceeding m and has a large work function of about 4.6 to 5.0 eV. The obtained thin film has little temperature dependence of the carrier (hole) concentration, and the electric conductivity exhibits degenerate conduction independent of temperature. In addition, in the photoelectron spectrum of the valence band, a Fermi edge is observed at the upper end of the valence band, which indicates that the semiconductor is a degenerate semiconductor. In both the “bottom emission type structure” and the “top emission type structure” organic EL elements, a junction having excellent adhesion between the p-type semiconductor and the organic semiconductor is formed by low-temperature film formation. Hole injection is possible at a low voltage.

The average thickness of the anode 12 is not particularly limited, but is preferably about 2 to 200 nm.
If the thickness of the anode 12 is too thin, the function as the anode may not be sufficiently exhibited. On the other hand, if it is too thick, the light transmittance decreases. When used as a hole injection electrode of an electronic device such as an organic thin film transistor, the thickness is preferably 80 to 120 nm. When used as a hole injection electrode of an organic EL element, the thickness is preferably about 2 to 20 nm, and more preferably 3 to 6 nm.

The anode is often formed by sputtering, vacuum vapor deposition, electron beam vapor deposition, plasma CVD, and coating, among which sputtering and coating methods can form a large area film at once, It is used relatively well.

An example of forming the hole injection electrode of the present invention by a vapor phase method will be described below. Formula Cu _2-x Ch (where C
h is a copper chalcogenide thin film having a composition represented by at least one of chalcogen elements of S, Se, or Te, and 0 <x <0.5), by a vapor phase method using the compound as a target. In particular, it can be produced under conditions that do not heat (room temperature substrate). For example, the value of x can be controlled by changing the composition of the target. The Cu _2-x Ch thin film is a vapor phase method using Cu ₂ Ch polycrystal as a target, and the substrate temperature is 300 ° C. or less, preferably less than 200 ° C., but from the simplicity of the production method, more preferably, It is produced at room temperature without heating. As a vapor deposition method, a laser deposition method (PLD method) is simple and excellent, but a vapor deposition method and a sputtering method are excellent in mass production.

In the bottom emission method shown in FIG. 9, when an organic semiconductor element is formed on a Cu _2-x Ch thin film formed as a hole injection electrode, the thin film can be formed on a substrate at room temperature. A crystal substrate, a glass substrate, a plastic substrate, or an organic film substrate can be used. The obtained thin film has a hole concentration of more than 10 ²⁰ cm ⁻³ , conductive carriers are holes (p-type), and electric resistance exhibits degenerate electric conduction almost independent of temperature.

By irradiating the surface of the Cu _2-x Ch thin film with oxygen plasma, the surface of the thin film is oxidized, and the state of Cu is changed from +1 to +2. The surface of the thin film after the oxidation treatment is mainly composed of Cu ²⁺ , O ²⁻ , and Ch ²⁻ , and its work function is about 6 eV. Therefore, it is preferable to form a film of an organic semiconductor layer on a surface oxidation-treated Cu _2-x Ch thin film. As long as the surface is oxidized, the surface oxidation treatment method is not limited to the oxygen plasma irradiation method.

When the semiconductor compound layer is laminated on a conventionally used anode body such as ITO as an anode buffer layer, it may be formed under the same conditions as described above. Similarly, surface oxidation treatment can be performed by oxygen plasma irradiation or the like. It is desirable that the material used for the anode buffer layer be capable of forming a thin film with a uniform surface and good contact with the anode body.

Cu _2-x Ch has a surface roughness of about 0.5 nm and can be used to create a flat and uniform thin film. It also has a large work function, easy hole injection from the anode, and high hole mobility. Therefore, it is suitable as a buffer layer. The layer thickness of the conventional anode buffer layer is usually 3 to 100 nm, preferably 10 to 50 nm. In the case of Cu _2-x Ch, it is 1 to 10 nm, preferably 3 to 6 nm. To do. If it is too thick, light is absorbed, which is not preferable. When the hole injection electrode of the present invention is used as an intermediate electrode layer, it may be formed in the same manner as the anode buffer layer.

In the case of a top emission type structure in which a cathode is formed on the substrate side and Cu _2-x Ch is used as a front electrode, Cu _2-x Ch can be directly deposited on the organic semiconductor layer at room temperature. In this case, the cathode material to be formed on the substrate may be a commonly used cathode material, but [Ca ₂₄ Al ₂₈ O ₆₄ ] ⁴⁺ having a work function of about 2.4 eV, which the present inventors previously found. (e ^-) _4-elect ride ( "C12A7: e ^-
"Is abbreviated as").

This electride is 1 × 10 ¹⁸ ions / cm ³ or more, 1.1 × 10 ^{2 of} free oxygen ions contained in the cage, as disclosed in re-published patent WO2005 / 000741.
Free oxygen ions of less than ¹ / cm ³ were replaced with 2 electrons per oxygen ion,
Compound having 2 × 10 ¹⁸ or more and 2.2 × 10 ²¹ / cm ³ electrons in a cage and having an electric conductivity at room temperature of 10 ⁻⁴ S / cm or more and less than 10 ³ S / cm . The cathode of the organic EL element must be able to inject electrons efficiently and have low electrical resistance, but C12A7: e ⁻
Shows metallic conduction, has a small work function of about 2.4 eV, and is stable in air, and is preferable as a high-efficiency electron injection electrode for organic semiconductors.

In addition, a Cu _2-x Ch ultra-thin film having a thickness of 1 to 10 nm, preferably 3 to 6 nm, is formed on the organic semiconductor layer, and a transparent electrode such as an ITO film is formed thereon as a front electrode. Compatibility with hole injection characteristics at a low voltage can be achieved. That is, even if the Cu _2-x Ch layer is used as the anode buffer layer of the front electrode, the drive voltage can be lowered. In this case, Cu _2-x Ch
Although the surface oxidation treatment of the ultrathin film cannot be performed, it functions as a buffer layer even if it is not treated.

An element structure having copper selenide as an anode was produced.
Glass (substrate) / Cu _2-x Se (anode) / CuPc (organic semiconductor layer) / Al (cathode) element <Preparation of Cu _2-x Se thin film>
A Cu _2-x Se thin film was deposited as an anode by a PLD method at room temperature on a glass substrate in a vacuum of about 10 ⁻⁵ Pa. A Cu _2-x Se (x≈0) sintered body was used as a target, and the film was deposited about 100 nm at a film forming speed of about 1 nm / min. It was found by fluorescent x-ray analysis that the obtained thin film had an x value of 0.3, that is, a composition of Cu _1.7 Se. The electrical conductivity, mobility, and carrier concentration of the thin film measured by the van der Poul method at room temperature were 4.5 × 10 ³ S / cm, 2 cm ² · V ⁻¹ · s ⁻¹ , 1.4, respectively.
× 10 ²² cm ⁻³ , and the work function determined from ultraviolet photoelectron spectroscopy (UPS) was 4.7 to 5.0 eV. Further, since the carrier concentration did not show a temperature change, it was found that the electric conductivity was degenerate electric conduction.

<Preparation of Cu _1.7 Se / CuPc interface>
A CuPc (copper phthalocyanine) film is formed on the Cu _1.7 Se thin film subjected to the surface oxidation treatment formed as described above.
Vacuum deposition was performed at a film forming rate of .5 nm / min (vacuum degree of vacuum: about 10 ⁻⁶ Pa) to prepare a Cu _1.7 Se / CuPc interface. Sublimation purified CuPc was used as the evaporation source. FIG. 1 shows the electronic state of this interface measured by UPS. The hole injection barrier estimated from the energy difference between the Fermi level (E _F ) of Cu _1.7 Se and the HOMO of CuPc is about 0.5 eV, indicating that a low hole injection barrier has been realized at the Cu _1.7 Se / CuPc interface. It was.

<Preparation of Cu _1.7 Se / CuPc / Al device>
An Al metal film was deposited as a cathode on the surface of the Cu _1.7 Se / CuPc bilayer film prepared above, and Cu _1.7 Se / CuPc
An / Al element was fabricated and its current-voltage characteristics were measured. As shown in FIG. 2, the current rose at 0.4 V or less, and the subsequent current-voltage characteristics showed a straight line and were ohmic characteristics. It was shown that a high current density of 1.5 A · cm ^-2 or more was obtained at an applied voltage of 1 V, a high current density was obtained at a low voltage, and hole injection was achieved at a low voltage.

An element structure having copper selenide as an anode was produced.
Glass (substrate) / Cu _2-x Se (anode) with surface oxidation treatment / NPB (organic semiconductor layer) / Al (cathode) element <Surface oxidation treatment of Cu _1.7 Se thin film>
The surface of the Cu _1.7 Se thin film obtained in Example 1 was irradiated with oxygen plasma for 30 seconds under the conditions of an oxygen partial pressure of 6.0 × 10 ⁻¹ Pa and an RF power of 50 W. As a result of XPS measurement on the surface after irradiation, it was found that the surface contaminants were almost completely removed. At the same time, the valence of Cu changed from monovalent to divalent, and the O 1s peak became stronger, indicating that it was oxidized. This surface oxidation treatment increased the work function to 6.1 eV, but did not change the carrier transport properties of the thin film.

<Preparation of Cu _1.7 Se / NPB interface>
NPB, which is a hole transport material, is deposited on the Cu _1.7 Se thin film that has been subjected to surface oxidation treatment at a deposition rate of about 2 nm / min by vacuum deposition (about 10 ^-6 Pa), and the Cu _1.7 Se / NPB interface is formed. Produced. Sublimation purified NPB was used as the vapor deposition source. FIG. 3 shows the electronic state of this interface measured by repeatedly performing UPS measurement and NPB film formation. Figure 3 shows the HOMO of NPB based on the Fermi level (E _F ) of Cu _1.7 Se.
And the vacuum level (E _VAC ) of Cu _1.7 Se plotted against the NPB film thickness. From the energy difference between the Fermi level (E _F ) of Cu _1.7 Se and the HOMO of NPB, it is clear that the hole injection barrier is about 0.4 eV, and that a low hole injection barrier was realized at the Cu _1.7 Se / NPB interface. Indicated.

<Preparation of Cu _1.7 Se / NPB / Al element>
An Al metal film was deposited as a cathode on the Cu _1.7 Se / NPB bilayer film obtained above to produce a Cu _2-x Se / NPB / Al element, and its current-voltage characteristics were measured. As shown in FIG. 4, the current rose at 0.6 V or less, and the subsequent current-voltage characteristic was a straight line, and an ohmic characteristic was obtained (FIG. 4 shows a semilogarithmic graph as an interpolated diagram). A high current density of 1 A · cm ^-2 or higher was obtained at an applied voltage of 1 V, indicating that hole injection was achieved at a low voltage. Assuming that the current-voltage characteristics are governed by the space charge limited current, the carrier concentration in NPB is over 2 × 10 ¹⁸ cm ⁻³ , and NPB
It was shown that holes were doped inside.

An organic EL element having a “top emission type structure” using copper selenide as an anode buffer layer was produced.
MgO (substrate) / C12A7: e ^- (cathode) / Alq ₃ (light emitting layer) / NPB (hole transport layer) / CuPc (hole injecting layer)
/ Cu _2-x Se (anode buffer layer) / ITO (front anode)

An organic EL device using C12A7: e ^- electride for the cathode, Alq _{3 for} the light emitting layer, and Cu _1.7 Se (5 nm) for the anode buffer layer was produced by the following method. First, using the PLD method on an MgO single crystal substrate,
Using 12CaO · 7Al ₂ O ₃ (C12A7) sintered body as a target, a C12A7 thin film (150 nm) was formed,
And kept in plasma in a vacuum, added electrons to the thin film C12A7: e ^- a thin film was obtained.

Thereafter, C12A7: e ^- on the thin film, Alq ₃ (60nm) by a vacuum deposition method, NPB (20nm), were successively film-forming a CuPc (50 nm). Sublimation-purified products were used as the organic vapor deposition sources. Next, a Cu _1.7 Se thin film was formed to 5 nm at room temperature by the PLD method, using an ITO sintered body as a target, and at room temperature by the PLD method.
ITO (100 nm) was formed into a device 1 having the structure shown in FIG. Cu as a comparative sample
_1.7 Device 2 in which ITO was directly formed on CuPc without using Se was fabricated.

FIG. 6 shows voltage-luminescence characteristics of the element 1 and the element 2. In the device 2, light emission started from 7.5 V, whereas in the device 1, the light emission start voltage decreased to 6 V, and the light emission intensity increased compared to the device 2. FIG. 7 shows the current density dependence of the luminous efficiency of the element 1 and the element 2. The luminous efficiency of device 1 increased with increasing current density, reaching 3.9 cd / A at 115 mA / cm ² . This value reached 2.6 times the value of element 2 (1.5 cd / A). From the above results, it was shown that the introduction of the Cu _1.7 Se anode buffer layer lowered the interface injection barrier, and the organic EL device could be driven at a low voltage.

An element structure having the following copper sulfide as an anode was produced.
By using a Cu _2-x S (x ≒ 0) sintered body as the target for the PLD method and forming a film in the same manner as in Example 1, Cu _1.7
An S (x = 0.3) thin film was obtained. The obtained thin film has electrical conductivity, mobility, carrier concentration and work function of 1.8 × 10 ³ S / cm, 0.9 cm ² · V ⁻¹ · s ⁻¹ , 1.42 × 10 ²² cm ^-3 and 4.6 eV, respectively. Cu _1.7 Se
It was equivalent to a thin film. The Cu _1.7 S thin film showed the characteristics of functioning as a hole injection electrode or an anode buffer layer like the Cu _1.7 Se thin film.

The hole injection electrode to the organic semiconductor of the present invention is used as an electrode capable of obtaining a large hole current at a low voltage by replacing with an ITO film which is a conventional typical hole injection electrode of an organic EL element. Can do. In addition, when a transparent electrode body such as an ITO film is used, the hole injection electrode in which the Cu _2-x Ch anode buffer layer is laminated functions as a transparent electrode because it can maintain transparency in the visible range. The Cu _2-x Ch thin film can obtain a large hole current at the low voltage mentioned above even with an ultra-thin film of about 5 nm, so use a transparent electrode such as an ITO film and the Cu _2-x Ch buffer layer as an anode. Thus, the transparency and the usefulness of low voltage driving of the mounted device can be exhibited.

2 is an energy level diagram of a Cu _1.7 Se / CuPc interface produced in Example 1. FIG. 3 is a graph showing current density-voltage characteristics of a Cu _1.7 Se / CuPc / Al element fabricated in Example 1. FIG. The energy level diagram of the Cu _1.7 Se / NPB interface produced in Example 2. Graph showing voltage characteristics - current density of Cu _1.7 Se / NPB / Al element manufactured in Example 2. FIG. 5 is a schematic diagram of an organic EL element produced in Example 3. 5 is a graph showing voltage-luminescence characteristics of the organic EL element produced in Example 3. 4 is a graph showing the light emission efficiency characteristics of the organic EL element produced in Example 3. The schematic diagram of a top emission type organic EL element. The schematic diagram of a bottom emission type organic EL element. The schematic diagram of the energy level of an organic semiconductor and an electrode.

Claims (6)

Formula Cu _2-x Ch (Ch is at least one of chalcogen elements of S, Se, Te, x is deficiency of monovalent copper)
An organic semiconductor having a composition expressed by 0.2 to 0.4 ), a work function of 4.6 eV or more, and a semiconductor compound layer exhibiting p-type degenerate electrical conductivity as an electrode Hole injection electrode to. Formula Cu _2-x Ch (Ch is at least one of chalcogen elements of S, Se, Te, x is deficiency of monovalent copper)
A semiconductor compound layer having a composition of 0.2 to 0.4 ), a work function of 4.6 eV or more, and p-type degenerate electrical conductivity is laminated as an anode buffer layer. A hole injection electrode for organic semiconductors. The hole injection electrode according to claim 1, wherein the semiconductor compound layer is formed at room temperature. The electrode according to claim 1 or 2, wherein the surface of the semiconductor compound layer is subjected to oxygen plasma treatment to have a work function of 6.0 eV or more. An organic EL device using the hole injection electrode according to claim 1. [Ca ₂₄ Al ₂₈ O ₆₄ ] ⁴ as a cathode using the hole injection electrode according to claim 1.
⁺ (E ^-) top emission type organic EL element characterized in that it uses a ₄ electride.