Preparation method and application of nickel oxide nanocrystalline particle with core-shell structure

Abstract

The invention discloses a preparation method and application of nickel oxide nanocrystalline particles with core-shell structures. The core-shell structure particle is composed of a core and a shell wrapping the core, the core is a nickel oxide nanocrystalline particle, and the material of the shell is selected from at least one of metal, metal nitride, metal sulfide, metal oxide and non-metal oxide. The preparation method comprises the following steps: firstly, preparing nickel oxide nanocrystalline particles as a core by adopting a chemical precipitation method, then depositing a coating layer on the core by adopting an atomic layer deposition method, and enabling the coating layer to have controllable thickness and uniform coverage on the core. The coating layer can passivate surface defects of the nickel oxide, fix surface charges of the nickel oxide and inhibit a surface oxidation-reduction reaction of the nickel oxide, and is beneficial to improvement of electrical properties and stability of the nickel oxide. The obtained nickel oxide nanocrystalline particles with the core-shell structure have the advantages of simplicity and convenience in synthesis, mild reaction conditions, uniform coating layer, controllable thickness, good electrical properties, high damp-heat stability and the like, and have strong application potential in the fields of catalysts, sensors, electrochemistry, solar cells and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of new material preparation, and particularly relates to a preparation method and application of nickel oxide nanocrystal particles with a core-shell structure. Background Art

[0002] Nickel oxide nanocrystal particles have the characteristics of low cost, easy availability of raw materials, suitable valence band, high stability, etc. Pure stoichiometric NiO is an insulator at room temperature. However, in the actual synthesis process, nickel oxide is in a non-stoichiometric state, denoted as NiOx. Since there is no space in the structure to accommodate the excess oxygen, nickel vacancies are usually generated. These excess vacancies endow it with p-type semiconductor properties and are widely used in the preparation of catalytic materials, sensing materials, electrode materials, and hole transport layer materials for solar cells, etc. However, there are still the following problems with current nickel oxide nanocrystal materials: 1) The conductivity of NiOx materials is related to the defect density. Limited by the number of defects, the conductivity of NiOx is generally lower than that of organic materials, resulting in poor conductivity; 2) The defects on the surface of NiOx will also cause adverse reactions to occur, providing reaction sites for adverse reactions and reducing the catalytic performance, electrical transport performance, and stability of the materials; 3) It has been found in the research that the Ni ions in the high valence state in the NiOx thin film are prone to redox reactions, which will not only degrade the reaction layer but also bring an additional decomposition risk to the NiOx layer, accelerating the attenuation of the performance of the materials and devices.

[0003] Therefore, to solve this series of problems, developing a more stable NiOx nanocrystal material is the current research focus. New passivation strategies and materials are redesigned to perfectly improve the catalytic performance, electrical properties, and stability of nickel oxide materials. Core-shell structure materials have special structural characteristics, consisting of a core material and a coating shell material, and combining the characteristics of both internal and external materials. The core material plays a major role as the main material, and the shell material acts as a coating layer to play a modifying and protecting role. In this study, a coating layer is deposited on the surface of nickel oxide nanocrystal particles by atomic layer deposition to obtain nickel oxide nanocrystal particles with a core-shell structure, which are used to prepare the hole transport layer in perovskite solar cells. The role of the shell, i.e., the coating layer, is to passivate the inherent defects on the surface of nickel oxide nanocrystal particles and construct a field-effect passivation to form an electrostatic field effect at the interface. This kind of nickel oxide nanocrystal particles with a core-shell structure is beneficial to improving the conductivity and stability of nickel oxide thin films, and reducing adverse reactions on the surface and interface by suppressing surface defects. Finally, the optoelectronic performance and long-term stability of perovskite solar cells are improved. It further verifies the strong application potential of this core-shell structured nickel oxide nanocrystal material in fields such as catalysts, sensors, electrochemistry, and solar cells. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the technical problem to be solved by the present invention is to prepare nickel oxide nanocrystal particles with a core-shell structure, which consists of nickel oxide nanocrystals as the core material and at least one of other metal, metal nitride, metal sulfide, metal oxide, and non-metal oxide materials as the shell material. The expected core-shell structured nickel oxide nanocrystal particles have fewer surface defects and higher stability. Such core-shell structured nickel oxide nanocrystal particles can be used to prepare a nickel oxide thin film as a hole transport layer to solve the problems of more surface defects in the nickel oxide thin film and easy occurrence of redox reactions at the interface, resulting in device instability, and to improve the device performance and stability of perovskite solar cells. Finally, the purpose of the present invention is to provide a preparation and application of core-shell structured nickel oxide nanocrystal particles.

[0005] In order to achieve the above object, the technical solution adopted in this experiment is as follows:

[0006] In order to obtain core-shell structured nickel oxide nanocrystal particle materials, nickel oxide nanocrystal particle materials need to be synthesized first, including the following steps: S1 synthesis of nickel hydroxide, S2 washing of nickel hydroxide, S3 drying of nickel hydroxide, and S4 calcination of nickel hydroxide. After the above steps, black NiOx nanocrystal particles are finally obtained.

[0007] Secondly, the synthesis of core-shell structured nickel oxide nanocrystal particles: Transfer the synthesized nickel oxide powder into the ALD reaction chamber and deposit an ultrathin Al2O3 film on its surface for coating, which requires six steps:

[0008] S1: First, place the NiOx powder in the ALD cavity;

[0009] S2: Introduce TMA. The -CH3 on TMA reacts with the -OH on the particle surface to form O-Al-CH3;

[0010] S3: Pump out the unreacted TMA and by-product CH4;

[0011] S4: Introduce H2O. H2O reacts with Al-CH3 on the substrate surface to form A1-OH;

[0012] S5: Pump out the unreacted H2O and by-product CH4;

[0013] S6: Introduce TMA again to start a new cycle. Repeat this step until an ultrathin Al2O3 with the required thickness is deposited on the surface of the nickel oxide powder to form an ultrathin Al2O3 coating layer, and coated NiOx nanocrystal particles are obtained.

[0014] Finally, prepare the core-shell structured nickel oxide nanocrystal particles into a core-shell structured nickel oxide thin film and apply it to the preparation of a perovskite solar cell, including the following steps:

[0015] S1: Cleaning of the ITO conductive substrate: The ITO substrate is first ultrasonically cleaned with a glass cleaning agent for 30 min, then ultrasonically cleaned with deionized water for 30 min, and then the ITO substrate is placed in an IPA solution and ultrasonically cleaned for 30 min, repeating twice. Finally, the ITO substrate is dried with a nitrogen gun and subjected to ozone treatment for 20 min before coating.

[0016] S2: Preparation of the core-shell structured nickel oxide layer: 20 mg of core-shell structured NiO X nanocrystals are dispersed in 1 ml of H2O to obtain a core-shell structured NiO X nanocrystal solution. The solution is spin-coated on the ITO substrate at a speed of 2000 rpm for 30 s to obtain a core-shell structured nickel oxide nanocrystal thin film.

[0017] S3: Preparation of the self-assembled molecular layer: 0.5 mg of Me-4PACz is dissolved in 1 ml of EtOH to obtain a Me-4PACz solution. Then, in a nitrogen glove box, the Me-4PACz solution is spin-coated on the NiOx HTLs at a speed of 3000 rpm for 30 s, and then annealed at 100 °C for 10 min to obtain a self-assembled molecular layer.

[0018] S4: Preparation of the perovskite layer: 1.5 M Cs 0.1 MA 0.1 FA 0.8 Pb(I 0.6 Br 0.4 )3 and 15% mol of MACl are dissolved in 800 μL of DMF and 200 μL of DMSO to obtain a perovskite precursor solution. The perovskite precursor solution is spin-coated on the Me-4PACz thin film at a speed of 4000 rpm for 30 s, and the antisolvent is dropped on the perovskite thin film at the 5th second from the end, and annealed at 100 °C for 30 min.

[0019] S5: Preparation of the passivation layer: 1.0 mg of PEABr is dissolved in 1 mL of IPA to obtain a PEABr passivation layer solution. It is spin-coated on the perovskite layer at a speed of 4000 rpm for 30 s.

[0020] S6: Preparation of the electron transport layer: 10 mg of PCBM is dissolved in 1 ml of CB to obtain a PCBM solution. The PCBM solution is spin-coated on the film at a speed of 2000 rpm for 30 s. 1 mg mL -1 of the BCP solution is spin-coated at a speed of 4000 rpm for 30 s.

[0021] S7: Preparation of the electrode: Finally, a 100-nm-thick Ag electrode is thermally evaporated to obtain a complete perovskite solar cell.

[0022] As described above, the above is only the preferred specific embodiment of the present invention, and it is not a limitation to the protection scope of the present invention. Although the present invention has been described in detail with reference to the embodiments, for any person skilled in the art in this technical field, they can still make changes or substitutions to the technical solutions described in the above embodiments. However, all changes made based on the design principle of the present invention and non-creative labor shall fall within the protection scope of the present invention. Brief Description of the Drawings

[0023] Some specific embodiments of the present invention will be described in detail hereinafter with reference to the drawings in an exemplary rather than restrictive manner. The same reference numerals in the drawings denote the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale.

[0024] Figure 1 It is a schematic diagram of the coating morphology of the core-shell structured NiOx nanocrystals prepared according to Example 1 of the present invention;

[0025] Figure 2 It is a scanning electron microscope image of the core-shell structured NiOx nanocrystal particles prepared according to Example 1 of the present invention;

[0026] Figure 3 It is an X-ray energy spectrum analysis diagram of the core-shell structured NiOx nanocrystal particles prepared according to Example 1 of the present invention;

[0027] Figure 4 It is a high-resolution transmission electron microscope image of the core-shell structured NiOx nanocrystals prepared according to Example 1 of the present invention;

[0028] Figure 5 It is a transmission spectrum diagram of the perovskite thin films based on NiOx and the core-shell structured NiOx according to Example 2 of the present invention;

[0029] Figure 6 It is a photoluminescence (PL) spectrum diagram of the NiOx and the core-shell structured NiOx thin films according to Example 2 of the present invention;

[0030] Figure 7 It is a scanning electron microscope image of the core-shell structured NiOx thin film according to Example 2 of the present invention;

[0031] Figure 8 It is a scanning electron microscope image of the perovskite thin films based on NiOx and the core-shell structured NiOx according to Example 2 of the present invention;

[0032] Figure 9 It is an I-V curve diagram of the perovskite solar cell based on NiOx and the core-shell structured NiOx according to Example 4 of the present invention.

[0033] Figure 10 It is the I-V curve diagram of the perovskite solar cell based on NiOx and the core-shell structure NiOx after aging at 85 °C for 24 h according to Embodiment 4 of the present invention. Detailed implementation manners

[0034] The following details the specific implementation manners of the present invention. It should be understood that the specific implementation manners described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention. It should also be understood that the method steps and related data involved in this embodiment do not exclude the combination of other method steps and other data ratios that can be inserted in the middle. The endpoints and any values within the scope disclosed herein are not limited to the exact scope or value. These ranges or values should be understood to include values close to these ranges or values, and will also be regarded as the implementation scope of the present invention.

[0035] Embodiment 1: A preparation method of Al2O3-coated core-shell structure nickel oxide nanocrystals. The specific steps are as follows:

[0036] Preparation of Al2O3-coated core-shell structure nickel oxide nanocrystals: Transfer nickel oxide powder into the ALD reaction chamber and deposit an ultrathin Al2O3 coating on its surface, which requires six steps: 1) First, place the NiOx powder in the ALD cavity; 2) Introduce TMA. The -CH3 on TMA reacts with the -OH on the particle surface to generate O-Al-CH3; 3) Withdraw the unreacted TMA and the by-product CH4; 4) Introduce H2O. H2O reacts with the Al-CH3 on the substrate surface to generate A1-OH; 5) Withdraw the unreacted H2O and the by-product CH4; 6) Introduce TMA again to start a new cycle. Repeat this step until an ultrathin Al2O3 with the required thickness is deposited on the nickel oxide powder surface to form an ultrathin Al2O3 surface layer. Obtain Al2O3-coated core-shell structure nickel oxide nanocrystals. With the influence of different deposition thicknesses or other experimental conditions, it is expected that three different coating morphologies will appear, as Figure 1 shown, including thin film type, non-uniform type, and island type coatings. By observing the powder surface with a scanning electron microscope, it can be seen that it is composed of many stacked core-shell structure nickel oxide nanocrystals ( Figure 2 ). Further, perform X-ray energy spectrum analysis and testing on the powder. From the Figure 3 element proportion analysis, it can be known that the powder is composed of oxygen element, nickel element, and aluminum element, which can confirm the successful preparation of Al2O3-coated core-shell structure nickel oxide nanocrystals. Use a high-resolution transmission electron microscope to test the core-shell structure nickel oxide nanocrystal particles. From the Figure 4 it can be seen that the synthesized core-shell structure nickel oxide particles have a particle size of 5-10 nm, and there is a relatively blurred layered area outside the nickel oxide particles, which is the coating layer.

[0037] Example 2: A preparation method of a core-shell structured nickel oxide nanocrystal thin film for a hole transport layer. The specific steps are as follows:

[0038] Weigh 5 mg of core-shell structured nickel oxide nanocrystal particles on an electronic balance and add them into a screw-cap bottle. Add 1 mL of deionized water, disperse and shake well, and then ultrasonicate for 5 min. Filter the solution with a 0.22 μm filter head to obtain 5 mg mL -1 Core-shell structured nickel oxide nanocrystal precursor solution. Take 80 μL of the solution and drop it onto the cleaned ITO substrate, spin-coat it at a speed of 2000 rpm for 30 s, and no annealing is required to obtain a core-shell structured nickel oxide nanocrystal thin film. Perform ultraviolet-visible spectroscopy tests on the core-shell structured nickel oxide thin film to obtain the transmission spectrum of the core-shell structured nickel oxide thin film ( Figure 5 ). Comparing with the nickel oxide thin film, it can be found that the positions of the transmission peaks of the two are the same and the transmittance is very close, indicating that introducing a thin coating layer will not affect the transmittance of the thin film. Figure 6 The photoluminescence (PL) spectra of perovskite thin films with NiOx and core-shell structured NiOx as the substrate show the influence of core-shell structured NiOx nanocrystal particles on the PL intensity of perovskite thin films. It can be found that the PL intensity of the perovskite thin film with the core-shell structured NiOx as the substrate is the lowest, which indicates that the extraction ability of the core-shell structured NiOx thin film is greater than that of the NiOx thin film, reducing the recombination at the interface between the hole transport layer and perovskite. Figure 7 This is the scanning electron microscope image of the core-shell structured NiOx nanocrystal thin film. It can be seen that the surface of the formed thin film is flat and the core-shell structured NiOx nanocrystals are evenly distributed. Spin-coat the perovskite solution on the prepared NiOx thin film and core-shell structured NiOx thin film and anneal to obtain perovskite thin films. Perform scanning electron microscope tests on the samples to characterize the growth of perovskite thin films based on different substrates. From Figure 8 As shown, the left figure is the perovskite thin film on the NiOx substrate. After annealing, there are some cracks on the surface, which may be caused by thermal stress. These cracks will become the regions of carrier recombination and affect the device performance. While the perovskite thin film on the core-shell structured nickel oxide substrate in the right figure is relatively flat and compact without cracks. This is because the Al2O3 coating layer has a low coefficient of thermal expansion, reducing the generation of thermal stress in the thin film during the annealing process.

[0039] Example 3: Application of a core-shell structured nickel oxide nanocrystal hole transport layer in a normal bandgap perovskite solar cell. The specific steps are as follows: The ITO substrate is first ultrasonically cleaned with a glass cleaning agent for 30 min, then ultrasonically cleaned with deionized water for 30 min, and then the ITO substrate is put into an IPA solution and ultrasonically cleaned for 30 min, repeating twice. Finally, dry the ITO substrate with a nitrogen gun and perform ozone treatment for 20 min before starting to coat the film. The concentration is 10 mg mL -1The core-shell structured NiOx nanocrystals are dispersed in deionized water to form a core-shell structured NiOx solution. The prepared core-shell structured NiOx solution is spin-coated on an ITO substrate at a speed of 2000 rpm for 30 s, and then annealed at 150 °C for 30 min in ambient air. 0.5 mg of Me-4PACz is dissolved in 1 mL of EtOH to obtain a Me-4PACz solution. Then, in a nitrogen glove box, the Me-4PACz solution is spin-coated on the core-shell structured NiOx HTLs at a speed of 3000 rpm for 30 s, and then annealed at 100 °C for 10 min. 1.5 M Cs 0.05 FA 0.85 MA 0.1 PbI3 and 15% mol of MACl and 0.08% mol of ODADI are dissolved in 800 μL of DMF and 200 μL of DMSO to obtain a perovskite precursor solution. The perovskite precursor solution is spin-coated on the Me-4PACz film at a speed of 4000 rpm for 30 s, and the antisolvent is dropped on the perovskite film at the 5th second from the end, and annealed at 100 °C for 10 min. The surface passivation layer is prepared by dissolving a mixture of CF3-PEAI (2 mg mL -1 ) and MAI (1 mg mL -1 ) in a mixed solvent of IPA:DMF (volume ratio of 150:1), dynamically rotating on the prepared perovskite film at a speed of 5000 rpm for 30 s, and then annealing at 100 °C for 10 min. 20 mg of PCBM is dissolved in 1 mL of CB to obtain a PCBM solution, and then spin-coated on the film at a speed of 2000 rpm for 30 s. Then, 1 mg mL -1 BCP solution is spin-coated at a speed of 4000 rpm for 30 s. Finally, a 100-nm-thick Ag electrode is thermally evaporated to obtain a complete perovskite solar cell.

[0040] Example 4: Application of a core-shell structured nickel oxide nanocrystal hole transport layer in a wide-bandgap perovskite solar cell. The specific steps are as follows: The ITO substrate is first ultrasonically cleaned with a glass cleaner for 30 min, then ultrasonically cleaned with deionized water for 30 min, and then the ITO substrate is put into an IPA solution and ultrasonically cleaned for 30 min, repeating twice. Finally, the ITO substrate is dried with a nitrogen gun and subjected to ozone treatment for 20 min before film coating. 20 mg of coated NiOx nanocrystals are dispersed in 1 mL of deionized water to obtain a core-shell structured NiOx nanocrystal solution. The core-shell structured NiOx nanocrystal solution is spin-coated on the ITO substrate at a speed of 2000 rpm for 30 s. 0.5 mg of Me-4PACz is dissolved in 1 mL of EtOH to obtain a Me-4PACz solution. Then, in a nitrogen glove box, the Me-4PACz solution is spin-coated on the NiOx HTLs at a speed of 3000 rpm for 30 s, and then annealed at 100 °C for 10 min. 1.5MCs 0.1 MA 0.1 FA 0.8 Pb(I 0.6 Br 0.4 )3 and 15% mol of MACl are dissolved in 800 μL of DMF and 200 μL of DMSO to obtain a perovskite precursor solution. The perovskite precursor solution is spin-coated on the Me-4PACz film at a speed of 4000 rpm for 30 s, and the anti-solvent is dropped on the perovskite film at the 5th second from the end, and annealed at 100 °C for 10 min. 1.0 mg of PEABr is dissolved in 1 mL of IPA to obtain a PEABr passivation layer solution. Then, it is spin-coated on the perovskite layer at a speed of 4000 rpm for 30 s and annealed at 100 °C for 5 min. 20 mg of PCBM is dissolved in 1 mL of CB to obtain a PCBM solution. The PCBM solution is spin-coated on the film at a speed of 2000 rpm for 30 s. Then, 1 mg / mL -1 BCP solution is spin-coated at a speed of 4000 rpm for 30 s. Finally, a 100-nm-thick Ag electrode is thermally evaporated to obtain a complete perovskite solar cell. The I-V curves of the perovskite solar cells based on the NiOx film and the core-shell structured NiOx film are obtained through I-V testing ( Figure 9 ), and it can be seen that the device prepared with the coated NiOx film shows higher performance, Voc = 1.326 V, Jsc = 16.94 mA / cm 2 , FF = 83.50%, PCE = 18.53%. The device is placed on a hot stage at 85 °C for 24 hours for an aging experiment, and then I-V testing is carried out to obtain the I-V curve graph of the aged device, as shown in Figure 10It can be seen that the sample based on the core-shell structured NiOx thin film has higher thermal stability. This is because the coating layer protects the surface of the NiOx thin film, passivates the defects on the surface of the NiOx thin film, inhibits the degradation at the perovskite interface, and improves the stability of the device.

[0041] As described above, it is only the preferred specific implementation mode of the present invention, and it is not a limitation on the protection scope of the present invention. Although the present invention has been described in detail with reference to the embodiments, for any person skilled in the technical field, they can still make changes or substitutions to the technical solutions described in the above embodiments. However, all changes made based on the design principle of the present invention and non-creative labor shall fall within the protection scope of the present invention.

Claims

1. A nickel oxide nanocrystalline particle with a core-shell structure, consisting of a core and a shell covering the core.

2. The core-shell structured nickel oxide nanocrystalline particles according to claim 1, characterized in that: The shell material is selected from metals, metal oxides, metal nitrides, metal sulfides, non-metallic compounds, etc. that can protect and passivate the surface of nickel oxide particles. The metal is selected from at least one of Pt, Au, Ag, and Cu; the metal oxide is selected from at least one of SnO2, Al2O3, TiO2, and ZnO; the metal nitride is selected from at least one of CdN, AlN, and GaN; the metal sulfide is selected from at least one of ZnS, K2S, and MgS; the non-metallic compound is selected from at least one of SiO2, Si3N4, and SiF4.

3. The core-shell structured nickel oxide nanocrystalline particles according to claim 1, characterized in that: The average particle size of the core is 1-100 nm, preferably 5-50 nm, more preferably 5-10 nm.

4. The core-shell structured nickel oxide nanocrystalline particles according to claim 1, characterized in that: The average thickness of the shell is 0.1-100 nm, preferably 0.1-50 nm, more preferably 0.1-10 nm.

5. The core-shell structured nickel oxide nanocrystalline particles according to claim 1, characterized in that: The surface ratio of the shell layer covering the core nanoparticles is adjustable. Based on different application scenarios, the shell layer can be completely covered or partially covered. The preferred covering ratio is 20%-100%.

6. The preparation of the core-shell structured nickel oxide nanocrystalline particles according to claim 1 comprises the following steps: Firstly, high-quality nickel oxide nanocrystalline particles are prepared, and then, shell materials are coated and deposited on the nickel oxide nanocrystalline particles. Finally, nickel oxide nanocrystalline particles with a core-shell structure are obtained.

7. The method for preparing a core according to claim 6, characterized in that: The method for preparing nickel oxide nanocrystals includes at least one of a chemical precipitation method, an alcohol solvent method, a low-heat solid phase method, and the like.

8. The shell material coating method according to claim 6, characterized in that: The method for preparing the shell includes at least one of atomic layer deposition, chemical vapor deposition, electrochemical deposition, solution synthesis, and the like.

9. The use of the core-shell structured nickel oxide nanocrystalline particles prepared according to claim 6, characterized in that: An inverted perovskite solar cell based on core-shell structured nickel oxide nanocrystalline particles as hole transport layer material is prepared.

10. The core-shell structured nickel oxide nanocrystalline particles prepared according to claim 6 can be used in the fields of catalysts, sensors, electrochemistry, etc.

Images