A gradient nickel oxide thin film, a preparation method and application thereof

Abstract

The application discloses a gradient nickel oxide film and a preparation method and application thereof, and comprises the following steps: first, vacuumizing a reaction chamber, then putting a target material into the reaction chamber, inputting argon, and starting illumination, wherein the target material is a pure nickel target; then inputting oxygen, gradiently adjusting the oxygen content, adopting a reaction magnetron sputtering method to deposit sputtering on the target material in an argon and oxygen mixed gas atmosphere, setting sputtering power and deposition time, and obtaining the gradient nickel oxide film with gradiently changed surface oxygen content; compared with an existing chemical deposition method, the preparation method is stable in process and stable in component, the obtained nickel oxide film has a thickness of 10 nm, small crystal grains make the film have the best conductivity, the film can not only block the electrons in the absorption layer from going to a bottom electrode ITO layer, but also can guide away holes due to the good conductivity, so that invalid recombination is reduced, and finally the battery efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sputtering coating, in particular to a gradient nickel oxide film, a preparation method and application thereof. BACKGROUND

[0002] Among various hole transport materials, nickel oxide has been studied for high-efficiency and stable thin-film solar cells, especially perovskite solar cells. Traditional deposition methods are difficult to perform large-scale conformal deposition, and traditional processes use methods such as spin coating and chemical deposition. Secondly, most traditional hole transport materials use organic small molecule materials, which are more expensive than nickel oxide, and the film stability is poor due to unstable molecular weight between batches.

[0003] The contact layer is the region between the high recombination active conductive interface and the photon absorption layer, and plays the role of a hole transport layer. Due to the presence of a large number of pores and defects in the absorption layer, serious non-radiative recombination occurs. In order to further improve the conversion efficiency of the thin-film solar cell, it is crucial to reduce the recombination loss between the photon absorption layer and the contact. Nickel oxide with a wide band gap and good thermal stability is widely used as a hole transport layer. Due to the poor conductivity and low mobility of nickel oxide, people usually use ion doping methods to improve the electrical properties of nickel oxide. In addition to this, adjusting the oxygen content during the annealing process is another simple method to improve the electrical properties of nickel oxide. However, this method uses an oxygen atmosphere annealing process, which can only adjust the oxygen content on the surface of the film, and cannot adjust the oxygen content in the overall longitudinal structure of the nickel oxide film. In addition, the traditional nickel oxide film layer uses a spin-coated and annealed method to obtain nanocrystalline nickel oxide, and the thickness is generally more than 30 nm, which affects the photoelectric conversion efficiency.

[0004] Therefore, the existing nickel oxide film preparation method still needs to be further improved. SUMMARY

[0005] The present application provides a gradient nickel oxide film, a preparation method and application thereof, which solves the technical problems of weak stability and poor thickness of the existing nickel oxide film preparation method, resulting in poor transmittance.

[0006] To solve the above problems, the present application provides the following technical solutions:

[0007] On the one hand, the present application provides a preparation method of a gradient nickel oxide film, comprising the following steps:

[0008] First, the reaction chamber is evacuated, then the target material is placed in the reaction chamber, argon is introduced, and the glow is started. The target material is a pure nickel target.

[0009] Then oxygen is introduced again, the oxygen content is adjusted in gradient, and the gradient nickel oxide film with gradient change of surface oxygen content is obtained by depositing sputtering on the target material in an argon and oxygen mixed gas atmosphere by using a reactive magnetron sputtering method, and by setting sputtering power and deposition time.

[0010] The reactive magnetron sputtering method is to make the material to be deposited into a film into a target material placed in the cathode of a sputtering deposition system, to be sputtered into high vacuum after filling argon and specific reaction gas (such as oxygen, or no reaction gas); the plasma formed by ionization of the gas under high pressure is accelerated under the action of electric field and alternating magnetic field, and the atoms on the surface of the target material are separated from the original lattice and escape, and are deposited into a film on the substrate surface of the anode sample table. The characteristics of the magnetron sputtering are high film deposition rate, low substrate temperature, good film adhesion, and large-area film coating can be realized. By installing different materials in different target positions, different component film materials can be obtained by using multi-target magnetron sputtering. The relative content of the components in the thin film material prepared by this method is related to the deposition rate of the target material on the substrate in different target positions. The deposition rate of a certain component depends on the nature of the component itself, the sputtering power of the target position, and the distance between the center of the target material plane and the center of the deposition sample table. In this way, the relative content of the components in the film material can be adjusted by changing the sputtering power of the target position and the distance between the center of the target material plane and the center of the deposition sample table. These characteristics of the multi-target magnetron sputtering technology make it suitable for preparing gradient thin film materials.

[0011] On the basis of this technical solution, further preferably, the sputtering power is 40-60 W.

[0012] On the basis of this technical solution, further preferably, the deposition time is 1-1.5 minutes.

[0013] On the basis of this technical solution, further preferably, the oxygen content is changed from low to high in gradient.

[0014] On the basis of this technical solution, further preferably, the oxygen content is changed from low to high in gradient.

[0015] On the basis of this technical solution, further preferably, the pressure of the vacuum environment is less than 7×10 -4 Pa.

[0016] On the basis of this technical solution, further preferably, the oxygen partial pressure of the deposition is 0.5 Pa.

[0017] In a second aspect, the present application provides a gradient nickel oxide film prepared by the preparation method of the first aspect.

[0018] On the basis of this technical solution, further preferably, the thickness of the gradient nickel oxide film is 10-15 nm.

[0019] Thirdly, the present invention also provides an application of the gradient nickel oxide thin film described in the second aspect, a perovskite solar cell comprising a substrate, a selective contact layer, an absorber layer, an electron transport layer, a hole blocking layer, and an electrode, wherein the selective contact layer is the gradient nickel oxide thin film described in the second aspect.

[0020] Compared with the prior art, the technical effects achieved by the present invention include:

[0021] Compared with existing spin coating and chemical deposition methods, the magnetron sputtering method used in this invention can achieve uniform, conformal and scalable films. At the same time, the magnetron sputtering nickel oxide process is stable and the composition is stable, making it suitable for large-scale mass production.

[0022] This invention uses ultrathin nickel oxide, which is easy to prepare. The film thickness is only about 10nm, which does not have a significant impact on light transmission and preserves the transmittance to the maximum extent.

[0023] This invention employs reactive magnetron sputtering to prepare nickel oxide, resulting in an ultrathin nickel oxide film approximately 10 nanometers thick. A high-purity nickel target is used as the sputtering target. By adjusting the oxygen content in the argon-oxygen ratio from an initial 5% to 13%, a gradual transition from pure nickel to nickel oxide is achieved, ultimately forming an ultrathin nickel oxide film with a gradient oxygen content. As the oxygen content gradually increases, the nickel oxide grain size gradually decreases from 600 nm in diameter to approximately 50 nm. The small grain size allows the film to achieve optimal conductivity, on the order of tens of nanoamperes. This not only blocks electrons from the absorber layer to the substrate (ITO) but also allows for hole conduction, reducing ineffective recombination and ultimately contributing significantly to improved battery efficiency. As a selective contact layer for perovskite solar cells, the prepared ultrathin nickel oxide effectively maintains the film's transmittance and improves its conductivity, exhibiting excellent performance. Attached Figure Description

[0024] Figure 1 This is a conductive atomic force microscope (AFM) test image from Embodiment 5 of the present invention;

[0025] Figure 2 This is a conductivity AFM test diagram of Embodiment 6 of the present invention;

[0026] Figure 3 This is a graph showing the relationship between the size and oxygen content of the gradient nickel oxide thin film described in this invention.

[0027] Figure 4 This is a schematic diagram of the perovskite solar cell structure layer in Application Example 1 of the present invention;

[0028] Figure 5 This is a perovskite solar cell transmittance test diagram from Application Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the embodiments to be described are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work, based on the technology to which the claims of the present application belong, are within the protection scope of the present application.

[0030] It should be understood that the terms used in the specification of the embodiments of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the embodiments of the present application. As used in the specification and the appended claims of the present application, the singular forms "a", "an" and "the" are intended to include the plural forms, unless the context clearly indicates otherwise.

[0031] Embodiment 1

[0032] The embodiment provides a preparation method of a gradient nickel oxide film, and specifically comprises the following steps:

[0033] S1, first, vacuumize the reaction chamber to a pressure of 6x10 -4 Pa, then put the target material into the reaction chamber, introduce argon, and ignite, specifically including: pure argon atmosphere ignition, power is 60W, open the argon valve, the fixed gun head argon flow Ar2 = 60sccm, and the sputtering target is a pure nickel target;

[0034] S2, then start oxygen, open the oxygen valve and mass flowmeter, and gradient adjust the oxygen content, which can be adjusted from 5% to 15% by using a high-precision flowmeter, and the sputtering is deposited on the target material in an argon and oxygen mixed gas atmosphere by using a reaction magnetron sputtering method, the oxidation degree of the direct current sputtering pure nickel target increases with the increase of the oxygen content, and the total pressure is kept at 0.5Pa during the whole deposition process; adjust the sputtering power, and the deposition time is 1.5 minutes, so that the surface oxygen content gradient change gradient nickel oxide film with a total thickness of 14nm is obtained.

[0035] Results: In the process of preparing large-area devices, only the perovskite layer with a thickness of 100nm is suitable for being prepared by a solution method, and the charge transport layer has a thickness of only several tens of nanometers, so it is difficult to prepare a uniform and non-porous large-area charge transport layer by using a solution method at the present stage, and therefore the pressure is less than 7x10 -4 Pa, the vacuum deposition technology is more controllable, and is more suitable for preparing an ultrathin large-size film.

[0036] The sputtering power is 60W. On the one hand, a certain low power sputtering can ensure the possibility of oxygen gradient adjustment. On the other hand, a too fast sputtering rate cannot accurately adjust the gradient oxygen content. Therefore, a low power can ensure a slow growth rate, thereby giving sufficient gradient adjustment time in the sputtering process. The total deposition time of the 10 nm nickel oxide film is 1.5 minutes, which can effectively realize the gradual transition of the film from pure nickel to nickel oxide.

[0037] Example 2

[0038] The embodiment provides a preparation method of a gradient nickel oxide film, and specifically comprises the following steps.

[0039] S1, first vacuumize the reaction chamber to a pressure of 5*10 -4 Pa, then put the target material into the reaction chamber, introduce argon, and ignite, specifically including: pure argon atmosphere ignition, power is 40W, open the argon valve, and fix the argon flow Ar2=60sccm, the sputtering target is a pure nickel target;

[0040] S2, then start oxygen, open the oxygen valve and the mass flowmeter, and adjust the oxygen content from 3% to 15% using a high-precision flowmeter. The gradient nickel oxide film with a surface oxygen content gradient is obtained by using a reactive magnetron sputtering method to deposit sputtering on the target material in an argon and oxygen mixed gas atmosphere. The pure nickel target used in direct current sputtering is oxidized with the increase of oxygen content. The total pressure is kept at 0.5Pa during the whole deposition process. The deposition time is 1 minute, and the total thickness of the gradient nickel oxide film is 15nm.

[0041] Results: The sputtering power is 40W. On the one hand, a certain low power sputtering can ensure the possibility of oxygen gradient adjustment. On the other hand, a too fast sputtering rate cannot accurately adjust the gradient oxygen content. Therefore, a low power can ensure a slow growth rate, thereby giving sufficient gradient adjustment time in the sputtering process. The total deposition time of the 14 nm nickel oxide film is 1 minute, which can effectively realize the gradual transition of the film from pure nickel to nickel oxide.

[0042] Example 3

[0043] The embodiment provides a preparation method of a gradient nickel oxide film, and specifically comprises the following steps.

[0044] S1, first vacuumize the reaction chamber to a pressure of 5*10 -4 Pa, then put the target material into the reaction chamber, introduce argon, and ignite, specifically including: pure argon atmosphere ignition, power is 40W, open the argon valve, and fix the argon flow Ar2=60sccm, the sputtering target is a pure nickel target;

[0045] S2, then start oxygen, open the oxygen valve and mass flowmeter, gradient adjustment of oxygen content, from 5% to 15% using high precision flowmeter adjustment, using reactive magnetron sputtering method in argon and oxygen mixed gas atmosphere in the target material on the deposition of sputtering, direct current sputtering of pure nickel target with the increase of oxygen content and the increase of oxidation degree, the whole deposition process keeps the total pressure at 0.5Pa; adjust the sputtering power, the deposition time is 1.2 minutes, that is, the total thickness of the surface oxygen content gradient change of gradient nickel oxide film is 13nm.

[0046] Results: sputtering power of 60W, compared with example 2, a certain low power sputtering can ensure the possibility of oxygen gradient adjustment, because of the too fast sputtering rate, it is impossible to accurately adjust the gradient oxygen content, so low power can ensure slower growth rate, so as to give sufficient gradient adjustment time in the sputtering process, and the total deposition time of 13nm nickel oxide film is 1.2 minutes, which can effectively realize the gradual transition of the film from pure nickel to nickel oxide.

[0047] Example 4

[0048] The embodiment provides a preparation method of gradient nickel oxide film, which specifically comprises the following steps:

[0049] S1, first vacuumize the reaction chamber, vacuumize to 5*10 -4 Pa, put the target material into the reaction chamber, introduce argon, ignite, specifically including: pure argon atmosphere ignition, power is 60W, open the argon valve, fixed gun head argon flow Ar2=60sccm, the sputtering target is pure nickel target;

[0050] S2, then start oxygen, open the oxygen valve and mass flowmeter, gradient adjustment of oxygen content, from 7% to 15% using high precision flowmeter adjustment, using reactive magnetron sputtering method in argon and oxygen mixed gas atmosphere in the target material on the deposition of sputtering, direct current sputtering of pure nickel target with the increase of oxygen content and the increase of oxidation degree, the whole deposition process keeps the total pressure at 0.5Pa; adjust the sputtering power, the deposition time is 1.5 minutes, that is, the total thickness of the surface oxygen content gradient change of gradient nickel oxide film is 12nm.

[0051] Results: the oxygen content of 7% nickel oxide film, after the increase of oxidation degree, the total deposition time of 12nm nickel oxide film is 1.5 minutes, which can effectively realize the gradual transition of the film from pure nickel to nickel oxide.

[0052] Example 5

[0053] The embodiment provides a preparation method of gradient nickel oxide film, which specifically comprises the following steps:

[0054] S1, first vacuum the reaction chamber, vacuum to the pressure is 5*10 -4 Pa, then put the target material into the reaction chamber, introduce argon, ignite, specifically including: pure argon atmosphere ignition, power is 60W, open the argon valve, fixed gun head argon flow Ar2=60sccm, the sputtering target is pure nickel target;

[0055] S2, then start oxygen, open the oxygen valve and mass flowmeter, gradient adjust the oxygen content, from 2% to 15%, use high precision flowmeter to adjust, use reactive magnetron sputtering method to deposit sputtering on the target material in argon and oxygen mixed gas atmosphere, the oxidation degree of direct current sputtering pure nickel target increases with the increase of oxygen content, the total pressure is kept at 0.5Pa during the whole deposition process; adjust the sputtering power, the deposition time is 1.2 minutes, that is, the total thickness of the surface oxygen content gradient change gradient nickel oxide film is 15nm.

[0056] And select the gradient nickel oxide film prepared in example 5, conduct conductive AFM test on the gradient nickel oxide film.

[0057] The test results are shown in Figure 1 , it can be seen that Figure 1 the upper side corresponds to the morphology of nickel oxide film, which is common nanocrystalline, when the oxygen content is 2%, rectangular nanometer network structure begins to form; at the same time, Figure 1 the lower side gives the surface morphology of the prepared gradient nickel oxide film, it can be seen from the figure that the nickel oxide film prepared by the reactive magnetron sputtering method in this embodiment has uniform bright and dark distribution film structure, and the thickness of the bright part of the film surface is less than 15nm, with the increase of oxygen content, the bright part also begins to increase, which is composed of smaller grains, indicating that the gradient nickel oxide film has nanometer ultra-thin size.

[0058] Example 6

[0059] The embodiment provides a preparation method of gradient nickel oxide film, which specifically includes the following steps:

[0060] S1, first vacuum the reaction chamber, vacuum to the pressure is 5*10 -4 Pa, then put the target material into the reaction chamber, introduce argon, ignite, specifically including: pure argon atmosphere ignition, power is 60W, open the argon valve, fixed gun head argon flow Ar2=60sccm, the sputtering target is pure nickel target;

[0061] S2, then start oxygen, open the oxygen valve and mass flowmeter, gradient adjustment oxygen content, from 13% to 15% using high precision flowmeter adjustment, using reactive magnetron sputtering method in argon and oxygen mixed gas atmosphere in the target material on the deposition of sputtering, direct current sputtering of pure nickel target with the increase of oxygen content, the whole deposition process to maintain the total pressure of 0.5 Pa; adjust the sputtering power, the deposition time is 1 minute, that is, the total thickness of 10 nm of the surface oxygen content gradient change of gradient nickel oxide film.

[0062] And select the gradient nickel oxide film prepared in example 6, the battery is tested by conductive AFM.

[0063] The test results are shown in Figure 2 , it can be seen that Figure 2 the upper side corresponds to the morphology of the nickel oxide film, which is commonly seen in nanocrystalline form, and when the oxygen content is 13%, a rectangular nanometer network structure begins to form. At the same time, Figure 2 the lower side of the prepared gradient nickel oxide film gives the surface morphology, it can be seen from the figure that the nickel oxide film prepared by the reactive magnetron sputtering method in this embodiment has a uniform bright and dark distribution of film structure, and the thickness of the bright part of the film surface is less than 10 nm, and with the increase of oxygen content, the bright part gradually increases, which is composed of smaller grains, indicating that the gradient nickel oxide film has a nanometer ultra-thin size.

[0064] Figure 3 The size of the gradient nickel oxide film and the oxygen content relationship diagram, it can be seen that when the oxygen content is low, about 2%, the thickness of the nickel oxide film is about 600 nm; and after the gradient adjustment to 13%, the thickness of the nickel oxide film can be reduced to 50 m. Small grains can make the film layer have the best conductivity, about several nanometer order, on the one hand, it can block the absorption layer electrons to the bottom electrode ITO layer, on the other hand, it can ensure good conductivity to lead away the holes, thereby reducing the invalid recombination, and finally make a good contribution to improve the battery efficiency.

[0065] Application example 1

[0066] A perovskite solar cell, the structure layer is shown in Figure 4 , it can be seen that it is divided into electrode layer (Ag electrode), hole blocking layer, electron transport layer, absorption layer, selective contact layer (NiO x ) and substrate (ITO), wherein the gradient nickel oxide film prepared in example 1 is selected as the selective contact layer, and the perovskite solar cell is tested by transmittance and spectral absorption.

[0067] The test results are shown in Figure 5As shown, the gradient nickel oxide film of the embodiment can be used as a selective contact layer for a perovskite solar cell, and the transmittance is more than 85%, and the influence on spectral absorption of the thin film solar cell is very limited; and the nickel oxide film of the embodiment does not need to be prepared at high temperature, and has excellent conductivity, about several nanamperes.

[0068] In conclusion, the gradient nickel oxide film, the preparation method and the application of the embodiment can effectively keep the transmittance of the film layer and improve the conductivity of the layer by reacting the nickel oxide by the magnetron sputtering and precisely controlling the oxygen doping amount by the fine tuning valve; and the surface oxygen content of the ultra-thin nickel oxide prepared by the method changes in a gradient, and the performance of the nickel oxide film as a selective contact layer for a thin film solar cell is excellent.

[0069] The above only describes the preferred embodiments of the present application and should not be used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a gradient nickel oxide thin film, characterized in that, Includes the following steps: First, the reaction chamber is evacuated, then the target material is placed into the reaction chamber, argon gas is introduced, and the ignition is started. The target material is a pure nickel target. Oxygen is then introduced, and the oxygen content is adjusted by gradient. Reactive magnetron sputtering is used to deposit sputtering on the target in an atmosphere of argon and oxygen mixed gas. The sputtering power and deposition time are set to obtain the gradient nickel oxide film with a gradient change in surface oxygen content. The sputtering power is 40-60W; The deposition time is 1-1.5 minutes; The gradient adjustment of oxygen content is a change from low to high; The gradient adjustment range for oxygen content is 5%-13%; The total pressure within the reaction chamber was maintained at 0.5 Pa throughout the deposition process.

2. The method for preparing gradient nickel oxide thin films as described in claim 1, characterized in that, The vacuuming condition is that the vacuum level is less than 7 × 10⁻⁶. -4 Pa.

3. A gradient nickel oxide thin film, characterized in that, It is prepared by the preparation method according to any one of claims 1-2.

4. The gradient nickel oxide thin film as described in claim 3, characterized in that, The thickness of the gradient nickel oxide film is 10-15 nm.

5. A perovskite battery, characterized in that, It includes a substrate, a selective contact layer, an absorption layer, an electron transport layer, a hole blocking layer, and an electrode layer, wherein the selective contact layer is a gradient nickel oxide thin film as described in any one of claims 3-4.

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