WO2017187885A1 - Electrode for organic element, and organic element - Google Patents

Abstract

Disclosed is an electrode for an organic element, said electrode being to be connected to an organic semiconductor. The electrode is provided with an electrode body, and an organic semiconductor polycrystalline film, which is provided on a first surface of the electrode body, and which reduces contact resistance at a contact interface to the organic semiconductor.

Description

Electrode for organic element and organic element

The present invention relates to an organic element electrode and an organic element.
This application claims priority based on Japanese Patent Application No. 2016-088459 filed in Japan on April 26, 2016, the contents of which are incorporated herein by reference.

Organic elements such as organic transistors and organic electroluminescence (EL) elements are highly flexible and excellent in processability. For this reason, attention has recently been focused on organic elements.

The organic element has an organic semiconductor and an electrode for energizing the organic semiconductor. The organic element has a higher contact resistance at the interface between the organic semiconductor and the electrode than the inorganic semiconductor element using the inorganic semiconductor. The contact resistance at the interface between the semiconductor and the electrode hinders the injection of electrons and holes into the semiconductor and the extraction of electrons and holes from the semiconductor. For this reason, the contact resistance at the interface between the semiconductor and the electrode is one of the causes of an increase in driving voltage and power consumption of the semiconductor element.

In an inorganic semiconductor element, a highly doped region is formed in a portion in contact with an electrode of a semiconductor substrate in order to reduce contact resistance. In the organic element, an attempt is made to provide a layer corresponding to a highly doped region in an inorganic semiconductor between the organic semiconductor and the electrode from the same idea.

For example, Non-Patent Document 1 describes that cesium fluoride is inserted into the interface between the organic semiconductor and the electrode. By inserting cesium fluoride having high electron conductivity at the interface between the organic semiconductor and the electrode, the efficiency of injecting electrons into the organic semiconductor is increased.

For example, Non-Patent Document 2 describes that an oxide such as molybdenum oxide is inserted at the interface between the organic semiconductor and the electrode. Through the valence band of the oxide, the hole injection efficiency at the interface between the organic semiconductor and the electrode is increased.

For example, Non-Patent Document 3 describes that a self-assembled monolayer (SAM) is inserted at the interface between an organic semiconductor and an electrode. Self-assembled monomolecules have a non-uniform charge distribution within the molecule and form electric dipoles. The electric dipole shifts the vacuum level at the contact interface between the organic semiconductor and the electrode. As a result, the Fermi level of the electrode changes relative to the energy level of electrons and holes in the organic semiconductor, and the efficiency of injecting electrons or holes into the organic semiconductor increases according to the direction of the electric dipole.

As described above, when any one of the layers described in Non-Patent Documents 1 to 3 is inserted between the organic semiconductor and the metal, the contact resistance at the interface between the organic semiconductor and the electrode is smaller than when no layer is inserted. To reduce. However, the insertion of these layers can only improve the conduction characteristics when either electron or hole carriers pass through the interface between the organic semiconductor and the electrode. That is, it is difficult to improve the contact resistance to both electrons and holes.

For the practical application of organic elements, organic elements with low contact resistance are required regardless of the carrier. However, such an organic element has not been realized.

The present invention has been made in view of the above problems, and by inserting an organic semiconductor polycrystalline film between an organic semiconductor and an electrode, contact at the contact interface between the organic semiconductor and the electrode body is possible regardless of the conductive carriers. An electrode for an organic element capable of reducing resistance is provided.

1st aspect of this invention is an electrode for organic elements connected to an organic semiconductor, Comprising: It is provided in the 1st surface of an electrode body and the said electrode body, and reduces the contact resistance in the contact interface with the said organic semiconductor An organic semiconductor polycrystalline film.

According to a second aspect of the present invention, there is provided the organic element electrode according to the first aspect, wherein the organic semiconductor polycrystal film is provided on the third surface opposite to the second surface on which the electrode body is provided. A molecular film may be further provided.

In a third aspect of the present invention, in the organic element electrode according to the first or second aspect, the organic semiconductor polycrystalline film may have a thickness of 1 nm to 50 nm.

According to a fourth aspect of the present invention, in the electrode for an organic element according to the second or third aspect, the thickness of the organic molecular film may be 1 nm or more and 10 nm or less.

According to a fifth aspect of the present invention, in the electrode for an organic element according to any one of the first to fourth aspects, the organic semiconductor polycrystalline film has an energy level of a lowest unoccupied molecular orbital (LUMO). However, it may be equal to or higher than the Fermi level of the electrode body and not more than a value obtained by adding 2.0 eV to the energy level of the lowest unoccupied molecular orbital (LUMO) of the organic semiconductor to be connected.

According to a sixth aspect of the present invention, in the organic element electrode according to any one of the first to fifth aspects, the organic semiconductor polycrystalline film has an energy level of a highest occupied molecular orbital (HOMO). Further, it may be equal to or lower than the Fermi level of the electrode body and a value obtained by subtracting 2.0 eV from the energy level of the highest occupied molecular orbital (HOMO) of the organic semiconductor to be connected.

According to a seventh aspect of the present invention, in the electrode for an organic element according to any one of the first to sixth aspects, the organic molecular film is a saturated hydrocarbon or a saturated hydrocarbon that is solid at room temperature. Derivatives may also be included.

An eighth aspect of the present invention is the electrode for an organic element according to any one of the first to seventh aspects, wherein the Fermi level of the electrode body is the lowest unoccupied molecular orbital of the organic semiconductor to be connected. (LUMO) energy level is not less than 3.0 eV or a value obtained by adding 4.0 eV to the highest occupied molecular orbital (HOMO) energy level of the organic semiconductor to be connected. .

According to a ninth aspect of the present invention, there is provided an organic element comprising the organic element electrode according to any one of the first to eighth aspects, and the organic semiconductor polycrystalline film of the organic element electrode. An organic semiconductor connected to the formed fourth surface.

According to the aspect of the present invention, an intermediate level between the energy level of the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO) of the organic semiconductor and the Fermi level of the electrode body. Has a level. Therefore, the electrode for organic elements according to the above aspect can reduce the contact resistance at the contact interface between the organic semiconductor and the electrode body regardless of the carriers to be conducted.

It is a cross-sectional schematic diagram of the organic element concerning 1st Embodiment. It is the figure which showed the energy state of the contact interface of an electrode body and an organic semiconductor. It is the figure which showed the energy state of the contact interface of an electrode body and an organic semiconductor. It is a graph which shows the relationship between an organic-semiconductor polycrystalline film and electron mobility. It is a cross-sectional schematic diagram of the organic element concerning 2nd Embodiment. It is a figure which shows the result of having measured the surface state of each layer of the organic element concerning 2nd Embodiment with the atomic force microscope (AFM). It is a graph which shows the relationship between an organic molecular film and electron mobility. It is a cross-sectional schematic diagram of the organic element concerning 3rd Embodiment. It is the figure which compared the contact resistance at the time of performing electron injection with respect to the field effect transistor of Example 1, Example 2, the comparative example 1, and the comparative example 2. FIG. It is the figure which compared the contact resistance at the time of hole-injecting with respect to the field effect transistor of Example 1, Example 2, the comparative example 1, and the comparative example 2. FIG. It is the graph which compared the contact resistance at the time of performing electron injection. It is the graph which compared the contact resistance at the time of performing hole injection. It is the result of having measured the electron mobility and the hole mobility of the field effect transistor of the Example which used the organic semiconductor as rubrene, and a comparative example. It is the result of having measured the electron mobility and the hole mobility of the field effect transistor of the Example which used organic semiconductor as BP2T, and a comparative example. It is a graph which shows the transistor characteristic of the field effect transistor of the structure of this application. It is a graph which shows the transistor characteristic of the field effect transistor of the modification of FIG.

Hereinafter, the present embodiment will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, in order to make the features of the present embodiment easier to understand, the features may be enlarged for the sake of convenience, and the dimensional ratios of the components are different from actual ones. There is. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present embodiment is not limited to these, and can be appropriately modified and implemented without changing the gist thereof.

The present invention has been made by finding that by inserting an organic semiconductor polycrystalline film between an organic semiconductor and an electrode, it is possible to reduce the contact resistance at the contact interface between the organic semiconductor and the electrode body regardless of conducting carriers. It is a thing.

First Embodiment FIG. 1 is a schematic cross-sectional view of an organic element 20 according to a first embodiment. The organic element 20 includes a substrate 5 having a gate substrate 5A and an insulating layer 5B, a protective layer 4, an organic semiconductor 3, and an organic element electrode 10. When a voltage is applied to the gate substrate 5A, a channel is formed in the organic semiconductor 3, and a current flows between the two organic element electrodes 10. That is, the organic element 20 shown in FIG. 1 is a field effect transistor (FET).

(Electrode for organic elements)
The organic element electrode 10 is a set of two. Hereinafter, the first organic element electrode 10 is referred to as an electron injection electrode 10A, and the second organic element electrode 10 is referred to as a hole injection electrode 10B.
When negative and positive voltages are applied to the electron injection electrode 10A and the hole injection electrode 10B, respectively, with reference to the potential of the gate substrate 5A, electrons are injected from the electron injection electrode 10A to the organic semiconductor 3, and the hole injection electrode 10B. Holes are injected into the organic semiconductor 3.

The organic element electrode 10 includes an electrode body 1 and an organic semiconductor polycrystalline film 2. Hereinafter, the electrode body 1 in the electron injection electrode 10A is referred to as an electron injection electrode body 1A, and the electrode body 1 in the hole injection electrode 10B is referred to as a hole injection electrode body 1B. The organic semiconductor polycrystalline film 2 in the electron injection electrode 10A is referred to as an electron injection polycrystalline film 2A, and the organic semiconductor polycrystalline film 2 in the hole injection electrode 10B is referred to as a hole injection polycrystalline film 2B.

The electrode body 1 has conductivity. For the electrode body 1, a single metal, an alloy of a plurality of metals, a metal compound of a plurality of metals, or the like can be used. The electrode body 1 may be a transparent conductor such as indium tin oxide (ITO).

Electron injection electrode body 1 A injects electrons into organic semiconductor 3. Therefore, it is preferable that the Fermi level of the electrode body for electron injection 1A is not less than a value obtained by subtracting 3.0 eV from the energy level of the lowest unoccupied molecular orbital (LUMO) of the organic semiconductor 3 to be connected. Hereinafter, the energy level of the lowest unoccupied molecular orbital is referred to as the LUMO level.

The energy level difference between the Fermi level of the electrode body 1A for electron injection and the LUMO level of the organic semiconductor 3 becomes an electron injection barrier when electrons are injected into the organic semiconductor 3. By reducing the energy level difference between the Fermi level of the electron injection electrode body 1A and the LUMO level of the organic semiconductor 3, the electron injection efficiency is increased.

For example, when 5,6,11,12-tetraphenylnaphthacene (hereinafter referred to as “rubrene”) or biphenylbithiophene (hereinafter referred to as “BP2T”) is used for the organic semiconductor 3, an electrode body 1 A for electron injection Alkali metal, alkaline earth metal, aluminum, and the like can be used for. The Fermi level of calcium approximates the LUMO level of rubrene and BP2T, and can be suitably used for the electrode body 1A for electron injection.

On the other hand, many of alkali metals and alkaline earth metals are unstable in the air and easily deteriorate. When long-term reliability is required for the organic element 20, it is preferable to select the electrode body for electron injection 1A with emphasis on stability. For example, a material having excellent conductivity and stability, such as gold, silver, copper, platinum, and ITO, is selected as the electron injection electrode body 1A.

From the viewpoint of improving the stability while reducing the electron injection barrier, it is preferable to use magnesium, aluminum, magnesium silver alloy or the like for the electron injection electrode body 1A.

The hole injection electrode body 1 </ b> B injects holes into the organic semiconductor 3. Therefore, the Fermi level of the hole injection electrode body 1B is preferably not more than a value obtained by adding 4.0 eV to the energy level of the highest occupied molecular orbital (HOMO) of the organic semiconductor 3 to be connected. Hereinafter, the energy level of the highest occupied molecular orbital is referred to as the HOMO level.

The energy level difference between the Fermi level of the hole injection electrode body 1 </ b> B and the HOMO level of the organic semiconductor 3 becomes a hole injection barrier when holes are injected into the organic semiconductor 3. Therefore, by reducing the energy level difference between the Fermi level of the hole injection electrode body 1B and the HOMO level of the organic semiconductor 3, the hole injection efficiency is increased.

For example, when rubrene or BP2T is used for the organic semiconductor 3, it is preferable to use gold, platinum, silver, or copper as the hole injection electrode body 1B. In particular, the Fermi level of gold is particularly preferable because it approximates the HOMO level of rubrene and BP2T.

If the electron injection electrode body 1A and the hole injection electrode body 1B are made of the same material, the organic element 20 can be easily manufactured. In order to maintain high electron and hole injection efficiency and high environmental stability, it is preferable to use gold for the electron injection electrode body 1A and the hole injection electrode body 1B.

The organic semiconductor polycrystalline film 2 is formed on one surface of the electrode body 1.
The “organic semiconductor polycrystalline film” includes everything except a single crystal of an organic semiconductor. For example, the “organic semiconductor polycrystalline film” includes a film in which a plurality of crystal structures are mixed, a film having an amorphous structure in which no crystal structure is formed, and the like.

Whether or not it is the organic semiconductor polycrystalline film 2 can be determined from X-ray diffraction (XRD). A diffraction pattern obtained by XRD measurement of the organic semiconductor polycrystalline film 2 is one of the following two diffraction patterns. The first diffraction pattern is a diffraction pattern in which a peak other than a peak corresponding to a predetermined crystal orientation is detected. This diffraction pattern corresponds to the case where a plurality of crystal structures are mixed in the organic semiconductor polycrystalline film 2. The second diffraction pattern is a diffraction pattern in which a prominent peak is not detected and a broad peak is detected. This diffraction pattern corresponds to the case where the organic semiconductor polycrystalline film 2 is amorphous.

Whether or not it is the organic semiconductor polycrystalline film 2 can also be judged from the manufacturing process. In order to produce a single crystal, it is necessary to perform crystal growth in any of a gas phase method, a liquid phase method, and a solid phase method. Therefore, it is difficult to obtain a single crystal by a method in which molecules collide with a deposition surface such as vacuum deposition. That is, it can be said that the organic film produced by a method such as vacuum deposition is not a single crystal but an organic semiconductor polycrystalline film 2.

The crystallinity of the organic semiconductor polycrystalline film 2 is worse than that of the organic semiconductor 3. Here, “crystallinity” is an index measured by XRD. When the crystallinity is good, only the peak of the diffraction pattern depending on the crystal plane is confirmed, and when the crystallinity is poor, each peak of the diffraction pattern depending on the crystal plane becomes broad and the peak of the diffraction pattern dependent on the crystal plane And a different peak is confirmed.

The difference in crystallinity can also be confirmed from the surface shape. If the crystallinity is poor, the grain size of the surface shape becomes small. Here, the grain means a region having the same crystal structure. The grain size of the organic semiconductor polycrystalline film 2 is preferably 5 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less. The lower limit value is preferably as small as possible, but about 450 nm is the grain size that is practically formed.

The grain size is obtained as follows. First, an area of 5 μm × 5 μm is measured by AFM. Arbitrary 15 grains in the region are selected, and the diameter of a circle inscribed in each grain is obtained. And let the average value of those diameters be a grain size.

The organic semiconductor polycrystalline film 2 can use any organic material according to the organic semiconductor 3 to be connected. For example, rubrene, BP2T, anthracene, tetracene, pentacene, tetracyanoquinodimethane, α, ω-bis (biphenyl) terthiophene, difnat [2,3-b: 2 ′, 3′-f] thiopheno [3,2 -B] Thiophene, 1,4-bis (5-phenylthiophen-2-yl) benzene and the like can be used. Rubrene and BP2T are particularly preferable because of high carrier mobility.

The organic semiconductor polycrystalline film 2 reduces the contact resistance at the contact interface between the electrode body 1 and the organic semiconductor 3. Hereinafter, the reason why the contact resistance is lowered will be described by taking the case where electrons are injected into the organic semiconductor 3 as an example.

2A and 2B are diagrams showing the energy state of the contact interface between the electrode body 1 and the organic semiconductor 3. FIG. 2A is an energy state diagram when the organic semiconductor polycrystalline film 2 is not inserted, and FIG. 2B is an energy state diagram when the organic semiconductor polycrystalline film 2 is inserted.

As shown in FIG. 2A, when the organic semiconductor polycrystalline film 2 is not inserted, in order to inject electrons from the electrode body 1 into the organic semiconductor 3, it is necessary to exceed the Schottky barrier. Many of electrons present in the Fermi surface E _F of the electrode body 1, when the large external force is not applied, can not exceed the Schottky barrier. Therefore, the electron injection efficiency at the interface between the electrode body 1 and the organic semiconductor 3 is poor.

On the other hand, as shown in FIG. 2B, when the organic semiconductor polycrystalline film 2 is inserted, a band gap level is formed in the organic semiconductor polycrystalline film 2. This is because the organic semiconductor polycrystalline film 2 has poor crystallinity compared to a single crystal and has a disordered crystal structure. Electrons present in the Fermi surface E _F of the electrode body 1, leading to the LUMO level of the organic semiconductor 3 via the bandgap level. Therefore, when electrons are injected from the electrode body 1 into the organic semiconductor 3, the effective barrier height that the electrons need to exceed is lowered. For example, this can be expected to lower the injection barrier of 1.97 eV for hole injection and 2.60 eV for electron injection. That is, the electron injection efficiency at the interface between the electrode body 1 and the organic semiconductor 3 is improved.

When the electron injection efficiency is improved, the electron conduction efficiency in the stacking direction of the organic element 20 is increased. That is, the contact resistance between the electrode body 1 and the organic semiconductor 3 is reduced by providing the organic semiconductor polycrystalline film 2. Even when holes are injected, the contact resistance is reduced by the same principle.

The thickness of the organic semiconductor polycrystalline film 2 is preferably 1 nm or more and 50 nm or less. Moreover, the result of having measured the electron mobility at the time of changing the thickness of the organic-semiconductor polycrystalline film (BP2T) 2 is shown in FIG. Thereby, the thickness of the organic semiconductor polycrystalline film 2 is more preferably 4 nm or more and 30 nm or less, and further preferably 8 nm or more and 20 nm or less.

By making the thickness of the organic semiconductor polycrystalline film 2 equal to or less than a predetermined thickness, the organic semiconductor polycrystalline film 2 becomes a resistor, and it is possible to avoid inhibiting the conduction between the electrode body 1 and the organic semiconductor 3. Further, by setting the thickness of the organic semiconductor polycrystalline film 2 to a predetermined thickness or more, a band gap level can be sufficiently formed at the interface between the electrode body 1 and the organic semiconductor 3.

The organic semiconductor polycrystalline film 2 may be made of different materials or the same material for the electron-injecting polycrystalline film 2A and the hole-injecting polycrystalline film 2B. From the viewpoint of ease of manufacture, it is preferable to use the same material for the electron injection polycrystalline film 2A and the hole injection polycrystalline film 2B.

From the viewpoint of energy, each of the electron injection polycrystalline film 2A and the hole injection polycrystalline film 2B preferably satisfies the following conditions.

The LUMO level of the electron injection polycrystalline film 2A is equal to or higher than the Fermi level of the electrode body 1 and is preferably equal to or less than the value obtained by adding 2.0 eV to the LUMO level of the organic semiconductor 3, and 0.2 eV is added. It is more preferable that the value is not more than the value. Further, it is more preferable to be between the Fermi level of the electrode body 1 and the LUMO level of the organic semiconductor 3.
Here, the LUMO level of the electron injection polycrystalline film 2A means the LUMO level of the main organic molecule constituting the electron injection polycrystalline film 2A.

The level in the band gap is generated due to disorder of the crystal structure of the polycrystalline film 2A for electron injection. Therefore, many band gap levels occur in the vicinity of the LUMO level of the electron injection polycrystalline film 2A. If the LUMO level of the electron injection polycrystalline film 2A is between the Fermi level of the electrode body 1 and the LUMO level of the organic semiconductor 3, the in-band gap level is also the same as the Fermi level of the electrode body 1 and the organic semiconductor. It is appropriately formed between the three LUMO levels. That is, in the injection of electrons from the electrode body 1 into the organic semiconductor 3, electrons can be injected through the band gap level, and the effective barrier height that the electrons need to exceed can be further reduced.

Even when the LUMO level of the polycrystalline film 2A for electron injection is equal to or higher than the LUMO level of the organic semiconductor 3, the level in the band gap has a certain energy distribution. Therefore, if the difference between the two LUMO levels is about 2.0 eV, there is an in-band gap level with sufficient density for energy lower than the LUMO level of the organic semiconductor 3. If the difference between the two LUMO levels is about 0.2 eV, the probability that a band gap level with sufficient density exists at an energy lower than the LUMO level of the organic semiconductor 3 is further increased. That is, it becomes easier to inject electrons from the electron injection polycrystalline film 2A into the organic semiconductor 3, and the electron injection efficiency at the interface between the electron injection polycrystalline film 2A and the organic semiconductor 3 is increased.

By the way, when the LUMO level of the electron injection polycrystalline film 2A and the LUMO level of the organic semiconductor 3 are approximated, the electron states of the electron injection polycrystalline film 2A and the organic semiconductor 3 are approximated. The electronic state of a substance is greatly affected by the crystal structure or molecular structure of the substance. That is, if the LUMO level of the electron injection polycrystalline film 2A is close to the LUMO level of the organic semiconductor 3, the crystal structure or molecular structure of the electron injection polycrystalline film 2A and the organic semiconductor 3 is similar. Yes. If the crystal structure or the molecular structure is similar, the structural change at the interface between the electron injection polycrystalline film 2A and the organic semiconductor 3 becomes gentle. That is, it is possible to avoid formation of an undesired energy barrier or the like at the interface between the electron injection polycrystalline film 2A and the organic semiconductor 3.

On the other hand, the HOMO level of the hole-injecting polycrystalline film 2B is less than or equal to the Fermi level of the electrode body 1, and is preferably equal to or more than a value obtained by subtracting 2.0 eV from the HOMO level of the organic semiconductor 3. It is more preferable that it is equal to or more than a value obtained by subtracting 0.2 eV from the HOMO level of 3. Further, it is more preferable to be between the Fermi level of the electrode body 1 and the HOMO level of the organic semiconductor 3.
Here, the HOMO level of the hole-injecting polycrystalline film 2B means the HOMO level of main organic molecules constituting the hole-injecting polycrystalline film 2B.

Also in the injection of holes, the transition of holes from the electrode body 1 to the organic semiconductor 3 is performed through the band gap level. If the in-band gap level is between the Fermi level of the electrode body 1 and the LUMO level of the organic semiconductor 3, the effective barrier height that must be exceeded by holes at the time of transition can be reduced. If the HOMO level of the hole-injecting polycrystalline film 2B is between the Fermi level of the electrode body 1 and the HOMO level of the organic semiconductor 3, the in-band gap level is also equal to the Fermi level of the electrode body 1 and the organic semiconductor. It is formed appropriately between the three HOMO levels.

Further, even when the HOMO level of the hole injection polycrystalline film 2B is lower than or equal to the HOMO level of the organic semiconductor 3, if the difference between the two HOMO levels is about 2.0 eV, the HOMO level of the organic semiconductor 3 There are in-bandgap levels of sufficient density for high energy. If the difference between the two HOMO levels is about 0.2 eV, the probability that a band gap level with sufficient density exists at an energy lower than the HOMO level of the organic semiconductor 3 is further increased. That is, holes are more easily injected from the hole-injecting polycrystalline film 2B into the organic semiconductor 3, and the hole-injecting efficiency at the interface between the hole-injecting polycrystalline film 2B and the organic semiconductor 3 is increased.

If the HOMO level of the hole-injecting polycrystalline film 2B and the HOMO level of the organic semiconductor 3 are close to each other, an unwanted energy barrier or the like is formed at the interface between the hole-injecting polycrystalline film 2B and the organic semiconductor 3. Can be avoided.

In order to make the material used for the electron injection polycrystalline film 2A and the hole injection polycrystalline film 2B the same and to reduce both the electron and hole injection barriers, the organic semiconductor polycrystalline film 2 is the same as the organic semiconductor 3 It preferably contains organic molecules, and more preferably consists of the same organic molecules.

(Organic semiconductor)
The organic semiconductor 3 functions as the organic element 20 to which the organic element electrode 10 is connected. The organic semiconductor 3 is connected to the surface of the organic element electrode 10 on the organic semiconductor polycrystalline film 2 side.

Any organic material can be used for the organic semiconductor 3. For example, rubrene, BP2T, anthracene, tetracene, pentacene, tetracyanoquinodimethane, α, ω-bis (biphenyl) terthiophene, difnat [2,3-b: 2 ′, 3′-f] thiopheno [3,2 -B] Thiophene, 1,4-bis (5-phenylthiophen-2-yl) benzene and the like can be used. Rubrene and BP2T are particularly preferable because of high carrier mobility.

The organic semiconductor 3 is preferably a single crystal. The single crystal organic semiconductor 3 has high carrier mobility. For example, a single crystal of rubrene exhibits very high mobility among organic semiconductors. When the organic semiconductor 3 is a single crystal, the contact resistance between the electrode body 1 and the organic semiconductor 3 is particularly high. That is, by using the organic element electrode 10 according to the present embodiment, the effect of reducing the contact resistance becomes remarkable.

(Protective layer, substrate)
A substrate 5 shown in FIG. 1 includes a gate substrate 5A and an insulating layer 5B. On the substrate 5, the organic semiconductor 3 is crystal-grown.

The gate substrate 5A applies a voltage to the organic semiconductor 3 through the insulating layer 5B. When a voltage is applied from the gate substrate 5A, a channel is formed in the organic semiconductor 3 and connects the electron injection electrode 10A and the hole injection electrode 10B.

As the gate substrate 5A, a known one can be used. The organic element 20 is often integrated on a semiconductor substrate. Therefore, it is preferable to use a semiconductor for the gate substrate 5A, and it is particularly preferable to use P-type rich silicon (p ^++- Si) or the like.

As the insulating layer 5B, a known layer can be used as long as it is not broken down by the gate voltage. When the gate substrate 5A is silicon, silicon oxide or the like is often used for the insulating layer 5B.

The protective layer 4 is a layer required when a semiconductor crystal such as silicon is used for the substrate 5. In semiconductor crystals, atoms near the surface of the crystal lose their covalent bond partners. Therefore, a dangling bond in which unpaired electrons are exposed is formed. Since dangling bonds are unstable, they supplement electrons. When some of the electrons flowing in the organic semiconductor 3 are captured by dangling bonds, the carrier mobility of the organic semiconductor 3 is lowered. Therefore, when silicon or the like is used for the substrate, it is preferable to have the protective layer 4 between the substrate 5 and the organic semiconductor 3.

It is preferable to use an insulating organic material for the protective layer 4. For example, parylene, polystyrene, polymethyl methacrylate (PMMA), or the like can be used.

(Method for manufacturing organic element)
The organic element 20 can be obtained by laminating each layer.
First, a substrate 5 having an insulating layer 5B formed on a gate substrate 5A is prepared. The substrate 5 can be produced by a known method. Moreover, you may purchase a commercial item.

When the substrate 5 is a semiconductor such as silicon, the protective layer 4 is formed on the substrate 5. The protective layer 4 can be produced by a known lamination method. For example, means such as spin coating and chemical vapor deposition (CVD) can be used.

The organic semiconductor 3 is laminated on the protective layer 4. The organic semiconductor 3 is preferably a single crystal. A single crystal organic semiconductor can be obtained by crystal growth of an organic film on a substrate. For example, it can be performed using a physical vapor transport method or the like.

The organic semiconductor polycrystalline film 2 and the electrode body 1 are stacked on the organic semiconductor 3. These layers are produced by a photolithography method, a vacuum deposition method using a mask, or the like. The organic semiconductor polycrystalline film 2 is formed by vacuum deposition or the like to become a polycrystalline film.

As described above, according to the electrode for an organic element according to the present embodiment, the effective barrier height at the time of carrier injection is obtained by inserting the organic semiconductor polycrystalline film 2 into the interface between the electrode body 1 and the organic semiconductor 3. Becomes lower. As a result, the injection of carriers from the electrode body 1 to the organic semiconductor 3 is facilitated, and the contact resistance at the interface between the electrode body 1 and the organic semiconductor 3 is reduced.

Second Embodiment FIG. 4 is a schematic cross-sectional view of an organic element 21 according to a second embodiment of the present invention. The organic element 21 according to the second embodiment is different from the organic element 20 according to the first embodiment in that the organic element electrode 11 includes the organic molecular film 6. In the following description, description of common parts is omitted. In the drawings used for the description, the same reference numerals are assigned to the same components as those in FIG.

The organic molecular film 6 is provided between the organic semiconductor 3 and the organic semiconductor polycrystalline film 2.
The organic molecular film 6 is provided on the organic element electrode 11 and is formed on the surface of the organic semiconductor polycrystalline film 2 opposite to the electrode body 1. As in the first embodiment, one of the organic element electrodes 11 is an electron injection electrode 11A, and the other is a hole injection electrode 11B.

FIG. 5 is a diagram showing the results of measuring the surface state of each layer of the organic element 21 with an atomic force microscope (AFM). FIG. 5A is an AFM image of the surface of the organic semiconductor 3. FIG. 5B is an AFM image of the surface of the organic molecular film 6. FIG. 5C is an AFM image of the surface of the organic semiconductor polycrystalline film 2 when the organic semiconductor polycrystalline film 2 is stacked on the organic semiconductor 3. FIG. 5D is an AFM image of the surface of the organic semiconductor polycrystalline film 2 when the organic semiconductor polycrystalline film 2 is laminated on the organic semiconductor 3 via the organic molecular film 6.

As shown in FIG. 5A, the surface of the organic semiconductor 3 is flat with almost no unevenness. When the organic molecular film 6 is laminated on the organic semiconductor 3, the surface shape becomes uneven as shown in FIG. Therefore, the organic molecular film 6 is not a film having a uniform thickness in the plane, but has irregularities having different thicknesses for each place. The organic molecular film 6 includes organic molecules scattered in an island shape on the organic semiconductor 3. Therefore, strictly speaking, the organic molecular film 6 is not a “film” continuous in the plane, but is a “film” because it is manufactured by a method such as vacuum deposition.

As shown in FIGS. 5C and 5D, when the organic semiconductor polycrystalline film 2 is laminated on the organic molecular film 6, the grains of the organic semiconductor polycrystalline film 2 are reduced. This is presumably because the organic semiconductor polycrystalline film 2 is laminated on the organic molecular film 6 having irregularities.

When the grain of the organic semiconductor polycrystalline film 2 is reduced, the crystallinity of the organic semiconductor polycrystalline film 2 is deteriorated. That is, many band gap levels are formed in the organic semiconductor polycrystalline film 2. As the number of band gap levels formed in the organic semiconductor polycrystalline film 2 increases, the number of routes by which carriers transition from the Fermi level of the electrode body 1 to the LUMO level or HOMO level of the organic semiconductor 3 increases. . As a result, a route with a lower effective barrier can be selected, and the carrier injection efficiency is further increased. That is, by providing the organic molecular film 6, the contact resistance at the interface between the electrode body 1 and the organic semiconductor 3 can be further reduced.

The thickness of the organic molecular film 6 is preferably 1 nm or more and 10 nm or less. Further, FIG. 6 shows the result of measuring the electron mobility when the thickness of the organic semiconductor polycrystalline film 2 is 20 nm, which has the highest electron mobility in FIG. 3, and the thickness of the organic molecular film 6 is changed. Thereby, the thickness of the organic molecular film 6 is more preferably 3 nm or more and 7 nm or less, and further preferably 4 nm or more and 6 nm or less. Here, the organic molecular film 6 has irregularities. Therefore, the thickness of the organic molecular film 6 is defined as follows. First, an area of 5 μm × 5 μm is measured by AFM. And let the average value of the thickness of all the measurement areas be the thickness of the organic molecular film 6.

By making the thickness of the organic molecular film 6 equal to or less than a predetermined thickness, the organic molecular film 6 becomes a resistor, and it is possible to avoid inhibiting the conduction between the electrode body 1 and the organic semiconductor 3. Further, by setting the thickness of the organic molecular film 6 to a predetermined thickness or more, irregularities for sufficiently reducing the grains of the organic semiconductor polycrystalline film 2 can be formed on the surface of the organic semiconductor 3.

The height of the unevenness of the organic molecular film 6 is preferably 1 nm or more and 10 nm or less, more preferably 3 nm or more and 7 nm or less, and further preferably 4 nm or more and 6 nm or less. When the unevenness of the organic molecular film 6 is high, many disturbances are introduced into the organic semiconductor polycrystalline film 2. Therefore, the polycrystallinity of the organic semiconductor polycrystalline film 2 can be improved.

The size of the organic molecular region constituting the organic molecular film 6 is preferably 5 μm or less, and more preferably 1 μm or less. Here, the organic molecule region means a region formed by organic molecules scattered in an island shape.

The organic molecule region is indefinite as shown in FIG. Therefore, the size of the organic molecule region is obtained as follows. First, an area of 5 μm × 5 μm is measured by AFM. And the average value of the length of the organic molecule area | region in the cross section cut | disconnected by the arbitrary surface perpendicular | vertical with respect to the measurement surface is calculated | required. Next, the same measurement is performed on each of the cross sections cut along nine different planes perpendicular to the measurement plane. And let the average value of the length measured in the cross section of a total of 10 places be the size of an organic molecule area | region.

The organic molecular film 6 preferably contains saturated hydrocarbons or derivatives thereof that are solid at room temperature. The saturated hydrocarbon is more preferably linear. For example, heptacosan, octacosan, nonacosan, triacontane, hentria contane, dotria contane, tritria contane, tetratria contane, pentatria contane, hexatria contane, heptatria contane, octatria contane, nonatria contane, tetra contane, Hentetracontane, detetracontane, tritetracontane, tetratetracontane and the like can be used.

A linear hydrocarbon or a derivative thereof has a long molecular structure in one direction. As one end portion of the molecular structure is bonded to the organic semiconductor 3 and the other end portion stands with respect to the laminated surface of the organic semiconductor 3, irregularities are formed in the organic molecular film 6.

In terms of energy, the organic molecular film 6 is preferably made of a material having a LUMO level higher than the Fermi level of the electrode body 1 and a HOMO level lower than the Fermi level of the electrode body 1. If the energy level of the material used for the organic molecular film 6 is within this range, it is possible to avoid the carrier injection at the interface between the electrode body 1 and the organic semiconductor 3 from being inhibited by the organic molecular film 6. Examples of such a material include perfluoroeicosane and tricosanoic acid methyl ester in addition to the above-described materials.

As described above, the organic element electrode according to the present embodiment can introduce more crystal disorder into the organic semiconductor polycrystalline film 2 by the organic molecular film 6. As a result, the injection of carriers from the electrode body 1 to the organic semiconductor 3 becomes easier, and the contact resistance at the interface between the electrode body 1 and the organic semiconductor 3 can be further reduced.

Third Embodiment FIG. 7 is a schematic cross-sectional view of an organic element 22 according to a third embodiment of the present invention. The organic element 22 according to the third embodiment is different from the organic element 20 according to the first embodiment in that it is not a field effect transistor (FET) but a light emitting element. The configuration of the organic element electrode 10 is the same as that of the organic element electrode 10 according to the first embodiment. In the following description, description of common parts is omitted. In the drawings used for the description, the same reference numerals are assigned to the same components as those in FIG.

The organic element 22 includes two organic element electrodes 10 with the organic semiconductor 3 interposed therebetween. When a current is passed from the two organic element electrodes 10 to the organic semiconductor 3, electrons and holes are injected into the organic semiconductor 3. The injected electrons and holes are combined in the organic semiconductor 3. The light emitting material in the organic semiconductor 3 is excited by the energy due to the coupling, and emits light when returning from the excited state to the ground state again.

Since the organic element electrode 10 includes the organic semiconductor polycrystalline film 2, the efficiency of injecting electrons and holes into the organic semiconductor 3 is increased. That is, the contact resistance at the interface between the electrode body 1 and the organic semiconductor 3 can be reduced not only in the field effect transistor but also in the light emitting element.

Also, the organic molecular film 6 may be inserted between the organic semiconductor 3 and the organic semiconductor polycrystalline film 2 in the same manner as the organic element 21 according to the second embodiment.

The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims. Can be modified or changed.

For example, the organic element is not limited to the above-described field effect transistor and light emitting element. For example, the present invention can be applied to elements such as diodes, organic solar cells, thermoelectric conversion elements, and sensors.

Example 1
As Example 1, a field effect transistor having the same structure as that of FIG. Each layer was as follows.
Gate substrate 5A: P-type rich silicon (p ^++- Si)
Insulating layer 5B: SiO ₂
Protective layer 4: Polystyrene Organic semiconductor 3: Rubrene single crystal Organic molecular film 6: Tetratetracontane (TTC, thickness 5 nm)
Organic semiconductor polycrystalline film 2: rubrene (thickness 20 nm)
Electrode injection electrode body 1A: Calcium Hole injection electrode body 1B: Gold Then, the contact resistance between the organic semiconductor 3, the electron injection electrode body 1A, and the hole injection electrode body 1B was determined by a four-terminal method. The contact resistance was normalized by the channel width formed in the organic semiconductor 3.

(Example 2)
As Example 2, a field effect transistor having a structure similar to that shown in FIG. That is, the field effect transistor of Example 1 is different in that the organic molecular film 6 is excluded. In Example 2, as in Example 1, the contact resistance between the organic semiconductor 3 and the electrode body 1A for electron injection and the electrode body 1B for hole injection was determined by a four-terminal method.

(Comparative Example 1)
As Comparative Example 1, the organic semiconductor polycrystalline film 2 was removed from the field effect transistor of Example 2. That is, the organic semiconductor 3 was directly brought into contact with the electrode body 1A for electron injection and the electrode body 1B for hole injection. Similarly to Example 1, in Comparative Example 1, the contact resistance between the organic semiconductor 3 and the electrode body 1A for electron injection and the electrode body 1B for hole injection was determined by the four-terminal method.

(Comparative Example 2)
As Comparative Example 2, a cesium fluoride thin film was provided in place of the organic semiconductor polycrystalline film 2 from the field effect transistor of Example 1. In Comparative Example 2, as in Example 1, the contact resistance between the organic semiconductor 3 and the electron injection electrode body 1A and hole injection electrode body 1B was determined by the four-terminal method.

FIG. 8 is a diagram comparing the contact resistance when electron injection is performed on the field effect transistors of Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

As shown in FIG. 8, in Examples 1 and 2, the contact resistance with the organic semiconductor 3 is reduced compared to Comparative Example 1 in both the gold electrode and the calcium electrode. In particular, the contact resistance of the gold electrode in Example 1 is as small as that of the calcium electrode of Comparative Example 1. In Comparative Example 2, although not as much as Example 1 and Example 2, contact resistance is reduced in both the gold electrode and the calcium electrode.

FIG. 9 is a diagram comparing the contact resistance when hole injection is performed on the field effect transistors of Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

As shown in FIG. 9, contrary to the case of electron injection, the calcium electrode shows a larger contact resistance than the gold electrode. In Example 1 and Example 2, the contact resistance with the organic semiconductor 3 in both the gold electrode and the calcium electrode is reduced as compared with Comparative Example 1. Further, in Comparative Example 2, unlike the case of electron injection, the contact resistance increased compared to Comparative Example 1 in both the gold electrode and the calcium electrode.

As shown in FIGS. 8 and 9, the electrodes shown in Example 1 and Example 2 had reduced contact resistance in both cases of injecting electrons and holes. On the other hand, the contact resistance of the electrode shown in Comparative Example 1 was reduced when electrons were injected, but the contact resistance was increased when holes were injected.

Further, the field effect transistors of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 in the case of using a BP2T organic semiconductor polycrystalline film instead of the rubrene organic semiconductor polycrystalline film of FIGS. FIG. 10 shows a graph comparing the contact resistance when electron injection is performed, and FIG. 11 shows a graph comparing the contact resistance when hole injection is performed.

Contact resistance is measured by a four-terminal method using an organic single crystal field effect transistor having a source electrode and a drain electrode of the organic element 21 of the second embodiment and two electrodes for voltage measurement between the electrodes. I was able to do it. The temperature of this transistor was controlled by a Peltier device, and contact resistance was measured at a plurality of temperatures in an argon atmosphere. The logarithm of the obtained contact resistance was plotted against the reciprocal of temperature (Arrhenius plot), and the activation energy required for carrier injection was determined from the slope. This experiment was conducted for electrons and holes using calcium and gold as electrode materials and BP2T and rubrene as organic semiconductors, respectively.

As shown in FIG. 10, in Example 1 and Example 2, the contact resistance with the organic semiconductor 3 is reduced in both the gold electrode and the calcium electrode as compared with Comparative Example 1. Also in Comparative Example 2, the contact resistance is reduced in the calcium electrode. Therefore, when an organic semiconductor polycrystalline film of BP2T is used, it is effective to provide a cesium fluoride thin film in place of the organic semiconductor polycrystalline film 2 in the electron injection.

As shown in FIG. 11, contrary to the case of electron injection, the calcium electrode shows a larger contact resistance than the gold electrode. In Example 1 and Example 2, the contact resistance with the organic semiconductor 3 in both the gold electrode and the calcium electrode is reduced as compared with Comparative Example 1. Further, in Comparative Example 2, unlike the case of electron injection, the contact resistance of the gold electrode was increased as compared with Comparative Example 1.

As shown in FIGS. 10 and 11, the electrodes shown in Example 1 and Example 2 had reduced contact resistance in both cases of injecting electrons and holes. On the other hand, the electrode shown in Comparative Example 2 decreased in contact resistance when electrons were injected, but increased in contact resistance when holes were injected.

From the above results, it can be seen that by forming the organic semiconductor polycrystalline film, the contact resistance is reduced for both electron injection and hole injection, and the contact resistance can be further reduced by combining the organic molecular film.

In addition, the mobility of electrons and the mobility of holes in the field effect transistors of the following examples and comparative examples were also measured. The layer configurations of Examples and Comparative Examples are shown in Table 1 and Table 2 below.

Examples 1 to 6 and Comparative Examples 1 to 6 differ in that the organic semiconductor 3 is rubrene, whereas Examples 7 to 11 differ in that the organic semiconductor 3 is BP2T. In Tables 1 and 2, cesium fluoride is not an organic semiconductor polycrystalline film, but is inserted as a film corresponding to it, so it is listed in the column of the organic semiconductor polycrystalline film.

FIG. 12 shows the results of measuring the electron mobility and the hole mobility of the field effect transistors of Examples and Comparative Examples (Table 1) in which the organic semiconductor 3 is rubrene. FIG. 13 shows the results of measurement of electron mobility and hole mobility of field effect transistors of Examples and Comparative Examples (Table 2) in which the organic semiconductor 3 is BP2T. The horizontal axis is electron mobility, and the vertical axis is hole mobility. Therefore, the carrier mobility becomes higher toward the upper right in FIGS. 12 and 13.

As shown in FIGS. 12 and 13, when the organic semiconductor polycrystalline film 2 is inserted between the electrode body 1 and the organic semiconductor 3, the mobility of electrons and holes increases. If the organic molecular film 6 is further inserted between the electrode body 1 and the organic semiconductor polycrystalline film 2, the mobility of electrons and holes is further increased.

The same tendency is confirmed even when the electron injection electrode body 1A and the hole injection electrode body 1B are changed. That is, it was confirmed that the electron and hole mobility were improved by inserting the organic semiconductor polycrystalline film 2 and the organic molecular film 6 regardless of the Fermi level of the electrode body 1.

The field effect transistor shown in Example 1 using rubrene as the organic semiconductor 3 has a hole mobility of 22.0 cm ² V ⁻¹ s ⁻¹ and an electron mobility of 5.0 cm ² V ⁻¹ s ^−1. It is. The field effect transistor shown in Example 7 using BP2T as the organic semiconductor 3 has a hole mobility of 0.5 cm ² V ⁻¹ s ⁻¹ and an electron mobility of 1.1 cm ² V ⁻¹ s ^−1. It is.

These electron mobility and hole mobility are very high values among the examples in which rubrene or BP2T is used for the organic semiconductor 3.

FIG. 14 shows the transistor characteristics. The solid line including the black square shows the result of measuring the drain current at the time of electron injection and hole injection by applying a voltage to the field effect transistor (Example 1) having the same structure as FIG. It is. A solid line including a white square applies a voltage to a field effect transistor having a configuration excluding the organic semiconductor polycrystalline film 2 and the organic molecular film 6 from the configuration of Example 1, and measures the drain current during electron injection and hole injection. It is the result. The horizontal axis is the applied voltage, and the vertical axis is the drain current.
From the result of FIG. 14, when the organic semiconductor polycrystalline film 2 and the organic molecular film 6 are inserted between the electrode body 1 and the organic semiconductor 3, the drain current increases in the case of electron injection and hole injection, and the transistor characteristics are improved. To do.
FIG. 15 shows the transistor characteristics. The solid line including the black squares has the same configuration except that the electron injection electrode body 1A is gold and the hole injection electrode body 1B is calcium in the field effect transistor of the first embodiment. It is the result of having measured the drain current at the time of applying a voltage in the field effect transistor which has, and injecting an electron and a hole. A solid line including a white square represents a drain current in the field effect transistor having the configuration in which the organic semiconductor polycrystalline film 2 and the organic molecular film 6 are removed from the field effect transistor, and in the same manner, electron injection and hole injection. It is the result of having measured. The horizontal axis is the applied voltage, and the vertical axis is the drain current.
From the results of FIG. 15, if the electron injection electrode body 1A is gold and the hole injection electrode body 1B is calcium, electron injection and hole injection are difficult without the organic semiconductor polycrystalline film 2 and the organic molecular film 6. is there. However, by inserting the organic semiconductor polycrystalline film 2 and the organic molecular film 6, electron injection and hole injection are possible, the drain current is increased, and the transistor characteristics are improved.

DESCRIPTION OF SYMBOLS 1 ... Electrode body, 1A ... Electron injection electrode body, 1B ... Electrode body for hole injection, 2 ... Organic semiconductor polycrystalline film, 2A ... Polycrystalline film for electron injection, 2B ... Polycrystalline film for hole injection, 3 ... Organic Semiconductor, 4 ... Protective layer, 5 ... Substrate, 5A ... Gate substrate, 5B ... Insulating layer, 6 ... Organic molecular film, 10, 11 ... Organic element electrode, 10A, 11A ... Electron injection electrode, 10B, 11B ... Hole Electrode for injection, 20, 21, 22, ... organic element

Claims (9)

1. An electrode for an organic element connected to an organic semiconductor,
   An electrode body;
   An organic element electrode comprising: an organic semiconductor polycrystalline film that is provided on a first surface of the electrode body and reduces contact resistance at a contact interface with the organic semiconductor.
2. The organic element electrode according to claim 1, further comprising an organic molecular film provided on a third surface opposite to a second surface on which the electrode body of the organic semiconductor polycrystalline film is provided.
3. The organic element electrode according to claim 1, wherein the organic semiconductor polycrystalline film has a thickness of 1 nm to 50 nm.
4. 4. The organic element electrode according to claim 2, wherein the thickness of the organic molecular film is 1 nm or more and 10 nm or less.
5. The organic semiconductor polycrystalline film has an energy level of the lowest unoccupied molecular orbital (LUMO) equal to or higher than the Fermi level of the electrode body, and the energy level of the lowest unoccupied molecular orbital (LUMO) of the organic semiconductor to be connected. The electrode for an organic element according to any one of claims 1 to 4, which is not more than a value obtained by adding 2.0 eV to the position.
6. In the organic semiconductor polycrystalline film, the energy level of the highest occupied molecular orbital (HOMO) is equal to or lower than the Fermi level of the electrode body, and the energy level of the highest occupied molecular orbital (HOMO) of the connected organic semiconductor is The organic element electrode according to any one of claims 1 to 5, which is at least a value reduced by 2.0 eV.
7. The organic element electrode according to any one of claims 2 to 6, wherein the organic molecular film contains a saturated hydrocarbon that is solid at room temperature or a derivative of the saturated hydrocarbon.
8. The Fermi level of the electrode body is not less than a value obtained by subtracting 3.0 eV from the energy level of the lowest unoccupied molecular orbital (LUMO) of the organic semiconductor to be connected, or the highest occupied molecular orbital (HOMO of the organic semiconductor to be connected). The electrode for an organic element according to any one of claims 1 to 7, which is not more than a value obtained by adding 4.0 eV to the energy level of.
9. An electrode for an organic element according to any one of claims 1 to 8,
   An organic semiconductor connected to a fourth surface of the electrode for organic element provided with the organic semiconductor polycrystalline film.

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