JP2018186261A - Electrode, structure, method for manufacturing the same, connection structure, and element using electrode hereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode which can be suitably used as a cathode of an organic light-emitting device, source and drain electrodes of a transistor, and a cathode of a solar battery, which has a low work function, which can be put in ohmic contact with a semiconductor layer, and which has high suitability to lithography.SOLUTION: An electrode comprises an alloy including at least Mg and Ca. In the alloy, the content of Ca is suitably 3-50 atom% to a total atomic number of the alloy. The content of Mg included in the alloy is suitably 50-95 atom% to the total atomic number of the alloy.SELECTED DRAWING: None

Description

  The present invention relates to an electrode, a structure, and a connection structure that can efficiently inject electrons into a semiconductor. The present invention also relates to an element using the electrode.

A semiconductor element such as a transistor or an organic light-emitting element has a structure in which a metal electrode is connected to a semiconductor layer, and is configured to operate through charge transfer between the metal electrode and the semiconductor layer.
For example, a field-effect transistor includes a source electrode and a drain electrode provided separately, a semiconductor layer provided in contact with each electrode between the source electrode and the drain electrode, and a semiconductor layer that overlaps the semiconductor layer. And a gate electrode provided through a gate insulating layer. In such a transistor, when a signal voltage is applied to the gate electrode in a state where a potential difference is generated between the drain electrode and the source electrode, a charge flow channel (channel) is formed in the semiconductor layer, and the source electrode and the drain electrode are connected to each other. Current flows. Accordingly, the transistor functions as a switching element or a current amplifying element that controls on / off of the element connected to the drain electrode, for example.
As an electrode material of such a semiconductor element, gold has been most frequently used so far (see, for example, Patent Documents 1 to 3). This is because gold is chemically stable, can be easily formed using vacuum deposition, and can be finely processed by a lift-off method using a photoresist.

Japanese Patent Laid-Open No. 2006-190826 Japanese Patent Laying-Open No. 2015-170760 JP 2014-0778730 A

  However, since gold has a high work function of about 4.9 eV, when the gold electrode is connected to the semiconductor layer, an energy barrier corresponding to the difference between the work function of the electrode and the electron affinity of the semiconductor layer increases, and the work function is increased. The driving voltage of the device is increased because the efficiency of electron injection into the semiconductor layer is reduced, the work function of the electrode is larger than the work function of the semiconductor layer, and the contact between the electrode and the semiconductor layer becomes a Schottky contact. Tend to be. In the case of a transistor, in the low voltage region, almost no current flows from the electrode to the semiconductor layer, and when the applied voltage reaches a certain value, a phenomenon that a large current suddenly flows to the semiconductor layer is observed, which is favorable. There is also a problem that voltage-current characteristics cannot be obtained.

  Under such circumstances, the present inventors provide an electrode, a structure, and a connection structure that have a low work function, can be brought into ohmic contact with a semiconductor layer, and have high lithography suitability. We have intensively studied the purpose. In addition, intensive investigations have been made for the purpose of providing an element having a low driving voltage and good characteristics by using such an electrode.

  In order to achieve the above-mentioned object, the inventors have made an exhaustive study of forming electrodes with various metals and alloys, connecting them to a semiconductor layer, and evaluating their voltage-current characteristics. In addition, when an electrode having an alloy containing Mg and Ca and a semiconductor layer are connected, an ideal result is obtained that the voltage-current curve increases linearly through the origin, and ohmic contact is realized. It came to obtain the knowledge that. The present inventors have been proposed based on these findings, and specifically have the following configurations.

[1] An electrode having an alloy containing at least Mg and Ca.
[2] The content of Ca contained in the alloy is 3 to 50 atomic% of the total number of atoms of the alloy, and the content of Mg contained in the alloy is 50 to 95 atomic% of the total number of atoms of the alloy. 1] The electrode according to 1].
[3] The electrode according to [1] or [2], wherein the alloy includes Ag, Al, Cr, Cu, Zn, or Li as a third component of an alloy other than Mg and Ca.
[4] The electrode according to [3], wherein the content of the third component contained in the alloy is 0.1 to 30 atomic% of the total number of atoms of the alloy.
[5] The electrode according to [4] or [5], wherein the total content of Ca and the third component contained in the alloy is 10 to 30 atomic% of the total number of atoms of the alloy.
[6] The electrode according to any one of [1] to [5], wherein a work function of the alloy is 4.0 eV or less.
[7] A structure having irregularities having a pitch of 500 nm to 200 μm on the surface, made of an alloy containing at least Mg and Ca.
[8] The structure according to [7], wherein the plurality of strips made of an alloy containing at least Mg and Ca have a structure in which the strips are arranged in parallel at a pitch of 500 nm to 200 μm.
[9] A method for manufacturing a structure including a step of forming an alloy containing at least Mg and Ca by a lithography method.
[10] The method for manufacturing a structure according to [9], wherein the step is a step of forming irregularities on a surface of an alloy containing at least Mg and Ca by a lithography method.
[11] The method for manufacturing a structure according to [9], wherein the step includes a step of forming an alloy containing at least Mg and Ca by a lift-off method.
[12] The method for manufacturing a structure according to any one of [9] to [11], wherein the lithography method is a photolithography method.
[13] The method for manufacturing a structure according to any one of [9] to [12], wherein the alloy is an alloy film formed on a substrate.
[14] The structure manufacturing method according to [13], wherein the alloy film is formed by a sputtering method.
[15] A connection structure having a structure in which an alloy containing at least Mg and Ca and a semiconductor are electrically connected.
[16] The connection structure according to [15], wherein the semiconductor is an organic semiconductor.
[17] The connection structure according to [15], wherein the semiconductor is an oxide semiconductor.
[18] The connection structure according to any one of [15] to [17], wherein the alloy and the semiconductor are in ohmic contact.
[19] An element having the electrode according to any one of [1] to [6].
[20] The element according to [19], wherein the element has a structure in which the electrode and the semiconductor are electrically connected.
[21] The device according to [19] or [20], wherein the device is an organic light-emitting device, a solar cell, or a transistor.
[22] The device according to [21], wherein the device is an organic transistor.
[23] The device according to [21], wherein the device is an oxide transistor.

  Since the electrode of the present invention has a small work function, when connected to the semiconductor layer, the energy barrier against electron injection from the electrode to the semiconductor layer is low, and electrons can be efficiently injected into the semiconductor layer. The contact state with the semiconductor layer can be ohmic contact. Further, the electrode of the present invention has high lithography suitability, and can be finely processed precisely using a lithography method. Since the element of the present invention uses such electrodes, the driving voltage is low and good characteristics can be obtained.

It is a schematic sectional drawing which shows the layer structural example of an organic electroluminescent element. It is a schematic sectional drawing which shows the layer structural example of a transistor. It is a schematic sectional drawing which shows the layer structural example of a solar cell. It is a reflectance spectrum of Mg94Ca6 alloy layer, Mg75Ca25 alloy layer, Al layer, MgAu layer, and Mg layer. It is the graph which took the energy of irradiation light about the structure which consists of Mg90Ca10 alloy, and took the square root of the photoelectron yield on the vertical axis. It is a graph which shows the drain voltage-drain current characteristic of the organic transistor which used MgCa alloy for the source electrode and the drain electrode. It is a graph which shows the time-dependent change of the light emission area of the organic electroluminescent element which used Mg70Ca30 alloy for the cathode, the organic electroluminescent element which used Al for the cathode, and the organic electroluminescent element which used MgAu alloy for the cathode. It is a reflectance spectrum of Mg88Ca12 alloy layer, Mg73Ca5Ag22 alloy layer, Mg88Ca9Al3 alloy layer, and Al layer. It is a graph which shows the time-dependent change of the light emission area of each organic electroluminescent element which used Mg88Ca12 alloy, Mg73Ca5Ag22 alloy, Mg88Ca9Al3 alloy, or Al for the cathode, respectively.

Hereinafter, the contents of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. In addition, the isotope species of the hydrogen atom present in the molecule of the compound used in the present invention is not particularly limited. For example, all the hydrogen atoms in the molecule may be ¹ H, or a part or all of the hydrogen atoms are ² H. (Deuterium D) may be used. In addition, the contents (atomic%) of materials other than Mg, Ca, the third component, and an alloy containing at least Mg and Ca in the present specification are measured by an energy dispersive X-ray analyzer.

(1) Electrode The electrode of the present invention is characterized by having an alloy containing at least Mg and Ca.
An alloy containing Mg and Ca has a very low work function of about 3.6 eV. For this reason, an electrode having an alloy containing Mg and Ca has a low energy barrier against electron injection from the electrode to the semiconductor layer in the connection structure between the electrode and the semiconductor layer, and can efficiently inject electrons into the semiconductor layer. In addition, the contact state with the semiconductor layer can be ohmic contact. Thereby, the drive voltage of the element using this electrode can be lowered and good element characteristics can be realized.
In addition, an alloy containing Mg and Ca can be easily formed by using a vapor phase process, and the alloy film can be precisely finely processed by using a lithography method. Is suitable. Further, Mg and Ca, which are constituent elements of this alloy film, are not rare elements such as Au, and thus are inexpensive. For this reason, the manufacturing cost of an element can be reduced by comprising an electrode with the alloy containing Mg and Ca.
Further, an alloy containing Mg and Ca has excellent barrier properties against oxygen and water vapor, and the weather resistance of the device can be improved by using this alloy for an electrode. Accordingly, an expensive gas barrier film having a relatively high barrier property can be used instead of a gas barrier film, and an inexpensive gas barrier film having a relatively low barrier property can be used. Therefore, the manufacturing cost of the element can be further reduced.
Furthermore, an alloy containing Mg and Ca has a high reflectance with respect to light in the visible region. For this reason, when this alloy is used, for example, in an electrode disposed on the side opposite to the light extraction side of the light emitting element, the light emitted from the light emitting layer to the side opposite to the light extraction side is efficiently reflected by the electrode. , It can be efficiently extracted from the light extraction side. Thereby, high luminous efficiency can be obtained.

[Ca and Mg contents in alloy]
In the electrode of the present invention, the content of Mg contained in the alloy is preferably 50 to 95 atomic% of the total number of atoms in the alloy.
Further, the content of Ca contained in the alloy is preferably 3 to 50 atomic% of the total number of atoms of the alloy, and the lower limit is preferably 5 atomic% of the total number of atoms of the alloy, and the upper limit is It is preferably 40 atomic% of the total number of atoms in the alloy. From the standpoint of obtaining higher lithographic suitability, the Ca content in the alloy is more preferably 5 to 20 atomic%, and further preferably 5 to 15 atomic% of the total number of atoms in the alloy. Moreover, when it is desired to use this electrode as a barrier layer against oxygen or water vapor, the Ca content in the alloy is more preferably 20 to 40 atomic%, and further preferably 25 to 35 atomic%. . Thereby, since the barrier property with respect to oxygen and water vapor | steam is provided to the element using this electrode, especially in an organic electroluminescent element etc. weak to oxygen and water, a high barrier property of 10 ⁻⁶ gm ⁻² day ⁻¹ level. It is sufficient to use an inexpensive gas barrier film (10 ⁻⁴ gm ⁻² day ⁻¹ level) having a lower barrier property even without using an expensive gas barrier film showing As a result, the manufacturing cost of such an element can be reduced.
The total content of Ca and Mg in the alloy is, for example, 70 atomic% or more, 77 atomic% or more, 84 atomic% or more, 90 atomic% or more, 95 atomic% or more, 99 atomic% or more, 99.9%, or 99.9%. You may select from the range of atomic% or more.

[Third component]
The alloy of the electrode of the present invention may be composed only of Mg and Ca, or may contain a metal element other than Mg and Ca as the third component of the alloy. Thereby, the work function of the electrode can be controlled, and the conductivity and barrier properties can be improved. The metal element used for the third component is not particularly limited, but is preferably a metal element having a work function of 4.0 eV or less, and preferably Ag, Al, Cr, Cu, Zn, or Li. These 3rd components may be used individually by 1 type, and may be used in combination of 2 or more type. Preferred examples of combinations of metal elements constituting the alloy include a combination of Mg and Ca, a combination of Mg, Ca and Ag, a combination of Mg, Ca and Al, and a combination of Mg, Ca, Ag and Al.
When the alloy includes a third component, the content of the third component is preferably 0.1 to 30 atomic percent of the total number of atoms of the alloy. For example, the lower limit is 1 atomic percent or more, 3 atomic percent or more, 5 You may select from the range of atomic% or more, and you may select from the range whose upper limit is 23 atomic% or less, 16 atomic% or less, 10 atomic% or less, and 6 atomic% or less. Further, the total content of Ca and the third component is preferably 5 to 50 atomic%, more preferably 10 to 30 atomic% of the total number of atoms of the alloy.
The content of the third component is preferably 0.2 to 5.0 times the number of Ca atoms. For example, the lower limit is 0.3 times or more, 0.6 times or more and 1 time the number of Ca atoms. You may select from the above range, and you may select from the range whose upper limit is 4.4 times or less of Ca atom number, 2 times or less, and 1.5 times or less.
Here, when two or more kinds of elements are used as the third component, the total number of atoms corresponds to the content of the third component.

[Ingredients other than alloys]
The electrode of the present invention and the layer having an alloy containing at least Mg and Ca constituting the laminated structure described later may be composed only of an alloy containing at least Mg and Ca, or may contain materials other than this alloy. You may go out. When the electrode and the layer include a material other than an alloy containing at least Mg and Ca, the content of the material other than the alloy is, for example, 20% by weight or less, 10% by weight or less, 5% by weight or less, and 1% by weight or less. May be selected within a range of 0.1 wt% or less.
The material other than the alloy may be an inorganic material or an organic material, or may be a composite material of an inorganic material and an organic material. Moreover, the aspect of materials other than an alloy is not specifically limited, For example, it may be disperse | distributed in the alloy film which contains Mg and Ca at least, and is formed in the layer form on the surface of the alloy film which contains Mg and Ca at least May be. However, it is preferable that the surface which becomes an electrical connection surface with respect to the to-be-connected body of an electrode is comprised with the alloy containing Mg and Ca at least.

[Electrode shape]
The shape of the electrode of the present invention is not particularly limited, and a known electrode shape such as a layer shape, a column shape, a bump shape, or a wire shape can be employed. For example, in the case of a semiconductor element such as a transistor, an organic light emitting element, or a solar cell, a layered electrode is provided.

[Layer structure]
When the electrode of the present invention is layered, it may be a single layer configuration of a layer having an alloy containing at least Mg and Ca, or a multilayer configuration in which two or more layers having an alloy containing at least Mg and Ca are stacked. There may be a multilayer structure in which a layer having an alloy containing at least Mg and Ca and another layer are laminated. Here, the other layer is a layer that does not have an alloy containing at least Mg and Ca, and may be a layer made of an inorganic material or a layer made of an organic material, or a composite of an inorganic material and an organic material. It may be a layer made of a material. The other layer may contain one of Mg and Ca. In the case of a multilayer structure in which a layer having an alloy containing at least Mg and Ca and another layer are laminated, the number of layers having an alloy containing at least Mg and Ca and the number of other layers may be one or more. It may be. In any multilayer configuration, the constituent components of each layer and the content ratios and thicknesses of the constituent components may be the same or different, but adjacent layers are at least a part of the constituent components. It is preferable that at least one of the content ratios of the constituent components is different.

[Electrode thickness, planar shape]
When the electrode of the present invention is layered, the thickness and planar shape of the electrode are not particularly limited, and can be appropriately selected according to the usage mode. Here, the “planar shape of the electrode” in the present specification means a shape in a plan view when the electrode is viewed from a direction orthogonal to the thickness direction. For example, in the case of an electrode used by being incorporated in a semiconductor element such as a transistor, an organic light emitting element, or a solar cell, the thickness is preferably 10 to 2000 nm, and more preferably 10 to 1000 nm. 10 to 100 nm is more preferable.
The planar shape of the electrode may be a continuous shape as a whole or a shape composed of a plurality of separated parts. The shape of each part of the whole continuous shape and the shape consisting of a plurality of parts is not particularly limited, and is a strip, a line, a lattice, a square, a rectangle, a circle, an ellipse, an oval, Any of semicircular shape, indefinite shape, etc. may be sufficient. Further, the electrode may form a repeating pattern in which two or more parts having the same shape are arranged in parallel with a space therebetween. Examples of the repetitive pattern include a stripe shape, a lattice shape, and a dot shape. The pitch between adjacent portions in the repetitive pattern is preferably 500 nm to 200 μm, more preferably 500 nm to 100 μm, and still more preferably 500 nm to 50 μm. Here, the pitch refers to the distance between the center of one part and the center of the adjacent part. For example, when the planar shape of the electrode is a stripe, The distance between the center of the electrode line in the minor axis direction and the center of the electrode line adjacent thereto in the minor axis direction corresponds to the pitch. Further, when the planar shape of the electrode is a stripe shape, the width (short axis length) of the electrode line is preferably 500 nm to 2000 μm, more preferably 500 nm to 1000 μm, and more preferably 500 nm to 500 μm. Further preferred.

[Characteristics of electrode]
(Work function)
In this specification, the “work function” refers to a photoelectric work function measured using a photoelectron spectrometer.
The work function of the electrode is preferably 4.5 eV or less, more preferably 2.5 to 4.5 eV, and even more preferably 2.5 to 4.0 eV. The work function of the electrode is preferably selected in accordance with the energy state of the connected body that is electrically connected to the electrode. For example, when the object to be connected is an organic semiconductor, the work function of the electrode is E _LUMO ± 1.5 eV, where the absolute value of the LUMO (Lowest Unoccupied Molecular Orbital) level of the organic semiconductor is E _LUMO. Preferably, it is more preferably E _LUMO ± 1.0 eV, and more preferably E _LUMO ± 0.5 eV. When the connected body is an inorganic semiconductor, the work function of the electrode is χ ± 1.5 eV, where χ is the electron affinity of the inorganic semiconductor, that is, the energy from the bottom of the conduction band to the vacuum level. Preferably, it is χ ± 1.0 eV, more preferably χ ± 0.5 eV. The work function of the electrode is particularly preferably less than or equal to the work function of the connected body.
The LUMO level of the organic semiconductor can be measured by an optical energy gap calculated from the absorption edge of the absorption spectrum or by inverse photoelectron spectroscopy. The electron affinity of the inorganic semiconductor can be measured by an optical energy gap calculated from the absorption edge of the absorption spectrum or inverse photoelectron spectroscopy.

(Reflectivity for visible light)
In the present specification, the “reflectance with respect to light in the visible region” refers to a value measured by a spectroscopic ellipsometry apparatus or a spectral transmittance / reflectance measuring apparatus.
The reflectance of the electrode with respect to light in the visible region (380 to 780 nm) is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. Here, the reflectance of the electrode is preferably in the above-mentioned range over the entire visible region, but the reflectance may be in the above-mentioned range may be a part of the visible region. For example, when the electrode of the present invention is used as an electrode on the side opposite to the light extraction side of the organic light emitting device, the reflectance of the light emitting wavelength region of the organic light emitting device is preferably in the above range.

(2) Structure The structure of the present invention is made of an alloy containing at least Mg and Ca, and has irregularities having a pitch of 500 nm to 200 μm on the surface.
For the description and preferred range of the alloy containing at least Mg and Ca, the description and preferred range of the alloy containing at least Mg and Ca included in the electrode can be referred to. The structure of the present invention may have a single layer configuration of a layer made of an alloy containing at least Mg and Ca, or a multilayer configuration of a layer made of an alloy containing at least Mg and Ca. In the case of a multilayer structure, the presence or absence of the third component of each layer, the type and the content ratio of the constituent components, and the thickness may be the same or different, but adjacent layers may be the presence or absence of the third component, the type and It is preferable that at least one of the content ratios of the constituent components is different.
The unevenness | corrugation in this invention contains the shape which convex parts isolate | separated through the bottom part of a recessed part other than the shape which the recessed part penetrated and does not have a bottom part, but the convex parts isolate | separated. It is preferable that the concave and convex portions of the structure have a repeating pattern in which two or more convex portions having the same shape are arranged in parallel with each other in a plan view viewed from the top side of the convex portion. . Examples of the repetitive pattern include a stripe shape, a lattice shape, and a dot shape in which a plurality of strips are arranged in parallel. In addition, the “pitch” in the present invention refers to the distance between the center of the convex portion in plan view and the center of the convex portion adjacent thereto, for example, when the convex portion is in a stripe shape or a lattice shape. The distance between the center of the convex part in the short axis direction and the center of the convex part adjacent to the convex part in the short axis direction corresponds to the pitch.

(3) Manufacturing method of structure The manufacturing method of the structure of this invention includes the process of forming an unevenness | corrugation by the lithography method on the surface of the alloy which contains Mg and Ca at least.
For the description of the unevenness and the specific examples of the preferable range and shape, the description of the unevenness and the preferable range and specific shape in the section of the structure can be referred to.

The “lithography method” in the present invention refers to forming an alloy containing at least Mg and Ca in a predetermined pattern.
The alloy containing at least Mg and Ca may be directly formed so as to have a predetermined pattern, or after forming an alloy film uniformly, forming a predetermined pattern by removing a part of the alloy film However, the latter method is preferred. In the latter method, part of the alloy film can be removed by, for example, locally etching an unnecessary part of the alloy film, and it is preferable to use a mask having a predetermined pattern. In a lithography method using a mask, a mask having a predetermined pattern is formed by irradiating and developing a part of a film made of an energy ray-sensitive material that is cured or solubilized by the action of energy rays, and developing the mask. The pattern or the reverse pattern is transferred to the alloy film.
Examples of the lithography method using a mask include a photolithography method, an X-ray lithography method, an electron beam lithography method, an extreme ultraviolet lithography method, an ion beam lithography method, and the like, and it is preferable to use a photolithography method. As the energy beam sensitive material used in the lithography method, a negative resin composition that is cured by the action of energy rays, a positive resist film that is solubilized by the action of energy rays, or the like can be used.
Although the manufacturing process of the structure by the lithography method is not particularly limited, for example, the following first manufacturing method or second manufacturing method can be used.

[First manufacturing method (lift-off method)]
A substrate for forming an alloy film is prepared, a film made of an energy beam sensitive material is formed on the substrate, and developed by irradiating the energy beam to develop a mask of a reverse pattern with respect to the target pattern. Form.
Next, an alloy film is obtained by uniformly forming an alloy containing at least Mg and Ca on the substrate so as to cover the mask.
The method for forming an alloy containing at least Mg and Ca is not particularly limited. For example, a vapor deposition process such as vacuum deposition, sputtering, ion plating, plating such as electrolytic plating, immersion plating, electroless plating, thermal spraying, joining of metal foil, etc. can be used. It is preferable to form an alloy film.
Next, the mask and the alloy film immediately above the mask are removed by using a solvent. As a result, only the alloy film in the region where the mask is not formed remains on the substrate, and an alloy film formed into a mask reversal pattern (target pattern) is obtained.

[Second production method]
An alloy film containing at least Mg and Ca is uniformly formed on the substrate to obtain an alloy film.
For the method for forming the alloy film, the method for forming the alloy film in the first manufacturing method can be referred to.
Next, a film made of an energy beam sensitive material is formed on the alloy film, and a mask having a target pattern is formed by developing by irradiating the energy beam. Then, after the alloy film exposed from the mask is removed by etching, the mask on the alloy film is removed by peeling. As a result, only the alloy film in the region where the mask was formed remains on the substrate, and an alloy film formed into a mask pattern (target pattern) is obtained.
As an etching method of the alloy film, a dry etching method such as plasma etching, sputter etching, reactive ion etching, sputter ion beam etching, reactive ion beam etching, or a wet etching method can be used.

In each of the above manufacturing methods, the base material for forming the alloy film can be appropriately selected according to the element to which the structure of the present invention is applied. For example, when the element to which the structure of the present invention is applied is an organic light-emitting element, a transistor, or a solar cell, the substrate illustrated below or a layer directly below the electrode may be used as a base material. it can.
Of the first manufacturing method and the second manufacturing method, it is preferable to use the first manufacturing method because unnecessary portions of the alloy film can be removed without etching and the process is simple. .

(4) Connection structure The connection structure of the present invention includes an electrode having an alloy containing at least Mg and Ca, and a semiconductor layer connected to the electrode. This connection structure can be used, for example, as a connection structure between an electrode and a semiconductor layer in a semiconductor element.
For the description of the electrode having an alloy containing at least Mg and Ca, the preferred range, and specific examples, the description in the above-mentioned section of the electrode can be referred to. The semiconductor layer connected to the electrode can be appropriately selected according to the element to which the connection structure of the present invention is applied. For example, an electron transport layer in an organic light-emitting element described later, a semiconductor layer in a transistor (preferably an n-channel semiconductor) Layer, n-type organic semiconductor layer), and a semiconductor layer corresponding to a photoelectric conversion layer or an electron extraction layer in a solar cell can be used.
According to the present invention, since the work function of the electrode is small, the energy barrier against electron injection from the electrode to the semiconductor layer is low, electrons can be efficiently injected into the semiconductor layer, and the contact state between the electrode and the semiconductor layer Can be in ohmic contact. Thereby, the connection structure which contributes to the reduction of the drive voltage of an element and the improvement of a voltage-current characteristic can be obtained.
Here, the ohmic contact between the electrode and the semiconductor layer means that a transistor in which the electrode is connected to the semiconductor layer as a source electrode and a drain electrode is manufactured, and the drain voltage-drain current curve passes through the origin and is a linear function. It can be confirmed with an increase.

(5) Element The element of the present invention has the electrode of the present invention.
Since the electrode of the present invention has a low work function, when connected to a semiconductor layer, the energy barrier against electron injection from the electrode to the semiconductor layer is low, and electrons can be efficiently injected into the semiconductor layer. The contact state with the layer can be ohmic contact. For this reason, the element having the electrode of the present invention has a low driving voltage and can obtain good element characteristics.
The element of the present invention is a semiconductor element having a connection structure in which an electrode and a semiconductor layer are electrically connected, and the electrode electrically connected to the semiconductor layer is preferably constituted by the electrode of the present invention. . Examples of the semiconductor element include an organic light emitting element, a transistor, and a solar cell. Hereinafter, an organic light emitting device, a transistor and a solar cell will be described as the device of the present invention. However, the element of the present invention should not be limitedly interpreted by these specific examples.

[Organic light emitting device]
The organic light emitting device of the present invention is preferably an organic electroluminescent device that emits light from a light emitting material by current excitation.
The organic electroluminescent element has at least an anode, a cathode, and a structure in which an organic layer is formed between the anode and the cathode, and the cathode is preferably composed of the electrode of the present invention. The organic layer includes at least a light emitting layer, and may consist of only the light emitting layer, or may have one or more organic layers in addition to the light emitting layer. Examples of such other organic layers include a hole transport layer, a hole injection layer, an electron blocking layer, a hole blocking layer, an electron injection layer, an electron transport layer, and an exciton blocking layer. The hole transport layer may be a hole injection / transport layer having a hole injection function, and the electron transport layer may be an electron injection / transport layer having an electron injection function. A specific example of the structure of an organic electroluminescence element is shown in FIG. In FIG. 1, 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, 5 is a light emitting layer, 6 is an electron transport layer, and 7 is a cathode.
Below, each member and each layer of an organic electroluminescent element are demonstrated.

(substrate)
The organic electroluminescence device of the present invention is preferably supported on a substrate. The substrate is not particularly limited and may be any substrate conventionally used for organic electroluminescence elements. For example, a substrate made of glass, transparent plastic, quartz, silicon, or the like can be used.

(anode)
As the anode in the organic electroluminescence element, an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a high work function (4 eV or more) is preferably used. Specific examples of such electrode materials include metals such as Au, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ and ZnO. Alternatively, an amorphous material such as IDIXO (In ₂ O ₃ —ZnO) capable of forming a transparent conductive film may be used. For the anode, a thin film may be formed by vapor deposition or sputtering of these electrode materials, and a pattern of a desired shape may be formed by photolithography, or when pattern accuracy is not so high (about 100 μm or more) ), A pattern may be formed through a mask having a desired shape at the time of vapor deposition or sputtering of the electrode material. Or when using the material which can be apply | coated like an organic electroconductivity compound, wet film-forming methods, such as a printing system and a coating system, can also be used. When light emission is extracted from the anode, it is desirable that the transmittance be greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually selected in the range of 10 to 1000 nm, preferably 10 to 200 nm.

(cathode)
The cathode is constituted by the electrode of the present invention. Since the electrode of the present invention has a small work function, by constituting the cathode with the electrode of the present invention, electrons can be efficiently transferred to the organic layer (the electron transport layer 6 in the organic electroluminescence device shown in FIG. 1) bonded thereto. While being able to inject | pour, the contact state of the organic layer and a cathode can be made into ohmic contact. Thereby, a drive voltage can be made low and a favorable characteristic can be acquired.
The work function of the electrode used for the cathode of the organic electroluminescence element is preferably E _LUMO ± 1.5 eV, where E _LUMO is the absolute value of the LUMO level of the organic layer bonded to the cathode, E _LUMO ± 1.0 eV is more preferable, and E _LUMO ± 0.5 eV is even more preferable.

(Light emitting layer)
The light emitting layer is a layer that emits light after excitons are generated by recombination of holes and electrons injected from each of the anode and the cathode, and the light emitting material may be used alone for the light emitting layer. , Preferably including a luminescent material and a host material. As the light emitting material, a fluorescent material, a phosphorescent material, a delayed fluorescent material, or the like can be used. In order for the organic electroluminescence device of the present invention to exhibit high luminous efficiency, it is important to confine singlet excitons and triplet excitons generated in the light emitting material in the light emitting material. Therefore, it is preferable to use a host material in addition to the light emitting material in the light emitting layer. As the host material, an organic compound in which at least one of excited singlet energy and excited triplet energy has a value higher than that of the light-emitting material can be used. As a result, singlet excitons and triplet excitons generated in the light emitting material can be confined in the molecule of the light emitting material, and the light emission efficiency can be sufficiently extracted. However, even if singlet excitons and triplet excitons cannot be sufficiently confined, there are cases where high luminous efficiency can be obtained, so that host materials that can achieve high luminous efficiency are particularly limited. And can be used in the present invention. In the organic electroluminescence device of the present invention, light emission is generated from the light emitting material contained in the light emitting layer. This emission includes both fluorescence and delayed fluorescence. However, light emission from the host material may be partly or partly emitted.
When the host material is used, the amount of the light emitting material contained in the light emitting layer is preferably 0.1% by weight or more, more preferably 1% by weight or more, and 50% by weight or less. Is preferably 20% by weight or less, more preferably 10% by weight or less.
The host material in the light-emitting layer is preferably an organic compound that has a hole transporting ability and an electron transporting ability, prevents the emission of longer wavelengths, and has a high glass transition temperature.

The light emitting material can be selected in consideration of the wavelength to be emitted. For example, a light emitting material such as a phosphorescent light emitting material, a fluorescent material such as a heat activated delayed fluorescent material, or an exciplex light emitting material can be appropriately selected and used. Examples of the light emitting material include a dye material, a metal complex material, a polymer material, and a dopant material.
Examples of dye-based materials include cyclopentamine derivatives, tetraphenylbutadiene derivative compounds, triphenylamine derivatives, oxadiazole derivatives, pyrazoloquinoline derivatives, distyrylbenzene derivatives, distyrylarylene derivatives, pyrrole derivatives, thiophene ring compounds. Pyridine ring compounds, perinone derivatives, perylene derivatives, oligothiophene derivatives, oxadiazole dimers, pyrazoline dimers, quinacridone derivatives, coumarin derivatives, and the like. Examples of the metal complex material include rare earth metals such as Tb, Eu, and Dy, or Al, Zn, Be, Pt, Ir, and the like as a central metal, and oxadiazole, thiadiazole, phenylpyridine, phenylbenzimidazole, and quinoline. Examples include metal complexes having a structure as a ligand, for example, iridium complexes, platinum complexes and other metal complexes having light emission from a triplet excited state, aluminum quinolinol complexes, benzoquinolinol beryllium complexes, benzoxazolyl zinc A complex, a benzothiazole zinc complex, an azomethylzinc complex, a porphyrin zinc complex, a phenanthroline europium complex, and the like can be given. As polymer materials, polyparaphenylene vinylene derivatives, polythiophene derivatives, polyparaphenylene derivatives, polysilane derivatives, polyacetylene derivatives, polyfluorene derivatives, polyvinyl carbazole derivatives, the above dye materials and metal complex light emitting materials are polymerized. The thing etc. can be mentioned.

Among the light emitting materials, examples of the material that emits blue light include distyrylarylene derivatives, oxadiazole derivatives, and polymers thereof, polyvinylcarbazole derivatives, polyparaphenylene derivatives, and polyfluorene derivatives. Of these, polymer materials such as polyvinyl carbazole derivatives, polyparaphenylene derivatives, and polyfluorene derivatives are preferred. Examples of materials that emit green light include quinacridone derivatives, coumarin derivatives, and polymers thereof, polyparaphenylene vinylene derivatives, polyfluorene derivatives, and the like. Of these, polymer materials such as polyparaphenylene vinylene derivatives and polyfluorene derivatives are preferred. Examples of materials that emit red light include coumarin derivatives, thiophene ring compounds, and polymers thereof, polyparaphenylene vinylene derivatives, polythiophene derivatives, and polyfluorene derivatives. Among these, polymer materials such as polyparaphenylene vinylene derivatives, polythiophene derivatives, and polyfluorene derivatives are preferable.

  Specific examples of phosphorescent materials include Irr complexes such as Flrpic, FCNIr, Ir (dbfmi), FIr6, Ir (fbppz) 2 (dfbdp), FIrN4, and [Cu (dnbp) (DPEPhos)] BF 4 described later. [Cu (dppb) (DPEPhos)] BF4, [Cu (μ-l) dppb] 2, [Cu (μ-Cl) DPEphos] 2, Cu (2-tzq) (DPEPhos), [Cu (PNP)) ] 2, compound 1001, Cu complexes such as Cu (Bpz4) (DPEPhos), and Pt complexes such as FPt and Pt-4 can be mentioned as preferred examples. These structures are shown below.

As the thermally activated delayed fluorescent material, for example, the following PIC-TRZ, [Cu (PNP-tBu)] 2 can be cited as a preferred example.

Preferred examples of the exciplex light emitting material include m-MTDATA and PBD, PyPySPyPy and NPB, and PPSPP and NPB described below.

  Specific examples of typical light-emitting materials are described above, but the light-emitting materials that can be used in the present invention are not limited to these, and other known light-emitting materials can also be used. Main light emitting materials are described in, for example, Chapter 9 of CMC Publishing, “Device Physics / Material Chemistry / Device Application of Organic EL”.

(Injection layer)
The injection layer is a layer provided between the electrode and the organic layer for lowering the driving voltage and improving the luminance of light emission. There are a hole injection layer and an electron injection layer, and between the anode and the light emitting layer or the hole transport layer. Further, it may be present between the cathode and the light emitting layer or the electron transport layer. The injection layer can be provided as necessary.

(Blocking layer)
The blocking layer is a layer that can prevent diffusion of charges (electrons or holes) and / or excitons existing in the light emitting layer to the outside of the light emitting layer. The electron blocking layer can be disposed between the light emitting layer and the hole transport layer and blocks electrons from passing through the light emitting layer toward the hole transport layer. Similarly, a hole blocking layer can be disposed between the light emitting layer and the electron transporting layer to prevent holes from passing through the light emitting layer toward the electron transporting layer. The blocking layer can also be used to block excitons from diffusing outside the light emitting layer. That is, each of the electron blocking layer and the hole blocking layer can also function as an exciton blocking layer. The term “electron blocking layer” or “exciton blocking layer” as used herein is used in the sense of including a layer having the functions of an electron blocking layer and an exciton blocking layer in one layer.

(Hole blocking layer)
The hole blocking layer has a function of an electron transport layer in a broad sense. The hole blocking layer has a role of blocking holes from reaching the electron transport layer while transporting electrons, thereby improving the recombination probability of electrons and holes in the light emitting layer. As the material for the hole blocking layer, the material for the electron transport layer described later can be used as necessary.

(Electron blocking layer)
The electron blocking layer has a function of transporting holes in a broad sense. The electron blocking layer has a role to block electrons from reaching the hole transport layer while transporting holes, thereby improving the probability of recombination of electrons and holes in the light emitting layer. .

(Exciton blocking layer)
The exciton blocking layer is a layer for preventing excitons generated by recombination of holes and electrons in the light emitting layer from diffusing into the charge transport layer. It becomes possible to efficiently confine in the light emitting layer, and the light emission efficiency of the device can be improved. The exciton blocking layer can be inserted on either the anode side or the cathode side adjacent to the light emitting layer, or both can be inserted simultaneously. That is, when the exciton blocking layer is provided on the anode side, the layer can be inserted adjacent to the light emitting layer between the hole transport layer and the light emitting layer, and when inserted on the cathode side, the light emitting layer and the cathode Between the luminescent layer and the light-emitting layer. Further, a hole injection layer, an electron blocking layer, or the like can be provided between the anode and the exciton blocking layer adjacent to the anode side of the light emitting layer, and the excitation adjacent to the cathode and the cathode side of the light emitting layer can be provided. Between the child blocking layer, an electron injection layer, an electron transport layer, a hole blocking layer, and the like can be provided. When the blocking layer is disposed, at least one of the excited singlet energy and the excited triplet energy of the material used as the blocking layer is preferably higher than the excited singlet energy and the excited triplet energy of the light emitting material.

(Hole transport layer)
The hole transport layer is made of a hole transport material having a function of transporting holes, and the hole transport layer can be provided as a single layer or a plurality of layers.
The hole transport material has any one of hole injection or transport and electron barrier properties, and may be either organic or inorganic. Known hole transport materials that can be used include, for example, triazole derivatives, oxadiazole derivatives, imidazole derivatives, carbazole derivatives, indolocarbazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, Examples include amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline copolymers, and conductive polymer oligomers, particularly thiophene oligomers. An aromatic tertiary amine compound and an styrylamine compound are preferably used, and an aromatic tertiary amine compound is more preferably used.

(Electron transport layer)
The electron transport layer is made of a material having a function of transporting electrons, and the electron transport layer can be provided as a single layer or a plurality of layers.
The electron transport material (which may also serve as a hole blocking material) may have a function of transmitting electrons injected from the cathode to the light emitting layer. Examples of the electron transport layer that can be used include nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide oxide derivatives, carbodiimides, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, oxadiazole derivatives, and the like. Furthermore, in the above oxadiazole derivative, a thiadiazole derivative in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron withdrawing group can also be used as an electron transport material. Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

The organic electroluminescence device of the present invention emits light by applying an electric field between an anode and a cathode. At this time, if the light is emitted by excited singlet energy, light having a wavelength corresponding to the energy level is confirmed as fluorescence emission and delayed fluorescence emission. In addition, in the case of light emission by excited triplet energy, a wavelength corresponding to the energy level is confirmed as phosphorescence. Since normal fluorescence has a shorter fluorescence lifetime than delayed fluorescence, the emission lifetime can be distinguished from fluorescence and delayed fluorescence.
On the other hand, with respect to phosphorescence, in ordinary organic compounds such as the compounds of the present invention, the excited triplet energy is unstable and is converted into heat and the like, and the lifetime is short and it is immediately deactivated. In order to measure the excited triplet energy of a normal organic compound, it can be measured by observing light emission under extremely low temperature conditions.

[Transistor]
The transistor of the present invention may be a bipolar transistor or a field effect transistor (unipolar transistor). When the transistor of the present invention is an npn-type bipolar transistor, it is preferable that at least one of the emitter electrode and the collector electrode is composed of the electrode of the present invention, and both the emitter electrode and the collector electrode are composed of the electrode of the present invention. More preferably. When the transistor of the present invention is a pnp bipolar transistor, the base electrode is preferably composed of the electrode of the present invention. When the transistor of the present invention is a field effect transistor, it is preferable that at least one of the source electrode and the drain electrode is composed of the electrode of the present invention, and both the source electrode and the drain electrode are composed of the electrode of the present invention. It is preferable. The semiconductor layer of the field effect transistor is preferably an n-channel semiconductor layer or an n-type organic semiconductor layer. The structure of a field effect transistor will be described below as a representative.

A field effect transistor is provided via a gate insulating layer so as to overlap a source layer and a drain electrode provided separately, a semiconductor layer provided between the source electrode and the drain electrode, and the semiconductor layer. And at least one of the source electrode and the drain is constituted by the electrode of the present invention. The electrode of the present invention may be composed of only the source electrode or only the drain electrode, or both the source electrode and the drain electrode, but both the source electrode and the drain electrode are the main electrodes. It is preferable that it is comprised by the electrode of invention. In this embodiment, the case where both the source electrode and the drain electrode are constituted by the electrodes of the present invention is taken as an example. A specific structure example of a field effect transistor is shown in FIG. In FIG. 2, 11 is a source electrode, 12 is a drain electrode, 13 is a semiconductor layer, 14 is a gate insulating layer, and 15 is a gate electrode also serving as a substrate. The field effect transistor shown in FIG. 2 is configured as a bottom contact / bottom gate transistor in which a source electrode, a drain electrode, and a gate electrode are closer to the substrate than the semiconductor layer.
Hereinafter, each member and each layer of the field effect transistor will be described.

(substrate)
The field effect transistor is preferably supported on a substrate. Specific examples of the substrate include the same examples as the specific examples of the substrate in the organic electroluminescence element.

(Gate electrode)
The constituent material of the gate electrode is not particularly limited as long as it is a conductive material, and any known material can be selected and used. Examples of gate electrode materials include platinum, gold, aluminum, chromium, nickel, copper, titanium, magnesium, calcium, barium, metals such as sodium, _INO2, SnO 2, conductive metal oxides such as ITO, camphorsulfonic Conductive polymer with doped conductive polymer such as polyaniline doped with acid, polyethylenedioxythiophene doped with para-toluenesulfonic acid, and carbon black, graphite powder, metal fine particles etc. dispersed in binder A composite material etc. are mentioned. Any one of these materials may be used alone, or two or more of these materials may be used in any ratio and combination. When a silicon substrate is used as the substrate, a region in which the silicon substrate is doped with n-type impurities may be used as the gate electrode. Examples of n-type impurities include Group 15 elements such as phosphorus (P) and arsenic (As).

  The thickness of the gate electrode is not particularly limited, but is preferably in the range of usually 0.01 μm or more, particularly 0.02 μm or more, and usually 2 μm or less, especially 1 μm or less.

(Gate insulation layer)
The gate insulating layer is a layer having a function of maintaining an overlapping region between the gate electrode, the source electrode, and the drain electrode and a channel region on the gate electrode as an electrically insulating region. Here, “electrical insulation” means that the electric conductivity is 10 ⁻⁹ S / cm or less.

The material of the gate insulating layer is not particularly limited as long as it is an insulating material. For example, polymethyl (meth) acrylate, polystyrene, polyvinylphenol, polyimide, polycarbonate, polyester, polyvinyl alcohol, polyvinyl acetate, polyurethane, polysulfone, polyimide Polymers such as resins, polyamide resins, epoxy resins, phenol resins and copolymers thereof, oxides such as silicon dioxide, aluminum oxide and titanium oxide, ferroelectric oxides such as SrTiO ₃ and BaTiO ₃ , silicon nitride And dielectrics such as nitrides, sulfides and fluorides, or polymers in which particles of these dielectrics are dispersed. Any one of these materials may be used alone, or two or more of these materials may be used in any ratio and combination. When a silicon substrate is used as the substrate, a SiO ₂ layer formed by thermally oxidizing the silicon substrate may be used as the gate insulating layer.

Since the gate insulating layer is related to the leakage current to the gate electrode and the low gate voltage driving of the field effect transistor, the electric conductivity at room temperature is usually 10 ⁻⁹ S / cm or less, particularly 10 ⁻¹⁴ S / cm. The following is preferable. The relative dielectric constant is usually 2.0 or more, preferably 2.5 or more.

  The thickness of the gate insulating layer is preferably 0.01 μm or more, particularly 0.1 μm or more, more preferably 0.2 μm or more, and usually 4 μm or less, especially 2 μm or less, more preferably 1 μm or less.

(Semiconductor layer)
The constituent material of the semiconductor layer may be an organic semiconductor or an inorganic semiconductor. An oxide semiconductor is preferably used as the inorganic semiconductor.
The organic semiconductor is preferably an n-type organic semiconductor. Examples of n-type organic semiconductors include fullerene (C60, C70, C76), octaazaporphyrin, p-type organic semiconductor perfluoro, naphthalene tetracarboxylic acid anhydride, naphthalene tetracarboxylic acid diimide, perylene tetracarboxylic acid anhydride, Examples thereof include aromatic carboxylic acid anhydrides such as perylenetetracarboxylic acid diimide, imidized products thereof, and derivatives containing these compounds as a skeleton. Moreover, the preferable range and specific example of the p-type organic semiconductor used with the below-mentioned solar cell can be referred for the preferable range and specific example of the p-type organic semiconductor used as a perfluoro body.
Examples of the oxide semiconductor include zinc oxide, nickel oxide, tin oxide, titanium oxide, vanadium oxide, indium oxide, strontium titanate, and an In—Ga—Zn—O-based compound.

  If the thickness of the organic semiconductor layer is too thin, the current flowing portion is limited and the characteristics tend to be insufficient, and if it is too thick, more materials are required for film formation and the film formation time is longer. As a result, the cost increases, and the off-current tends to flow, and the on / off ratio tends not to be increased. Accordingly, the preferable thickness of the organic semiconductor layer is usually 5 nm or more, particularly 10 nm or more, more preferably 30 nm or more, and usually 10 μm or less, especially 1 μm or less, and further 500 nm or less.

(Source electrode and drain electrode)
The source electrode and the drain electrode are constituted by the electrodes of the present invention. Since the electrode of the present invention has a small work function, the source electrode and the drain electrode can be efficiently injected into the semiconductor layer by configuring the source electrode and the drain electrode with the electrode of the present invention. The contact state of the drain electrode can be ohmic contact. As a result, the driving voltage is lowered and good voltage-current characteristics can be obtained.
The work function of the electrodes used for the source electrode and the drain electrode of the transistor, if the semiconductor layer bonded to the these electrodes is an organic semiconductor layer, and the absolute value E _LUMO of the LUMO level of the organic semiconductor layer E _LUMO ± 1.5 eV, more preferably E _LUMO ± 1.0 eV, and even more preferably E _LUMO ± 0.5 eV.
In addition, the work functions of the electrodes used for the source electrode and the drain electrode of the transistor are determined from the electron affinity of the inorganic semiconductor layer, that is, the bottom of the conduction band, when the semiconductor layer bonded to these electrodes is an inorganic semiconductor layer. When the energy up to the vacuum level is χ, it is preferably χ ± 1.5 eV, more preferably χ ± 1.0 eV, and even more preferably χ ± 0.5 eV.
Furthermore, the work functions of the electrodes used for the source electrode and the drain electrode are particularly preferably equal to or lower than the work functions of the semiconductor layer bonded to these electrodes.

  The thicknesses of the source electrode and the drain electrode are not particularly limited, but are preferably 0.01 μm or more, particularly 0.02 μm or more, and usually 2 μm or less, particularly 1 μm or less.

(channel)
An organic electric field transistor performs switching or amplification operation by controlling a current in a channel portion sandwiched between a source electrode and a drain electrode by a gate electrode. In general, as the length of the channel portion (gap interval between the source electrode and the drain electrode) becomes narrower, the characteristics as a transistor increase. However, when the length is too narrow, the off-current increases or the on / off ratio decreases. There is a tendency for short channel effects to occur. Further, it is preferable that the channel width (the width between the source electrode and the drain electrode) is large in that it allows a large current to flow. However, if the channel width is too large, the area of the element increases, which is disadvantageous in terms of integration. It may become. Note that a long channel length can be obtained by using a comb electrode as the source electrode and the drain electrode.

  Accordingly, the channel length is preferably in the range of usually 100 nm or more, particularly 500 nm or more, more preferably 1 μm or more, and usually 1 mm or less, especially 100 μm or less, and more preferably 50 μm or less. The width of the channel is preferably in the range of usually 500 nm or more, especially 5 μm or more, more preferably 10 μm or more, and usually 20 mm or less, especially 5 mm or less, more preferably 1 mm or less.

[Solar cell]
The solar cell of the present invention has at least an anode, a cathode, and a structure in which a power generation layer is formed between the anode and the cathode, and the cathode is preferably composed of the electrode of the present invention. The power generation layer includes at least a photoelectric conversion layer, may be composed of only a photoelectric conversion layer, or may have one or more functional layers in addition to the photoelectric conversion layer. Examples of such other functional layers include a hole extraction layer, a hole transport layer, an electron blocking layer, a hole blocking layer, an electron transport layer, and an electron extraction layer. A specific structural example of the solar cell is shown in FIG. In FIG. 3, 21 is a substrate, 22 is a cathode, 23 is an electron extraction layer, 24 is a photoelectric conversion layer, 25 is a hole extraction layer, and 26 is an anode.
Below, each member and each layer which comprise a solar cell are demonstrated.

(substrate)
The solar cell of the present invention is preferably supported by a substrate. About the specific example of a board | substrate, the thing similar to the specific example of the board | substrate in an organic electroluminescent element can be mentioned. In addition, a metal foil or a laminate of a metal foil and a resin film can also be used as the substrate.

(cathode)
The cathode has a function of taking out electrons from the power generation layer.
The cathode is constituted by the electrode of the present invention. Since the electrode of the present invention has a small work function, the difference between the work function of the cathode and the work function of the anode is increased by forming the cathode with the electrode of the present invention, and a high open circuit voltage can be obtained. In addition, since the contact state between the cathode and the semiconductor layer (in the solar cell shown in FIG. 3, the electron extraction layer 23) can be ohmic contact, electrons from the semiconductor layer can be efficiently extracted to the cathode. Thereby, high energy conversion efficiency can be obtained.
When the semiconductor layer bonded to the cathode is an organic semiconductor layer, the work function of the electrode used for the cathode of the solar cell is E _LUMO when the absolute value of the LUMO level of the organic semiconductor layer is E _{LUMO. LUMO} ± 1.5 eV is preferred, E _LUMO ± 1.0 eV is more preferred, and E _LUMO ± 0.5 eV is even more preferred.
In addition, the work function of the electrode used for the cathode of the solar cell is as follows. When the semiconductor layer bonded to the cathode is an inorganic semiconductor layer, the electron affinity of the inorganic semiconductor layer, that is, from the bottom of the conduction band to the vacuum level. Χ ± 1.5 eV, more preferably χ ± 1.0 eV, and even more preferably χ ± 0.5 eV.
Furthermore, the work function of the electrode used for the cathode of the solar cell is preferably equal to or lower than the work function of the semiconductor layer bonded to the cathode.

(anode)
The anode has a function of taking out holes from the power generation layer.
It is preferable to use a conductive transparent material having a large work function for the anode. Specific examples of the conductive material used for the anode include the same materials as the specific examples of the anode in the organic electroluminescence element.

(Photoelectric conversion layer).
The photoelectric conversion layer is a layer that converts light energy into electric energy.
Examples of the material used for the photoelectric conversion layer include thin film single crystal silicon, thin film polycrystalline silicon, amorphous silicon, microcrystalline silicon, spherical silicon, an inorganic semiconductor, an organic dye, and an organic semiconductor. The photoelectric conversion layer may be a multi-junction type such as a stack type, a stacked type, or a tandem type.
The inorganic semiconductor (compound semiconductor) is preferably a chalcogenide-based semiconductor containing a chalcogen element such as S, Se, or Te, more preferably a group I-III-VI2 semiconductor (chalcopyrite), and a group I element. It is more preferable to use a Cu-III-VI2 group semiconductor using Cu as a CIS-based semiconductor [CuIn (Se1-ySy) 2; 0 ≦ y ≦ 1] or a CIGS-based semiconductor [Cu (In1-xGax) (Se1). −ySy) 2; 0 <x <1, 0 ≦ y ≦ 1]] is particularly preferable.

  When the photoelectric conversion layer is composed of an organic semiconductor, a bulk heterojunction type having a layer (i layer) in which a p-type organic semiconductor and an n-type organic semiconductor are phase-separated in the layer, and a layer (p layer) including a p-type organic semiconductor; It is preferable to use a laminated type (hetero pn junction type) in which layers (n layers) including an n-type organic semiconductor are laminated, a PIN type, a Schottky type, or a combination of these, and in particular, a bulk hetero junction type. Is more preferable.

  As the p-type organic semiconductor, a π-conjugated polymer material, a π-conjugated low molecular organic compound, or the like can be preferably used. The conjugated polymer material is obtained by polymerizing single or plural kinds of π-conjugated monomers. As π-conjugated monomers, thiophene, fluorene, carbazole, diphenylthiophene, dithienothiophene, dithienosilole, dithienocyclohexane, benzothiadiazole, thienothiophene, imidothiophene, benzodithiophene, and derivatives containing these compounds as a skeleton Etc. These monomers may be directly bonded, or may be bonded via CH═CH, C 3 C, N, or O. Low molecular organic semiconductor materials include condensed aromatic hydrocarbons such as pentacene and naphthacene, oligothiophenes having four or more thiophene rings, porphyrin compounds, tetrabenzoporphyrin compounds and their metal complexes, phthalocyanine compounds and their metal complexes, etc. Is mentioned.

  Examples of n-type semiconductor compounds include fullerenes (C60, C70, C76), octaazaporphyrins, perfluoro compounds of the above p-type organic semiconductors, naphthalenetetracarboxylic acid anhydride, naphthalenetetracarboxylic acid diimide, and perylenetetracarboxylic acid anhydride. And aromatic carboxylic acid anhydrides such as perylenetetracarboxylic acid diimide, imidized products thereof, and derivatives containing these compounds as a skeleton.

(Electronic extraction layer)
The electron extraction layer is a layer that facilitates electron injection into the cathode.
Examples of the material for the electron extraction layer include alkali metal salts such as LiF, n-type oxide semiconductors such as titanium oxide (TiOx) and zinc oxide (ZnO). In addition, phenanthrene derivatives such as bathocuproin (BCP) and bathophenanthrene (Bphen), and phosphine compounds having a P = O or P = S structure can also be used as the material for the electron extraction layer. It is preferable to use a phosphine compound to which a hydrogen group or an aromatic heterocyclic group is bonded.

(Hole extraction layer)
The hole extraction layer is a layer that facilitates hole injection into the anode.
As a material for the hole extraction layer, a conductive polymer in which polythiophene, polypyrrole, polyaniline, or the like is doped with sulfonic acid, halogen, or the like, or a metal oxide having a high work function such as molybdenum oxide or nickel oxide can be used.

  In this solar cell, when light such as sunlight is irradiated, the material constituting the photoelectric conversion layer is excited to generate charges. Among the charges, holes are transported to the positive electrode side and taken out to the anode, and electrons are transported to the cathode side and taken out to the cathode, and an electromotive force is generated between the anode and the cathode. A current flowing from the anode to the cathode can be obtained by connecting a conductor between the anode where the electromotive force is generated and the cathode.

  The formation method of each layer and each member constituting the element of the present invention is not particularly limited, and either a dry process or a wet process may be used. Moreover, when patterning each layer and each member, the lithography method can be used. For the description of the lithography method, specific methods and steps, reference can be made to the description of the lithography method in the method for producing a structure of the present invention, specific methods and steps.

The features of the present invention will be described more specifically with reference to the following examples. The following materials, processing details, processing procedures, and the like can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.
The reflectance was measured using a 1280 type tabletop thin film analyzer (n & k), and the work function was measured using a photoelectron spectrometer (AC-2) manufactured by Riken Keiki Co., Ltd. The output characteristics of the transistor were measured using a semiconductor parameter analyzer (manufactured by Agilent Technologies: HP4155) in an inert atmosphere having an oxygen concentration and a water concentration of 1 ppm or less. The light emitting area of the organic electroluminescence element was measured using an organic EL reliability evaluation apparatus evaluation and measurement apparatus EAS-26B (System Giken). Moreover, the film formation by the vacuum evaporation method was performed by a co-evaporation method using a separate evaporation source for each constituent element at a vacuum degree of 1 × 10 ⁻⁴ Pa or less.

Example 1 Production and Evaluation of Electrode Consisting of MgCa Alloy An MgCa film having a thickness of 50 nm was formed on a glass substrate by a vacuum vapor deposition method to obtain an electrode. At this time, the Ca concentration was 6 atomic% or 25 atomic%, and two types of MgCa layers were formed.
For comparison, an Al layer, an MgAu layer, and an Mg layer were each formed to a thickness of 50 nm on a glass substrate by vacuum deposition. At this time, the concentration of Au in the MgAu layer was 10 atomic%.
FIG. 4 shows the reflectance spectrum of each layer produced. In FIG. 4, “Mg94Ca6” represents an MgCa layer containing 6 atomic% of Ca, and “Mg75Ca25” represents an MgCa layer containing 25 atomic% of Ca.
As shown in FIG. 4, the MgCa layer had a high reflectance in the visible region regardless of whether the Ca concentration was low or high.

Example 2 Production and Evaluation of Structure Made of MgCa Alloy A comb-shaped MgCa layer was produced by photolithography on a silicon substrate with an oxide film as described below to obtain a structure.
First, after cleaning the silicon substrate with an oxide film, surface treatment was performed with hexamethyldisilazane (HMDS). Next, a lift-off layer forming solution (Rohm and Haas Co., Ltd .: LOL1000) is applied onto this substrate by spin coating, and then baked at 150 ° C., and then a positive resist (Tokyo Ohka Kogyo Co., Ltd.) Co., Ltd .: TMSR-8900) was applied by spin coating and baked at 110 ° C. Next, the positive resist is exposed through a quartz photomask having a reversal pattern with respect to the target pattern (comb pattern), and the exposed portion is removed with a developer (manufactured by Tokyo Ohka Kogyo Co., Ltd .: NMD-3). A resist film patterned in a reverse pattern was obtained. Subsequently, an MgCa alloy was formed on the glass or silicon oxide-coated silicon or quartz substrate by a vacuum deposition method so as to cover the resist mask, thereby forming an MgCa layer having a thickness of 50 nm. At this time, the concentration of Ca in the MgCa alloy was 10 atomic%. Thereafter, the resist film and the MgCa layer immediately above the resist film were peeled off using N-methylpyrrolidone. Through the above steps, a comb-shaped MgCa layer (structure) was produced.
When the cross section of the produced MgCa layer was observed, the corners of each comb tooth (convex portion) were relatively sharp and stable. From this, it was confirmed that the MgCa layer has very high lithography suitability.
Moreover, about the produced MgCa layer of the comb-shaped pattern, the photoelectron yield was measured by irradiating ultraviolet rays with a photoelectron spectrometer. FIG. 5 is a graph in which the irradiation light energy of ultraviolet rays is plotted on the horizontal axis and the photoelectron yield 0.5 power (square root) is plotted on the vertical axis. In FIG. 5, “0h”, “6h”, and “24h” represent sample storage (atmosphere) time from the completion of the process to the measurement of the electron yield. From FIG. 5, the work function of the MgCa layer of this comb pattern is 3.6 eV, which is a very small value.

(Example 3) Production and evaluation of organic transistor using MgCa alloy as source electrode and drain electrode Heavy doped n ⁺ -Si wafer (hereinafter referred to as thermal insulation film (SiO ₂ ) having a thickness of 300 nm as an insulating layer) And “n ⁺ -Si substrate”). Here, the n ⁺ -Si substrate was used as a substrate, the n ⁺ region was used as a gate electrode, and a thermal oxide film was used as a gate insulating layer.
Next, a comb-shaped MgCa layer was formed on the n ⁺ -Si substrate in the same procedure as in Example 2. However, here, the Ca concentration in the MgCa alloy is 10 atomic%, and the resist film and the MgCa layer immediately above the resist film are peeled off using a remover solution (Rohm and Haas: Micro posit remover 116) and acetone. went. In the formed MgCa layer, the comb teeth alternately correspond to the source electrode and the drain electrode, respectively, and have a total of 20 electrode pairs. The distance between the source electrode and the drain electrode was 25 μm, and the channel width was 4 mm.
Next, a C60 (n-type semiconductor) film was formed on the n ⁺ -Si substrate by vacuum deposition so as to cover the source electrode and the drain electrode, thereby forming a C60 layer having a thickness of 50 nm. At this time, the deposition rate was 0.01 nm / s.
Through the above process, a bottom-gate / bottom-contact transistor was manufactured.
The drain voltage-drain current characteristics of the manufactured transistor are shown on the left of FIG.
Looking at the left side of FIG. 6, it can be seen that the drain voltage-drain current curve increases linearly through the origin. Therefore, in this transistor, the current path composed of the source electrode, the C60 layer, and the drain electrode satisfies V = IR (V: drain voltage, I: drain current, R: resistance). Was confirmed to be in ohmic contact.

Comparative Example 1 Fabrication and Evaluation of Organic Transistor Using Au as Source and Drain Electrode A transistor was formed in the same manner as in Example 3 except that source electrode and drain electrode were formed using Au instead of MgCa alloy. Was made.
The drain voltage-drain current characteristics of the manufactured transistor are shown on the right of FIG.
Looking at the right side of FIG. 6, the drain current could not be observed in this measured voltage range, and good output characteristics as shown in FIG. 6 could not be obtained. This is presumably because the energy barrier between the source and drain electrodes and the C60 layer is large and is in a Schottky contact.

(Example 4) Production and evaluation of organic electroluminescence device using MgCa alloy as cathode Cathodic thin film was deposited on glass substrate on which an anode made of indium tin oxide (ITO) having a thickness of 100 nm was formed. And the degree of vacuum was 1 × 10 ⁻⁴ Pa. Specifically, first, HATCN was formed to a thickness of 10 nm on ITO, and TrisPCz was formed to a thickness of 30 nm thereon. Next, mCBP and 4CzIPN were co-evaporated from different deposition sources to form a layer having a thickness of 30 nm as a light emitting layer. At this time, the concentration of 4CzIPN was 15% by weight. Next, T2T was formed to a thickness of 10 nm, and BPyTP2 was formed thereon to a thickness of 55 nm. Next, except that a quartz photomask having a pattern corresponding to the planar shape of the cathode was used, a cathode was formed in the same manner as in the source electrode and drain electrode formation process of Example 3 to obtain an organic electroluminescence element. At this time, the concentration of Ca in the MgCa alloy was 30 atomic%.

(Comparative Example 2) Production and evaluation of organic electroluminescence device using Al or MgAu alloy as cathode The same procedure as in Example 4 was performed except that Al or MgAu alloy was used instead of MgCa alloy when forming the cathode. Thus, two types of organic electroluminescence elements having different cathode materials were produced.
The organic electroluminescent elements produced in Example 4 and Comparative Example 2 were left under conditions of room temperature of 25 ° C. and relative humidity of 50%, and the change with time of the size of the light emitting region was examined. The result is shown in FIG.
As shown in FIG. 7, the organic electroluminescence device having a cathode made of an MgCa alloy hardly changed the light emission area even when time passed, and kept a wide light emission area even after 200 hours passed. From this, it was confirmed that the electrode made of MgCa alloy was excellent in barrier properties.

(Example 5) Production and evaluation of electrode made of MgCa alloy, MgCaAg alloy or MgCaAl alloy By vacuum deposition, an MgCa layer, MgCaAg layer or MgCaAl layer was formed on a glass substrate with a film thickness of 100 nm, respectively. It was.
For comparison, an Al layer having a thickness of 100 nm was formed on a glass substrate by a vacuum deposition method to form an electrode.
Table 1 shows the composition ratio and work function of each layer produced. Moreover, the reflectance spectrum of each produced layer is shown in FIG. The composition of the alloy shown in FIG. 8 corresponds to the composition of the alloy shown in Table 1, and the numerical value represents the composition ratio in atomic%. The same applies to the alloy composition in the following description.

As shown in Table 1, the work functions of the MgCaAg alloy and the MgCaAl alloy were extremely small values as in the case of the MgCa alloy.
Further, from FIG. 8, the MgCa layer, the MgCaAg layer, and the MgCaAl layer all show a high reflectance in the visible light region. In particular, the MgCaAg layer and the MgCaAl layer are shorter than the MgCa layer in the short wavelength region of 450 nm or less. It can be seen that a high reflectance of 80% or more is exhibited. From this, it was found that by adding Ag or Al to the alloy as the third component, a high reflectance of 80% or more can be achieved in the entire visible light region.

(Example 6) Preparation and evaluation of organic electroluminescence device using MgCaAg alloy or MgCaAl alloy as cathode When forming the cathode, MgCa having the composition shown in Table 2 instead of the MgCa alloy having a Ca concentration of 30 atomic% Three types of organic electroluminescence elements having different cathode materials were produced in the same manner as in Example 4 except that an alloy, MgCaAg alloy, and MgCaAl alloy were used.
The produced organic electroluminescence device was left standing under conditions of room temperature 25 ° C. and relative humidity 50%, and the change over time of the size of the light emitting region was examined. FIG. Table 2 shows the time to reach% (electrode life). For comparison, the measurement results of the organic electroluminescence element using Al as the cathode are also shown in FIG. The composition of the alloy shown in FIG. 9 corresponds to the alloy composition of the cathode shown in Table 2, and each indicates an organic electroluminescence element using the alloy as a cathode.

From the measurement results of the electrode lifetime shown in FIG. 9 and Table 2, the organic electroluminescence device using the MgCaAg alloy or MgCaAl alloy as the cathode decreases the emission region over time as compared with the organic electroluminescence device using the MgCa alloy as the cathode. It can be seen that is significantly suppressed. From this, it was found that the atmospheric stability of the electrode is greatly improved by adding Ag or Al as the third component to the electrode alloy.
When the same test was performed on the Mg77Ca8Ag15 alloy layer, the same reflection characteristics and electrode life characteristics (atmospheric stability) as the Mg73Ca5Ag22 alloy layer were shown.
Further, when the Mg73Ca5Ag22 alloy, the Mg77Ca8Ag15 alloy, or the Mg88Ca9Al3 alloy was formed in a comb pattern by the same method as in Example 2, a good pattern shape equivalent to the MgCa alloy in Example 2 was obtained. It was confirmed that the aptitude was very high. Further, using a Mg73Ca5Ag22 alloy, a Mg77Ca8Ag15 alloy, or a Mg88Ca9Al3 alloy as a source electrode material and a drain electrode material, a transistor was fabricated in the same manner as in Example 3, and the drain voltage-drain current characteristics were measured. Thus, it was confirmed that each electrode and the C60 layer were in ohmic contact.

  The electrode of the present invention has a low work function, can be brought into ohmic contact with the semiconductor layer, and has high lithography suitability. For this reason, by using the electrode of the present invention, it is possible to realize an element having a low driving voltage and good element characteristics. For this reason, this invention has high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole injection layer 4 Hole transport layer 5 Light emitting layer 6 Electron transport layer 7 Cathode 11 Source electrode 12 Drain electrode 13 Semiconductor layer 14 Gate insulating layer 15 Gate electrode 21 Substrate 22 Cathode 23 Electron extraction layer 24 Photoelectric conversion Layer 25 Hole extraction layer 26 Anode

Claims (23)

  An electrode having an alloy containing at least Mg and Ca.   The content of Ca contained in the alloy is 3 to 50 atomic% of the total number of atoms of the alloy, and the content of Mg contained in the alloy is 50 to 95 atomic% of the total number of atoms of the alloy. The electrode as described.   The electrode according to claim 1, wherein the alloy contains Ag, Al, Cr, Cu, Zn, or Li as a third component of an alloy other than Mg and Ca.   The electrode according to claim 3, wherein the content of the third component contained in the alloy is 0.1 to 30 atomic% of the total number of atoms of the alloy.   The electrode according to claim 4 or 5, wherein a total content of Ca and the third component contained in the alloy is 10 to 30 atomic% of the total number of atoms of the alloy.   The electrode according to claim 1, wherein a work function of the alloy is 4.0 eV or less.   A structure made of an alloy containing at least Mg and Ca and having irregularities with a pitch of 500 nm to 200 μm on the surface.   The structure according to claim 7, wherein the plurality of strips made of an alloy containing at least Mg and Ca have a structure in which the strips are arranged in parallel at a pitch of 500 nm to 200 μm.   A manufacturing method of a structure including a step of forming an alloy containing at least Mg and Ca by a lithography method.   The method of manufacturing a structure according to claim 9, wherein the step is a step of forming irregularities on a surface of an alloy containing at least Mg and Ca by a lithography method.   The method of manufacturing a structure according to claim 9, wherein the step includes a step of forming an alloy containing at least Mg and Ca by a lift-off method.   The manufacturing method of the structure according to any one of claims 9 to 11, wherein the lithography method is a photolithography method.   The manufacturing method of the structure according to any one of claims 9 to 12, wherein the alloy is an alloy film formed on a substrate.   The method for manufacturing a structure according to claim 13, wherein the alloy film is formed by a sputtering method.   A connection structure having a structure in which an alloy containing at least Mg and Ca and a semiconductor are electrically connected.   The connection structure according to claim 15, wherein the semiconductor is an organic semiconductor.   The connection structure according to claim 15, wherein the semiconductor is an oxide semiconductor.   The connection structure according to claim 15, wherein the alloy and the semiconductor are in ohmic contact.   The element which has an electrode of any one of Claims 1-6.   The device according to claim 19, wherein the device has a structure in which the electrode and the semiconductor are electrically connected.   21. The device according to claim 19 or 20, wherein the device is an organic light emitting device, a solar cell, or a transistor.   The device of claim 21, wherein the device is an organic transistor.   The device of claim 21, wherein the device is an oxide transistor.

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