A copper cluster-based near-infrared electroluminescent device suitable for evaporation process

Abstract

This invention discloses a copper cluster-based near-infrared electroluminescent device suitable for vapor deposition processes, belonging to the field of electroluminescence. This invention provides a deep near-infrared electroluminescent device, comprising using a copper cluster compound as the electroluminescent material. The copper cluster compound includes Cu6(BTT)6, where BTT is benzo[d]thiazole-2-thiol. The hexanuclear copper core of the copper cluster compound approaches an ideal symmetrical octahedron, and the Cu-Cu-Cu bond angle is 58-62°. The specific copper cluster compound selected in this invention possesses a highly symmetrical core geometry that imparts an excited state, thereby significantly enhancing its sulfur-to-metal charge transfer (SMCT) characteristics, which is beneficial for generating longer-wavelength deep near-infrared triplet cluster centers (…). 3 (CC) phosphorescence emission; at the same time, this copper cluster compound is suitable for vapor deposition process, breaking through the bottleneck of the limited wavelength of electroluminescence and the limitation of vapor deposition processing of existing copper cluster compounds.

Description

Technical Field

[0001] This invention belongs to the field of electroluminescence, specifically relating to a copper cluster-based near-infrared electroluminescent device suitable for vapor deposition processes. Background Technology

[0002] Near-infrared light-emitting diodes (LEDs) represent a crucial frontier in modern optoelectronics, finding wide application in advanced fields such as biomedical imaging, wearable sensors, night vision systems, and secure optical communications. Currently, materials capable of achieving near-infrared electroluminescence primarily include noble metal phosphorescent complexes, rare earth complexes, purely organic thermally activated delayed fluorescence materials, and semiconductor quantum dots; however, each possesses significant inherent drawbacks. Noble metal phosphorescent complexes, such as platinum(II) and iridium(III) complexes, achieve highly efficient phosphorescence emission due to strong spin-orbit coupling, achieving record-breaking external quantum efficiency in the deep near-infrared region. However, these materials heavily rely on scarce and expensive noble metals, resulting in high synthesis costs and significant environmental toxicity, hindering their ability to meet the fundamental requirements of sustainability and low cost for large-scale commercial applications. Rare earth complexes, such as erbium(III), neodymium(III), and ytterbium(III) complexes, while possessing extremely narrow emission bandwidths, suffer from extremely small light absorption cross-sections and very low excitation efficiency, resulting in device brightness and external quantum efficiency far from practical levels. Pure organic thermally activated delayed fluorescence materials do not rely on noble metal elements, but in the deep near-infrared region, due to the strict constraint of the bandgap law, the nonradiative transition rate increases exponentially with the redshift of the emission wavelength, leading to a sharp decline in luminous efficiency. Furthermore, they generally suffer from severe triplet-triplet annihilation and poor device stability. Semiconductor quantum dots, such as lead sulfide and indium arsenide quantum dots, can achieve free tuning of the near-infrared emission wavelength, but they typically contain highly toxic heavy metal elements such as lead and cadmium. In electroluminescent devices, they face key technical obstacles such as exciton dissociation, efficiency roll-off during charging, and insufficient film uniformity and long-term operational stability.

[0003] Atomically precise copper clusters, as a class of highly anticipated luminescent materials, bridge a unique gap between discrete organic molecules and colloidal quantum dots. Their closed-shell d¹ 0The electronic configuration fundamentally eliminates the parity-forbidden dd nonradiative relaxation pathway, thus possessing immense intrinsic photoluminescence potential. The multinuclear structure of copper clusters boasts abundant and highly hybridized excited-state energy levels, with the energy level and charge-transfer state in triplet clusters jointly determining their luminescence behavior. This unique electronic tunability makes copper clusters a highly competitive candidate material for next-generation light-emitting diodes (LEDs). In the past decade, significant progress has been made in electroluminescence research based on copper clusters, with device performance in the visible light region gradually approaching that of traditional noble metal phosphorescent materials. However, significantly pushing the electroluminescence boundary of these abundant materials into the near-infrared region, especially the deep near-infrared region with wavelengths greater than 750 nm, remains a decisive challenge.

[0004] Therefore, developing sustainable, low-cost, and high-performance copper cluster near-infrared luminescent materials has extremely high scientific and application value, but it is technically exceptionally difficult. The realization of high-performance near-infrared devices based on copper clusters has long been hindered by two mutually coupled and persistent key challenges: First, achieving efficient emission in the deep near-infrared region is inherently extremely difficult, as this typically requires a significant reduction in the material's optical bandgap. This reduction often leads to a significant increase in non-radiative attenuation, resulting in a sharp decline in quantum efficiency. Second, most copper clusters inherently suffer from poor thermal stability or unstable coordination structures. During the thin-film forming process necessary for device fabrication, their structural integrity is severely degraded, making it difficult to obtain high-quality, robust thin-film materials. These dual bottlenecks of excited-state structural distortion and thermally induced structural brittleness constitute a major obstacle to the development of copper cluster-based near-infrared optoelectronic devices.

[0005] Therefore, how to overcome the inherent defects of existing copper cluster materials and provide a luminescent material that can achieve efficient deep near-infrared emission while also possessing excellent thermal stability and film-forming properties has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] [Technical Issues] A copper cluster-based near-infrared electroluminescent device is provided, which effectively extends the emission wavelength to the deep near-infrared region above 800nm, while maintaining sufficient luminous efficiency and processing stability, and is suitable for evaporation deposition processes.

[0007] [Technical Solution] This invention has conducted in-depth research on the technical problems existing in this field and found that one or more of the above-mentioned technical problems can be solved by the following technical solutions.

[0008] In a first aspect, the present invention proposes the use of a copper cluster compound in an electroluminescent device, wherein the copper cluster compound comprises Cu6(BTT)6, where BTT is benzo[d]thiazol-2-thiol, and the hexanuclear copper core of the copper cluster compound approaches an ideal symmetrical octahedron with Cu-Cu-Cu bond angles of 58-62°.

[0009] In some embodiments, the copper cluster emits wavelengths equal to or greater than 800 nm.

[0010] In some embodiments, the copper cluster compound emits wavelengths of 800 nm to 950 nm.

[0011] In some embodiments, the Cu···Cu distance within the hexa-core copper core is 2.8 Å to 3.2 Å.

[0012] In some embodiments, the ratio of the shortest distance between two adjacent Cu cores to the longest distance between two adjacent Cu cores is greater than or equal to 0.95.

[0013] In some embodiments, the method for preparing the copper cluster compound includes: (1) Place the cuprous source, benzothiazole thiol derivative, and mineralizing agent in a mixed solvent containing water, organic nitriles, and hydrogen halides; (2) The system of step (1) is heated to allow the cluster to nucleate and grow, and then cooled to obtain the copper cluster.

[0014] In some embodiments, in step (1), the molar ratio of the cuprous source to the benzothiazole thiol derivative is 0.5-3:1. Specifically, 1:1 may be selected.

[0015] In some embodiments, the cuprous source includes at least one of cuprous iodide, cuprous acetate, cuprous nitrate, and copper hexafluorophosphate tetraacetonitrile.

[0016] In some embodiments, the benzothiazole thiol derivative may specifically be 2-mercaptobenzothiazole.

[0017] In some embodiments, the molar ratio of the copper sub-source to the mineralizing agent is 1:2-5. Specifically, 1:4 may be selected.

[0018] In some embodiments, the mineralizing agent may specifically be potassium iodide.

[0019] In some embodiments, the organic nitrile is acetonitrile.

[0020] In some embodiments, in step (1), the concentration of the cuprous source relative to the mixed solvent is 20-40 mmol / L. Specifically, 25 mmol / L may be selected.

[0021] In some embodiments, the volume ratio of water to organic nitriles in the mixed solvent is 0.5-3:1. Specifically, 2:1 is an option.

[0022] In some embodiments, the content of hydrohalic acid in the mixed solvent is 3 wt%-6 wt%. Specifically, 4.5 wt% is optional.

[0023] In some embodiments, the hydrohalic acid may specifically be hydroiodic acid.

[0024] In some embodiments, in step (2), the system of step (1) is heated to 100-200°C and kept at a constant temperature for 12 hours to 5 days.

[0025] In some embodiments, the cooling rate is 0.5-10°C / min.

[0026] Secondly, the present invention proposes an electroluminescent thin film comprising a copper cluster compound, wherein the copper cluster compound comprises Cu6(BTT)6, where BTT is benzo[d]thiazol-2-thiol, and the hexanuclear copper core is close to an ideal symmetrical octahedron with Cu-Cu-Cu bond angles of 58-62°.

[0027] In some embodiments, the thickness of the electroluminescent film is from 10 nm to 200 nm.

[0028] Thirdly, the present invention proposes a method for preparing an electroluminescent thin film, comprising: placing a copper cluster compound in an evaporation source of a vapor deposition apparatus, and then performing vapor deposition to obtain an electroluminescent thin film, wherein the copper cluster compound comprises Cu6(BTT)6, BTT being benzo[d]thiazol-2-thiol, the hexanuclear copper core being close to an ideal symmetrical octahedron, and the Cu-Cu-Cu bond angle being 58-62°.

[0029] In some embodiments, the vacuum degree of the vapor deposition is 1×10⁻⁶. -7 -1×10 -5 Torr, wherein the heating temperature of the evaporation source is from 150°C to 400°C.

[0030] In some embodiments, the deposition rate of the vapor phase deposition is 0.1 Å / s to 5 Å / s.

[0031] Fourthly, the present invention provides an electroluminescent device comprising the electroluminescent thin film described in the second aspect of the present invention or an electroluminescent thin film obtained by the method described in the third aspect of the present invention.

[0032] Furthermore, the present invention proposes a copper cluster-based near-infrared electroluminescent device suitable for vapor deposition process, which includes an electroluminescent material using the above-mentioned copper cluster compound as the light-emitting layer in the device.

[0033] In some embodiments, the electroluminescent device includes a thin-film stack structure, which sequentially comprises: a hole injection layer, a hole transport layer, a pure light-emitting layer, an electron transport layer, an electron injection layer, and a top electrode; the electroluminescent material in the pure light-emitting layer includes the aforementioned copper cluster compound.

[0034] In some embodiments, the hole injection layer is composed of MoO3 and has a thickness of 10 nm.

[0035] In some embodiments, the hole transport layer is composed of NPB (N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine) with a thickness of 20-80 nm. Specifically, a thickness of 70 nm may be selected.

[0036] In some implementations, the thickness of the pure light-emitting layer is 10-100 nm. Specifically, a thickness of 30 nm may be selected.

[0037] In some embodiments, the electron transport layer is composed of CN-T2T(3′,3′″,3′″″-(1,3,5-triazine-2,4,6-triyl)tris(([1,1′-biphenyl]-3-carbonitrile)) with a thickness of 20-80 nm.

[0038] In some implementations, the electron injection layer is composed of Liq (lithium 8-hydroxyquinoline) and has a thickness of 10 nm.

[0039] In some embodiments, the top electrode is composed of Al and has a thickness of 50-200 nm. Specifically, the thickness can be 100 nm.

[0040] This invention has at least one of the following technical effects: The copper cluster compound Cu6(BTT)6 of this invention comprises a hexanuclear copper atom and a benzothiazole thiol ligand. This ligand coordinates with copper via sulfur and nitrogen atoms. The hexanuclear copper core approximates an ideal symmetrical octahedron, with Cu-Cu-Cu bond angles of 58-62°, forming a highly symmetrical core geometry that imparts an excited state. This significantly enhances its sulfur-to-metal charge transfer (SMCT) characteristics, which is beneficial for generating longer-wavelength deep near-infrared triplet cluster centers. 3 CC phosphorescence emission breaks through the bottleneck of limited wavelength of electroluminescence of existing copper clusters.

[0041] Meanwhile, this copper cluster compound has both high thermal stability and excellent film-forming properties, making it suitable for vapor deposition processes. High-quality electroluminescent thin films can be prepared through vapor deposition. Light-emitting devices based on this film can achieve efficient deep near-infrared electroluminescence, breaking through the bottleneck of existing copper cluster compound vapor deposition processing limitations. Attached Figure Description

[0042] The embodiments illustrated herein are further described below with reference to the accompanying drawings, which are provided merely to enable those skilled in the art to better understand the invention and are not intended to limit the scope of the invention.

[0043] Figure 1 This is a schematic diagram of the crystal structure of a highly symmetrical octahedral copper cluster of the copper cluster compound of the present invention; Figure 2 The photoluminescence spectrum of the copper cluster compound and the luminescent thin film in Example 1 is shown below. Figure 3 The thermogravimetric curve of the copper cluster compound in Example 1; Figure 4 An atomic force microscope image of the luminescent thin film of Example 1; Figure 5 This is a schematic diagram of the structure and energy level arrangement of the light-emitting diode device in Example 1; Figure 6 The electroluminescence spectra of the light-emitting diode device in Example 1 under different driving voltages are shown. Figure 7 The current density-voltage characteristic curve of this light-emitting diode; Figure 8 This is the voltage-brightness characteristic curve of the light-emitting diode; Figure 9 The curve showing the external quantum efficiency of the light-emitting diode device in Example 1 as a function of current density is shown. Figure 10 The image shows the operating life test curve of the LED device in Example 1 under constant current drive. Detailed Implementation

[0044] The inventive concept of this invention will be further described below with reference to specific embodiments. However, the specific embodiments listed are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art will recognize that specific features in any of the following embodiments can be used in any other embodiments, as long as they do not depart from the inventive concept described herein.

[0045] In one aspect of the invention, the invention proposes the use of copper clusters in electroluminescent devices, the copper clusters comprising Cu6(BTT)6, where BTT is benzo[d]thiazol-2-thiol, the hexanuclear copper core approximating an ideal symmetrical octahedron, and the Cu-Cu-Cu bond angle being 58-62°.

[0046] The copper cluster Cu6(BTT)6 of this invention comprises a hexanuclear copper atom and a benzothiazole thiol ligand. This ligand coordinates with copper via sulfur and nitrogen atoms, forming a robust chelate structure. This rigid coordination environment effectively suppresses structural relaxation in the excited state, counteracting the bandgap law to maintain a certain quantum yield; furthermore, it endows the entire copper cluster with excellent thermal stability. (See also...) Figure 1 The hexanuclear copper core in this copper cluster approaches an ideal symmetrical octahedron, meaning the copper cluster contains a highly symmetrical octahedral hexanuclear copper core, and the Cu-Cu-Cu bond angle is 58-62°, close to the 60° of an ideal octahedron. This uniform geometry suppresses the copper-loving interactions dominated by the metallic center, resulting in the lowest triplet excited state ( 3 The electronic properties of this copper cluster (CC) are transformed to be dominated by sulfur-to-metal charge transfer (SMCT), resulting in a narrower band gap. This facilitates longer-wavelength deep near-infrared emission, overcoming the bottleneck of wavelength limitation in electroluminescence of existing copper clusters. Simultaneously, this copper cluster exhibits high thermal stability and excellent film-forming properties, allowing for the fabrication of high-quality electroluminescent films via vapor deposition. Light-emitting devices based on these films can achieve highly efficient deep near-infrared electroluminescence.

[0047] In some embodiments of the present invention, the emission wavelength of the copper cluster compound is equal to or higher than 800 nm, preferably the emission wavelength of the copper cluster compound is 800 nm-950 nm, that is, the electroluminescence emission wavelength of the copper cluster compound is extended to the deep near-infrared region above 800 nm, breaking through the bottleneck of the limited electroluminescence wavelength of existing copper cluster compounds.

[0048] In some embodiments of the present invention, the Cu...Cu distance within the hexanuclear copper core of the copper cluster is 2.8 Å-3.2 Å, and the ratio of the shortest distance to the longest distance between two adjacent Cu atoms within the hexanuclear copper core is greater than or equal to 0.95. That is, the distance distribution between adjacent Cu atoms within the core is very concentrated.

[0049] In some embodiments of the present invention, the preparation method of the copper cluster compound includes: (1) placing a cuprous source and a benzothiazole thiol derivative in a mixed solvent containing water, an organic nitrile and a hydrohalic acid; (2) heating the system of step (1) to allow the cluster compound to nucleate and grow, and then cooling to obtain the copper cluster compound.

[0050] Specifically, a cuprous source and a benzothiazole thiol derivative are mixed with a mixed solvent containing water, an organic nitrile, and a hydrohalic acid. After thorough mixing, the mixture is sealed in a reaction vessel. The molar ratio of the cuprous source to the benzothiazole thiol derivative is 0.5-3:1. The volume ratio of water to the organic nitrile in the mixed solvent is 0.5-3:1, and the concentration of the hydrohalic acid is 30%-60%. The reaction system is then heated to 100-200°C and maintained at this temperature for 12 hours to 5 days to allow for sufficient nucleation and growth of the clusters. After the reaction is complete, the mixture is slowly cooled to room temperature at a rate of 0.5-10°C / min, resulting in the precipitation of crystalline products. These products are then separated, washed, and dried to obtain the copper clusters.

[0051] In some embodiments of the present invention, the cuprous source includes at least one of cuprous iodide, cuprous acetate, cuprous nitrate, and copper hexafluorophosphate tetraacetonitrile; the benzothiazole thiol derivative includes 2-mercaptobenzothiazole, thereby further modulating the energy level and emission wavelength of the copper cluster compound.

[0052] In a second aspect, the present invention provides an electroluminescent thin film comprising a copper cluster compound comprising Cu6(BTT)6, wherein BTT is benzo[d]thiazol-2-thiol, and the hexanuclear copper core is approximately an ideal symmetrical octahedron with Cu-Cu-Cu bond angles of 58-62°.

[0053] Therefore, this copper cluster compound possesses both high thermal stability and excellent film-forming properties, enabling the fabrication of high-quality electroluminescent thin films via vapor deposition. Light-emitting devices based on this film can achieve highly efficient deep near-infrared electroluminescence. Furthermore, thanks to the high thermal stability of the copper cluster compound itself, its molecular structure remains intact during evaporation and deposition; that is, the highly symmetrical octahedral core structure of the hexanuclear copper cluster compound is preserved in the film, and it can spontaneously form a flat film with a specific preferred orientation.

[0054] In some embodiments of the present invention, the thickness of the electroluminescent thin film is 10 nm to 200 nm.

[0055] In a third aspect, the present invention provides a method for preparing an electroluminescent thin film, comprising: placing a copper cluster compound in an evaporation source of a vapor deposition apparatus, and then performing vapor deposition to obtain an electroluminescent thin film, wherein the copper cluster compound comprises Cu6(BTT)6, BTT being benzo[d]thiazol-2-thiol, the hexanuclear copper core being close to an ideal symmetrical octahedron, and the Cu-Cu-Cu bond angle being 58-62°.

[0056] Taking the vapor deposition equipment of this invention as a vacuum evaporation equipment as an example, the copper cluster compound is placed in the evaporation source of the vacuum evaporation equipment, at a depth of 1×10⁻⁶. -7 Up to 1×10 -5Under the vacuum of Torr, the evaporation source is heated to 150-400°C, causing copper clusters to sublimate and deposit on the surface of a pretreated substrate at a deposition rate of 0.1 Å / s to 5 Å / s, forming a uniform and dense thin film. The thickness of this film can be controlled within the range of 10 nm to 200 nm by adjusting the deposition time.

[0057] It should be noted that the features and advantages described above for copper cluster compounds also apply to this method for preparing electroluminescent thin films, and will not be repeated here.

[0058] In a fourth aspect, the present invention provides an electroluminescent device comprising the electroluminescent thin film described in the second aspect of the present invention or an electroluminescent thin film obtained by the method described in the third aspect of the present invention.

[0059] As an example, electroluminescent devices may include, but are not limited to, deep near-infrared light sources, biological tissue penetration imaging devices, night vision surveillance systems, or optical security communication devices.

[0060] Taking deep near-infrared organic light-emitting diodes (OLEDs) as an example, an electroluminescent thin film can be used as its light-emitting layer.

[0061] The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0062] Example 1 Preparation of copper clusters 0.25 mmol cuprous iodide, 0.25 mmol 2-mercaptobenzothiazole (BTT) ligand, 1.0 mmol potassium iodide, 3 mL water, 6 mL acetonitrile, and 1.0 mL hydroiodic acid (45%) were mixed and stirred until homogeneous. The mixture was then sealed in a reaction vessel. The mixture was then heated to 140 °C and maintained at this temperature for 3 days to allow the cluster to fully nucleate and grow. After the reaction was completed, the mixture was slowly cooled to room temperature at a cooling rate of 5 °C / min. Crystalline products precipitated out. After separation, washing, and drying, the target hexanuclear copper cluster single crystal (denoted as Cu6(BTT)6) was obtained, with a yield of 73% based on copper.

[0063] Structural analysis revealed that the obtained cluster compound possesses a highly symmetrical octahedral Cu6 core. The Cu···Cu distances within the core are distributed within a narrow range of 2.8 Å to 3.2 Å, with the ratio of the shortest to the longest Cu···Cu distance not less than 0.95. The Cu-Cu-Cu bond angles range from 58° to 62°, extremely close to the 60° of an ideal octahedron, exhibiting near-ideal symmetrical geometric characteristics. The single-crystal diffraction pattern is shown below. Figure 1 As shown.

[0064] Its crystallographic data are shown in the table below:

[0065] The emission spectrum curve is as follows Figure 2 As shown, the emission wavelength of the obtained copper cluster compound is significantly red-shifted, emitting deep near-infrared phosphorescence with a peak position between 800 nm and 950 nm at room temperature, and the photoluminescence quantum yield is not less than 10%.

[0066] Thermogravimetric analysis was performed on the copper cluster compound, and the thermogravimetric curve is shown below. Figure 3 As shown, it has a weightless step, with an initial decomposition temperature of 360℃ and a final decomposition temperature of 400℃, indicating that it has high thermal stability.

[0067] Example 2: Preparation of luminescent thin film The synthesized copper cluster compound was placed in the evaporation source of a vacuum evaporation equipment and heated at 4 × 10⁻⁶ ℃. -5 Under the vacuum of Torr, the evaporation source is heated to 200°C, causing the material to sublimate and deposit on the pretreated substrate surface at a deposition rate of 1 Å / s, forming a uniform and dense film with a thickness of 50 nm (denoted as Film-Cu6(BTT)6).

[0068] Figure 4 The image shows the atomic force microscopy morphology of the obtained thin film, indicating that the prepared thin film has a smooth and flat surface with a root mean square roughness of no more than 2 nm, which is beneficial to good interfacial contact between functional layers in the device.

[0069] X-ray diffraction and X-ray absorption fine structure analysis confirmed that the evaporation process did not alter the core configuration of the copper cluster, and the thin film exhibited a clear preferred orientation characteristic. Optical tests showed that the emission spectrum curve was as follows: Figure 2 As shown, the deviation of its photoluminescence peak position from that of the original powder is no more than 30 nm, confirming the excellent vacuum processability of the material.

[0070] Example 3: Fabrication of Deep Near-Infrared Organic Light Emitting Diode Devices A transparent conductive substrate with an electrode pattern already formed on its surface is taken, cleaned, and surface activated, then placed in a vacuum evaporation chamber at a depth of 4×10⁻⁶. -7Under the vacuum conditions of Torr, a hole injection layer MoO3 (10 nm thick), a hole transport layer NPB (70 nm thick), a pure light-emitting layer Cu Clusters (30 nm thick) composed of the aforementioned copper cluster material, an electron transport layer CN-T2T (80 nm thick), an electron injection layer Liq (8-hydroxyquinoline lithium) (10 nm thick), and a top electrode Al (100 nm thick) are sequentially deposited by vapor deposition to form a complete thin film stack structure ITO / MoO3 / NPB / Cu6cluster / CN-T2T / Liq / Al (e.g., Figure 5 shown). (Where, NPB = N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine,CN-T2T = 3′,3′″,3′″″-(1,3,5-triazine-2,4,6-triyl)tris(([1,1′-biphenyl]-3-carbonitrile.) Figure 6 The emission spectra of the device under different voltages are shown. The packaged device was tested with a forward bias applied. Under electrical drive, the device emits deep near-infrared electroluminescence with peaks between 800 nm and 950 nm.

[0071] Figure 7 This is the current density-voltage characteristic curve of the LED. Figure 8 This is the voltage-brightness characteristic curve of the light-emitting diode; Figure 9 The curve shows the external quantum efficiency as a function of current density; Figure 10 This is a test curve of the operating life of a light-emitting diode under constant current drive.

[0072] Depend on Figure 7-10 It is known that the device’s turn-on voltage is no higher than 3V, the device’s maximum external quantum efficiency is no less than 2%, and the brightness decay is no more than 50% after 24 hours of continuous operation under a constant current of 50mA.

[0073] Comparative Example Referring to Example 1, the ligands were replaced with 4-bromo-2-pyridinethiol (BrPT) and 2-pyridinethiol (PT), while other aspects remained unchanged, to prepare the corresponding copper clusters Cu6(BrPT)6 and Cu6(PT)6.

[0074] Referring to Example 3, electroluminescent devices were prepared using the above copper clusters. It was found that during the evaporation process, the two copper clusters Cu6(BrPT)6 and Cu6(PT) turned black and decomposed, making it difficult to generate an effective and uniform light-emitting film, and they could not be constructed into OLED devices.

[0075] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A copper cluster-based near-infrared electroluminescent device suitable for vapor deposition process, characterized in that, The invention comprises an electroluminescent material using copper clusters as the light-emitting layer in a device; the copper clusters include Cu6(BTT)6, wherein BTT is benzo[d]thiazole-2-thiol, the hexanuclear copper core of Cu6(BTT)6 is close to an ideal symmetrical octahedron, and the Cu-Cu-Cu bond angle is 58°-62°.

2. The copper cluster-based near-infrared electroluminescent device according to claim 1, characterized in that, The copper cluster emits wavelengths equal to or greater than 800 nm.

3. The copper cluster-based near-infrared electroluminescent device according to claim 1, characterized in that, The Cu···Cu distance within the hexanuclear copper core of the copper cluster is 2.8 Å–3.2 Å.

4. The copper cluster-based near-infrared electroluminescent device according to claim 1, characterized in that, The ratio of the shortest distance between two adjacent Cu cores to the longest distance between two adjacent Cu cores in the six-core copper core is greater than or equal to 0.

95.

5. The copper cluster-based near-infrared electroluminescent device according to any one of claims 1-4, characterized in that, The preparation method of the copper cluster compound includes: (1) Place the cuprous source, benzothiazole thiol derivative, and mineralizing agent in a mixed solvent containing water, organic nitriles, and hydrogen halides; (2) The system of step (1) is heated to allow the cluster to nucleate and grow, and then cooled to obtain the copper cluster.

6. An electroluminescent thin film, characterized in that, The invention includes copper clusters comprising Cu6(BTT)6, where BTT is benzo[d]thiazole-2-thiol, and the hexanuclear copper core of the copper clusters approximates an ideal symmetrical octahedron with Cu-Cu-Cu bond angles of 58°-62°.

7. The electroluminescent thin film according to claim 6, characterized in that, The thickness of the electroluminescent film is from 10 nm to 200 nm.

8. A method for preparing an electroluminescent thin film, characterized in that, include: The copper cluster compound is placed in the evaporation source of a vapor deposition apparatus and then vapor deposition is performed to obtain an electroluminescent thin film. The copper cluster compound includes Cu6(BTT)6, where BTT is benzo[d]thiazole-2-thiol. The hexanuclear copper core of the copper cluster compound is close to an ideal symmetrical octahedron, and the Cu-Cu-Cu bond angle is 58°-62°.

9. The method for preparing an electroluminescent thin film according to claim 8, characterized in that, The vacuum degree of the vapor deposition is 1×10⁻⁶. -7 -1×10 -5 Torr, wherein the heating temperature of the evaporation source is 150°C to 400°C, and the deposition rate of the vapor phase deposition is 0.1 Å / s to 5 Å / s.

10. The use of a copper cluster compound in an electroluminescent device, characterized in that, The copper cluster compound includes Cu6(BTT)6, where BTT is benzo[d]thiazole-2-thiol. The hexanuclear copper core of the copper cluster compound is close to an ideal symmetrical octahedron, and the Cu-Cu-Cu bond angle is 58°-62°.

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