Method for improving electrochromic cycling stability of nickel oxide film prepared by chemical bath by introducing homogeneous template layer

Abstract

The invention discloses a method for improving electrochromic cycling stability of a nickel oxide film prepared by chemical bath by introducing a homogeneous template layer. The method comprises the following steps: preparing nickel sulfate hexahydrate and potassium hydroxide into a plating solution, electrochemically depositing nickel hydroxide by adopting a three-electrode system which takes conductive glass as a working electrode, a platinum sheet as a counter electrode and a saturated calomel electrode as a reference electrode, washing, drying and carrying out first heat treatment, and depositing a nickel oxide homogeneous template layer on the conductive surface of the conductive glass; and taking a nickel sulfate hexahydrate solution and a potassium persulfate solution as precursor solutions, covering a non-conductive surface with a polyimide adhesive tape, vertically putting the conductive glass deposited with the nickel oxide homogeneous template layer into the precursor solutions, slowly adding ammonia water, performing chemical bath deposition, washing, drying and performing secondary heat treatment to obtain the nickel oxide film. The homogeneous template layer is introduced to prepare the nickel oxide film, the nickel oxide film does not fall off after 1000 times of electrochromic cycles, and the charge capacity is only attenuated by 38.1% after 600 times of cycles.

Description

Technical Field

[0001] The present invention belongs to the field of electrochromic materials, and particularly relates to a method for improving the electrochromic cycling stability of nickel oxide thin films prepared by chemical bath by introducing a homogeneous template layer, and nickel oxide thin films obtained by using this method. Background Art

[0002] Electrochromism refers to the phenomenon that the transmittance, reflectivity, color, etc. of a material change under an alternating electric field, which appears as a reversible change in color and transparency in appearance. Electrochromic materials have a series of advantages such as environmental protection, pollution-free, intelligent, and low energy consumption.

[0003] Nickel oxide (NiO) thin film, as a typical anodic electrochromic material, has a large optical modulation amplitude and can achieve reversible optical property changes under different optoelectronic conditions. Due to its relatively low cost, it shows good economic advantages in large-scale applications. The above advantages make nickel oxide thin films often selected as the ion storage layer in complementary electrochromic devices, playing an important role in the charge storage and transmission process. At the same time, it can also be widely used as an anodic electrochromic material in the design and manufacture of optoelectronic devices, and has received extensive research and high attention in the industry.

[0004] Combining NiO thin films with metals, oxides, conductive polymers, carbon-based materials, etc., the electrochromic performance can be improved by using the synergistic effect. When it is compounded with a metal, the high conductivity of the metal helps the rapid transmission of electrons, making up for the shortcoming of the poor conductivity of NiO; compounding with oxides is to optimize the energy band structure of NiO by means of the characteristics of different oxides to enhance its light absorption and modulation ability; the introduction of a conductive polymer can improve the flexibility and processability of NiO, and at the same time, the unique conductive mechanism of the polymer can also improve the electrochromic response speed. However, due to the compounding of different materials in the heterogeneous structure composite material, defects such as holes, cracks or incomplete bonding are likely to occur at the interface, resulting in stress concentration in the film layer and reduced durability.

[0005] Among the numerous preparation methods of nickel oxide thin films, the chemical bath method for preparing nickel oxide thin films has received extensive attention due to its simple operation, low cost, and suitability for mass production. The morphology of the nickel oxide thin film prepared by the chemical bath method is nanosheets growing perpendicular to the substrate. The nanosheet structure provides a larger specific surface area for the injection / extraction of ions and electrons, making the nickel oxide thin film have a good optical modulation amplitude. However, the contact area between the nanosheet structure and the substrate is small and the crystallinity is low, resulting in more lattice defects inside the film, which are prone to cracks or peeling, leading to poor cycling stability.

[0006] To solve the above problems, in the prior art, the impregnation method is used to first deposit a nickel oxide thin film, and then the chemical bath method is used to continue depositing a nickel oxide thin film on its surface. The morphology of the thin film is a coral-like structure. Although this technology improves the diffusion rate of electrons and ions, this structure often undergoes volume changes during the electrochromic reversible cycle and is significantly affected by stress, resulting in the performance of the thin film starting to decline after 10 electrochromic cycles, and the stability is poor. Summary of the Invention

[0007] To solve various defects caused by lattice mismatch of heterogeneous films and poor interfacial compatibility, etc., the present invention provides a method for introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath and the nickel oxide thin films obtained by using this method.

[0008] The technical solution of the present invention is specifically as follows:

[0009] On the one hand, the present invention provides a method for introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath, including the following steps:

[0010] Step S1: Prepare a plating solution by mixing nickel sulfate hexahydrate and potassium hydroxide, then put the cleaned and dried conductive glass into the plating solution, and perform electrochemical deposition of nickel hydroxide using a three-electrode system with the conductive glass as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The deposition voltage is 0.8 - 1.5V, the deposition time is 30 - 60min. After deposition, rinse with deionized water to remove the residual plating solution, dry, and then perform the first heat treatment, that is, deposit a cubic-phase nickel oxide homogeneous template layer with a certain thickness on the conductive surface of the conductive glass;

[0011] Step S2: Mix a nickel sulfate hexahydrate solution and a potassium persulfate solution to prepare a precursor solution. Cover the non-conductive surface of the conductive glass with polyimide tape to prevent deposition on this side. Then vertically put the conductive glass coated with the nickel oxide homogeneous template layer into the precursor solution, slowly add ammonia water to form a nickel ammonia complex, and after the ammonia water is in excess, nickel hydroxide is generated. After chemical bath deposition for 30 - 60min, rinse with deionized water, dry, and then perform the second heat treatment to obtain a nickel oxide thin film.

[0012] Preferably, the conductive glass is ITO or FTO conductive glass.

[0013] Preferably, in step S1, the cleaning and drying steps of the conductive glass before putting it into the plating solution: Ultrasonically clean the conductive glass with deionized water, absolute ethanol, and acetone for 15 - 25min, and then put it into a drying oven to dry.

[0014] Preferably, in step S1, the plating solution is prepared as follows: nickel sulfate hexahydrate and potassium hydroxide are respectively dissolved in deionized water to obtain a nickel sulfate hexahydrate solution with a concentration of 0.8 - 1.2 mol / L and a potassium hydroxide solution with a concentration of 0.8 - 1.2 mol / L. The two are mixed and stirred according to a volume ratio of 10:1 to obtain the plating solution.

[0015] Preferably, in step S1, the conditions for the first heat treatment are as follows: the conductive glass deposited with nickel hydroxide film is placed in a box-type resistance furnace, heated at a heating rate of 5 - 10 °C / min to 300 - 400 °C, held at a constant temperature for 1 - 3 h, and then cooled to deposit a nickel oxide homogeneous template layer.

[0016] Preferably, in step S1, the thickness of the deposited nickel oxide homogeneous template layer is 120 - 240 nm.

[0017] Preferably, in step S2, the precursor solution is prepared as follows: nickel sulfate hexahydrate and potassium persulfate are respectively dissolved in deionized water to obtain a nickel sulfate hexahydrate solution with a concentration of 0.6 - 0.7 mo / L and a potassium persulfate solution with a concentration of 0.2 - 0.3 mol / L. Then the two are mixed and stirred according to a volume ratio of 1:1 to obtain the precursor solution.

[0018] Preferably, in step S2, the precursor solution needs to be kept at a constant temperature and stirred in a water bath. The water bath temperature is 20 - 40 °C, and the stirring rate is 300 - 500 r / min. After chemical bath deposition, take it out, rinse the film layer with deionized water, remove the polyimide tape, dry it at a temperature of 50 - 80 °C for 1 - 3 h, and then perform the second heat treatment.

[0019] Preferably, in step S2, the conditions for the second heat treatment are as follows: heat it at a heating rate of 5 - 10 °C / min to 250 - 350 °C, keep it warm for 1 - 2 h, and then cool to obtain a nickel oxide film.

[0020] On the other hand, the present invention provides a nickel oxide film with electrochromic cycle stability prepared by the above method.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention uses nickel oxide composites with the same structure. This method can form a more coordinated and unified structure system inside the nickel oxide, making the ion and electron transmission more efficient and smooth, thereby significantly improving the electrochromic performance.

[0023] (2) The present invention prepares a nickel oxide homogeneous template layer by an electrochemical method. Electrochemical deposition can prepare a nickel oxide homogeneous template layer with uniform structure, good crystallinity and strong binding force with the substrate, which is not prone to deformation or rupture, effectively improving the mechanical properties and stability of the thin film. It provides a template for the subsequent chemical bath deposition of nickel oxide thin film, thereby improving the electrochromic cycle stability of the nickel oxide thin film prepared by chemical bath.

[0024] (3) After the present invention introduces the homogeneous template layer, the nickel oxide prepared by chemical bath is more stable and exhibits good electrochromic cycle stability. The present invention deposits a uniform nickel oxide homogeneous template layer on the conductive glass by optimizing parameters such as electrochemical deposition voltage and deposition time, and then continues to deposit by chemical bath method to prepare a nickel oxide thin film. Since it grows on the homogeneous network structure template layer, the defects occurring during chemical bath deposition are reduced, making the thin film have a strong binding force and not easy to fall off.

[0025] (4) The electro-deposited homogeneous template layer in the present invention improves the performance of the nickel oxide thin film prepared by chemical bath. It can be known from the electrochemical cyclic voltammetry test that in a 0.1 mol / L KOH electrolyte, the charge capacity of the nickel oxide thin film is 32.9 mC·cm -2 . It can be known from the transmittance test that the light modulation amplitude between the colored state and the bleached state of the nickel oxide thin film reaches 57.41%. Compared with the nickel oxide thin film prepared by a single chemical bath method, the electrochromic cycle of the nickel oxide thin film prepared by introducing a homogeneous template layer in the present invention can reach 1000 times without falling off, and the charge capacity only decays by 38.1% after 600 cycles.

[0026] (5) The nickel oxide thin film prepared by the present invention exhibits good cycle stability and has potential commercial prospects in future market applications. It is expected to be widely used in many fields such as electronics, energy, and optics, providing strong support for the innovation of related industries. Description of the Drawings

[0027] Figure 1 It is a cross-sectional scanning electron microscope photograph of the nickel oxide thin film prepared by chemical bath after introducing the homogeneous template layer in Example 1 of the present invention;

[0028] Figure 2 It is a cross-sectional scanning electron microscope photograph of the nickel oxide thin film in Example 1 of the present invention after 20 cycles;

[0029] Figure 3 It is a cross-sectional scanning electron microscope photograph of the nickel oxide thin film in Example 1 of the present invention after 1000 cycles;

[0030] Figure 4 It is the transmittance spectrum of the nickel oxide thin film in Example 1 of the present invention;

[0031] Figure 5Cyclic voltammetry curve of the nickel oxide thin film in Embodiment 1 of the present invention;

[0032] Figure 6 Cross-sectional scanning electron microscope photograph of the nickel oxide thin film prepared by the single chemical bath method in Comparative Example 1;

[0033] Figure 7 Cross-sectional scanning electron microscope photograph of the nickel oxide thin film in Comparative Example 1 after 20 cycles;

[0034] Figure 8 Cyclic voltammetry curve of the nickel oxide thin film in Comparative Example 1. Specific embodiments

[0035] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] The present invention provides a method for improving the electrochromic cycling stability of nickel oxide thin films prepared by chemical bath by introducing a homogeneous template layer in the first aspect. This method first deposits a uniform nickel oxide homogeneous template layer on the conductive glass by electrochemical deposition, and then continues to deposit by chemical bath to obtain a nickel oxide thin film with better electrochromic cycling stability.

[0037] Specifically, the method provided by the present invention includes the following steps:

[0038] Step S1: Prepare a plating solution by mixing nickel sulfate hexahydrate and potassium hydroxide, then put the cleaned and dried conductive glass into the plating solution, and perform electrochemical deposition of nickel hydroxide using a three-electrode system with the conductive glass as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. The deposition voltage is 0.8 - 1.5V, the deposition time is 30 - 60min. After deposition, rinse with deionized water to remove the residual plating solution, dry, and then perform the first heat treatment, that is, deposit a cubic-phase nickel oxide homogeneous template layer with a certain thickness on the conductive surface of the conductive glass;

[0039] Step S2: Mix a nickel sulfate hexahydrate solution and a potassium persulfate solution to prepare a precursor solution. Cover the non-conductive surface of the conductive glass with polyimide tape to prevent deposition on this side. Then vertically place the conductive glass coated with the nickel oxide homogeneous template layer into the precursor solution, slowly add ammonia water to form a nickel ammonia complex, and after the ammonia water is in excess, nickel hydroxide is generated. After chemical bath deposition for 30 - 60min, rinse with deionized water, dry, and then perform the second heat treatment to obtain a nickel oxide thin film.

[0040] It is found that during the electrochemical deposition process, when the deposition voltage is too high, the grain growth rate is too fast, which easily forms larger particles, affecting the uniformity and compactness; when the deposition voltage is too low, the ion migration rate is slow and it is not easy to form a film. When the deposition time is too short, the film growth is insufficient; when the deposition time is too long, the particles on the film surface agglomerate and the particle size increases, resulting in performance degradation. Therefore, the present invention limits the deposition voltage to 0.8 - 1.5 V and the deposition time to 30 - 60 min.

[0041] In some preferred embodiments, the conductive glass is ITO or FTO conductive glass.

[0042] In some preferred embodiments, in step S1, the cleaning and drying steps before putting the conductive glass into the plating solution: The conductive glass is ultrasonically cleaned with deionized water, absolute ethanol and acetone for 15 - 25 min, and then put into a drying oven for drying.

[0043] In some preferred embodiments, in step S1, the preparation of the plating solution: 10.51 - 15.77 g of nickel sulfate hexahydrate and 2.24 - 3.36 g of potassium hydroxide are respectively dissolved in 50 ml of deionized water to obtain a nickel sulfate hexahydrate solution with a concentration of 0.8 - 1.2 mol / L and a potassium hydroxide solution with a concentration of 0.8 - 1.2 mol / L. The two are mixed and stirred according to a volume ratio of 10:1 to obtain the plating solution.

[0044] It is found that during the electro - deposition process, the concentration of the plating solution affects the deposition rate. When the concentration of the plating solution is too small, the deposition rate is slow and the deposition efficiency is low; when the concentration of the plating solution is too large, the deposition rate is fast, resulting in uneven film growth. Based on this, the present invention uses a nickel sulfate hexahydrate solution containing 0.8 - 1.2 mol / L and a potassium hydroxide solution containing 0.8 - 1.2 mol / L, and the two are mixed and stirred according to a volume ratio of 10:1 as the plating solution to ensure the formation of a uniform nickel hydroxide film on the conductive glass.

[0045] In some preferred embodiments, in step S1, the first heat - treatment conditions: The conductive glass deposited with the nickel hydroxide film is placed in a box - type resistance furnace, heated at a heating rate of 5 - 10 °C / min to 300 - 400 °C, kept at a constant temperature for 1 - 3 h, and after cooling, the nickel oxide homogeneous template layer is deposited.

[0046] In some preferred embodiments, in step S1, the thickness of the deposited homogeneous template layer is 100 - 300 nm; more preferably 120 - 240 nm.

[0047] In some preferred embodiments, in step S2, the preparation of the precursor solution is as follows: dissolve 12.62 - 14.72 g of nickel sulfate hexahydrate in 80 ml of deionized water to obtain a nickel sulfate hexahydrate solution with a concentration of 0.6 - 0.7 mol / L; dissolve 3.24 - 4.86 g of potassium persulfate in 60 ml of deionized water to obtain a potassium persulfate solution with a concentration of 0.2 - 0.3 mol / L; then mix and stir the two according to a volume ratio of 1:1 to obtain the precursor solution.

[0048] It has been found that during the chemical bath deposition process, the structure of the nickel oxide thin film is affected by the concentration of the precursor solution. When the concentration of the precursor solution is too small or too large, it will affect the nanosheet structure of the thin film. Based on this, the present invention uses a nickel sulfate hexahydrate solution with a concentration of 0.6 - 0.7 mol / L and a potassium persulfate solution with a concentration of 0.2 - 0.3 mol / L, and mixes and stirs them according to a volume ratio of 1:1 as the precursor solution to ensure the formation of a nickel hydroxide thin film with a nanosheet structure.

[0049] In some preferred embodiments, in step S2, the precursor solution needs to be placed in a water bath and stirred at a constant temperature. The water bath temperature is 20 - 40°C, and the stirring rate is 300 - 500 r / min; after chemical bath deposition, take it out, rinse the film layer with deionized water, remove the polyimide tape, and dry it at a temperature of 50 - 80°C for 1 - 3 h, and then perform the second heat treatment.

[0050] In some preferred embodiments, according to the decomposition temperature of nickel hydroxide, the conditions for the second heat treatment are as follows: heat up at a heating rate of 5 - 10°C / min to 250 - 350°C, keep warm for 1 - 2 h, and then cool to obtain the nickel oxide thin film.

[0051] In the present invention, nickel hydroxide is thermally decomposed by heat treatment to generate nickel oxide. The temperature of the second heat treatment should be lower than that of the first heat treatment; the time of the second heat treatment should be less than that of the first heat treatment, mainly to ensure that the second heat treatment will not affect the electrochemically deposited nickel oxide thin film.

[0052] Both heat treatments use a stepwise temperature increase. If the heating rate is too fast, it will cause large thermal stress inside the thin film, and defects such as cracks and peeling will appear in the thin film, affecting the performance of the thin film. If the heating rate is too slow, it will lead to too long heat treatment time, reduce production efficiency, and increase production costs.

[0053] On the other hand, the present invention provides a nickel oxide thin film with good electrochromic cycle stability prepared by the above method.

[0054] In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention will be further explained below with reference to examples and comparative examples.

[0055] Example 1:

[0056] A method for improving the electrochromic cycling stability of nickel oxide thin films prepared by chemical bath by introducing a homogeneous template layer, the specific steps are as follows:

[0057] The ITO conductive glass was ultrasonically cleaned with deionized water, absolute ethanol and acetone in turn for 20 min, and then placed in a drying oven after cleaning for drying.

[0058] Step S1: Dissolve 13.14 g of nickel sulfate hexahydrate and 2.8 g of potassium hydroxide in 50 ml of deionized water respectively to obtain a nickel sulfate hexahydrate solution with a concentration of 1.0 mol / L and a potassium hydroxide solution with a concentration of 1.0 mol / L. Mix and stir the two according to a volume ratio of 10:1 to obtain a plating solution. Then place the cleaned and dried ITO conductive glass into the plating solution, and use a three-electrode system with the conductive glass as the working electrode, a platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode for electrochemical deposition of nickel hydroxide. Adjust the deposition voltage to 1.0 V and the deposition time to 30 min. After deposition, rinse with deionized water to remove the residual plating solution, dry, and place the conductive glass deposited with nickel hydroxide in a box-type resistance furnace for the first heat treatment. Heat it to 350 °C at a heating rate of 10 °C / min, keep it at a constant temperature for 1.5 h, and then cool it to room temperature, that is, deposit a nickel oxide homogeneous template layer with a thickness of 180 nm on the conductive surface of the ITO conductive glass;

[0059] Step S2: Dissolve 12.62 g of nickel sulfate hexahydrate in 80 ml of deionized water to obtain a nickel sulfate hexahydrate solution with a concentration of 0.6 mo / L; dissolve 4.054 g of potassium persulfate in 60 ml of deionized water to obtain a potassium persulfate solution with a concentration of 0.25 mol / L; then mix and stir the two according to a volume ratio of 1:1 to obtain a precursor solution. Place the precursor solution in a water bath and stir at a constant temperature of 30 °C with a stirring rate of 300 r / min. Cover the non-conductive surface of the conductive glass with polyimide tape to prevent deposition on this side. Then vertically place the conductive glass coated with the nickel oxide homogeneous template layer into the precursor solution, and then slowly add 12 ml of ammonia water to generate nickel hydroxide. After chemical bath deposition for 30 min, rinse the film layer with deionized water, remove the polyimide tape, dry it at 60 °C for 2 h, and then perform the second heat treatment. Heat it to 300 °C at a heating rate of 10 °C / min, keep it warm for 1 h, and cool to obtain a nickel oxide thin film.

[0060] The nickel oxide thin film prepared in Example 1 was subjected to structure and performance tests, and the test results are as Figures 1 to 5 shown.

[0061] Among them,

Electrochemical cyclic voltammetry test conditions

[0062] Testing device: Electrochemical workstation A25328; Three-electrode system: Conductive glass as the working electrode, platinum sheet as the counter electrode, and saturated calomel electrode as the reference electrode; Electrolyte solution: 0.1 mol / L potassium hydroxide solution; Scanning rate: 50 mv / s; Applied voltage: -1.2V - 1.2V.

[0063]

Light transmittance test conditions

[0064] Testing device: UV-Vis spectrophotometer LAMBDA750; Test wavelength: 300 nm - 700 nm; Coloring state voltage: 1.2V, Fading state voltage: -1.2V.

[0065] Figure 1 It is the cross-sectional electron microscope photograph of the nickel oxide thin film prepared by chemical bath after introducing the homogeneous template layer. The structure of the nickel oxide homogeneous template layer is uniform and has good crystallinity; Figure 2 It is the cross-sectional electron microscope photograph of the nickel oxide thin film after 20 cycles. From Figure 1 and Figure 2 it can be seen that after 20 cycles, there is no obvious change in the nickel oxide thin film.

[0066] From Figure 3 it can be seen that after 1000 cycles, the structure of the nickel oxide thin film changes, but the film still does not fall off. This shows that electrochemically deposited nickel oxide homogeneous template layer with strong binding force to the substrate (conductive glass) can be prepared, which is not easy to deform or break, effectively improving the mechanical strength and stability of the film; due to growth on the homogeneous network structure template layer, the defects during chemical bath deposition are reduced, making the film have strong binding force and not easy to fall off.

[0067] After the light transmittance test of the nickel oxide thin film, as Figure 4 it can be known that at a wavelength of 600 nm, the optical modulation amplitude between the colored state and the bleached state of the nickel oxide thin film reaches 57.41%; the nickel oxide thin film has a lower transmittance in the colored state and is suitable for anodic electrochromic materials.

[0068] Figure 5 It is the electrochemical cyclic voltammetry curve (i.e., CV curve). The charge capacity is obtained by integrating the area of the CV curve. Through the electrochemical cyclic voltammetry test, it can be known that in 0.1 mol / L KOH electrolyte, the charge capacity of the nickel oxide thin film is 32.9 mC·cm -2; It shows that the nickel oxide thin film has good charge storage capacity. After 600 cycles, the charge capacity of the nickel oxide thin film only decays by 38.1%; after 1000 cycles, the thin film still does not peel off. This shows that after introducing the homogeneous template layer and then preparing by chemical bath in the present invention, the obtained nickel oxide thin film is more stable and exhibits good electrochromic cycling stability; the electro-deposited homogeneous template layer improves the stability of the nickel oxide thin film prepared by chemical bath.

[0069] Examples 2 - 3

[0070] The methods of Examples 2 - 3 are basically the same as that of Example 1, the difference lies in the conditions of electrochemical deposition in step S1:

[0071] Example 2: In step S1, the deposition voltage is 0.8V and the deposition time is 60min;

[0072] Example 3: In step S1, the deposition voltage is 1.5V and the deposition time is 30min.

[0073] The nickel oxide thin films prepared in Examples 2 - 3 are tested in the same way as in Example 1, and the test results are similar to those of Example 1, and the electrochromic cycling stabilities are all very good. Moreover, it is found that during the process of electrochemical deposition, when the deposition voltage is too high, the grain growth rate is too fast, and large particles are easily formed, which affects the uniformity and denseness; when the deposition voltage is too low, the ion migration speed is slower and it is not easy to form a film. When the deposition time is too short, the thin film growth is insufficient; when the deposition time is too long, the particles on the thin film surface agglomerate and the particle size increases, resulting in performance degradation. Therefore, the present invention limits the deposition voltage to 0.8 - 1.5V and the deposition time to 30 - 60min.

[0074] Examples 4 - 5

[0075] The methods of Examples 4 - 5 are basically the same as that of Example 1, the difference lies in the concentration of the plating solution in step S1:

[0076] Example 4: In step S1, 10.51g of nickel sulfate hexahydrate and 2.24g of potassium hydroxide are respectively dissolved in 50ml of deionized water to obtain a 0.8mol / L nickel sulfate hexahydrate solution and a 0.8mol / L potassium hydroxide solution. The two are mixed and stirred according to a volume ratio of 10:1 to obtain the plating solution.

[0077] Example 5: In step S1, 15.77g of nickel sulfate hexahydrate and 3.36g of potassium hydroxide are respectively dissolved in 50ml of deionized water to obtain a 1.2mol / L nickel sulfate hexahydrate solution and a 1.2mol / L potassium hydroxide solution. The two are mixed and stirred according to a volume ratio of 10:1 to obtain the plating solution.

[0078] The nickel oxide thin films prepared in Examples 4 - 5 were tested in the same way as in Example 1, and the test results were similar to those in Example 1, with good electrochromic cycle stability. Moreover, it was found that during the electrodeposition process, the concentration of the plating solution affects the deposition rate. When the concentration of the plating solution is too low, the deposition rate is slow and the deposition efficiency is low; when the concentration of the plating solution is too high, the deposition rate is fast, resulting in uneven growth of the thin film. Based on this, the present invention uses a nickel sulfate hexahydrate solution containing 0.8 - 1.2 mol / L and a potassium hydroxide solution containing 0.8 - 1.2 mol / L, and the two are mixed and stirred according to a volume ratio of 10:1 as the plating solution to ensure the formation of a uniform nickel hydroxide thin film on the conductive glass.

[0079] Examples 6 - 7

[0080] Examples 6 - 7 are basically the same as the method of Example 1, except that in step S2, the concentration of the precursor solution is as follows:

[0081] Example 6: In step S2, 12.62 g of nickel sulfate hexahydrate was dissolved in 80 ml of deionized water to obtain a nickel sulfate hexahydrate solution with a concentration of 0.6 mo / L; 3.24 g of potassium persulfate was dissolved in 60 ml of deionized water to obtain a potassium persulfate solution with a concentration of 0.2 mol / L; then the two were mixed and stirred according to a volume ratio of 1:1 to obtain the precursor solution.

[0082] Example 7: In step S2, 14.72 g of nickel sulfate hexahydrate was dissolved in 80 ml of deionized water to obtain a nickel sulfate hexahydrate solution with a concentration of 0.7 mo / L, and 4.86 g of potassium persulfate was dissolved in 60 ml of deionized water to obtain a potassium persulfate solution with a concentration of 0.3 mol / L; then the two were mixed and stirred according to a volume ratio of 1:1 to obtain the precursor solution.

[0083] The nickel oxide thin films prepared in Examples 6 - 7 were tested in the same way as in Example 1, and the test results were similar to those in Example 1, with good electrochromic cycle stability. Moreover, it was found that during the chemical bath deposition process, the structure of the nickel oxide thin film is affected by the concentration of the precursor solution. When the concentration of the precursor solution is too low or too high, it will affect the nanosheet structure of the thin film. Therefore, the present invention uses a nickel sulfate hexahydrate solution with a concentration of 0.6 - 0.7 mol / L and a potassium persulfate solution with a concentration of 0.2 - 0.3 mol / L, and the two are mixed and stirred according to a volume ratio of 1:1 as the precursor solution to ensure the formation of a nickel hydroxide thin film with a nanosheet structure.

[0084] Examples 8 - 9

[0085] Examples 8 - 9 are basically the same as the method of Example 1, except that in step S2, the chemical bath deposition conditions are as follows:

[0086] Example 8: In step S2, 10 ml of ammonia water was then slowly added, and chemical bath deposition was carried out for 60 min;

[0087] Example 9: In step S2, 20 ml of ammonia water was then slowly added, and chemical bath deposition was carried out for 30 min.

[0088] The nickel oxide thin films prepared in Examples 8-9 were tested in the same way as in Example 1, and the test results were similar to those in Example 1, and the electrochromic cycle stability was very good. Moreover, slowly dropping ammonia water in an appropriate amount can avoid too fast local reaction and poor film uniformity.

[0089] Examples 10-13

[0090] Examples 10-13 are basically the same as the method of Example 1, except for the conditions of the first heat treatment in step S1 and the conditions of drying and the second heat treatment in step S2:

[0091] Example 10: In step S1, the condition of the first heat treatment was to heat up to 300 °C at a heating rate of 5 °C / min and hold for 3 h; in step S2, after drying at 50 °C for 3 h, then heat up to 250 °C at a heating rate of 10 °C / min and hold for 2 h;

[0092] Example 11: In step S1, the condition of the first heat treatment was to heat up to 400 °C at a heating rate of 10 °C / min and hold for 1 h; in step S2, after drying at 80 °C for 1 h, then heat up to 350 °C at a heating rate of 5 °C / min and hold for 1 h;

[0093] Example 12: In step S1, the condition of the first heat treatment was to heat up to 350 °C at a heating rate of 8 °C / min and hold for 2 h; in step S2, after drying at 60 °C for 2 h, then heat up to 300 °C at a heating rate of 8 °C / min and hold for 1.5 h;

[0094] Example 13: In step S1, the condition of the first heat treatment was to heat up to 350 °C at a heating rate of 10 °C / min and hold for 1.5 h; in step S2, after drying at 70 °C for 1.5 h, then heat up to 300 °C at a heating rate of 10 °C / min and hold for 1 h.

[0095] The nickel oxide thin films prepared in Examples 10 to 13 were tested in the same manner as in Example 1, and the test results were similar to those in Example 1, with good electrochromic cycling stability. Moreover, in the present invention, nickel hydroxide is thermally decomposed by heat treatment to generate nickel oxide. The temperature of the second heat treatment should be lower than that of the first heat treatment; the time of the second heat treatment should be less than that of the first heat treatment, mainly to ensure that the second heat treatment does not affect the electrochemically deposited nickel oxide thin film. Both heat treatments are carried out with a gradual temperature increase. If the heating rate is too fast, large thermal stresses will be generated inside the thin film, and defects such as cracks and peeling will appear in the thin film, affecting the performance of the thin film. If the heating rate is too slow, the heat treatment time will be too long, reducing production efficiency and increasing production costs.

[0096] Comparative Example 1:

[0097] The difference between Comparative Example 1 and Example 1 is that: there is no step S1, that is, there is no prior electrochemically depositing a nickel oxide homogeneous template layer on the conductive glass, but a single chemical bath method is used to prepare the nickel oxide thin film.

[0098] The nickel oxide thin film prepared in Comparative Example 1 was subjected to structure and performance tests using the same test method as in Example 1, and the test results are as Figures 6 to 8 shown.

[0099] Figure 6 is a cross-sectional scanning electron microscope photograph of the nickel oxide thin film deposited by the single chemical bath method; Figure 7 is a cross-sectional scanning electron microscope photograph of the nickel oxide thin film deposited by the single chemical bath method after 20 cycles. From Figure 6 and Figure 7 it can be seen that after 20 cycles, the nanosheets of the nickel oxide thin film are no longer perpendicular to the ITO substrate, and the bottom of the nickel oxide thin film becomes disordered, indicating that the film structure is damaged, and under the action of stress, the binding force of the nickel oxide thin film is weakened. Figure 8 is the cyclic voltammogram of the nickel oxide thin film prepared by the chemical bath; after 40 cycles, since part of the nickel oxide thin film has peeled off, the area of the cyclic voltammogram becomes smaller and the charge capacity decreases.

[0100] By comparing Figure 1 with Figure 6 it can be seen that: by using the method of Example 1 of the present invention, electrochemically depositing can prepare a nickel oxide homogeneous template layer with a uniform structure, good crystallinity and strong binding force with the conductive glass, and then chemically depositing the nickel oxide thin film; by using the method of Comparative Example 1 to deposit the nickel oxide thin film, the contact area between its nanosheet structure and the conductive glass is small and the crystallinity is low, resulting in more lattice defects inside the nickel oxide thin film.

[0101] By comparing Figure 3 with Figure 7It can be seen from the comparison that the nickel oxide thin film prepared by the method of Embodiment 1 of the present invention has a strong binding force and is not easily detached because it grows on the homogeneous network structure template layer rather than on the ITO or FTO surface. However, for the nickel oxide thin film prepared by the method of Comparative Example 1, since it directly contacts the ITO or FTO surface, the binding force of the thin film is weakened and its electrochemical stability is relatively poor.

[0102] Comparative Example 2:

[0103] The difference between Comparative Example 2 and Embodiment 1 is that there is no first heat treatment in Step S1, that is, the conductive glass deposited with nickel hydroxide is not heat-treated.

[0104] When preparing the nickel oxide thin film by the method of Comparative Example 2 and performing structure and performance tests under the same test method as in Embodiment 1, it is found that Comparative Example 2 forms nickel hydroxide with a lower crystallinity instead of nickel oxide, and it is impossible to first deposit a cubic-phase nickel oxide homogeneous template layer with a certain thickness on the conductive surface of the conductive glass, resulting in poor stability of the subsequently chemically deposited nickel oxide thin film.

[0105] Comparative Example 3:

[0106] The difference between Comparative Example 3 and Embodiment 1 is that the steps are carried out in the order of Step S2 and then Step S1, that is, chemical bath deposition is first carried out and then electrochemical deposition.

[0107] When preparing the nickel oxide thin film by the method of Comparative Example 3 and performing structure and performance tests under the same test method as in Embodiment 1, it is found that similar to the chemical bath deposition in Comparative Example 1, since the nickel oxide thin film is directly chemically deposited on the conductive glass, the contact area between its nanosheet structure and the conductive glass is small and the crystallinity is low, resulting in more defects inside the nickel oxide thin film. The subsequently electrochemically deposited nickel oxide thin film only changes its surface morphology and the stability is not improved.

[0108] Comparative Examples 4 - 5

[0109] The methods of Comparative Examples 4 - 5 are basically the same as those of Embodiment 1, and the differences are as follows:

[0110] Comparative Example 4: In Step S1, the deposition voltage is 0.5V;

[0111] Comparative Example 5: In Step S1, the deposition voltage is 2V.

[0112] When preparing the nickel oxide thin film by the methods of Comparative Examples 4 - 5 and performing structure and performance tests under the same test method as in Embodiment 1, it is found that when the deposition voltage is too low, the ion migration speed is slow and it is not easy to form a film; when the deposition voltage is too high, the grain growth speed is too fast and large particles are easily formed, affecting the uniformity and denseness.

[0113] Comparative Example 6

[0114] The method of Comparative Example 6 is basically the same as that of Example 1, except that:

[0115] Comparative Example 6: In step S3, 10 ml to 20 ml of ammonia water was added quickly.

[0116] The nickel oxide thin film was prepared by the method of Comparative Example 6, and the structure and performance were tested under the same test method as in Example 1. It was found that: dropping ammonia water too fast led to too fast local reaction and poor film uniformity.

[0117] Comparative Example 7

[0118] The method of Comparative Example 7 is basically the same as that of Example 1, except that:

[0119] Comparative Example 7: In step S2, the precursor solution was not placed in a water bath for constant temperature stirring, and the stirring rate was 0 to 200 r / min.

[0120] The nickel oxide thin film was prepared by the method of Comparative Example 7, and the structure and performance were tested under the same test method as in Example 1. It was found that: without stirring or too slow stirring rate, the reactants in the solution could not be evenly distributed throughout the system in time, resulting in poor film quality.

[0121] Comparative Example 8

[0122] The method of Comparative Example 8 is basically the same as that of Example 1, except that:

[0123] Comparative Example 8: In step S2, the non-conductive surface of the conductive glass was not covered with polyimide tape, so that a nickel oxide thin film was deposited on this side.

[0124] The nickel oxide thin film was prepared by the method of Comparative Example 8, and the structure and performance were tested under the same test method as in Example 1. It was found that: after a nickel oxide thin film was deposited on the non-conductive surface of the conductive glass, the color change could not occur, and the film was always in a darker color, affecting the optical performance test.

[0125] Comparative Example 9

[0126] The difference between Comparative Example 9 and Example 1 is that: there is no second heat treatment in step S2.

[0127] The nickel oxide thin film was prepared by the method of Comparative Example 9, and the structure and performance were tested under the same test method as in Example 1. It was found that: nickel hydroxide with low crystallinity was formed by chemical bath deposition instead of nickel oxide, and its crystal structure was irregular with many defects, and the electrochromic cycle stability was worse than that of the nickel oxide thin film.

[0128] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath by introducing a homogeneous template layer, characterized in that: The steps include: Step S1: nickel sulfate hexahydrate and potassium hydroxide are prepared into a plating solution, and then the cleaned and dried conductive glass is placed in the plating solution, and nickel hydroxide is electrochemically deposited using a three-electrode system with the conductive glass as a working electrode, a platinum sheet as a counter electrode, and a saturated calomel electrode as a reference electrode. The deposition voltage is 0.8 to 1.5 V, and the deposition time is 30 to 60 minutes. After the deposition is completed, the residual plating solution is rinsed with deionized water to remove it, and after drying, a first heat treatment is performed, that is, a cubic nickel oxide homogeneous template layer with a certain thickness is deposited on the conductive surface of the conductive glass; Step S2: nickel sulfate hexahydrate solution and potassium persulfate solution are mixed to prepare a precursor solution, and the non-conductive surface of the conductive glass is covered with polyimide tape to prevent deposition on this side. The conductive glass coated with a nickel oxide homogeneous template layer is then placed vertically into the precursor solution, and ammonia water is slowly added to form a nickel ammonia complex. Nickel hydroxide is generated after an excess of ammonia water. After chemical bath deposition for 30 to 60 minutes, the solution is rinsed with deionized water, dried, and subjected to a second heat treatment to obtain a nickel oxide film.

2. The method of introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath according to claim 1, characterized in that: The conductive glass is ITO or FTO conductive glass.

3. The method of introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath according to claim 1, characterized in that: In step S1, the conductive glass is cleaned and dried before being placed in the plating solution: the conductive glass is ultrasonically cleaned with deionized water, anhydrous ethanol and acetone for 15 to 25 minutes, and then placed in a drying oven for drying.

4. The method of introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath according to claim 1, characterized in that: In step S1, the plating solution is prepared by dissolving nickel sulfate hexahydrate and potassium hydroxide in deionized water respectively to obtain nickel sulfate hexahydrate with a concentration of 0.8-1.2 mol / L and potassium hydroxide solution with a concentration of 0.8-1.2 mol / L, and mixing the two in a volume ratio of 10:1 to obtain a plating solution.

5. The method of introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath according to claim 1, characterized in that: In step S1, the conditions of the first heat treatment are as follows: placing the conductive glass deposited with the nickel hydroxide film in a box-type resistance furnace, heating it to 300-400°C at a heating rate of 5-10°C / min, keeping the temperature constant for 1-3h, and depositing a nickel oxide homogeneous template layer after cooling.

6. The method of introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath according to claim 1, characterized in that: In step S1, the nickel oxide homogeneous template layer is deposited to a thickness of 120-240 nm.

7. The method of introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath according to claim 1, characterized in that: In step S2, the precursor solution is prepared by dissolving nickel sulfate hexahydrate and potassium persulfate in deionized water respectively to obtain 0.6-0.7 mol / L nickel sulfate hexahydrate solution and 0.2-0.3 mol / L potassium persulfate solution, and then mixing the two in a volume ratio of 1:1 and stirring to obtain a precursor solution.

8. The method of introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath according to claim 1, characterized in that: In step S2, the precursor solution needs to be placed in a water bath and stirred at a constant temperature, the water bath temperature is 20-40°C, and the stirring rate is 300-500r / min; after chemical bath deposition, the film layer is taken out and rinsed with deionized water, the polyimide tape is removed, and it is dried at 50-80°C for 1-3h, and then a second heat treatment is performed.

9. The method of introducing a homogeneous template layer to improve the electrochromic cycle stability of nickel oxide thin films prepared by chemical bath according to claim 1 or 8, characterized in that: In step S2, the conditions of the second heat treatment are: heating to 250-350°C at a heating rate of 5-10°C / min, keeping the temperature for 1-2 hours, and cooling to obtain a nickel oxide film.

10. A nickel oxide film with good electrochromic cycle stability, characterized in that: The nickel oxide film is prepared by the method according to any one of claims 1 to 9.

Images