Porous gradient aluminum-doped zinc oxide transparent conductive film and preparation method and application thereof

Abstract

The invention discloses a porous gradient aluminum-doped zinc oxide transparent conductive thin film and a preparation method and application thereof, and belongs to the field of functional thin film materials.The porous gradient aluminum-doped zinc oxide transparent conductive thin film has the advantages that through introduction of a through porous structure and aperture gradient distribution design and combination of a magnetron sputtering process, high light transmittance (gt; 82%), and at the same time, the electrical performance is significantly improved; the carrier concentration of the thin film is as high as 5.1 * 10 < 20 > cm <-3 >, the mobility is greater than 28 cm < 2 > / V.s, and the resistivity is as low as 4.3 * 10 <-4 > omega.cm. The porous structure improves the light utilization rate by enhancing the light scattering effect; a three-dimensional conductive network constructed by the through hole channels effectively reduces grain boundary scattering; the stress distribution is optimized by the gradient aperture design, so that the problem that the conductivity and the light transmittance of the traditional compact AZO film are difficult to synergistically improve is solved, and the functionalization of a pore channel structure is realized.

Description

Technical Field

[0001] The present invention belongs to the field of functional film materials, and in particular relates to a porous gradient aluminum-doped zinc oxide transparent conductive film and a preparation method and application thereof. Background Art

[0002] Transparent conductive materials provide a transparent conductive film layer, enabling electronic devices to not only transmit current but also maintain excellent light transmittance. Transparent conductive oxide (TCO) films are widely used in solar cells, flat-panel displays, touch screens, and other optoelectronic devices due to their excellent conductivity, transparency, and chemical stability. Traditional TCO materials primarily include tin-doped indium oxide (ITO) and fluorine-doped tin oxide (FTO), but these materials are subject to costly raw materials and environmental pollution, limiting their widespread application.

[0003] Aluminum-doped zinc oxide (AZO) targets significantly improve the conductivity of zinc oxide by aluminum doping, while maintaining its good transparency and reducing costs. They are widely used in optoelectronic devices, flat panel displays, and solar cells. However, traditional AZO films face two major bottlenecks: first, high doping leads to lattice distortion and limited mobility (usually <20cm 2 / V·s); Second, there is an inverse relationship between transmittance and conductivity (such as carrier concentration>10 20 cm -3 Most existing studies have improved interface scattering by gradually varying the concentration, but have not addressed the issues of light management and stress release. Summary of the Invention

[0004] In response to the above problems, the present invention provides a porous gradient aluminum-doped zinc oxide transparent conductive film and its preparation method and application. The present invention breaks through the above limitations by introducing a gradient porous structure. By designing a multilayer film with a gradient pore size and combining it with a magnetron sputtering process, through-hole channels are realized in the AZO film to construct a three-dimensional conductive network to reduce grain boundary scattering. The stress distribution is optimized by gradient pore size design, which solves the problem that the conductivity and transmittance of traditional dense AZO films are difficult to improve synergistically, and effectively improves the conductive performance, stability and uniformity of the film.

[0005] One of the technical solutions provided by the present invention:

[0006] A method for preparing a porous gradient aluminum-doped zinc oxide transparent conductive film comprises the following steps:

[0007] preparing a homogeneous multilayer AZO target material, wherein, based on Al ion doping concentration, the homogeneous multilayer AZO target material comprises, from the center to the periphery, a high-concentration region target material, a medium-concentration region target material, and a low-concentration region target material;

[0008] Spin-coating PS microspheres on a substrate to obtain a near-substrate layer template; using the homogeneous multilayered AZO target as a cathode, and controlling power and rotation speed to use the high-concentration region target as a raw material to magnetron sputter deposit in the near-substrate layer template to prepare an underlying thin film;

[0009] Spin-coating PS microspheres on the bottom film to obtain an intermediate layer template; and preparing an intermediate layer film by magnetron sputtering deposition in the intermediate layer template using the medium concentration region target as a raw material by controlling power and rotation speed;

[0010] Spin-coating PS microspheres on the middle layer film to obtain a surface layer template; and preparing a surface layer film by magnetron sputtering deposition in the surface layer template using the low-concentration region target as a raw material by controlling power and rotation speed;

[0011] Removing the template and vacuum annealing to prepare the porous gradient aluminum-doped zinc oxide transparent conductive film;

[0012] Among them, the particle sizes of PS microspheres in the near-base layer template, the intermediate layer template and the surface layer template are gradient distributed.

[0013] Furthermore, the gradient distribution of the particle size of the PS microspheres is:

[0014] Substratum template: microspheres with a particle size of 800nm-1000nm, where the microspheres are spin-coated to ensure a target porosity of 40-50%;

[0015] Intermediate layer template: microspheres with a particle size of 300-500 nm, where the microspheres are spin-coated to ensure a target porosity of 30-40%;

[0016] Surface layer template: microspheres with a particle size of 50-100 nm, where the microspheres are spin-coated to ensure a target porosity of 10-20%.

[0017] Furthermore, the Al ion doping concentration in the target material in the high concentration region is 3 mol%; the Al ion doping concentration in the target material in the medium concentration region is 2 mol%; and the Al ion doping concentration in the target material in the low concentration region is 1 mol%.

[0018] Furthermore, when preparing the bottom film, the power is 300W and the rotation speed is 5rpm; when preparing the middle film, the power is 200W and the rotation speed is 10rpm; when preparing the surface film, the power is 200W and the rotation speed is 10rpm.

[0019] The present invention adopts a three-zone power-speed linkage coating process for the target material. By dividing the target surface into three aluminum-doping concentration areas of high (3 mol%), medium (2 mol%), and low (1 mol%), the gradient aperture structure requirements are matched to achieve "concentration-pore" coordinated regulation.

[0020] The present invention adopts the above-mentioned zone coating mechanism as follows:

[0021] High concentration area process: Using a combination of high power (300W) and low speed (5rpm), by extending the ion bombardment time and enhancing the sputtering efficiency, a large number of aluminum atoms are doped into the AZO lattice, forming a high carrier concentration (reaching 5.1×10 20 cm -3 ), this area corresponds to the macroporous structure of the bottom layer of the film. The high doping concentration of Al ions cooperates with the through-hole channels to build a three-dimensional conductive network and reduce grain boundary scattering.

[0022] Medium concentration process: The power and speed are set to the middle value (200W, 10rpm), balancing the amount of aluminum atoms doped and the degree of lattice distortion, corresponding to the pore size of the film middle layer (300-500nm), and optimizing the carrier mobility (breaking 28cm 2 / V·s), while the porosity reaches 30-40%, achieving a balance between light scattering and light transmittance (visible light transmittance>82%).

[0023] Low-concentration zone process: Low power (150W) and high rotation speed (15rpm) are used to reduce the amount of aluminum atoms sputtered and minimize lattice distortion. Corresponding to small pores (50-100nm) in the film surface layer, the low doping concentration reduces free carrier absorption of light. Combined with the small pore size, it reduces light reflection, keeping the haze value within 22-30%.

[0024] Furthermore, the deposited film is placed in an organic solvent, and the template is removed by ultrasonic treatment, and the pre-arranged microsphere template is removed to construct a film with a specific pore size.

[0025] Furthermore, the vacuum annealing temperature is 120-150° C. and the time is 20-30 minutes.

[0026] Furthermore, the substrate is selected from a quartz substrate, a flexible PET substrate or a glass substrate.

[0027] Furthermore, the bottom film, middle film and surface film are 90% of the thickness of the base layer template, middle layer template and surface layer template respectively.

[0028] The preparation process provided by the present invention exhibits a synergistic effect, which is mainly reflected in the two aspects of conductivity control and structure-concentration matching. In terms of conductivity control, the high-concentration region lays the foundation for carrier concentration, the medium-concentration region is responsible for optimizing mobility, and the low-concentration region plays a role in reducing grain boundary defects. The three work together to achieve a resistivity as low as 4.3×10 -4Ω·cm. In terms of structure-concentration matching, each concentration region corresponds to a PS template with a specific pore size. For example, the high-concentration region matches 800nm-1000nm microspheres. After sputtering deposition, the template is removed by ultrasonic treatment with toluene, ultimately forming a gradient structure with "high concentration - large pores - high conductivity" and "low concentration - small pores - high transmittance."

[0029] The second technical solution provided by the present invention is:

[0030] A porous gradient aluminum-doped zinc oxide transparent conductive film prepared by the above preparation method has a through three-dimensional porous network structure and a pore wall thickness of 20-50 nm.

[0031] The structure of the porous gradient aluminum-doped zinc oxide transparent conductive film provided by the present invention is innovative. On the one hand, by forming through channels, a high-speed transmission path is constructed for electrons, effectively reducing grain boundary scattering losses; on the other hand, a gradient aperture design is realized, with small holes of 50-100nm on the surface to reduce light reflection, and large holes of 800nm-1000nm set in the bottom layer to release the internal stress of the film, and improve light utilization through light scattering, which cooperates with the anti-reflection function of the small holes on the surface to achieve high transmittance; in addition, the porosity increases from the surface to the bottom layer, thereby balancing the transmittance and carrier transport performance.

[0032] The third technical solution provided by the present invention is:

[0033] An application of the porous gradient aluminum-doped zinc oxide transparent conductive film in the preparation of optoelectronic devices.

[0034] Compared with the prior art, the present invention has the following advantages and technical effects:

[0035] By introducing a through-hole porous structure and a gradient pore size distribution design, combined with a magnetron sputtering process, this invention significantly improves electrical performance while maintaining high transmittance (>82%). The through-hole porous structure optimizes the carrier migration path; the gradient pore size design achieves coordinated regulation of light transmission, combining surface anti-reflection and bottom-layer light trapping functions; at the same time, the pores can release stress within the film. When using a flexible substrate, the resistance change is less than 5% at a bending radius of 2mm; the carrier concentration of the film is as high as 5.1×10 20 cm -3 , the migration rate exceeded 28cm 2 / V·s, and the resistivity is as low as 4.3×10 -4The porous structure improves light utilization by enhancing the light scattering effect; the three-dimensional conductive network constructed by the through-hole channels effectively reduces grain boundary scattering; and the gradient pore size design optimizes stress distribution, thus solving the problem of the difficulty in synergistically improving the conductivity and transmittance of traditional dense AZO films and realizing the functionalization of the pore structure. This technology is suitable for optoelectronic fields such as high-efficiency solar cells and flexible touch devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 Schematic diagram of the preparation process of the homogeneous multilayer AZO target in Example 1, where a and b are the powder filling and compaction of the high-concentration target; c and d are schematic diagrams of enlarging the diameter and placing the pressed high-concentration target into a larger diameter mold for further pressing;

[0038] Figure 2 (a) is a schematic diagram of the gradient porous structure of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared by the present invention; (b) is a SEM image before the PS template is removed (taken from the surface layer); (c) is a SEM image after the PS template is removed (taken from the surface layer);

[0039] Figure 3 This is an SEM image of the near-base layer template prepared in step 2) of Example 1;

[0040] Figure 4 This is a SEM image of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in Example 1 (taken from the near-base layer);

[0041] Figure 5 This is an SEM image of the surface layer template prepared in step 2) of Example 2;

[0042] Figure 6 This is a SEM image of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in Example 2 (taken from the surface layer). DETAILED DESCRIPTION

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0045] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0046] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0047] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0048] The embodiment of the present invention provides a method for preparing a porous gradient aluminum-doped zinc oxide transparent conductive film, comprising the following steps:

[0049] Submicron ZnO powder and Al2O3 powder or AZO powder pre-doped with aluminum are weighed in appropriate proportions, and the mixed powder is fully mixed and homogenized by high-energy ball milling to obtain a uniform powder, which is then cold-pressed in different areas and sintered at high temperature to obtain a homogeneous multilayered AZO target; a homogeneous multilayered AZO target is prepared, and the homogeneous multilayered AZO target is divided into a high-concentration area target, a medium-concentration area target and a low-concentration area target from the center to the periphery in terms of Al ion doping concentration; the high-energy ball milling is to use a planetary high-energy ball mill to mix the powder; the high-energy ball milling adopts an oxidation Zirconium grinding balls have a ball-to-material ratio of 8-15:1; the high-energy ball mill adopts a wet grinding method, the additive is anhydrous ethanol, the agent-to-powder ratio is 1.5-2:1, and the slurry solid content is 80%; the high-energy ball milling method adopts a ball mill revolution speed of 300-600rpm and a ball milling time of 4-6 hours; the high-energy ball mill powder is dried by vacuum drying; the applied pressure of the cold pressing is 10-40MPa; the sintering equipment is a high-temperature muffle furnace with a rapid heating rate of 10℃ / min; the sintering temperature is 1100-1300℃; and the holding time is 2-6h.

[0050] The method comprises the steps of spin-coating PS microspheres on a substrate to obtain a near-substrate layer template; using the homogeneous multilayer structure AZO target as a cathode, and using the high-concentration region target as a raw material to perform magnetron sputtering deposition in the near-substrate layer template by controlling the power and rotation speed to prepare a bottom film; spin-coating PS microspheres on the bottom film to obtain a middle layer template; controlling the power and rotation speed to use the medium-concentration region target as a raw material to perform magnetron sputtering deposition in the middle layer template to prepare a middle layer film; spin-coating PS microspheres on the middle layer film to obtain a surface layer template; controlling the power and rotation speed to use the low-concentration region target as a raw material to perform magnetron sputtering deposition in the surface layer template to prepare a surface film; removing the template, performing vacuum annealing, and preparing the porous gradient aluminum-doped zinc oxide transparent conductive film.

[0051] When preparing each layer of film, the prepared homogeneous multilayer AZO target material needs to be installed on the target holder of the magnetron sputtering equipment, the substrate needs to be fixed on the sample table, and the distance between the substrate and the target material needs to be adjusted to a suitable range. The vacuum is pumped to 10 -5 -10 -4 After Pa, an appropriate amount of working gas (argon) is introduced into the vacuum chamber, and the gas flow rate and sputtering power are adjusted to the optimal working state, where the argon flow rate is 20-50sccm, the substrate temperature is 50-200℃, and the substrate temperature is 50-200℃.

[0052] In some preferred embodiments of the present invention, the gradient distribution of the PS microsphere particle size is as follows: near-base layer template: microsphere particle size is 800nm-1000nm, wherein the microsphere spin coating ensures the target porosity of 40-50%; intermediate layer template: microsphere particle size is 300-500nm, wherein the microsphere spin coating ensures the target porosity of 30-40%; surface layer template: microsphere particle size is 50-100nm, wherein the microsphere spin coating ensures the target porosity of 10-20%.

[0053] The purity of the ZnO powder and Al2O3 powder used in the present invention is greater than 99.5%, the purity of the pre-doped AZO powder is also greater than 99.5%, and the average particle size of all the powders is 0.1-1 μm.

[0054] In some preferred embodiments of the present invention, the mass ratio of the ZnO powder to the Al2O3 powder is 98:2-99:1, and the metal ion doping ratio of the pre-doped AZO powder is 0.5-4 mol%.

[0055] In some preferred embodiments of the present invention, the Al ion doping concentration in the high concentration region target material is 3 mol%; the Al ion doping concentration in the medium concentration region target material is 2 mol%; and the Al ion doping concentration in the low concentration region target material is 1 mol%.

[0056] In some preferred embodiments of the present invention, when preparing the bottom film, the power is 300W and the speed is 5rpm; when preparing the middle film, the power is 200W and the speed is 10rpm; when preparing the surface film, the power is 200W and the speed is 10rpm.

[0057] In some preferred embodiments of the present invention, the specific operation of removing the template is: placing the deposited thin film in an organic solvent and performing ultrasonic treatment to remove the template.

[0058] In some preferred embodiments of the present invention, the vacuum annealing temperature is 120-150° C., and the time is 20-30 minutes.

[0059] In some preferred embodiments of the present invention, the substrate is selected from a quartz substrate, a flexible PET substrate or a glass substrate.

[0060] The embodiment of the present invention also provides a porous gradient aluminum-doped zinc oxide transparent conductive film prepared by the above preparation method.

[0061] Figure 2 (a) is a schematic diagram of the gradient porous structure of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared by the present invention; (b) is a SEM image before the PS template is removed (taken from the surface layer), and (c) is a SEM image after the PS template is removed (taken from the surface layer).

[0062] The embodiment of the present invention also provides the use of the porous gradient aluminum-doped zinc oxide transparent conductive film in the preparation of optoelectronic devices.

[0063] Example 1 A method for preparing a porous gradient aluminum-doped zinc oxide transparent conductive film

[0064] 1) Preparation of homogeneous multilayer AZO target

[0065] S1. ZnO powder and Al2O3 powder were weighed and mixed by high-energy ball milling (ball-to-material ratio of 10:1, wet milling, ethanol-to-powder ratio of 1.8:1, ball milling for 5 h, speed of 400 rpm), and cold pressed (40 MPa, 45 s) to obtain a high-concentration target (Al doping concentration of 3 mol%, diameter of 10 mm).

[0066] S2. Expanding the diameter: The compacted, high-concentration, small-diameter block was placed in a larger-diameter (25 mm) mold. ZnO powder and Al2O3 powder were weighed and mixed using high-energy ball milling (ball-to-material ratio of 10:1, wet milling, ethanol-to-powder ratio of 1.8:1, ball milling for 5 h, rotation speed of 400 rpm). The ground mixture was then filled into a larger-diameter mold and cold-pressed (40 MPa, 45 s) to obtain a medium-concentration target (Al doping concentration of 2 mol%). The medium-concentration ring thickness was 15 mm.

[0067] S3. Continue to expand the diameter and place the block obtained in S2 into a larger diameter mold (diameter of 40 mm), weigh ZnO powder and Al2O3 powder, mix them by high-energy ball milling (ball-to-material ratio of 10:1, wet grinding method, ethanol-to-powder ratio of 1.8:1, ball milling for 5 hours, rotation speed of 400 rpm), fill the ground mixture into a larger diameter mold, and cold press (40 MPa, 45 seconds) to obtain a low-concentration area target (Al doping concentration of 1 mol%), and the thickness of the low-concentration area ring is 15 mm; sinter at 1200 ° C (heating rate of 10 ° C / min, insulation for 4 hours) to obtain a homogeneous multilayer structure AZO target; the porous gradient aluminum-doped zinc oxide transparent conductive film has a through three-dimensional porous network structure with a pore wall thickness of 50 nm.

[0068] Figure 1 Schematic diagram of the preparation process of the homogeneous multilayer AZO target in Example 1, where a and b are the powder filling and compacting of the high-concentration target; c and d are the steps of expanding the diameter to place the pressed high-concentration target into a larger diameter mold, filling it with powder with lower doping concentration around it, and continuing to press.

[0069] 2) Preparation of thin films

[0070] PS microspheres with a particle size of 800 nm were spin-coated on a glass substrate. The target porosity of the microspheres was 45% to prepare a near-substrate template. The homogeneous multilayer AZO target prepared in step 1) was mounted on the target holder of a magnetron sputtering device. The substrate was fixed on a sample stage, and the distance between the substrate and the target was adjusted to 8 mm. The vacuum was then applied to 10 -5 -10 -4 After the evaporation temperature reaches 150°C, an appropriate amount of working gas (argon, 40 sccm) is introduced into the vacuum chamber, and the substrate temperature is set at 150°C. A combination of high power (300 W) and low rotation speed (5 rpm) is used to form a bottom film (720 nm thick) on the template near the substrate layer with the target in the high-concentration area.

[0071] The bottom film was then spin-coated with 300nm PS microspheres, with the target porosity of 35% ensured, to prepare the intermediate layer template. A combination of medium power (200W) and medium rotation speed (10rpm) was used to form a 270nm thick intermediate film in the intermediate layer template using the medium concentration target.

[0072] The middle layer was then spin-coated with 100nm PS microspheres, ensuring a target porosity of 15%, to create a surface layer template. Low power (150W) and high rotation speed (15rpm) were used to form a surface film (90nm thick) of the low-concentration target in the surface layer template.

[0073] 3) Demolding: The film deposited in step 2) was placed in a 120°C toluene solution and ultrasonically treated for 10 min to remove the templates of each layer to form a through-porous structure film, and then vacuum annealed (150°C, 10 -3 Pa, 30min), a porous gradient aluminum-doped zinc oxide transparent conductive film was prepared, which had a through three-dimensional porous network structure and a pore wall thickness of 50nm.

[0074] Figure 3 This is an SEM image of the near-base layer template prepared in step 2) of Example 1;

[0075] Figure 4 This is a SEM image of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in Example 1 (taken from the near-base layer).

[0076] The electrical properties of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in this embodiment were tested by the integrating sphere method. The test results were as follows: carrier concentration: 5.1×10 20 cm -3 , migration rate: 28cm 2 / V·s, resistivity: 4.3×10 -4Ω·cm; visible light transmittance: 85%, haze: 25%.

[0077] Example 2 A method for preparing a porous gradient aluminum-doped zinc oxide transparent conductive film

[0078] 1) Preparation of a homogeneous multilayer AZO target: same as in Example 1;

[0079] 2) Preparation of thin film:

[0080] PS microspheres with a particle size of 900 nm were spin-coated on a flexible PET substrate. The target porosity of the microspheres was 48% to prepare a near-substrate template. The homogeneous multilayer AZO target prepared in step 1) was mounted on the target holder of the magnetron sputtering device. The substrate was fixed on the sample stage, and the distance between the substrate and the target was adjusted to 8 mm. The vacuum was then applied to 10 -5 -10 -4 After Pa, an appropriate amount of working gas (argon, 35 sccm) was introduced into the vacuum chamber, and the substrate temperature was 100°C. A combination of high power (300 W) and low rotation speed (5 rpm) was used to make the high-concentration target form a bottom film (810 nm thick) in the template near the substrate layer.

[0081] The bottom film was then spin-coated with 400nm PS microspheres, with the target porosity of 38% ensured, to prepare the intermediate layer template. A combination of medium power (200W) and medium rotation speed (10rpm) was used to form a 360nm thick intermediate film in the intermediate layer template using the medium concentration target.

[0082] The middle layer was then spin-coated with 80nm PS microspheres, distributed to ensure a target porosity of 20%, to create a surface layer template. Low power (150W) and high rotation speed (15rpm) were used to form a surface film (72nm thick) of the low-concentration target in the surface layer template.

[0083] 3) Demolding: The film deposited in step 2) was placed in a 120°C toluene solution and ultrasonically treated for 10 min to remove the templates of each layer to form a through-porous structure film, and then vacuum annealed (120°C, 10 -3 Pa, 20min), a porous gradient aluminum-doped zinc oxide transparent conductive film was prepared, which had a through three-dimensional porous network structure and a pore wall thickness of 40nm.

[0084] Figure 5 This is an SEM image of the surface layer template prepared in step 2) of Example 2;

[0085] Figure 6This is a SEM image of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in Example 2 (taken from the surface layer).

[0086] The electrical properties of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in this embodiment were tested by the integrating sphere method. The test results were as follows: carrier concentration: 4.9×10 20 cm -3 , migration rate: 27cm 2 / V·s, visible light transmittance: 84%; resistivity: 4.3×10 -4 Ω·cm, with a resistance change of <5% at a bending radius of 2mm, demonstrating that the pores can release internal stress in the film; haze: 22%. This example demonstrates that the present invention, using the PS microsphere template method combined with low-temperature sputtering (<200°C), is compatible with flexible substrates.

[0087] Example 3: A method for preparing a porous gradient aluminum-doped zinc oxide transparent conductive film

[0088] 1) Preparation of target homogeneous multilayer structure AZO target: same as in Example 1;

[0089] 2) Preparation of thin film:

[0090] PS microspheres with a particle size of 1000 nm were spin-coated on a glass substrate. The target porosity of the microspheres was 50% to prepare a near-substrate template. The homogeneous multilayer AZO target prepared in step 1) was mounted on the target holder of a magnetron sputtering device. The substrate was fixed on a sample stage, and the distance between the substrate and the target was adjusted to 6 mm. The vacuum was then applied to 10 -5 -10 - 4 After Pa, an appropriate amount of working gas (argon, 50 sccm) was introduced into the vacuum chamber, and the substrate temperature was 200°C. A combination of high power (300W) and low rotation speed (5rpm) was used to make the high-concentration target form a bottom film (900nm thick) in the template near the substrate layer.

[0091] The bottom film was then spin-coated with 500nm PS microspheres, with the target porosity of 40% ensured, to prepare the intermediate layer template. A combination of medium power (200W) and medium rotation speed (10rpm) was used to form a 450nm thick intermediate film from the target in the intermediate layer template.

[0092] The middle layer was then spin-coated with 50nm PS microspheres, distributed to ensure a target porosity of 10%, to create a surface layer template. Low power (150W) and high rotation speed (15rpm) were used to form a thin film (45nm thick) of the low-concentration target material in the surface layer template.

[0093] 3) Demolding: The film deposited in step 2) was placed in a 120°C toluene solution and ultrasonically treated for 10 min to remove the templates of each layer to form a through-porous structure film, and then vacuum annealed (150°C, 10 -3 Pa, 30min), a porous gradient aluminum-doped zinc oxide transparent conductive film was prepared.

[0094] The electrical properties of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in this embodiment were tested by the integrating sphere method. The test results were as follows: carrier concentration: 5.0×10 20 cm -3 , migration rate: 26cm 2 / V·s, resistivity: 4.5×10 -4 Ω·cm; visible light transmittance: 82%, haze: 30%.

[0095] Comparative Example 1

[0096] 1) Preparation of a homogeneous multilayer AZO target: the target material is the same as that in Example 1;

[0097] 2) Template preparation:

[0098] A template was prepared by spin coating a single-size PS microsphere (particle size of 100 nm) on a glass substrate with a thickness of 100 nm and a porosity of 10%. The homogeneous multilayered AZO target prepared in step 1) was mounted on the target holder of the magnetron sputtering equipment, the substrate was fixed on the sample stage, and the distance between the substrate and the target was adjusted to 8 mm. The vacuum was then applied to 10 -5 -10 -4 After Pa, an appropriate amount of working gas (argon, 40 sccm) was introduced into the vacuum chamber, and the substrate temperature was 150°C. A combination of high power (300W) and low rotation speed (5rpm) was used to make the high-concentration target form a bottom film (100nm thick) in the template near the substrate layer.

[0099] The bottom film was then spin-coated with 100nm PS microspheres, with the target porosity of 10% ensured, to prepare a middle layer template. A combination of medium power (200W) and medium speed (10rpm) was used to form a middle layer film (100nm thick) in the middle layer template using the medium concentration target.

[0100] The middle layer film was then spin-coated with 100nm PS microspheres, with the target porosity of 10% ensured, to prepare a surface layer template. Low power (150W) and high rotation speed (15rpm) were used to form a surface film (100nm thick) of the low-concentration target in the surface layer template.

[0101] 3) Demolding: The film deposited in step 2) was placed in a 120°C toluene solution and ultrasonically treated for 10 min to remove the templates of each layer to form a through-porous structure film, and then vacuum annealed (150°C, 10 -3 Pa, 30min), and an aluminum-doped zinc oxide transparent conductive film was prepared.

[0102] The electrical properties of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in this comparative example were tested by the integrating sphere method. The test results were as follows: carrier concentration: 4.5×10 20 cm -3 , migration rate: 18cm 2 / V·s. Since there is no gradient change in the particle size of the microspheres on the template, the grain boundary scattering of the prepared transparent conductive film increases, resulting in a 36% decrease in mobility compared with Example 1; the transmittance is 78%. Since the transparent conductive film prepared in Comparative Example 1 has no macropore-enhanced light scattering, the transmittance decreases by 8.2% compared with the example; the haze is 5%. The lack of pore gradient will destroy the synergistic mechanism of "macropore scattering-small pore light transmission", resulting in a decrease in haze; the resistivity is 7.72×10 -4 Ω·cm.

[0103] Comparative Example 2

[0104] 1) Preparation of target material

[0105] ZnO powder and Al2O3 powder were weighed and mixed by high-energy ball milling (ball-to-material ratio of 10:1, wet grinding method, ethanol-to-powder ratio of 1.8:1, ball milling for 5 h, speed of 400 rpm), cold pressed (40 MPa, 45 s), and sintered at 1200°C (heating rate of 10°C / min, holding temperature for 4 h) to produce an AZO uniform target with an Al doping concentration of 3 mol%.

[0106] 2) Template preparation:

[0107] The PS microspheres with a particle size of 800 nm were spin-coated on the glass substrate. The target porosity of the microspheres was 45% and a near-substrate template was prepared. The AZO uniform target prepared in step 1) was mounted on the target holder of the magnetron sputtering equipment. The substrate was fixed on the sample stage and the distance between the substrate and the target was adjusted to 8 mm. The vacuum was evacuated to 10 -5 -10 -4 After the evaporation temperature reaches 150°C, an appropriate amount of working gas (argon, 40 sccm) is introduced into the vacuum chamber, and the substrate temperature is set at 150°C. A combination of high power (300 W) and low rotation speed (5 rpm) is used to form a bottom film (720 nm thick) on the template near the substrate layer with the target in the high-concentration area.

[0108] The bottom film was then spin-coated with 300 nm PS microspheres, with the target porosity of 35% ensured, to prepare a middle layer template. A combination of medium power (200 W) and medium rotation speed (10 rpm) was used to form a middle layer film (270 nm thick) in the middle layer template using the uniform AZO target prepared in step 1).

[0109] The middle layer film was then spin-coated with 100 nm PS microspheres, with the target porosity of 15% ensured, to prepare a surface layer template. A combination of low power (150 W) and high rotation speed (15 rpm) was used to form a surface film (90 nm thick) of the AZO uniform target prepared in step 1) within the surface layer template.

[0110] 3) As in Example 1, a transparent conductive aluminum-doped zinc oxide film was prepared.

[0111] The electrical properties of the porous gradient aluminum-doped zinc oxide transparent conductive film prepared in this comparative example were tested by the integrating sphere method. The test results were as follows: carrier concentration: 4.7×10 20 cm -3 , migration rate: 22cm 2 / V·s. Due to the lack of gradient change in the Al doping concentration in the prepared transparent conductive film, the high concentration of Al ions in the whole layer leads to serious lattice distortion of ZnO, and there is no concentration gradient to buffer stress, resulting in stress concentration. The scattering of carriers due to lattice defects increases during carrier migration, and the mobility decreases by 21% compared with Example 1; and the absorption of light by high-concentration carriers is enhanced, and the transmittance decreases from 85% to 80%; in addition, due to the lack of matching between concentration gradient and aperture gradient, the light scattering efficiency decreases (haze 10%), and the transmittance decreases due to carrier absorption, and the "light trapping-light transmission" balance cannot be achieved. It is proved that the light scattering efficiency of the transparent conductive film without Al doping concentration gradient change is lower than that of the transparent conductive film prepared in Example 1; resistivity: 6.05×10 -4 Ω·cm.

[0112] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a porous gradient aluminum-doped zinc oxide transparent conductive film, characterized in that: The following steps are involved: preparing a homogeneous multilayer AZO target material, wherein, based on Al ion doping concentration, the homogeneous multilayer AZO target material comprises, from the center to the periphery, a high-concentration region target material, a medium-concentration region target material, and a low-concentration region target material; The PS microspheres were spin-coated on the substrate to obtain a near-substrate template; Using the homogeneous multilayered AZO target as a cathode, and controlling the power and rotation speed to use the high-concentration region target as a raw material, magnetron sputtering deposition is performed in the near-base layer template to prepare a bottom film; Spin-coating PS microspheres on the bottom film to obtain an intermediate layer template; and preparing an intermediate layer film by magnetron sputtering deposition in the intermediate layer template using the medium concentration region target as a raw material by controlling power and rotation speed; Spin-coating PS microspheres on the middle layer film to obtain a surface layer template; and preparing a surface layer film by magnetron sputtering deposition in the surface layer template using the low-concentration region target as a raw material by controlling power and rotation speed; Removing the template and vacuum annealing to prepare the porous gradient aluminum-doped zinc oxide transparent conductive film; Among them, the particle sizes of PS microspheres in the near-base layer template, the intermediate layer template and the surface layer template are gradient distributed.

2. The preparation method according to claim 1, characterized in that The gradient distribution of the PS microsphere particle size is: Substratum template: microspheres with a particle size of 800nm-1000nm, where the microspheres are spin-coated to ensure a target porosity of 40-50%; Intermediate layer template: microspheres with a particle size of 300-500 nm, where the microspheres are spin-coated to ensure a target porosity of 30-40%; Surface layer template: microspheres with a particle size of 50-100 nm, where the microspheres are spin-coated to ensure a target porosity of 10-20%.

3. The preparation method according to claim 1, characterized in that The Al ion doping concentration in the target material of the high concentration region is 3 mol %; the Al ion doping concentration in the target material of the medium concentration region is 2 mol %; and the Al ion doping concentration in the target material of the low concentration region is 1 mol %.

4. The preparation method according to claim 1, characterized in that When preparing the bottom film, the power is 300W and the rotation speed is 5rpm; when preparing the middle film, the power is 200W and the rotation speed is 10rpm; when preparing the surface film, the power is 150W and the rotation speed is 15rpm.

5. The preparation method according to claim 1, characterized in that The specific operation of removing the template is: placing the deposited thin film in an organic solvent and performing ultrasonic treatment to remove the template.

6. The preparation method according to claim 1, characterized in that The vacuum annealing temperature is 120-150° C. and the time is 20-30 minutes.

7. The preparation method according to claim 1, characterized in that The substrate is selected from a quartz substrate, a flexible PET substrate or a glass substrate.

8. The preparation method according to claim 1, characterized in that The bottom film, middle film and surface film are respectively 90% of the thickness of the base layer template, the middle layer template and the surface layer template.

9. A porous gradient aluminum-doped zinc oxide transparent conductive film prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The porous gradient aluminum-doped zinc oxide transparent conductive film has a through three-dimensional porous network structure, and the pore wall thickness is 20-50 nm.

10. Use of the porous gradient aluminum-doped zinc oxide transparent conductive film according to claim 9 in the preparation of optoelectronic devices.

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