Preparation method of ultrafine nickel oxide nanoparticles and application thereof

Abstract

This invention relates to the field of nanomaterials and photovoltaic devices, specifically a method for preparing ultrafine nickel oxide nanoparticles, comprising the following steps: weighing Ni(NO3)2·6H2O into a beaker, adding deionized water, preparing a nickel nitrate solution with a concentration of 3-5 mol / L, adding ammonia dropwise to the solution until the pH value of the solution is 9-10, obtaining a deep blue mixed solution; centrifuging the mixed solution with deionized water, repeating this process three times to obtain a uniform green colloidal precipitate; drying the colloidal precipitate in a freeze dryer for 6-24 hours, removing it, grinding it into powder, and calcining it in a muffle furnace to obtain black nickel oxide nanoparticles. The prepared ultrafine nickel oxide nanoparticles have small size and good solution dispersibility, and can be used to prepare flat and dense hole transport layer films, showing good application prospects in the field of perovskite solar cells.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials and photovoltaic devices, specifically to a method for preparing ultrafine nickel oxide nanoparticles and their applications. Background Technology

[0002] Perovskite solar cells have attracted much attention due to their low manufacturing cost and excellent electronic performance. In recent years, the photoelectric conversion efficiency of perovskite solar cells has exceeded 26%, making them comparable to crystalline silicon solar cells and accelerating the commercialization wave. Inverted perovskite solar cells may be more valuable than nip perovskite solar cells because the former have easily mitigated hysteresis and long-term durability, making them more suitable for commercial development.

[0003] Hole transport materials in perovskite devices perform functions such as transporting holes, blocking electron reverse injection, and suppressing charge accumulation and nonradiative recombination, thereby reducing carrier quenching and improving charge extraction and transport capabilities. Excellent hole transport materials must possess characteristics such as energy level matching, high transport capacity, and good thermochemical stability. Although inverted perovskite solar cells have high photoelectric conversion efficiency, the initially used doped or organic hole transport materials (such as PTAA and PEDOT:PSS) suffer from poor stability, large batch variations, high cost, and thermal degradation, limiting their commercial application. Inorganic P-type semiconductors (such as CuSCN and NiOX) are expected to replace them due to their high stability, strong carrier mobility, and low cost. Among them, undoped NiOx has been widely studied as an inorganic hole transport material for inverted PSCs due to its wide bandgap (>3.5 eV), energy-friendly energy level alignment with most perovskite photoactive layers, and stable chemical properties. Common methods for preparing nickel oxide include the sol-gel method and solution combustion method. Nickel oxide nanoparticles used as hole transport materials in perovskite solar cells are mostly prepared by the sol-gel method. The current common preparation method uses NaOH as a precipitant and precipitates the colloidal particles in an oven. However, this method has drawbacks: the strong alkaline precipitant makes the reaction rate too fast, and the particle size of the product is difficult to control and tends to be large; high-temperature drying in a vacuum oven will aggravate the agglomeration of nanoparticles, resulting in larger particle sizes and making the product difficult to disperse.

[0004] Therefore, it is urgent to find a technical route for preparing nickel oxide nanoparticles that are small in size, not prone to agglomeration, simple to prepare, and low in cost. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing ultrafine nickel oxide nanoparticles and their application, solving the problems of large particle size and difficulty in dispersing agglomerated nanoparticles.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing ultrafine nickel oxide nanoparticles, comprising the following steps: S1. Weigh Ni(NO3)2·6H2O into a beaker and prepare a nickel nitrate solution with a concentration of 3-5 mol / L. Add ammonia water dropwise to the solution until the pH value of the solution is 9-10, and a dark blue mixed solution is obtained. S2. The resulting dark blue mixed solution was centrifuged with deionized water. This process was repeated three times to obtain a uniform green colloidal precipitate. The centrifuge speed was 5000-10000 rpm / min and the centrifugation time was 3-10 minutes. S3. Place the green colloidal precipitate in a freeze dryer and dry it for 6 to 24 hours. The cold trap temperature of the freeze dryer is -60 to -110°C. After removing it, grind it into powder using a grinder. S4. The obtained powder is transferred to a crucible and placed in a muffle furnace for calcination to obtain black nickel oxide nanoparticles. The calcination temperature of the muffle furnace is 250-270℃ and the calcination time is 0.5-2 hours.

[0007] Preferably, a method for preparing a nickel oxide hole transport layer includes the following steps: S1. Weigh nickel oxide nanoparticles, disperse them in deionized water, and then treat them with ultrasound to obtain a nano nickel oxide dispersion. S2. Coat the nano-nickel oxide dispersion onto the substrate and anneal it to obtain a nickel oxide hole transport layer. The annealing temperature is 100-150℃ and the annealing time is 10-30 minutes.

[0008] Preferably, a perovskite solar cell comprises, from bottom to top, a substrate material with an anode layer, a hole transport layer, a perovskite photoactive layer, an electron transport layer, and a cathode, to obtain a perovskite solar cell device with a nickel oxide thin film as the hole transport layer.

[0009] Preferably, a method for fabricating a perovskite solar cell includes the following steps: S1. First, the substrate material is ultrasonically cleaned sequentially with cleaning agent, deionized water and ethanol, and then placed in an oven to dry and store. S2. Place the cleaned and dried substrate material in an ultraviolet ozone generator for activation treatment; S3. Weigh out nickel oxide nanoparticles and disperse them in deionized water, and then treat them with ultrasound to obtain a nickel oxide nanoparticle dispersion. Coat the dispersion on a substrate and anneal it to obtain a nickel oxide hole transport layer. The concentration of the nickel oxide nanoparticle dispersion is 10-25 mg / mL. S4. Coat the perovskite precursor solution onto the nickel oxide hole transport layer obtained in S3, and inject antisolvent before the coating is finished. Anneal the obtained perovskite mesophase wet film at 100-150℃ for 10-30 minutes to obtain the perovskite photoactive layer. S5. Coating PC61BM onto the obtained perovskite photoactive layer to obtain an electron transport layer; S6. Electron beam evaporation is performed on the obtained electron transport layer to deposit a cathode (Ag), with the thickness of the deposited top electrode layer being 80–130 nm.

[0010] This invention provides a method for preparing ultrafine nickel oxide nanoparticles and their applications. It has the following beneficial effects: 1. This invention uses a weak base as a precipitant to reduce the agglomeration effect of precursor precipitation by forming an ammonium nickel complex intermediate phase during the reaction process, and uses a freeze dryer instead of a vacuum drying oven to obtain ultrafine, highly dispersed nickel oxide nanoparticles. The resulting nanoparticles are smaller in size and have no agglomeration effect.

[0011] 2. In the technical route of this invention, the concentration of nickel precursor is much higher than that of the prior art, thus the yield of nickel oxide is higher, which is of great significance for the large-scale production of nickel oxide nanoparticles in the future.

[0012] 3. This invention prepares a hole transport layer using nickel oxide, which can significantly improve the uniformity of nickel oxide film formation and the carrier transport efficiency, effectively improving the photoelectric conversion efficiency of perovskite solar cells, and has broad application prospects in the field of perovskite solar cells. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the stacked structure of the perovskite solar cell device of the present invention; Figure 2 The X-ray diffraction pattern of nickel oxide nanoparticles prepared in Example 1 of this invention; Figure 3 The X-ray photoelectron spectrum of the nickel oxide nanoparticles prepared in Example 1 of this invention is shown below. Figure 4 TEM images of nickel oxide nanoparticles prepared in Example 1 of this invention and comparative example TEM images; Figure 5 The image shows a (1 μm) SEM image of the surface of the nickel oxide film obtained in Example 1 of the present invention, where a is an aqueous dispersion of nickel oxide nanoparticles with a concentration of 10 mg / mL, b is an aqueous dispersion of nickel oxide nanoparticles with a concentration of 15 mg / mL, c is an aqueous dispersion of nickel oxide nanoparticles with a concentration of 20 mg / mL, and d is an aqueous dispersion of nickel oxide nanoparticles with a concentration of 25 mg / mL. Figure 6The image shows a (500nm) SEM image of the surface of the nickel oxide film obtained in Example 1 of the present invention, where a is an aqueous dispersion of nickel oxide nanoparticles with a concentration of 10 mg / mL, b is an aqueous dispersion of nickel oxide nanoparticles with a concentration of 15 mg / mL, c is an aqueous dispersion of nickel oxide nanoparticles with a concentration of 20 mg / mL, and d is an aqueous dispersion of nickel oxide nanoparticles with a concentration of 25 mg / mL. Figure 7 This is a comparison chart of the dispersibility test results of the nickel oxide dispersant prepared in Example 2 of the present invention; Figure 8 The photocurrent-voltage curves are shown for the perovskite solar cells prepared using nickel oxide as the hole transport layer in Example 2 of this invention and the comparative example of nickel oxide. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Example 1: like Figure 2-6 As shown in the figure, this invention provides a method for preparing ultrafine nickel oxide nanoparticles, comprising the following steps: S1. Weigh Ni(NO3)2·6H2O into a beaker, add deionized water, mix and stir until completely dissolved to obtain a nickel nitrate solution with a concentration of 5 mol / L, and add ammonia water dropwise to the solution until the pH value of the solution is 10, to obtain a dark blue mixed solution; S2. The mixed solution was centrifuged with deionized water. This step was repeated 3 times to obtain a uniform green colloidal precipitate. S3. Place the obtained green colloidal precipitate into a freeze dryer and dry it for 18 hours at a cold trap temperature of -80℃. After freeze drying, take it out and grind it into powder using a grinder. S4. The obtained powder was transferred to a crucible and placed in a muffle furnace and calcined at 270°C for 2 hours to obtain black nickel oxide nanoparticles.

[0016] Figure 2The X-ray diffraction pattern of the nickel oxide nanoparticles prepared in this embodiment shows three diffraction angles of 37.14°, 43.16°, and 62.68°, consistent with standard card #47-1049, indicating that the product is a pure phase without impurities. The three diffraction peaks correspond to the (111), (200), and (220) crystal planes, indicating that the nickel oxide nanoparticles used in this invention have a typical cubic structure and good crystallinity. Furthermore, the significant broadening of the diffraction peaks indicates that the product particle size is very small.

[0017] Figure 3 The image shows the X-ray photoelectron spectrum of the nickel oxide nanoparticles prepared in this embodiment. The XPS peak centered at 853.96 eV corresponds to the Ni-O bond in the octahedral structure. 2+ 2p 3 / 2 The XPS peak centered at 855.56 eV is attributed to Ni vacancies. 3+ The peak appearing at 861.30 eV is Ni 2p 3 / 2 The satellite peaks in the orbit indicate that the Ni to O content in nickel oxide nanoparticles does not conform to a specific stoichiometric ratio, denoted as NiO. X Moreover, Ni 3+ / Ni 2+ Changes in the ratio will significantly affect the conductivity of the thin film. The conductivity of nickel oxide is due to the Ni generated by vacancies in the crystal structure. 3+ Ni₂O₃ has a higher electrical conductivity than NiO, therefore Ni 3+ The concentration of NiO determines X The key to thin film conductivity. Calculations show that NiO... x Ni in nanoparticles 3+ / Ni 2+ The value is approximately 4.27, indicating that NiO x Ni in nanoparticles 3+ It has a high concentration, therefore it has good conductivity.

[0018] Figure 4 The image shows a TEM image of the nickel oxide nanoparticles prepared in this embodiment. The image shows that the nickel oxide nanoparticles are smaller than 5 nm, uniformly distributed, and without agglomeration. The comparative example shows a TEM image of nickel oxide particles prepared using sodium hydroxide as a precipitant; the image shows obvious agglomeration of the nickel oxide particles.

[0019] The method for preparing a nickel oxide hole transport layer based on nickel oxide nanoparticles includes the following steps: S1. First, the FTO conductive glass is ultrasonically cleaned with cleaning agent, deionized water and ethanol in sequence, and then placed in an oven to dry at 70°C. Then, the FTO conductive glass is activated in an ultraviolet ozone generator for 15 minutes before use. S2. Weigh 10-25 mg of the nickel oxide nanoparticles prepared in this example, disperse them in 1 mL of deionized water, prepare aqueous dispersions with concentrations of 10 mg / mL, 15 mg / mL, 20 mg / mL and 25 mg / mL respectively, and then perform ultrasonic treatment for 10 min to obtain nano nickel oxide dispersions. S3. The nano-nickel oxide dispersion was coated onto FTO conductive glass in air at a rotation speed of 4000 rpm / s for 30s. Finally, the FTO conductive glass was annealed at 100℃ for 15min to obtain the nickel oxide hole transport layer.

[0020] The nickel oxide thin film was analyzed using a scanning electron microscope, and its scanning electron microscope images were obtained, such as... Figure 5 , Figure 6 As shown. By Figure 5 It can be seen that the prepared nickel oxide film is dense, flat, and uniformly distributed on the surface of the substrate material; Figure 6 It can be seen that the thickness of the nickel oxide film can be adjusted by adjusting the concentration of the nano nickel oxide dispersion.

[0021] Example 2: like Figure 1 and Figure 7-8 As shown in the figure, this invention provides a method for preparing ultrafine nickel oxide nanoparticles, comprising the following steps: S1. Weigh Ni(NO3)2·6H2O into a beaker, add deionized water, mix and stir until completely dissolved to obtain a nickel nitrate solution with a concentration of 3 mol / L, and add ammonia water dropwise to the solution until the pH value of the solution is 9.5, to obtain a dark blue mixed solution; S2. The mixed solution was centrifuged with deionized water. This step was repeated 3 times to obtain a uniform green colloidal precipitate. S3. The obtained green colloidal precipitate was placed in a freeze dryer and an oven for drying. The drying time in the freeze dryer was 12 hours and the cold trap temperature was -100℃. The drying temperature in the oven was 70℃ and the drying time was 8 hours. After drying, the precipitate was taken out and ground into powder using a grinder. S4. The obtained powder was transferred to a crucible and placed in a muffle furnace and calcined at 260°C for 2 hours to obtain black nickel oxide nanoparticles.

[0022] Equal masses of nickel oxide nanoparticles obtained by different drying methods were weighed and dispersed in the same volume of deionized water to prepare an aqueous dispersion. After ultrasonic treatment for 10 min, a nano-nickel oxide dispersion was obtained.

[0023] Figure 7This example demonstrates the dispersibility test of nickel oxide nanoparticle dispersions prepared using two different drying methods. After standing for 24 hours, the nickel oxide nanoparticles dried in an oven showed obvious stratification, while the nickel oxide nanoparticles prepared by freeze drying remained uniformly dispersed. This indicates that the nickel oxide nanoparticles dried in the oven exhibited significant agglomeration.

[0024] The method for fabricating perovskite solar cells based on nickel oxide nanoparticles includes the following steps: S1. First, the FTO conductive glass is ultrasonically cleaned with cleaning agent, deionized water and ethanol in sequence, and then placed in an oven to dry at 70°C. Then, the FTO conductive glass is activated in an ultraviolet ozone generator for 15 minutes before use. S2. Weigh the nano nickel oxide dispersion prepared above, treat it with ultrasound, and then coat it on FTO conductive glass with a spin coater to obtain a nickel oxide hole transport layer. The coating speed is 3000 rpm / s and the coating time is 30s. S3. Take an appropriate amount of perovskite precursor and drop it onto the nickel oxide hole transport layer. Before the coating is finished, inject an anti-solvent and heat-anneal the obtained perovskite mesophase wet film to obtain a perovskite photoactive layer with a thickness of 500 nm. S4. Coat the perovskite photoactive layer with PC at a concentration of 15 mg / mL. 61 An electron transport layer was obtained using a BM chlorobenzene solution; finally, an 80 nm silver electrode was vacuum-deposited on top of the electron transport layer to complete the fabrication of the perovskite solar cell. A schematic diagram of the stacked structure of the perovskite solar cell device is shown below. Figure 1 As shown, from bottom to top, they are FTO / NiOx / Perovskite / PC 61 BM / Ag.

[0025] Figure 8 The figures show the photocurrent-voltage curves of perovskite solar cells fabricated using nickel oxide as the hole transport layer in this embodiment and the comparative embodiment. The open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) of the devices are 1.19 V, 23.76 mA / cm², and 1.19 V, 23.76 mA / cm², respectively. 2 The efficiency of the battery is 79.33%, with a final photoelectric conversion efficiency of 22.43%. In contrast, the efficiency of the battery based on comparative nickel oxide is only 19.09%.

[0026] Comparative example: The comparative examples of this invention adopt the paper "Pinhole-Free and Surface-Nanostructured NiOx Film by Room-Temperature Solution Process for High-Performance Flexible Perovskite SolarCells with Good Stability and Reproducibility" proposed by Zhang Hong, Jiaqi Cheng et al. in ACS Nano (American Chemical Society Nano), Vol. 10, 2016, pp. 1503-1511.

[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing ultrafine nickel oxide nanoparticles, characterized in that: Includes the following steps: S1. Weigh Ni(NO3)2·6H2O into a beaker and prepare a nickel nitrate solution with a concentration of 3-5 mol / L. Add ammonia water dropwise to the solution until the pH value of the solution is 9-10, and a dark blue mixed solution is obtained. S2. The resulting dark blue mixed solution was centrifuged with deionized water. This process was repeated three times to obtain a uniform green colloidal precipitate. S3. Place the green colloidal precipitate in a freeze dryer and dry it for 6 to 24 hours. After removing it, grind it into powder using a grinder. S4. The obtained powder is transferred to a crucible and placed in a muffle furnace for calcination to obtain black nickel oxide nanoparticles.

2. The method for preparing ultrafine nickel oxide nanoparticles according to claim 1, characterized in that: In step S2, the centrifuge speed is 5000-10000 rpm / min, and the centrifugation time is 3-10 minutes.

3. The method for preparing ultrafine nickel oxide nanoparticles according to claim 1, characterized in that: In step S3, the cold trap temperature of the freeze dryer is -60 to -110°C.

4. The method for preparing ultrafine nickel oxide nanoparticles according to claim 1, characterized in that: In step S4, the calcination temperature of the muffle furnace is 250–270°C, and the calcination time is 0.5–2 hours.

5. The application of nickel oxide nanoparticles prepared by the method according to any one of claims 1 to 4 in the nickel oxide hole transport layer of a perovskite solar cell.

6. A method for preparing a nickel oxide hole transport layer, characterized in that: Includes the following steps: S1. Weigh nickel oxide nanoparticles, disperse them in deionized water, and then treat them with ultrasound to obtain a nano nickel oxide dispersion. S2. Coat the nano-nickel oxide dispersion onto the substrate and anneal it to obtain a nickel oxide hole transport layer. The annealing temperature is 100-150℃ and the annealing time is 10-30 minutes.

7. A perovskite solar cell, characterized in that: The perovskite solar cell consists of a substrate material with an anode layer, a hole transport layer, a perovskite photoactive layer, an electron transport layer, and a cathode stacked sequentially from bottom to top, resulting in a perovskite solar cell device with a nickel oxide thin film as the hole transport layer.

8. The method for preparing a perovskite solar cell according to claim 7, characterized in that: Includes the following steps: S1. First, the substrate material is ultrasonically cleaned sequentially with cleaning agent, deionized water and ethanol, and then placed in an oven to dry and store. S2. Place the cleaned and dried substrate material in an ultraviolet ozone generator for activation treatment; S3. Weigh out nickel oxide nanoparticles and disperse them in deionized water, and then treat them with ultrasound to obtain a nickel oxide nanoparticle dispersion. Coat the dispersion on a substrate and anneal it to obtain a nickel oxide hole transport layer. The concentration of the nickel oxide nanoparticle dispersion is 10-25 mg / mL. S4. Coat the perovskite precursor solution onto the nickel oxide hole transport layer obtained in S3, and inject antisolvent before the coating is finished. Then, perform thermal annealing on the obtained perovskite mesophase wet film to obtain the perovskite photoactive layer. S5. Coat the obtained perovskite photoactive layer with PC. 61 BM obtains an electron transport layer; S6. Electron beam evaporation is performed on the obtained electron transport layer to deposit a cathode (Ag).

9. The method for preparing a perovskite solar cell according to claim 8, characterized in that: In step S4, the obtained perovskite mesophase wet film is annealed at 100-150°C for 10-30 minutes to obtain a perovskite photoactive layer.

10. The method for preparing a perovskite solar cell according to claim 8, characterized in that: In step S6, the thickness of the top electrode layer deposited by vapor deposition is 80–130 nm.

Images