Laminated organic light-emitting device and application thereof

Abstract

The invention relates to the technical field of electroluminescence, and discloses a laminated organic light-emitting device and application thereof, and the laminated organic light-emitting device comprises an anode layer, a first light-emitting unit, an electron transport layer, an interface modification layer, a connection layer, a second light-emitting unit and a cathode layer which are sequentially arranged from bottom to top; the electron transport layer comprises a hole blocking layer and an n-type electron transport layer; wherein the n-type electron transport layer is composed of an n-type dopant and an organic electron transport material, has the functions of electron transport, charge separation and injection and regulation and control of the optical microcavity effect of the laminated device, can simplify the electron transport and connection layer structure of the laminated device, and effectively improves the conductivity of the laminated device; according to the laminated organic light-emitting device, the voltage drop of the body is obviously reduced, and the interface electron injection barrier is reduced, so that the laminated organic light-emitting device has the advantages of low driving voltage, high efficiency and long service life, and the effect of adjusting the optical microcavity of the device can be achieved by utilizing the n-type electron transport layer.

Description

Technical Field

[0001] This invention relates to the field of electroluminescence technology, and more particularly to a multilayer organic electroluminescent device and its applications. Background Technology

[0002] Organic light-emitting diodes (OLEDs) technology, with its advantages of self-emission, wide color gamut, and thinness and flexibility, has been widely used in small-to-medium-sized display products such as smartphones and wearable devices. Typically, an OLED device has a single light-emitting unit (called a single-junction OLED), meaning it uses a single light-emitting layer for electroluminescence. However, the accelerated decay of luminous efficiency and lifetime stability at high brightness levels poses a significant challenge for single-junction devices in high-brightness displays, micro-displays, and indoor lighting applications. To address this issue, a charge generation layer (CGL) structure is used to connect multiple light-emitting units in series, creating a stacked OLED device. Compared to single-junction devices, stacked devices exhibit significantly increased luminous brightness under the same current drive, resulting in a longer device lifetime.

[0003] Pursuing high brightness, low driving voltage and long working life are the key to realizing high-performance stacked OLED devices. To this end, the following technical difficulties need to be addressed for the stacked device structure: (1) In order to obtain a lower driving voltage, it is important to reduce the voltage drop on the interconnect layer and electron transport layer units. This requires the interconnect layer and electron transport layer to have good carrier generation capability and electron transport capability, respectively; (2) There is usually an energy level barrier at the interface between the interconnect layer and the electron transport layer, which increases the driving voltage of the device and is not conducive to improving the power efficiency of the device; (3) The number of organic functional layers constituting the stacked device is large, which makes the device fabrication process complicated. How to simplify the stacked device structure is an effective way to reduce the difficulty of the fabrication process.

[0004] In addressing the technical challenges of multilayer OLED devices, academic researchers and panel manufacturers have conducted relevant research. For example, patent application CN117700432A discloses an organic compound as an n-type dopant material for multilayer devices, resulting in multilayer devices exhibiting low driving voltage, excellent stability, and high efficiency. On the other hand, patent application CN114520301A introduces a spacer layer composed of electron transport materials between the n-type and p-type doped layers of a multilayer device, effectively mitigating the driving voltage rise and device aging problems caused by n-type dopant diffusion, thereby significantly improving the lifetime and stability of the multilayer device. However, the multilayer device structures designed in the above schemes are still relatively complex, and currently there is still no electron transport structure scheme that combines the functions of an electron transport layer and an n-type connection layer. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a novel n-type electron transport layer for stacked OLED devices. The n-type electron transport layer is composed of an n-type dopant and an organic electron transport material, simultaneously possessing electron transport, charge separation, and the ability to modulate the optical microcavity effect of the stacked device. On the one hand, this simplifies the structure of the stacked device and reduces the difficulty of device fabrication. On the other hand, the organic electron transport material of the n-type electron transport layer, after modification with a power-supplying unit free of lone pairs of electrons, can effectively coordinate and activate n-doping with the n-type dopant at a low doping concentration, achieving efficient n-type doping, improving electron injection and transport performance, and helping to reduce the driving voltage of the stacked device. Simultaneously, the lower n-type dopant concentration helps to improve the luminous efficiency and lifetime of the device, resulting in a stacked OLED device with low driving voltage, high efficiency, and long lifetime.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A stacked organic electroluminescent device includes, from bottom to top, an anode layer, a first light-emitting unit, an interface modification layer, a connecting layer, a second light-emitting unit, and a cathode layer; an electron transport layer is further disposed between the first light-emitting unit and the interface modification layer, the electron transport layer including a hole blocking layer near the anode layer and an n-type electron transport layer near the cathode layer. The n-type electron transport layer is composed of an n-type dopant and an organic electron transport material, enabling the n-type electron transport layer to achieve electron transport, charge separation, and adjustment of the optical microcavity of the stacked organic electroluminescent device. The connecting layer is composed of a p-type dopant and an organic hole-electron transport material; The interface modification layer is either a single-layer interface modification layer composed of p-type dopants or a double-layer interface modification layer composed of n-type and p-type dopants.

[0007] An application of a multilayer organic electroluminescent device, wherein the multilayer organic electroluminescent device is used to fabricate display devices, lighting devices, solar cells, optical sensors, organic thin-film transistors, organic field-effect transistors, information tags, electronic artificial skin sheets or electronic paper.

[0008] Beneficial effects: (1) The n-type electron transport layer in the first light-emitting unit has the functions of both an electron transport layer and an n-type connection layer. Compared with traditional devices, it effectively simplifies the electron transport and connection layer structure of the stacked device, which is conducive to reducing the difficulty of the fabrication process of the stacked device.

[0009] (2) The organic electron transport material of the n-type electron transport layer is modified with a power supply unit that does not contain lone pair electrons, which enhances the electron nucleophilicity of the nitrogen atom chelate site. When the above power supply unit is coordinated with the organic electron transport material, it will not compete with the nitrogen atom chelate site. Therefore, the above modification enhances the in-situ coordinated n-doping effect, improves the n-doping efficiency, effectively improves the conductivity of the n-type electron transport layer, and reduces the driving voltage of the stacked device.

[0010] (3) The n-type electron transport layer can generate effective coordination when the n-type dopant concentration is low, thus achieving good n-doping effect. The lower n-doping concentration can avoid luminescence quenching and visible light absorption of the n-dopant, and maintain high device luminescence efficiency.

[0011] (4) When the n-type electron transport layer is combined with the interface modification layer and the connection layer of the present invention, efficient charge separation can be achieved. Electrons are separated and injected into the n-type electron transport layer without a potential barrier, while holes are separated and injected into the connection layer and further transported to the hole transport layer of the second light-emitting unit. The efficient charge separation, injection and transport process can also be achieved under the simplified connection layer structure, so that the stacked OLED device has a low driving voltage, which is beneficial to improving the power efficiency of the stacked device.

[0012] (5) Since the n-type electron transport layer has high conductivity, it can be used as the optical microcavity control layer of the device to replace the traditional method (using the hole transport layer as the optical microcavity control layer). Compared with the traditional method, the above method has less impact on the rise of the device driving voltage, which is beneficial to improving the power efficiency of the stacked device. Attached Figure Description

[0013] Figure 1 A schematic diagram of the structure of the stacked organic electroluminescent device of the present invention is shown.

[0014] Figure 2 The device current density-voltage characteristic curves of Embodiment 1 and Comparative Example 1 of the present invention are shown.

[0015] Figure 3 The graphs showing the highest external quantum efficiency characteristics of the devices in Embodiment 1 and Comparative Examples 9 and 10 of the present invention are shown.

[0016] Explanation of key component symbols: 100, Anode layer; 101, Hole injection layer; 102, First hole transport layer; 103, Second hole transport layer; 104, First light-emitting layer; 105, Second electron transport layer; 106, n-type electron transport layer; 107, Interface modification layer; 108, Connecting layer; 111, Second light-emitting layer; 113, First electron transport layer; 114, Electron injection layer; 115, Cathode layer. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this invention. It should be understood that, without conflict, any and all embodiments of the present invention can be combined with technical features of any other embodiment or multiple other embodiments to obtain other embodiments. The present invention includes such combinations to obtain other embodiments.

[0018] In this specification, groups and their substituents may be selected by those skilled in the art to provide stable structural moieties and compounds. When a substituent is described by a conventional chemical formula written from left to right, the substituent also includes chemically equivalent substituents obtained when the structural formula is written from right to left.

[0019] The chapter headings used in this specification are for organizational purposes only and should not be construed as limiting the subject matter. All references or portions thereof cited in this invention, including but not limited to patents, patent applications, articles, books, user manuals, and papers, are incorporated herein by reference in their entirety.

[0020] Unless otherwise specified, all technical and scientific terms used herein have the standard meaning in the field to which the claimed subject matter pertains. Where multiple definitions exist for a term, the definition herein shall prevail.

[0021] It should be understood that the singular forms used in this invention, such as "a," include plural references unless otherwise specified. Furthermore, the term "comprising" is an open-ended limitation, not a closed one; that is, it includes the contents specified in this invention but does not exclude other aspects.

[0022] This invention provides a stacked organic electroluminescent device, comprising an anode layer, a first light-emitting unit, an interface modification layer, a connecting layer, a second light-emitting unit, and a cathode layer; wherein, the first light-emitting unit is provided with a hole injection layer, a hole transport layer, a first light-emitting layer, and an electron transport layer in sequence from the side near the anode layer; the second light-emitting unit is provided with a hole transport layer, a second light-emitting layer, an electron transport layer, and an electron injection layer in sequence from the side near the anode layer.

[0023] Next, the first and second light-emitting units of the stacked organic electroluminescent device of this application will be further described.

[0024] Specifically, the hole transport layer in the first light-emitting unit is an organic layer formed between the first light-emitting layer and the anode layer (or hole injection layer), and its main function is to transport holes from the anode to the first light-emitting layer. The hole transport layer may consist of one layer of organic material, defined as the first hole transport layer; or it may consist of two layers of organic material, with the organic layer closer to the anode layer defined as the first hole transport layer and the organic layer closer to the first light-emitting layer defined as the second hole transport layer.

[0025] Specifically, the hole transport layer in the second light-emitting unit is an organic layer formed between the connecting layer and the second light-emitting layer. The hole transport layer may consist of one layer of organic material, defined as the first hole transport layer; or it may consist of two layers of organic material, with the organic layer closer to the connecting layer defined as the first hole transport layer and the organic layer closer to the second light-emitting layer defined as the second hole transport layer.

[0026] As the hole transport material for the hole transport layer, an aromatic amine compound is preferably used, wherein the aromatic amine compound is a first aromatic amine derivative or a second aromatic amine derivative, the general structural formula of the first aromatic amine derivative is shown in structural formula (I), and the general structural formula of the second aromatic amine derivative is shown in structural formula (II). (I), (II); Wherein, Ar1 to Ar4 represent substituted or unsubstituted aromatic hydrocarbon groups with 6 to 50 (preferably 6 to 30, more preferably 6 to 20, and even more preferably 6 to 12) cyclic carbon atoms, or fused aromatic hydrocarbon groups with 6 to 50 (preferably 6 to 30, more preferably 6 to 20, and even more preferably 6 to 12) cyclic carbon atoms, substituted or unsubstituted aromatic heterocyclic groups with 5 to 50 (preferably 5 to 30, more preferably 5 to 20, and even more preferably 5 to 12) cyclic carbon atoms, or fused aromatic heterocyclic groups with 5 to 50 (preferably 5 to 30, more preferably 5 to 20, and even more preferably 5 to 12) cyclic carbon atoms, or groups formed by bonding these aromatic hydrocarbon groups or fused aromatic hydrocarbon groups with aromatic heterocyclic groups or fused aromatic heterocyclic groups. Rings can be formed between Ar1 and Ar2, and between Ar3 and Ar4.

[0027] L represents an aromatic hydrocarbon group with 6 to 50 (preferably 6 to 30, more preferably 6 to 20, and even more preferably 6 to 12) substituted or unsubstituted cyclic carbon groups, or a fused aromatic hydrocarbon group with 6 to 50 (preferably 6 to 30, more preferably 6 to 20, and even more preferably 6 to 12) substituted cyclic carbon groups, or an aromatic heterocyclic group with 5 to 50 (preferably 5 to 30, more preferably 5 to 20, and even more preferably 5 to 12) substituted or unsubstituted cyclic carbon groups, or a fused aromatic heterocyclic group with 5 to 50 (preferably 5 to 30, more preferably 5 to 20, and even more preferably 5 to 12) substituted or unsubstituted cyclic carbon groups.

[0028] Furthermore, the hole transport layer in the first and second light-emitting units, according to the compound described in structural formula (I), is preferably selected from the following compounds, but is not limited to the following structures:

[0029] The compounds according to structural formula (II) are preferably selected from the following compounds, but are not limited to the following structures: .

[0030] Furthermore, in the first light-emitting unit of this application, a hole injection layer is preferably disposed between the anode layer and the hole transport layer (or between the anode layer and the first light-emitting layer). The main function of the hole injection layer is to promote the injection of holes from the anode layer to the hole transport layer or the first light-emitting layer, thereby reducing the driving voltage of the organic electroluminescent device and improving the luminous brightness and device lifetime. Here, the hole injection layer material is a p-type dopant containing a deep LUMO energy level, and as a specific example, it is preferably selected from HI-1 to HI-18. The structural formulas of HI-1 to HI-18 are shown below: .

[0031] Furthermore, the thickness of the hole injection layer is not particularly limited, but is preferably 5 to 100 nm.

[0032] Furthermore, the thickness of the hole transport layer is not particularly limited, but is preferably 20–200 nm. Specifically, when the hole transport layer of the organic electroluminescent device is composed of a first hole transport layer, the thickness of the first hole transport layer is preferably 20–200 nm; when the hole transport layer of the organic electroluminescent device is composed of a first hole transport layer and a second hole transport layer, the thickness of the first hole transport layer is preferably 19–150 nm, and the thickness of the second hole transport layer is preferably 1–50 nm.

[0033] Specifically, when the hole transport layer contains the p-type dopant and the hole transport material, the doping concentration of the p-type dopant is preferably 0.1 to 10.0 wt%.

[0034] Furthermore, the main function of the first and second emitting layers in an organic electroluminescent device is to generate excitons by recombination of holes and electrons injected into the first and second emitting layers. The excitons then complete the electro-optic conversion process through radiative transitions. The materials constituting the first and second emitting layers can be undoped luminescent compounds consisting only of the first compound, binary luminescent compositions consisting of the first and third compounds, or ternary luminescent compositions consisting of the first, second, and third compounds.

[0035] Specifically, for the first compound, which is a luminescent material that generates radiative transitions, it can be selected from fluorescent materials, phosphorescent materials, thermally activated delayed fluorescence materials, etc., according to the luminescence mechanism. Preferably, it is a phosphorescent material containing coordinating metals such as iridium and platinum; a thermally activated delayed fluorescence material containing boron nitrogen derivatives, boron oxide derivatives, indole-carbazole derivatives, or boron fluorine derivatives; or a fluorescent material containing fluoranthene derivatives, pyrene derivatives, or imidazole derivatives. The second compound preferably contains one or more thermally activated delayed fluorescence materials containing benzonitrile derivatives, triazine derivatives, pyrimidine derivatives, pyridine derivatives, pyrazine derivatives, imidazole derivatives, benzothiophene oxide derivatives, phenanthroline derivatives, benzonitrile derivatives, or phosphorus oxide derivatives. The third compound preferably contains one or more of carbazole derivatives, triazine derivatives, pyrimidine derivatives, aniline derivatives, benzothiophene derivatives, benzofuran derivatives, or fluorene derivatives.

[0036] Furthermore, an electron transport layer is disposed between the first light-emitting unit and the interface modification layer, the electron transport layer including a hole blocking layer (second electron transport layer) near the anode layer and an n-type electron transport layer near the cathode layer.

[0037] Specifically, the n-type electron transport layer is composed of an n-type dopant and an organic electron transport material, wherein the organic electron transport material is composed of nitrogen heterocyclic units without lone pair electron-donating units; wherein the lone pair electron-donating units are selected from at least one of the following structures D-1 to D-14: ; X is selected from carbon, silicon, and germanium; R1 to R7 are each independently selected from one of C1 to C10 alkyl, C3 to C10 cycloalkyl, silyl, and C6 to C30 aryl. Y1 and Y2 are each independently selected from one of C1-C10 alkyl, C3-C10 cycloalkyl, silyl, and C6-C30 aryl, wherein Y1 and Y2 can be further cyclically formed to form a cycloalkyl group.

[0038] Traditional electron transport materials modified with units containing lone pairs of electrons suffer from strong nucleophilicity, which competes with the n-type dopant for coordination. This means the lone pairs may bind to the n-type dopant, affecting the coordination between the n-type dopant and the nitrogen atom in the nitrogen heterocycle, requiring higher doping concentrations to achieve n-type doping. In contrast, this approach modifies the nitrogen heterocycle unit with electron-donating units that do not contain lone pairs. The electron-donating properties of these units enhance the nucleophilicity of the nitrogen atom in the nitrogen heterocycle. Since the electron-donating units lack strong nucleophilicity, they do not compete with the nitrogen heterocycle unit for coordination. This allows the n-type dopant to directly form stable coordination with the nitrogen atom in the nitrogen heterocycle at low concentrations (0.1%–2 wt%), achieving coordination activation of the n-type dopant and causing the reversible ionization reaction of the n-type dopant (M→M) to shift in the forward direction. + +e - e - (These are free electrons), which generate a large number of free electrons in the n-type electron transport layer, thus improving its conductivity.

[0039] Furthermore, the high free electron density formed under low-concentration doping significantly reduces the resistance of the n-type electron transport layer. When electrons enter the n-type electron transport layer from the connecting layer, there is no need to overcome the voltage loss caused by high resistance. At the same time, the enhanced nucleophilicity of nitrogen atoms in nitrogen heterocyclic rings makes their LUMO energy level closer to the Fermi level of the connecting layer, which greatly reduces the electron injection barrier at the interface. The two work together to directly reduce the driving voltage of the device.

[0040] In traditional structures, a separate n-type connecting layer is required to achieve charge separation. However, in this scheme, the n-type electron transport layer, due to its high conductivity and the energy level matching between the n-type electron transport layer and the connecting layer (the interface modification layer is p-type doped, forming a "pn contact" with the n-type electron transport layer), can directly cooperate with the interface modification layer and the connecting layer to achieve charge separation. Electrons generated by the interface modification layer can be injected into the n-type electron transport layer without a potential barrier, while holes are captured by the connecting layer and transferred to the second light-emitting unit. This simplifies the two-layer structure of the electron transport layer and the n-type connecting layer in the traditional structure into a single-layer structure of the n-type electron transport layer.

[0041] More specifically, the organic electron transport material is selected from at least one of compounds N-1 to N-63: .

[0042] In one embodiment, the n-type dopant of the n-type electron transport layer is selected from at least one of lithium, sodium, potassium, cesium, magnesium, gold, silver, copper, zinc, ytterbium, cesium carbonate, lithium carbonate, cesium nitride, and lithium nitride; preferably, the n-type dopant is selected from lithium, silver, cesium, or ytterbium.

[0043] In one embodiment, the thickness of the n-type electron transport layer is 10–300 nm; preferably, the thickness of the n-type electron transport layer is 50–300 nm.

[0044] Furthermore, the connecting layer is composed of p-type dopant and organic hole-electron transport material; the interface modification layer is a single-layer interface modification layer composed of p-type dopant or a double-layer interface modification layer composed of n-type dopant and p-type dopant.

[0045] In one embodiment, when the interface modification layer is a bilayer interface modification layer composed of an n-type dopant and a p-type dopant, the n-type dopant is selected from at least one of lithium, sodium, potassium, cesium, magnesium, gold, silver, copper, zinc, ytterbium, cesium carbonate, lithium carbonate, cesium nitride, and lithium nitride; preferably, the n-type dopant is selected from lithium, silver, cesium, or ytterbium.

[0046] In another embodiment, when the interface modification layer is a single-layer interface modification layer composed of p-type dopants or a double-layer interface modification layer composed of n-type dopants and p-type dopants, the p-type dopants are materials with deep LUMO energy levels, preferably at least one selected from MoO3, WO3, V2O5, MoO2, Co3O4 and compounds HI-1 to HI-18: .

[0047] In another embodiment, the connecting layer includes one or two of a p-type dopant and an aromatic amine compound, wherein the p-type dopant is at least one of MoO3, WO3, V2O5, MoO2, Co3O4 and the above compounds HI-1 to HI-18.

[0048] Specifically, the thickness of the interface modification layer is 1–10 nm, and the thickness of the connecting layer is 5–20 nm.

[0049] The interface modification layer can be either a single layer (p-type dopant only) or a double layer (n-type dopant and p-type dopant). In a double-layer structure, the side closer to the n-type electron transport layer uses an n-type dopant, which can form an energy level gradient match with the n-type electron transport layer, eliminating the potential barrier for electrons to enter the interface modification layer from the n-type electron transport layer and ensuring smooth electron transport. The side closer to the connecting layer uses a p-type dopant, whose deep LUMO energy level can intercept electrons and only allow holes to pass through, achieving electron-hole separation. That is, electrons remain on the side of the interface modification layer closer to the n-type electron transport layer, while holes enter the connecting layer. Even in a single-layer p-type structure, its deep LUMO energy level can form a "pn contact" with the n-type electron transport layer, promoting charge separation through a built-in electric field and avoiding efficiency losses caused by electron-hole recombination at the interface.

[0050] The connecting layer consists of p-type dopant (1%–10% doping mass ratio) and organic hole transport material, serving to enhance hole transport and facilitate charge transfer. The p-type dopant transfers charge to the organic hole transport material, generating a large number of hole carriers, significantly improving hole transport conductivity and reducing hole transport resistance and voltage drop within the layer. Simultaneously, it forms a conductive channel with the p-type dopant in the interface modification layer, allowing holes separated from the interface modification layer to enter the connecting layer unimpeded and rapidly transport to the hole transport layer of the second light-emitting unit, ultimately being injected into the second light-emitting layer and recombine with electrons. This synergistic mechanism ensures efficient charge transfer between adjacent light-emitting units while avoiding the increased driving voltage caused by energy level mismatch in traditional connecting layers. It complements the function of the n-type electron transport layer, jointly supporting the low-voltage, high-efficiency operation of the stacked device.

[0051] Furthermore, the electron transport layer (hole blocking layer) in the first light-emitting unit is an organic layer formed between the first light-emitting layer and the interface modification layer. The electron transport layer may consist of one organic layer material, defined as the first electron transport layer; or it may consist of two organic layer materials, with the organic layer closer to the first light-emitting layer defined as the first electron transport layer and the organic layer closer to the cathode layer defined as the second electron transport layer.

[0052] The electron transport layer in the second light-emitting unit is an organic layer formed between the second light-emitting layer and the cathode layer (or electron injection layer). Its main function is to transport electrons from the cathode to the second light-emitting layer. The electron transport layer may consist of one layer of organic material, defined as the first electron transport layer; or it may consist of two layers of organic material, with the organic layer closer to the cathode layer defined as the first electron transport layer and the organic layer closer to the second light-emitting layer defined as the second electron transport layer.

[0053] For the electron transport material used in the second electron transport layer, aromatic heterocyclic compounds containing one or more heteroatoms within the molecule are preferred, and nitrogen-containing ring derivatives are particularly preferred. Furthermore, as nitrogen-containing ring derivatives, aromatic rings having a nitrogen-containing six-membered or five-membered ring skeleton, or fused aromatic ring compounds having a nitrogen-containing six-membered or five-membered ring skeleton, are preferred.

[0054] Furthermore, the second electron transport layer of the organic electroluminescent device of the present invention is preferably derived from, but is not limited to, the following compounds: ; The first electron transport layer material in the organic electroluminescent device of this application is preferably selected from the following compounds, but not limited to the following structures: .

[0055] Furthermore, the thickness of the electron transport layer is not particularly limited, but is preferably 10–100 nm. Specifically, when the electron transport layer of the organic electroluminescent device is composed of a first electron transport layer, the thickness of the first electron transport layer is preferably 10–100 nm; when the electron transport layer of the organic electroluminescent device is composed of a first electron transport layer and a second electron transport layer, the thickness of the first electron transport layer is preferably 9–70 nm, and the thickness of the second electron transport layer is preferably 1–30 nm.

[0056] The nitrogen-containing ring derivatives of the hole-blocking layers (first and second electron transport layers) possess deep LUMO (low electron affinity) energy levels. These LUMO levels are significantly lower than the HOMO (hole-generating) energy levels of the emitting layer, forming an energy barrier. This means that when a hole enters the first emitting layer from the hole transport layer and attempts to escape towards the cathode, it is blocked by the deep LUMO energy levels of the hole-blocking layer and cannot cross it. Conversely, when an electron enters the hole-blocking layer from the n-type electron transport layer, it can pass smoothly into the first emitting layer because the material itself is electron-transporting. By utilizing these hole-blocking and electron-passing properties, holes and electrons are forced to meet and form excitons only within the first emitting layer, preventing recombination in non-emitting regions and directly improving the device's luminous efficiency.

[0057] Furthermore, the primary function of the anode layer in an organic electroluminescent device is to inject holes into the hole transport layer or the first light-emitting layer. Anode layer materials with a work function of 4.5 eV or higher are preferred. The anode layer material is preferably selected from indium tin oxide (ITO), tin oxide (NESA), indium gallium zinc oxide (IGZO), silver, etc. The anode layer can be formed into a thin film by thermal evaporation, sputtering, or other methods. Preferably, the light transmittance of the visible area of ​​the anode is greater than 80%. Additionally, the sheet resistance of the anode layer is preferably below 500 Ω / cm, and the film thickness is preferably selected in the range of 10–200 nm.

[0058] Furthermore, the primary function of the cathode layer in an organic electroluminescent device is to inject electrons into the electron injection layer, electron transport layer, or second light-emitting layer, and a material with a low work function is preferred. The cathode material is not particularly limited, but aluminum, magnesium, silver, magnesium-silver alloys, magnesium-aluminum alloys, and aluminum-lithium alloys are preferred. Similar to the anode layer, the cathode layer can be formed into a thin film using methods such as thermal evaporation or sputtering, and the film thickness is preferably in the range of 10–200 nm. Additionally, light emission can be extracted from the cathode side as needed.

[0059] This invention also provides an application of the stacked organic electroluminescent device, which can be used to manufacture display devices, lighting devices, solar cells, optical sensors, organic thin-film transistors, organic field-effect transistors, information tags, electronic artificial skin sheets, or electronic paper.

[0060] Furthermore, the present invention also provides a specific method for fabricating a multilayer organic electroluminescent device, and the fabrication method of the present invention will be further described below through specific embodiments.

[0061] The present invention does not impose any particular restrictions on the source of the raw materials used in the following embodiments, which can be commercially available products or prepared by methods known to those skilled in the art.

[0062] Examples 1-18 (1) Place a 30 mm × 30 mm × 0.7 mm thick transparent electrode with ITO (such as...) Figure 1 The glass substrate with the anode layer 100 (ITO film thickness set to 95 nm) shown was sequentially ultrasonically cleaned in acetone, washing solution, ultrapure water (3 times), and isopropanol, with each ultrasonic cleaning step lasting 10 minutes. The cleaned ITO glass substrate was then placed in an oven at 120 °C and baked for 3 hours. (2) The baked ITO glass substrate was subjected to vacuum plasma cleaning treatment for 10 minutes; (3) The above-mentioned glass substrate after plasma treatment is mounted on the substrate frame of the vacuum evaporation apparatus. First, compound HI-7 and compound HT-10 are co-deposited on the side where transparent electrode lines are formed in a manner that covers the transparent electrode. The concentration of compound HI-7 is set to 2 wt%, and a hole injection layer 101 with a film thickness of 10 nm is formed. (4) HT-10 compound is vapor-deposited on hole injection layer 101 to form first hole transport layer 102 with a film thickness of 50 nm; (5) HT-46 compound is vapor-deposited on the first hole transport layer 102 to form a second hole transport layer 103 with a film thickness of 5 nm; (6) A third compound combination GH and a first compound GD are co-deposited on the second hole transport layer 103 to form a first light-emitting layer 104 with a film thickness of 40 nm. The concentration of the first compound GD in the first light-emitting layer 104 is set to 4 wt%. The structures of the third compound combination GH and the first compound GD used are shown below:

[0063] (7) EB-4 is deposited on the first light-emitting layer 104 to form a film with a thickness of 15 nm. Figure 1 The second electron transport layer 105 is shown; (8) An n-type electron transport layer 106 with a thickness of 25 nm is deposited on the second electron transport layer 105. (9) An interface modification layer 107 is deposited on the n-type electron transport layer 106 by vapor deposition; (10) Compound HI-7 and compound HT-10 were co-deposited on the interface modification layer 107 to form a connecting layer 108 with a film thickness of 10 nm. The concentration of compound HI-7 was set to 2 wt%. (11) HT-10 compound is deposited on the bonding layer 108 to form a first hole transport layer 102 with a film thickness of 50 nm; (12) HT-46 compound is vapor-deposited on the first hole transport layer 102 to form a second hole transport layer 103 with a film thickness of 10 nm; (13) A third compound combination GH and a first compound GD are co-deposited on the second hole transport layer 103 to form a second light-emitting layer 111 with a film thickness of 40 nm. The concentration of the first compound GD in the second light-emitting layer 111 is set to 4 wt%. (14) EB-4 is deposited on the second light-emitting layer 111 to form a second electron transport layer 105 with a film thickness of 10 nm; (15) ET-9 is deposited on the second electron transport layer 105 to form a first electron transport layer 113 with a film thickness of 30 nm; (16) Liq is deposited on the first electron transport layer 113 to form an electron injection layer 114 with a film thickness of 2 nm; the structure of the compound Liq used is shown below:

[0064] (17) Metal Al is deposited on the electron injection layer 114 to form a cathode layer 115 with a film thickness of 100 nm.

[0065] The compound combinations used in the n-type electron transport layer 106 formed in step (8) are shown in Table 1, Examples 1-18.

[0066] Table 1. Compound combinations used in n-type electron transport layer 106

[0067] The combination of compounds used in the interface modification layer 107 formed in step (9) is shown in Table 2, Examples 1-18.

[0068] Table 2. Compound combinations used in interface modification layer 107

[0069] Comparative Examples 1-12 In Comparative Examples 1-6, the multilayer organic light-emitting devices were prepared by replacing the n-type electron transport layer 106 with the electron transport layer ' and the connecting layer ' shown in Table 3, respectively, with the electron transport layer ' having a thickness of 20 nm and the connecting layer ' having a thickness of 5 nm as the n-type connecting layer. Otherwise, the multilayer organic light-emitting devices were prepared using the same procedures as in Example 1. In Comparative Examples 7-12, the n-type electron transport layer ' used compound combinations as shown in Table 4. Otherwise, the multilayer organic light-emitting devices were prepared using the same procedures as in Example 1.

[0070] Table 3. Compound combinations used in the electron transport layer and link layer of Comparative Examples 1-6

[0071] Table 4. Compound combinations used in the n-type electron transport layers of Comparative Examples 7-12

[0072] Performance evaluation of organic electroluminescent devices The organic electroluminescent devices prepared in Examples 1-18 and Comparative Examples 1-12 were measured using a spectroradiometer CS-2000 (Konica Minolta) and a digital source meter 2400 (Keithley). The organic electroluminescent devices were measured at 3000 cd / m². 2 Drive voltage, external quantum efficiency, and CIE 1931 chromaticity coordinates (x, y) at luminance were measured using device lifetime testing at a current density of 10 mA / cm². 2 When driving the fabricated organic electroluminescent device, the lifetime (T95) during which the device brightness decays to 95% of the initial brightness and the difference between the driving voltage and the driving voltage at the initial brightness are considered. The performance evaluation results of the devices in Examples 1-7 and Comparative Examples 1-3 are shown in Table 5 below.

[0073] Table 5

[0074] Comparing the driving voltages of the stacked devices in Examples 1-18 and Comparative Examples 1-6 in Table 5, replacing the traditional electron transport material and the connection layer' (as an n-type connection layer) structure with the n-type electron transport layer provided by this invention can significantly reduce the driving voltage of the device. This indicates that the n-type electron transport layer constructed by modifying the power supply unit without lone pair electrons can effectively improve its electron transport conductivity, achieving the combined effects of an electron transport layer and an n-type connection layer. Compared with the traditional method of using an electron transport layer' and an n-type connection layer respectively, it has a lower device driving voltage and also improves the device's operating life. On the other hand, comparing the driving voltages and luminous efficiencies of the stacked devices in Examples 1, 12, 13, 14 and Comparative Examples 9-12 in Table 5, when the concentration of the n-type dopant in the n-type electron transport layer is relatively high (more than 2 wt%), the luminous efficiency of the stacked device will decrease significantly. This indicates that a high concentration of n-type dopant will cause exciton quenching in the luminescent layer, leading to a decrease in the luminous efficiency of the device. Furthermore, at higher n-type dopant concentrations, the device's driving voltage gradually increases. This is because n-type doping causes the LUMO level to approach the Fermi level, increasing the barrier for electrons to be injected from the n-type electron transport layer into the second electron transport layer, thus raising the device's driving voltage. In addition, comparing the driving voltage and luminous efficiency of the stacked devices in Example 1 and Comparative Examples 7-8 in Table 5, it can be seen that introducing power-generating units without lone pairs of electrons into the organic electron transport material constituting the n-type electron transport layer enhances the in-situ coordination n-doping effect, effectively improving the conductivity of the n-type electron transport layer and reducing the driving voltage of the stacked device.

[0075] It is understood that those skilled in the art can make equivalent substitutions or changes to the technical solution and inventive concept of the present invention, and all such changes or substitutions should fall within the protection scope of the present invention.

Claims

1. A stacked organic electroluminescent device, characterized in that, The stacked organic electroluminescent device includes, from bottom to top, an anode layer, a first light-emitting unit, an interface modification layer, a connecting layer, a second light-emitting unit, and a cathode layer; an electron transport layer is also disposed between the first light-emitting unit and the interface modification layer, the electron transport layer including a hole blocking layer near the anode layer and an n-type electron transport layer near the cathode layer. The n-type electron transport layer is composed of an n-type dopant and an organic electron transport material, enabling the n-type electron transport layer to achieve electron transport, charge separation, and adjustment of the optical microcavity of the stacked organic electroluminescent device. The connecting layer is composed of a p-type dopant and an organic hole-electron transport material; The interface modification layer is either a single-layer interface modification layer composed of p-type dopants or a double-layer interface modification layer composed of n-type and p-type dopants.

2. The stacked organic electroluminescent device according to claim 1, characterized in that, The organic electron transport material constituting the n-type electron transport layer is composed of nitrogen heterocyclic units that do not contain lone pair electron-powering units modified with such units.

3. The stacked organic electroluminescent device according to claim 2, characterized in that, The lone-pair electron-free power supply unit is selected from at least one of the following structures D-1 to D-14: ； X is selected from carbon, silicon, and germanium; R1 to R7 are each independently selected from one of C1 to C10 alkyl, C3 to C10 cycloalkyl, silyl, and C6 to C30 aryl. Y1 and Y2 are each independently selected from one of C1-C10 alkyl, C3-C10 cycloalkyl, silyl, and C6-C30 aryl, wherein Y1 and Y2 can be further cyclically formed to form a cycloalkyl group.

4. The stacked organic electroluminescent device according to claim 3, characterized in that, The organic electron transport material is selected from at least one of compounds N-1 to N-63: 。 5. The stacked organic electroluminescent device according to claim 1, characterized in that, The n-type dopant in the n-type electron transport layer is selected from at least one of lithium, sodium, potassium, cesium, magnesium, gold, silver, copper, zinc, ytterbium, cesium carbonate, lithium carbonate, cesium nitride, and lithium nitride; when the interface modification layer is a bilayer interface modification layer composed of an n-type dopant and a p-type dopant, the n-type dopant is selected from at least one of lithium, sodium, potassium, cesium, magnesium, gold, silver, copper, zinc, ytterbium, cesium carbonate, lithium carbonate, cesium nitride, and lithium nitride.

6. The stacked organic electroluminescent device according to claim 1, characterized in that, The doping mass ratio of the n-type dopant in the n-type electron transport layer is 0.1% to 2%.

7. The stacked organic electroluminescent device according to claim 1, characterized in that, The thickness of the n-type electron transport layer is 10–300 nm.

8. The stacked organic electroluminescent device according to claim 1, characterized in that, The p-type dopant in the connecting layer and the p-type dopant in the interface modification layer are deep LUMO level materials, and the deep LUMO level materials are selected from at least one of MoO3, WO3, V2O5, MoO2, Co3O4 and the following compounds HI-1-HI-18: 。 9. The stacked organic electroluminescent device according to claim 1, characterized in that, The doping mass ratio of the p-type dopant in the connecting layer is 1% to 20%; the thickness of the interface modification layer is 1 to 10 nm; and the thickness of the connecting layer is 5 to 20 nm.

10. An application of a multilayer organic electroluminescent device, characterized in that, The multilayer organic electroluminescent device as described in any one of claims 1-9 is used to prepare display devices, lighting devices, solar cells, optical sensors, organic thin-film transistors, organic field-effect transistors, information tags, electronic artificial skin sheets, or electronic paper.

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