KR100859821B1 - Organic Semiconductor Device with Double Interface Layer - Google Patents

Abstract

Disclosed are an organic semiconductor device having a hybrid double interface layer in which double interfaces of ultra-thin films made of different materials are doubled. The organic semiconductor device includes an anode, a cathode, and an organic semiconductor thin film interposed between the anode and the cathode, and between the organic semiconductor thin film and the cathode, a first thin film interface layer made of an organic material having a HOMO level of -5.5 eV or less; A second thin film interface layer made of a metal or an inorganic salt having a work function of 3.7 eV or less is sequentially formed.

Description

Organic Semiconductor Devices Having Double Interfacial Layers

1 is a view showing the configuration of an organic semiconductor device according to an embodiment of the present invention.

Figure 2 is a graph showing the results of measuring the HOMO and LUMO levels of polyoxyethylene tridecyl ether by cyclic voltammetry.

3 to 6 are graphs showing changes in luminance (cd / m ² ) according to voltage (V) and efficiency (cd / A) according to current, for organic light emitting devices manufactured in Examples and Comparative Examples.

7 and 8 are graphs showing changes in photocurrent density (mA / cm ² ) and power conversion efficiency (%) according to voltage (V) for organic solar cells manufactured in Examples and Comparative Examples.

The present invention relates to an organic semiconductor device having a double interface layer, and more particularly, to an organic semiconductor device having a hybrid inter interface layer (double interfacial layers) formed by double forming the interface of the ultra-thin film made of different materials. .

In general, an organic semiconductor device is an organic light emitting diode (OLED) that uses an electrical semiconductor property related to the highest occupied molecular orbital (HOMO) level and the lowest unoccupied molecular orbital (LUMO) level. Organic diode devices such as organic electroluminescent diodes or organic ELs, organic transistor devices, organic solar cells, and the like. Hereinafter, the structure and operation of the organic semiconductor device will be described with reference to the organic light emitting device. An organic light emitting element, commonly referred to as "organic EL", is one of self-luminous display elements, and has a structure in which a thin film made of a light emitting organic compound is interposed between electrodes. The organic EL device using a low molecular weight or high molecular organic compound as a light emitting material has a simpler manufacturing method, a lower driving voltage, a large area and an overall color compared to the inorganic EL device using an inorganic material as a light emitting material. (full color) has the advantage of easy display manufacturing. In such an organic EL device, electrons and holes are injected and recombined into the LUMO level and the HOMO level of the luminescent organic compound, respectively, to generate excitons, which emit light while the excitons lose their activity (fluorescence or Phosphorescence).

In organic EL devices, the anode (or anode) is typically made of a material with a large work function, for example silver, nickel, gold, platinum, palladium, selenium, rhenium. , Iridium, alloys thereof, tin oxide, indium-tin-oxide (ITO), indium-zinc-oxide (IZO), copper iodide Or the like. Also conductive polymers such as polyaniline, poly (3-methylthiophene), polyphenylenesulfide, polypyrrole, PEDOT-PSS (poly (3,4-ethylenedioxythiophene) -poly (4-styrenesulfonate)) polymers, and the like. Can be used as the anode material. On the other hand, the cathode (or cathode) is usually made of a material having a small work function, for example, aluminum (Al), magnesium (Mg), lithium (Li), cesium (Cs), barium (Ba), potassium (K), beryllium (Be), calcium (Ca), mixtures thereof, and the like, and specifically, MgAg electrodes (Mg: Ag = 10: 1), CaAg electrodes, MgAgAl electrodes, LiAl electrodes, etc. may be used. have. The cathode may be formed by a deposition method or a sputtering method. In addition, in a conventional organic EL device, a protective electrode for protecting the cathode from external moisture or the like may be further formed, and the protective electrode may be formed of a material containing aluminum (Al), silver (Ag), or the like. .

In addition, in order to increase the light emission luminance and efficiency of the organic light emitting device, smooth electron injection and transport should be achieved. For this purpose, a single ultra-thin interfacial layer is usually interposed between the organic light emitting thin film and the cathode. As the interfacial layer forming method, a method of forming an insulating inorganic material such as LiF, CsF, MgO, NaCl, NaF as an ultra-thin thin film between the organic light emitting thin film and the cathode (LS Hung et. Al: Appl Phys. Lett. Vol 70, p152, 1997, P. Piromeriun et.al: Appl. Phys. Lett. Vol 77, p2403, 2000). And a method of forming between the cathode and the cathode (US Pat. No. 6,255,774).

However, as the single interface layer, electron injection is not sufficient, and when the single interface layer is formed using a metal or inorganic salt having a low work function, these ions diffuse into the organic light emitting thin film, There are problems such as shortening the life. In addition, the thickness of the single interfacial layer is usually within a few nm, and if the thickness of the interfacial layer is changed, the luminous brightness and efficiency of the device is drastically reduced, so far no deformation or improvement of the interfacial layer has been considered Only the element in which the single interface layer is formed to an appropriate thickness is used. Therefore, the conventional light emitting device having a single interface layer has a limitation in improving efficiency and extending life, and there is a demand for development of a new technology to overcome this problem.

It is an object of the present invention to provide an organic semiconductor device having a double interface layer capable of improving electron injection, transport and hole blocking properties between an electrode and an organic semiconductor thin film.

Another object of the present invention is to provide an organic semiconductor device having a double interface layer, which can not only improve the operation efficiency and electrical characteristics of the device, but also increase the life of the device.

In order to achieve the above object, the present invention includes an anode, a cathode and an organic semiconductor thin film interposed between the anode and the cathode, and between the organic semiconductor thin film and the cathode, an organic material having a HOMO level of -5.5 eV or less An organic semiconductor device is provided in which a first thin film interface layer and a second thin film interface layer made of a metal or an inorganic salt having a work function of 3.7 eV or less are sequentially formed. Here, the first thin film interface layer is made of a surfactant, the second thin film interface layer is made of an inorganic salt, the thickness of the first thin film interface layer is 0.1 to 5.0 nm, of the second thin film interface layer The thickness is preferably 0.1 to 5.0 nm.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in more detail.

1 is a view illustrating a configuration of an organic semiconductor device according to an embodiment of the present invention. As shown in FIG. 1, in the organic semiconductor device 10 according to the present invention, an organic semiconductor thin film 20 is interposed between an anode 15 and an anode 30, and the anode ( A hole injection and transport layer may be further formed between 15 and the organic semiconductor thin film 20, and an electron injection and transport layer may be further formed between the cathode 30 and the organic semiconductor thin film 20. The organic semiconductor thin film 20 may be formed of a conventional semiconducting organic compound, for example, a conventional organic light emitting compound. In the organic semiconductor device 10 according to the present invention, between the organic semiconductor thin film 20 and the cathode 30, ultra-thin films 22a, 22b made of different materials are sequentially formed in a double, hybrid double An interfacial layer 22 is formed. Since the dual interface layer 22 has a complex function of controlling the charge injection barrier, electron injection and transport, hole blocking, diffusion blocking of metal ions into the organic thin film 20, and when used in an organic light emitting device, It is possible to improve the brightness and luminous efficiency of (10), increase the lifespan, and when used in an organic solar cell, it is possible to improve the power conversion efficiency of the device (10).

The double interface layer 22 replaces the existing single interface layer, and includes the first thin film interface layer 22a and the second thin film interface layer 22b. The first thin film interface layer 22a stacked on the organic semiconductor thin film 20 is for efficiently blocking the movement of holes from the organic semiconductor thin film 20 to the cathode 30 which is a metal electrode. It is composed of an organic material having a level of -5.5 eV or less, preferably a sigma-bonded organic material having a wide band gap, and more preferably a surfactant. As the material for forming the first thin film interface layer 22a, polyoxyethylene alkyl ether which is a kind of surfactant (wherein the number of oxyethylene repeating units is 2 to 20, preferably 5 to 18, The number of carbon atoms is 3 to 16, preferably 5 to 13. The same applies to the following)), polyoxyethylene fatty acid ester, polyoxyethylene alkylphenol ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, sucrose fatty acid ester, It is preferable to use a nonionic surfactant in which hydrophobic units and hydrophilic units such as mixtures thereof are bonded by block polymerization or graft polymerization, and specifically, polyoxyethylene tridecyl ether tridecylether: PTE, C ₁₃ H ₂₇ (OCH ₂ CH ₂ ) _n OH, n ˜6, 10, 12, 18). 2 is a graph showing the results of measuring the HOMO and LUMO levels of the PTE by cyclic voltametry. The measurement result of FIG. 2 is the result obtained about the solution which melt | dissolved PTE at 0.1 mole concentration in the acetonitrile solvent. As shown in FIG. 2, the HOMO level of the PTE is −8.1 eV (−4.4 eV [Ag / Ag +] − (+3.7 eV) = − 8.1 eV) and the LUMO level is −2.1 eV (−4.4 eV [Ag / Ag +]-(-2.3eV) = -2.1eV), it can be seen that PTE is useful as a hole blocking material. The first thin film interface layer 22a may be formed by a conventional thin film forming method. For example, a solution obtained by dissolving a material constituting the first thin film interface layer 22a may be formed in the organic semiconductor thin film 20. The organic semiconductor thin film 20 is formed by spin coating and drying the surface, or the material forming the first thin film interface layer 22a, wherein the material forming the first thin film interface layer 22a is the organic semiconductor. The first thin film interface layer 22a may be formed (surfactant) on the surface of the organic semiconductor thin film 20 by being moved to and deposited on the surface of the thin film 20. The thickness of the first thin film interface layer 22a is 0.1 nm to 5.0 nm, preferably 0.5 to 2.0 nm. If the thickness of the first thin film interface layer 22a is too thick, the electron transport may be disturbed. If the thickness of the first thin film interface layer 22a is too thin, the hole blocking effect may be reduced.

The second thin film interfacial layer 22b is stacked on top of the first thin film interfacial layer 22a to efficiently transport, inject, and deliver electrons, and has a small work function, specifically, 3.7 eV or less. It is preferable that the inorganic substance having a work function of, for example, metal or inorganic salt. Specific materials for forming the second thin film interface layer 22b include aluminum (Al), magnesium (Mg), lithium (Li), cesium (Cs), barium (Ba), potassium (K), and beryllium (Be). ), Metals such as calcium (Ca), inorganic salts such as LiF, CsF, MgO, NaCl, NaF, and mixtures thereof (including alloys such as Al: Li and Mg: Ag alloys). For example, as the second thin film interface layer 22b, an ultra-thin thin film of an insulating inorganic film such as ultra-thin LiF, CsF, MgO, NaCl, NaF, or a metal having a low work function such as Li: Al, Mg: Ag alloy, etc. It can be formed and used. The second thin film interface layer 22b may be formed by a conventional thin film forming method, and preferably, may be formed by a vacuum deposition method. The thickness of the second thin film interface layer 22b is 0.1 nm to 5.0 nm, preferably 0.5 nm to 2.0 nm. If the thickness of the second thin film interface layer 22b is too thick or too thin, there is a problem that the electron transport ability is significantly reduced. In addition, the total thickness of the first thin film interface layer 22a and the second thin film interface layer 22b is preferably 0.2 to 10.0 nm.

As such, by forming the double interface layer 22, electrons are smoothly transferred from the cathode 30 to the organic semiconductor thin film 20, and at the same time, the holes that move from the organic semiconductor thin film 20 to the cathode 30 are blocked. The operating efficiency of the device 10 can be increased. In addition, the first thin film interface layer 22a blocks the diffusion of the compound constituting the second thin film interface layer 22b or its ions into the organic semiconductor thin film 20, thereby increasing the life of the device 10. These features are important effects that cannot be achieved with existing single interface layers.

In the organic semiconductor device 10 according to the present invention, the anode 15 may be formed of a conventional anode forming material having a large work function, and the cathode 30 has a work function. It may be made of small conventional cathode forming materials. In addition, the organic semiconductor thin film 20 may be formed of a conventional organic compound having semiconductor properties, depending on the purpose of use of the organic electro-electronic device to be manufactured. For example, when the organic semiconductor device 10 is an organic light emitting device, the organic semiconductor thin film 20 may be formed of alumina quinone (Alq 3, Tris (8-hydroxyquinolato) aluminum), tris- (5-chloro-8-hydride). Tris- (5-chloro-8-hydroxy-quinolinato) -aluminium, BeBq2 (10-benzo [h] quinolinol-beryllium complex), Ir (ppy) 3 (Tris (2- phenyl pyridine) iridium) and the like, and when the organic semiconductor device 10 is an organic solar cell, the organic semiconductor thin film 20 is formed of P3HT (poly (3-hexylthiophene), PCBM ([ 6,6] -phenyl-C61-butric acid methyl ester), etc. Also, a conventional hole injection layer and / or may be formed between the anode 15 and the organic semiconductor thin film 20. Alternatively, a hole transporting layer may be further formed.The organic semiconductor device according to the present invention may be arranged in an array or a matrix to emit organic light. Here, it can be used in a variety of organic electronic devices such as organic solar cells.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

Example 1 Fabrication of Organic Light-Emitting Element

After spin-coating PEDOT-PSS (Bayer AG, trade name: BAYTRON-P) aqueous solution on a transparent anode electrode made of indium-tin-oxide (ITO) at room temperature, using a hot plate (150 ℃, By annealing for 1 hour to remove the solvent, a polymer buffer layer of about 60 nm thickness was formed. Next, PVK (Poly N-vinylcarbazole) 0.0160 g, TPD (N, N-dipheny-N, N-bis (3-methylphenyl) -1,1-biphenyl-4,4-diamine) 0.0050g, PBD (2 0.0160 g of-(4-biphenyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole) and 0.0015 g of phosphorescent dopant Ir (ppy) 3 (fac tris (2-phenylpyridine) iridium) Was dissolved in 5 g of a 3: 1 (weight ratio) mixed solvent of dichloroethane and chloroform at a speed of 800 rpm on the PEDOT-PSS thin film to form a light emitting layer having a thickness of 80 nm. Next, a solution of 0.0010 g of PTE (C ₁₃ H ₂₇ (OCH ₂ CH ₂ ) _n OH, n to 12) dissolved in 1 g of distilled water was spin-coated and dried at a speed of 4000 rpm on the light emitting layer thin film, and then, about 1 A first thin film interface layer having a thickness of nm was formed, and a second thin film interface layer was formed by vacuum depositing an Al: Li ultrathin film having a thickness of 1 nm at 2 × 10 ⁻⁶ torr to form a hybrid double interface layer. . In addition, an Al cathode electrode layer having a thickness of about 100 nm was further formed on the double interface layer to manufacture an organic light emitting device.

Example 2 Fabrication of Organic Light-Emitting Element

The light emitting layer was formed by a mixture of PTE, which is a surfactant, was directly mixed (the ratio of 0.004 g of PTE per 1 g of solution) to the light emitting layer solution used in Example 1, so that the PTE moved to the surface of the light emitting layer to form a first thin film interface layer. After that, an organic light-emitting device was manufactured in the same manner as in Example 1, except that an Al: Li second thin film interface layer having a thickness of 1 nm was formed.

Example 3 Fabrication of Organic Light Emitting Diode

An organic light-emitting device was manufactured in the same manner as in Example 1, except that a CsF thin film having a thickness of 1 nm was formed instead of the Al: Li ultrathin film as the second thin film interface layer.

Example 4 Fabrication of Organic Light-Emitting Element

An organic light-emitting device was manufactured in the same manner as in Example 2, except that a CsF thin film having a thickness of 1 nm was formed instead of the Al: Li ultrathin film as the second thin film interface layer.

Comparative Example 1 Fabrication of Organic Light-Emitting Element

An organic light emitting device having an organic light emitting thin film / PTE interface layer / Al structure was manufactured in the same manner as in Example 1, except that the second thin film interface layer was not formed.

Comparative Example 2 Fabrication of Organic Light-Emitting Element

An organic light emitting diode having an organic light emitting thin film / Al: Li interface layer / Al structure was produced in the same manner as in Example 1 except that the first thin film interface layer was not formed.

Comparative Example 3 Fabrication of Organic Light-Emitting Element

An organic light emitting device having an organic light emitting thin film / CsF interface layer / Al structure was produced in the same manner as in Example 3, except that the first thin film interface layer was not formed.

For each of the organic light emitting diodes manufactured in Examples 1 and 3 and Comparative Examples 1, 2 and 3, the luminance (cd / m ² , Luminance) change according to the voltage V and the efficiency (cd / A, Efficiency) according to the current ) Was measured, and the results are shown in FIGS. 3 to 6, respectively. 3 to 6, it can be seen that the luminance and efficiency of the device including the double interface layer of the present invention are much superior to those of the device including the single interface layer (Comparative Examples 1-3). In addition, for each of the organic light emitting diodes of Examples 2 and 4 in which the first thin film interface layer is formed together with the light emitting layer among the double interface layers formed in the organic semiconductor thin film, the luminance (cd / m ² ) according to the voltage V As a result of measuring the change in efficiency (cd / A) according to the change and the current, results similar to those of Examples 1 and 3 were obtained.

Example 5 Fabrication of Organic Solar Cell

In the same manner as in Example 1, a PEDOT-PSS polymer buffer layer was formed on a transparent anode made of ITO. 0.0100 g of poly (3-hexylthiophene: P3HT), and [6,6] -phenyl C61-butyric acid methyl ester: PCBM) A solution prepared by dissolving 0.0080 g in 1 g of chlorobenzene was spin-coated on the polymer buffer layer at a speed of 1200 rpm to form an active layer having a thickness of 100 nm, and then heated to 150 ° C. using a hot plate. Annealing for 3 minutes at, the solvent was removed. Next, a solution of 0.0010 g of PTE (C ₁₃ H ₂₇ (OCH ₂ CH ₂ ) _n OH, n to 12) dissolved in 1 g of distilled water was spin-coated and dried at a speed of 3000 rpm on the organic thin film, and then, 1 A first thin film interfacial layer having a thickness of nm was formed, and a second thin film interfacial layer was formed by vacuum depositing a 1 nm thick Al: Li alloy ultra thin film at 2 × 10 ⁻⁶ torr. In addition, an Al cathode electrode layer having a thickness of about 100 nm was further formed on the double interface layer, thereby manufacturing an organic solar cell.

Comparative Example 4 Fabrication of Organic Solar Cell

An organic solar cell was manufactured in the same manner as in Example 5, except that the first thin film interface layer made of PTE was not formed.

Comparative Example 5 Fabrication of Organic Solar Cell

The organic film for a solar cell was manufactured in the same manner as in Example 5, except that a CsF thin film having a thickness of 1 nm was formed instead of the Al: Li ultrathin film as the second thin film interface layer without forming the first thin film interface layer made of PTE. An organic solar cell having a thin film / single CsF interface layer / Al structure was fabricated.

Change of photocurrent density (mA / cm ² , photo-current density) and power conversion efficiency (%, PCE) according to voltage (V) for each of the organic solar cells manufactured in Example 5 and Comparative Example 4-5 Was measured, and the results are shown in FIGS. 7 and 8, respectively. 7 and 8, the photocurrent density, Voc (open-circuit voltage) of an organic solar cell including a double interface layer, compared to a device having a single interface layer of Al: Li or CsF (Comparative Example 4-5). 5 (0.5960 V), Comparative Example 4 (0.5556 V), Comparative Example 5 (0.51252 V), and power conversion efficiency (Example 5: 2%, Comparative Example 4: 1.5%, Comparative Example 5: 0.8%) were excellent. It can be seen that excellent. Therefore, it can be seen from the above embodiments and comparative examples that the organic semiconductor device according to the present invention is superior in device operation efficiency compared to the conventional device. In addition, it was observed that when the thicknesses of the first and second thin film interface layers were increased to 5 nm or more, the efficiency of the device was drastically decreased. Therefore, it can be seen that the dual interface layers of the present invention are boundary layers that are physically separated from the electron injection transport layer and the hole blocking layer of the existing device.

As described above, the organic semiconductor device having the double interface layer according to the present invention improves the electron injection, transport and hole blocking characteristics between the electrode and the organic semiconductor thin film, thereby improving the operation efficiency and electrical characteristics of the device. In addition, the lifetime of the device can be increased. Since the organic semiconductor device according to the present invention has improved electrical properties, it is useful as an electric device such as an organic light emitting device and an organic solar cell.

Claims (7)

An anode, a cathode and an organic semiconductor thin film interposed between the anode and the cathode, Between the organic semiconductor thin film and the cathode, a first thin film interface layer made of an organic material having a HOMO level of -5.5 eV or less and a second thin film interface layer made of a metal or an inorganic salt having a work function of 3.7 eV or less are sequentially formed. That is, The first thin film interface layer is made of a nonionic surfactant, The second thin film interface layer may include aluminum (Al), magnesium (Mg), lithium (Li), cesium (Cs), barium (Ba), potassium (K), beryllium (Be), calcium (Ca), LiF, and CsF. , MgO, NaCl, NaF and an organic semiconductor device consisting of a material selected from the group consisting of a mixture thereof. The organic thin film of claim 1, wherein the organic semiconductor thin film is formed together with a material constituting the first thin film interface layer, and a material forming the first thin film interface layer is deposited on the surface of the organic semiconductor thin film, thereby forming a first thin film. An organic semiconductor device forming an interface layer. delete The polyoxyethylene alkyl ether of claim 1 or 2, wherein the first thin film interface layer comprises polyoxyethylene alkyl ether (wherein the number of oxyethylene repeating units is 2 to 20, and the alkyl group has 3 to 16 carbon atoms). An organic semiconductor device comprising a material selected from the group consisting of fatty acid esters, polyoxyethylene alkyl phenol ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, sucrose fatty acid esters, and mixtures thereof. delete The organic semiconductor device of claim 1, wherein the thickness of the first thin film interface layer is 0.1 to 5.0 nm and the thickness of the second thin film interface layer is 0.1 to 5.0 nm. The organic semiconductor device of claim 1, wherein the organic semiconductor device is selected from the group consisting of an organic light emitting device and an organic solar cell.

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