An organic electroluminescent device based on a multi-component interfacial exciplex

Abstract

The present invention belongs to the technical field of light-emitting devices, and in particular relates to an organic electroluminescent device based on a multi-component interfacial exciplex. The device is successively composed of a substrate, an anode, a hole transport layer, an organic light-emitting layer, an electron transport layer, and a cathode. The organic light-emitting layer includes a donor material doped layer doped with a first donor material and a second donor material, and an acceptor material doped layer doped with an acceptor material and a host material. The device has a simple structure and improves the efficiency and lifetime of the exciplex.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic electroluminescent devices, and particularly relates to an organic electroluminescent device based on a multi-component interfacial exciplex. Background Art

[0002] Organic Light-Emitting Diodes (OLEDs) have attracted the attention of the scientific research community and the industrial community due to their characteristics such as full-color display, self-luminescence, wide viewing angle, high response speed, high definition, high contrast, ultra-thin, and flexible display. Currently, OLEDs generally use phosphorescent materials as the light-emitting body of the device. By utilizing the heavy atom effect to enhance the spin-orbit coupling between the singlet state and the triplet state, radiative transitions from the triplet state to the ground state are achieved, thereby theoretically achieving 100% internal quantum efficiency. However, due to the presence of heavy metal atoms in phosphorescent materials, the cost of the materials is high, which limits the large-scale commercial application of OLEDs. Reducing the use of phosphorescent materials and developing efficient alternative light-emitting bodies have become the key research directions for OLEDs. In most exciplexes, there is an intermolecular thermally activated delayed fluorescence emission mechanism. At room temperature, the exciplex can convert triplet excitons into singlet excitons through the reverse intersystem crossing process, which enables the exciplex emission to utilize not only 25% of the singlet excitons but also a large number of triplet excitons. However, currently, the light-emitting efficiency of OLED devices using exciplexes as the light-emitting body is not high and the stability is poor, which greatly restricts the large-scale application of exciplex light-emitting bodies. Summary of the Invention

[0003] To solve the above technical problems, the present invention proposes a device structure based on a multi-component interfacial exciplex, specifically an organic electroluminescent device based on a multi-component interfacial exciplex.

[0004] To achieve the above invention object, the technical solution of the present invention is described as follows:

[0005] An organic electroluminescent device based on a multi-component interfacial exciplex, comprising a transparent substrate, an anode on the transparent substrate, a cathode, and a plurality of functional layers between the anode and the cathode.

[0006] The plurality of functional layers are sequentially composed of a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, and an electron injection layer.

[0007] The organic light-emitting layer is composed of a donor material doping layer and an acceptor material doping layer.

[0008] Moreover, the donor material doping layer is located on one side of the hole transport layer, and the acceptor material doping layer is located on one side of the electron transport layer. The donor doping layer is doped with a first donor material and a second donor material, and the acceptor material doping layer is doped with an acceptor material and a host material. The mass doping concentration of the first donor material in the donor material doping layer is 10-90%, and the mass doping concentration of the acceptor material in the acceptor material doping layer is 10-99%.

[0009] Among them, the absolute value of the difference between the LUMO energy level of the host material and the LUMO energy levels of the first donor material and the second donor material is less than 0.6 eV, and the absolute value of the difference between the HOMO energy level of the host material and the HOMO energy level of the acceptor material is less than 0.6 eV; moreover, the first donor material can form a first interfacial exciplex with the acceptor material, and the second donor material can form a second interfacial exciplex with the acceptor material. However, the host material cannot form an exciplex with the first donor material, the second donor material, or the acceptor material.

[0010] Furthermore, the above-mentioned first donor material and second donor material include organic compounds with hole transport properties such as 4,4',4''-tris(carbazol-9-yl)triphenylamine (TCTA), 9,9-spirobifluorene-diphenylphosphine oxide (SPPO1), 4,4′,4''-tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA), but are not limited thereto. And the first donor material and the second donor material cannot be the same.

[0011] The above-mentioned acceptor material includes organic compounds with electron transport properties such as 4,7-diphenyl-1,10-phenanthroline (Bphen), 1,3,5-tris(1-phenyl-1H-benzoimidazol-2-yl)benzene (TPBi), 2,4,6-tris[3-(diphenylphosphoryloxy)phenyl]-1,3,5-triazole (PO-T2T), but are not limited thereto.

[0012] The above-mentioned host material includes organic compounds with wide band gaps such as bis[2-((oxo)diphenylphosphino)phenyl]ether (DPEPO), 2,6-bis(9H-carbazol-9-yl-3,1-phenylene pyridine) (26DCzPPy), 1,3-di-9-carbazolylbenzene (MCP), 1,3-bis(triphenylsilyl)benzene (UGH3), 4,4'-bis(9H-carbazol-9-yl)-2,2'-dimethylbiphenyl (CDBP), but are not limited thereto.

[0013] Generally, the first donor material and the second donor material are organic materials with relatively high hole mobility, and the HOMO energy level of the first donor material is lower than that of the second donor material. The host material is a wide-bandgap material, and the acceptor material is an organic material with relatively high electron mobility. Therefore, when the first donor material can form a first interfacial exciplex with the acceptor material and the second donor material can form a second interfacial exciplex with the acceptor material, the singlet energy level of the first interfacial exciplex is greater than that of the second interfacial exciplex, and the emission spectrum of the first exciplex and the absorption spectrum of the second exciplex overlap on the longest wavelength side.

[0014] In a further improved solution, the above-mentioned anode can be a transparent metal oxide such as ITO or FTO, or a high work function metal such as Ag, Au, or Cu, and any anode material can also be used. The hole injection layer can adopt materials such as MoO3, WO3, V2O5, 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN), etc.

[0015] In a further improved solution, the above-mentioned hole transport layer material is preferably an organic material with relatively high hole mobility, and can be 4,4',4''-tris(carbazol-9-yl)triphenylamine (TCTA), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC), N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB), etc.

[0016] In a further improved solution, the above-mentioned electron transport layer material is preferably an organic material with relatively high electron mobility, and can be 4,6-bis(3,5-bis(4-pyridyl)phenyl)-2-phenylpyrimidine (B4PyPPM), 1,3,5-tris(1-phenyl-1H-benzoimidazol-2-yl)benzene (TPBi), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), tris(8-hydroxyquinoline)aluminum (Alq3), 2,4,6-tris[3-(diphenylphosphoryloxy)phenyl]-1,3,5-triazole (PO-T2T), etc.

[0017] In a further improved solution, the above-mentioned electron injection layer material can adopt materials such as LiF, Liq, etc.

[0018] In a further improved solution, the above-mentioned cathode can be any cathode material such as metals with low work function, such as Al, Ca, Ba, etc.

[0019] For a further improved solution, the hole transport layer material can be the same as or different from the interface exciplex donor material; the electron transport layer material can be the same as or different from the interface exciplex acceptor material.

[0020] The beneficial effects of the present invention are as follows:

[0021] For the first interface exciplex formed by the first donor material and the acceptor material, the triplet excitons that have not been converted into singlet excitons can transfer the exciton energy to the triplet excitons of the second interface exciplex formed by the second donor material and the acceptor material through energy transfer, and then further up-convert into singlet excitons for radiative emission, thereby improving the luminescence efficiency of the exciplex.

[0022] In addition, since the acceptor material is doped in the host material, the contact distances between the first donor material molecules, the second donor molecules and the acceptor material molecules are increased, thereby reducing the ΔE of the generated first interface exciplex and second interface exciplex. st Furthermore, the reverse intersystem crossing efficiency of the two is further enhanced, the mutual collision effect of charge transfer excitons is reduced, and the utilization rate of triplet excitons and the lifetime of the exciplex are increased. Description of the Drawings

[0023] Figure 1 : Schematic structural diagram of the organic electroluminescent device based on multiple interface exciplexes of the present invention;

[0024] Among them, 01 is the anode and hole injection layer, 02 is the hole transport layer, 03 is the multiple interface exciplex donor material doping layer, 04 is the multiple interface exciplex acceptor material doping layer, 05 is the electron transport layer, and 06 is the electron injection layer and cathode.

[0025] Figure 2 : Voltage-current efficiency curve of the organic electroluminescent device based on multiple interface exciplexes of the present invention;

[0026] Figure 3 : Spectral curve of the organic electroluminescent device based on multiple interface exciplexes of the present invention.

[0027] Figure 4 : Lifetime curve of the organic electroluminescent device based on multiple interface exciplexes of the present invention. Detailed Embodiments

[0028] The present invention will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the embodiments given are not intended to limit the present invention.

[0029] The meanings of the abbreviated names in the examples are as follows:

[0030] ITO: Indium Tin Oxide, used as a transparent anode;

[0031] HAT-CN: 2,3,6,7,10,11-Hexacyano-1,4,5,8,9,12-hexaazatriphenylene, a hole injection material, which is beneficial to hole injection;

[0032] TAPC: 4,4'-Cyclohexylbis[N,N-bis(4-methylphenyl)aniline], a hole transport material;

[0033] MCP: 1,3-Bis(9-carbazolyl)benzene

[0034] DPEPO: Bis[2-((oxo)diphenylphosphino)phenyl]ether

[0035] PO-T2T: 2,4,6-Tris[3-(diphenylphosphinyloxy)phenyl]-1,3,5-triazole

[0036] Liq: Lithium 8-hydroxyquinolate, an electron injection layer;

[0037] Al: Aluminum, the cathode.

[0038] Example 1: An organic light-emitting device based on a multi-component interfacial exciplex

[0039] The preparation of the organic light-emitting device can be carried out by a multi-source organic molecular vapor deposition system. The detailed process is as follows:

[0040] In the experiment, ITO conductive glass was selected as the substrate. First, the ITO glass substrate was repeatedly scrubbed with acetone and ethanol to remove surface impurities, and then rinsed with deionized water to remove the cotton balls adhered during the scrubbing process;

[0041] The scrubbed ITO substrate was placed in a clean beaker and sonicated with acetone, ethanol, and deionized water for 10 minutes in sequence, then placed in an oven to dry. Finally, the dried ITO glass substrate was subjected to ultraviolet treatment for 10 minutes;

[0042] The treated substrate was placed in a multi-source organic molecular vapor deposition system. There were 10 organic material evaporation sources and 3 metal evaporation sources in the vacuum chamber of the evaporation system. The vacuum degree of the evaporation system could reach 10 -5 Pa, and all the tests of the system were completed at room temperature in the atmosphere during the film growth process.

[0043] In this example, the white light device structure based on the exciplex host is fabricated by sequentially depositing a 10-nm hole injection layer of HAT-CN, a 35-nm hole transport layer of TAPC, a 10-nm donor-doped layer, a 10-nm acceptor-doped layer, a 30-nm electron transport layer of PO-T2T, a 0.8-nm electron injection layer of Liq, and a 100-nm Al cathode on an ITO glass substrate. The material of the donor-doped layer is doped with TAPC and MCP in a ratio of 1:2, where MCP is the first donor material and TAPC is the second donor material. The material of the acceptor-doped layer is doped with DPEPO and PO-T2T in a ratio of 1:9, where DPEOP is the host material and PO-T2T is the acceptor material.

[0044] The performance test results of the electroluminescent device in this example are as follows:

[0045] Figure 2 The luminance-current efficiency curves of this example and the comparative device are shown. It can be seen that the current efficiency and lifetime of Example 1 are the highest. This is because the use of a multi-component interfacial exciplex system can greatly increase the reverse intersystem crossing process in the device and improve the utilization efficiency of triplet excitons. Figure 3 The spectrum of this example is shown. Compared with other comparative examples, only a slight blue shift appears in the emission spectrum of Example 1. It can be seen that the introduction of the second donor material and the host material has a very limited impact on the exciplex spectrum.

[0046] Comparative Example 1 (without acceptor material doped layer)

[0047] The device fabrication process is similar to that of Example 1.

[0048] In this Comparative Example 1, the light-emitting layer is changed to an interfacial exciplex composed of a donor-doped layer and an acceptor material. The donor-doped layer is doped with the first donor material MCP and the second donor material TAPC in a ratio of 2:1, and the acceptor material is PO-T2T.

[0049] The performance test shows that: From Figure 2 It can be seen that the current efficiency of Comparative Example 1 is higher than that of Comparative Example 2. This is because the addition of an extra donor material increases the reverse intersystem crossing efficiency within the exciplex, enabling more triplet excitons to be utilized and increasing the efficiency of the exciplex. However, due to the still severe donor-acceptor molecular interaction at the interface, exciton quenching is still relatively severe, resulting in the efficiency and lifetime of Comparative Example 1 being lower than those of Example 1.

[0050] Comparative Example 2 (without donor material doped layer and without acceptor material doped layer)

[0051] The device fabrication process is similar to that of Example 1.

[0052] In this comparative example, the light-emitting layer is changed to a conventional interfacial exciplex composed of a single donor TAPC and a single acceptor PO-T2T.

[0053] Performance tests show that: from Figure 2 it can be seen that the current efficiency and lifespan of the conventional interfacial exciplex with only a single donor and a single acceptor are relatively low. This is because the recombination region of the conventional interfacial exciplex is relatively narrow, and a large number of charge-transfer excitons accumulate at the interface of the exciplex, resulting in severe exciton quenching, thereby reducing the efficiency and lifespan of the device.

[0054] As described above, it is only used to illustrate the technical solution of the present invention and not to limit it. Any other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solution of the present invention should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. An organic electroluminescent device based on a multi-component interfacial exciplex, comprising a transparent substrate, an anode, a cathode on the transparent substrate, and a plurality of functional layers between the anode and the cathode, It is characterized in that: wherein the plurality of functional layers are sequentially composed of a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, and an electron injection layer, and the organic light-emitting layer is composed of a donor material doped layer and an acceptor material doped layer, moreover, the donor material doped layer is located on the side of the hole transport layer, and the acceptor material doped layer is located on the side of the electron transport layer. The donor doped layer is doped with a first donor material and a second donor material, and the acceptor material doped layer is doped with an acceptor material and a host material. The mass doping concentration of the first donor material in the donor material doped layer is 10-90%, and the mass doping concentration of the acceptor material in the acceptor material doped layer is 10-99%. Among them, the absolute value of the difference between the LUMO energy levels of the host material and the first donor material and the second donor material is less than 0.6 eV, and the absolute value of the difference between the HOMO energy levels of the host material and the acceptor material is less than 0.6 eV; moreover, the first donor material can form a first interfacial exciplex with the acceptor material, and the second donor material can form a second interfacial exciplex with the acceptor material. However, the host material cannot form an exciplex with the first donor material, the second donor material, or the acceptor material. The first donor material and the second donor material are any one of 4,4',4''-tris(carbazol-9-yl)triphenylamine (TCTA), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), and N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB), and the first donor material and the second donor material cannot be the same. The acceptor material is any one of 1,3,5-tris(1-phenyl-1H-benzoimidazol-2-yl)benzene (TPBi), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), tris(8-hydroxyquinoline)aluminum (Alq3), and 2,4,6-tris[3-(diphenylphosphoryl)phenyl]-1,3,5-triazole (PO-T2T). The host material is any one of bis[2-((oxo)diphenylphosphino)phenyl]ether (DPEPO), 1,3-di-9-carbazolylbenzene (MCP), 1,3-bis(triphenylsilyl)benzene (UGH3), and 4,4'-bis(9H-carbazol-9-yl)-2,2'-dimethylbiphenyl (CDBP). The anode is a transparent metal oxide ITO, FTO, or any one of Ag, Au, and Cu. The hole injection layer is MoO3, WO3, V2O5, or 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN). The hole transport layer is 4,4',4''-tris(carbazol-9-yl)triphenylamine (TCTA), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), 4,4'-cyclohexylbis[N,N-bis(4-methylphenyl)aniline] (TAPC), N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB); The electron transport layer is 4,6-bis(3,5-di(4-pyridyl)phenyl)-2-phenylpyrimidine (B4PyPPM), 1,3,5-tris(1-phenyl-1H-benzoimidazol-2-yl)benzene (TPBi), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), tris(8-hydroxyquinoline)aluminum (Alq3), 2,4,6-tris[3-(diphenylphosphoryloxy)phenyl]-1,3,5-triazole (PO-T2T); The electron injection layer is LiF, Liq; The cathode is Al, Ca, Ba.

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