Bismuth ferrite-based ferroelectric film photovoltaic device and preparation method thereof

Abstract

The invention discloses a bismuth ferrite-based ferroelectric film photovoltaic device and a preparation method thereof, and belongs to the technical field of preparation of photovoltaic devices.The method comprises the steps that glass with the surface plated with an FTO film serves as a substrate, a gold nanoparticle layer is sputtered on the FTO surface, and a first sample is obtained; spin-coating the SnO2 precursor solution on the first sample, and annealing to form a SnO2 film to obtain a second sample; spin-coating the BiFeO3 precursor solution on the second sample, forming a multi-layer BiFeO3-based ferroelectric film (BSFCO-g) through gradient doping, and annealing to form a functional layer with a gradient built-in electric field to obtain a third sample; spin-coating the third sample with the NiO precursor solution, and annealing to form a NiO layer to obtain a fourth sample; and plating a gold electrode on the fourth sample to obtain the bismuth ferrite-based ferroelectric film photovoltaic device. According to the invention, the energy conversion efficiency of the bismuth ferrite-based ferroelectric film photovoltaic device is greatly improved, so that the bismuth ferrite-based ferroelectric film photovoltaic device has better applicability and application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of photovoltaic devices, and particularly relates to a bismuth ferrite-based ferroelectric thin film photovoltaic device and a preparation method thereof. Background Art

[0002] As a direct and effective way to replace traditional fossil energy in the future, solar photovoltaic power generation technology has become a research hotspot in the new energy field and an important direction for building a modern energy system. Currently, the most widely used silicon-based solar cells have problems such as an energy conversion efficiency limit, a low open-circuit voltage, and a high unit power generation cost, which severely limit their large-scale application. At present, efforts are being made in this field to explore new types of photovoltaic cells and technologies. In the past two decades, the research hotspot of photovoltaic cells has mainly focused on low-cost and high-energy-conversion-efficiency organic perovskite solar cells (represented by CH3NH3PbI3). However, this type of solar cell has two major fatal defects: the decomposition of the organic component (CH3NH3-) leads to extremely poor performance of the battery device in a humid and hot environment (short service life), and the use of the toxic heavy metal element lead (Pb) does not meet the requirements of environmental protection.

[0003] Recently, the ferroelectric photovoltaic effect and devices based on bismuth ferrite (BiFeO3), which have a brand-new photovoltaic power generation mechanism, have attracted wide attention. In ferroelectric photovoltaic devices, the built-in electric field induced by ferroelectric polarization and penetrating the entire ferroelectric semiconductor can efficiently separate photo-generated carriers, thereby obtaining a huge open-circuit voltage V that far exceeds its bandgap width E g of OC(It can be up to dozens of volts). Theoretical simulation calculations show that: Based on this special mechanism of photo-generated carrier separation, ferroelectric photovoltaic devices can achieve an energy conversion efficiency exceeding the efficiency limit of traditional solar cells, greatly reducing the unit power generation cost of photovoltaic cells. Moreover, bismuth ferrite-based (BiFeO3) ferroelectric semiconductor materials are ordinary metal oxides (the material cost is less than 50% of that of single-crystalline silicon cells), with a simple synthesis process and low equipment cost; they do not contain organic components, have excellent performance in resisting humid and hot environments, and the device life is extremely long; they do not contain toxic heavy metal elements and are environmentally friendly, etc. Therefore, bismuth ferrite-based (BiFeO3) ferroelectric semiconductor materials are considered to be potential materials that are most likely to achieve breakthrough application progress in future new-generation photovoltaic cells or optoelectronic devices. Although the research field of the BiFeO3 ferroelectric photovoltaic effect has developed rapidly in recent years, previous research mainly focused on the theoretical mechanism research of the ferroelectric photovoltaic effect, and the research and reports on the energy conversion efficiency of ferroelectric photovoltaic devices are not extensive enough. The reason is that the low short-circuit current density Jsc of ferroelectric photovoltaic devices, as their core shortcoming, has not been solved, which also leads to a still low energy conversion efficiency of BiFeO3-based photovoltaic devices. Currently, the energy conversion efficiency of BiFeO3 photovoltaic devices is basically below 5%, far from meeting the actual application requirements in photovoltaic devices (an energy conversion efficiency of 10% is considered the basic standard for judging whether a solar cell has commercial development value). Currently, the research work on improving the energy conversion efficiency of BiFeO3 ferroelectric photovoltaic devices is basically concentrated on the modification research of the BiFeO3 ferroelectric material itself, mainly by means of technical approaches such as ion doping to regulate the energy band and selecting different electrodes to introduce Schottky barrier electric fields to increase its open-circuit voltage Voc or short-circuit current Jsc. However, these improvement measures targeting the characteristics of the ferroelectric material itself have a very limited effect on improving the energy conversion efficiency of photovoltaic devices. Therefore, in summary, the current energy conversion efficiency of bismuth ferrite-based ferroelectric photovoltaic devices is relatively low, resulting in relatively limited applicability. Summary of the Invention

[0004] The present invention provides a bismuth ferrite-based ferroelectric thin-film photovoltaic device and a preparation method thereof, aiming to solve the problem that the current energy conversion efficiency of bismuth ferrite-based ferroelectric photovoltaic devices is relatively low, resulting in relatively limited applicability.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A preparation method of a bismuth ferrite-based ferroelectric thin-film photovoltaic device of the present invention includes the following steps:

[0007] S1. Using glass with an FTO thin film plated on its surface as a substrate, sputtering a gold nanoparticle layer on the surface of the FTO thin film to obtain a first sample;

[0008] S2. Spin-coat the SnO2 precursor solution on the first sample and form a SnO2 thin film by annealing to obtain a second sample;

[0009] S3. Spin-coat the BiFeO3 precursor solution on the second sample, form a multi-layer BiFeO3-based ferroelectric thin film by gradient doping, and anneal to form a functional layer with a gradient built-in electric field to obtain a third sample;

[0010] S4. Spin-coat the NiO precursor solution on the third sample and form a NiO layer by annealing to obtain a fourth sample;

[0011] S5. Deposit a gold electrode on the fourth sample in a magnetron sputtering instrument to obtain a bismuth ferrite-based ferroelectric thin film photovoltaic device with a complete structure.

[0012] In some embodiments, in S1, the parameters for sputtering the gold nanoparticle layer are controlled as follows:

[0013] The vacuum degree is 10 - 15 Pa, the sputtering current is 25 - 30 mA, and the sputtering time is 0.5 - 2 minutes.

[0014] In some embodiments, in S2, the preparation of the SnO2 precursor solution includes: dissolving SnCl2 and thiourea in pure water according to a mass ratio of 2.5:1 - 3.5:1, stirring at 60 - 70 °C until clear, and standing and aging for 20 - 25 hours to form a sol;

[0015] Among them, the molar concentration of SnCl2 in the SnO2 precursor solution is 0.05 - 0.15 mol / L.

[0016] Furthermore, in S2, the spin-coating parameters are: the initial rotation speed is 600 - 700 rpm for 7 - 10 seconds, rising to 4000 - 4500 rpm for 30 - 40 seconds, the annealing temperature is 200 - 230 °C, and the annealing time is 50 - 70 minutes.

[0017] In some embodiments, in S3, the functional layer includes:

[0018] Bi 0.975 Sm 0.025 Fe 0.95 Co 0.05 O3;

[0019] Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O3;

[0020] And Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05Multilayer BiFeO3-based ferroelectric thin films of O3.

[0021] In some embodiments, in S3, the annealing conditions for spin-coating the BiFeO3 thin film are: annealing at a temperature of 200-230 °C for 2-3 minutes after each layer of spin-coating, and finally annealing at a temperature of 500-550 °C for 30-40 minutes.

[0022] In some embodiments, in S3, the functional layer with a gradient built-in electric field is achieved by repeating spin-coating 9-10 times.

[0023] In some embodiments, in S4, the preparation of the NiO precursor solution includes: dissolving Ni(CH3COO)2 in ethylene glycol monomethyl ether, stirring at 60-70 °C until clear, and standing and aging for 20-25 hours to form the NiO precursor solution;

[0024] Among them, the mass percentage of Ni(CH3COO)2 in the NiO precursor solution is 5.2%-5.4%.

[0025] Furthermore, in S4, the spin-coating parameters are: an initial rotation speed of 600-700 rpm for 7-10 seconds, rising to 4000-4500 rpm for 30-40 seconds, and the annealing conditions are pre-annealing at 130-150 °C for 2-3 minutes, and then annealing at a temperature of 430-460 °C for 30-40 minutes.

[0026] The present invention also provides a bismuth ferrite-based ferroelectric thin film photovoltaic device, which is prepared by the above-mentioned preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device;

[0027] Among them, in the bismuth ferrite-based ferroelectric thin film photovoltaic device: the multilayer BiFeO3-based ferroelectric thin film can introduce a gradient built-in electric field, and the crystal structure of each layer of the BiFeO3-based ferroelectric thin film is consistent with that of the parent phase BiFeO3;

[0028] The energy conversion efficiency of the bismuth ferrite-based ferroelectric thin film photovoltaic device is 10%-15%.

[0029] Compared with the prior art, the bismuth ferrite-based ferroelectric thin film photovoltaic device and its preparation method of the present invention have the following beneficial effects:

[0030] The present invention discloses a method for preparing a bismuth ferrite-based ferroelectric thin film photovoltaic device, and adopts sol-gel spin coating technology to prepare a BiFeO3-based ferroelectric thin film photovoltaic device. First, a layer of "gold (Au) nanoparticle layer" is sputtered on a "glass / FTO" substrate to introduce a plasma exciton resonance effect (LSPR); a layer of electron transport layer (SnO2) is spin-coated thereon; then, a (Sm, Co) co-doped BiFeO3 film (BSFCO) is deposited; finally, a layer of hole transport layer (NiO) is spin-coated, thereby constructing a BiFeO3-based ferroelectric thin film photovoltaic device with a complete structure. X-ray diffraction (XRD) analysis confirms that the (Sm, Co) co-doped BiFeO3 film (BSFCO) has the same crystal structure as the parent phase BiFeO3, and the appearance of the Au diffraction peak confirms that the photovoltaic device contains a gold (Au) nanoparticle layer. The test results of the photovoltaic characteristics show that the open circuit voltage V of the ferroelectric photovoltaic device OC It is 1.9 volts, which is much higher than the open circuit voltage of traditional silicon-based solar cells (less than 1 volt), which is also the unique advantage of ferroelectric photovoltaic devices.

[0031] Furthermore, the present invention introduces comprehensive improvement technologies such as gradient built-in electric field, plasma resonance effect and carrier transport layer during the preparation process, thereby greatly improving the energy conversion efficiency of bismuth ferroelectric thin film photovoltaic devices. The energy conversion efficiency of bismuth ferroelectric thin film (BSFCO) photovoltaic devices is as high as 10.3%, which can ensure its basic performance and make its energy conversion efficiency greater than 10%, thereby greatly improving the applicability and wide application of bismuth ferroelectric thin film photovoltaic devices, making bismuth ferroelectric thin film photovoltaic devices initially have the value of commercial development, and achieving certain technical advantages in the field of ferroelectric photovoltaic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings in the specification are used to provide further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0033] Figure 1 A schematic diagram of the microstructure of a bismuth ferroelectric thin film photovoltaic device based on bismuth ferroelectric thin film and a preparation method thereof according to the present invention;

[0034] Figure 2 The XRD spectrum of a bismuth ferroelectric thin film photovoltaic device sample in a bismuth ferroelectric thin film photovoltaic device and a preparation method thereof according to the present invention;

[0035] Figure 3 A photovoltaic performance test data diagram of a bismuth ferroelectric thin film photovoltaic device based on bismuth ferroelectric thin film photovoltaic device and a preparation method thereof according to the present invention;

[0036] Among them, Figure 3 (a) is the short-circuit current JSC, Figure 3 (b) is the open-circuit voltage VOC, Figure 3 (c) is the current-voltage curve under illumination (the energy conversion efficiency η and fill factor FF of the photovoltaic device can be calculated). Specific implementation manners

[0037] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0038] The theories or mechanisms described and disclosed in the present invention, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0039] In the present invention, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the ranges (including integers and fractions).

[0040] In the present invention, unless otherwise specified, the terms "comprise", "include", "contain", "have" or similar terms cover the meanings of "consist of" and "consist essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0041] In the present invention, for the sake of brevity, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0042] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0043] Conventional instruments and equipment in the art are used in the following examples. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples. Unless otherwise specified, commercially available products with conventional specifications in the art are used. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0044] How to significantly improve the energy conversion efficiency of bismuth ferrite-based ferroelectric photovoltaic devices so that they can meet the application requirements.

[0045] As Figure 1 shown, a preparation method of a bismuth ferrite-based ferroelectric thin film photovoltaic device of the present invention includes the following steps

[0046] S1. Using glass with an FTO thin film plated on its surface as a substrate, sputtering a gold nanoparticle layer on the surface of the FTO thin film to obtain a first sample;

[0047] S2. Spin-coating the SnO2 precursor solution on the first sample and annealing to form an SnO2 thin film to obtain a second sample;

[0048] S3. Spin-coating the BiFeO3 precursor solution on the second sample, forming a multi-layer BiFeO3-based ferroelectric thin film through gradient doping, and annealing to form a functional layer with a gradient built-in electric field to obtain a third sample;

[0049] S4. Spin-coating the NiO precursor solution on the third sample and annealing to form a NiO layer to obtain a fourth sample;

[0050] S5. Gold-plating the electrodes on the fourth sample in a magnetron sputtering instrument to obtain a bismuth ferrite-based ferroelectric thin film photovoltaic device with a complete structure.

[0051] As Figure 1 shown, the structural composition of a bismuth ferrite-based ferroelectric thin film photovoltaic device of the present invention from bottom to top is successively: an FTO bottom electrode, a gold (Au) nanoparticle layer, an electron transport layer (SnO2 thin film), a Sm and Co co-doped BiFeO3 thin film (BSFCO thin film), a hole transport layer (NiO thin film), and a top electrode (Au). In this delicate ferroelectric photovoltaic device structure: the gold (Au) nanoparticle layer is used to introduce the surface plasmon resonance effect (LSPR effect) to enhance the energy of photo-generated electrons, improve the separation efficiency of photo-generated carriers, and thus enhance the photovoltaic characteristics of the device.

[0052] The core functional layer of the present invention is a Sm and Co co-doped BiFeO3 thin film (BSFCO thin film), and this thin film can be a BiFeO3 thin film with a fixed doping concentration (for example, Bi0.975 Sm 0.025 Fe 0.95 Co 0.05 The BiFeO₃ thin film, BSFCO-1), can also be a multi-layer gradient thin film composed of BiFeO₃ with different doping concentrations. The functional layer includes:

[0053] Bi 0.975 Sm 0.025 Fe 0.95 Co 0.05 O₃;

[0054] Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O₃;

[0055] And Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05 O₃, labeled as BSFCO-g thin film. Tests have found that such a gradient-doped thin film can introduce an additional gradient built-in electric field (oxygen defect gradient electric field, flexoelectric field), accelerate the separation of photo-generated carriers, and improve the photovoltaic properties of the device. The carrier transport layers (NiO and SnO₂ thin films) on the upper and lower surfaces of the BiFeO₃ thin film can promptly capture the photo-generated carriers (electrons and holes) generated by the BiFeO₃ thin film under illumination, prevent the recombination between electrons and holes, and quickly transfer them to the upper and lower electrodes (Au and FTO), thereby greatly improving the energy conversion efficiency of the ferroelectric photovoltaic device. The present invention has greatly improved the energy conversion efficiency of the bismuth ferrite (BiFeO₃)-based ferroelectric photovoltaic device, thus meeting the basic requirements of applications and constructing a bismuth ferrite-based ferroelectric thin film photovoltaic device with an energy conversion efficiency greater than 10%.

[0056] In some embodiments, the preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device of the present invention is carried out in the following manner:

[0057] 1. Depositing a gold (Au) nanoparticle layer: Clean the "glass / FTO" substrate, and then use a magnetron sputtering instrument to spray gold on the FTO surface for 0.5 - 2 minutes (vacuum degree: 10 Pa, sputtering current: 30 mA) to introduce the surface plasmon resonance effect.

[0058] 2. Spin-coating the electron transport layer (SnO₂): Drop the SnO₂ precursor solution on the FTO substrate with the sputtered gold layer and perform spin-coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, and then increase the rotation speed to 4000 rpm, with a duration of 30 s. Anneal the spin-coated sample at 200 - 230 °C for 50 - 70 minutes to form a dense SnO₂ thin film.

[0059] 3. Spin - coating bismuth ferrite (BiFeO3) - based ferroelectric thin films: Drop the BiFeO3 precursor solution onto the sample obtained in the second step for spin - coating. Set the rotation speed to 600 rpm for 9 seconds, then increase the rotation speed to 4000 rpm for 30 s. Anneal the spin - coated sample at 200 - 230 °C for 2 - 3 minutes. Repeat the above experimental operations 9 times to obtain the set film thickness. Finally, anneal the sample at 550 °C for 30 - 40 minutes to form a dense bismuth ferrite (BiFeO3) - based ferroelectric thin film. During this process, gradient - doped multilayer thin films can also be constructed to introduce a gradient built - in electric field.

[0060] 4. Spin - coating hole - transporting layer (NiO): Drop the NiO precursor solution onto the sample obtained in the third step for spin - coating. Set the rotation speed to 600 rpm for 9 seconds, then increase the rotation speed to 4000 rpm for 30 s. Anneal the spin - coated sample at 130 - 150 °C for 2 - 3 minutes, and then anneal the sample at 450 °C for 30 - 40 minutes to form a dense NiO thin film.

[0061] 5. Finally, use a mask plate in a magnetron sputtering instrument to deposit a gold electrode on the sample obtained in the fourth step for 5 - 7 minutes (vacuum degree: 10 Pa, sputtering current: 30 mA) for subsequent photovoltaic performance testing.

[0062] The present invention also provides a bismuth ferrite - based ferroelectric thin film photovoltaic device, which is prepared by the preparation method of the above - mentioned bismuth ferrite - based ferroelectric thin film photovoltaic device;

[0063] Among them, in the bismuth ferrite - based ferroelectric thin film photovoltaic device, the multilayer BiFeO3 - based ferroelectric thin film can introduce a gradient built - in electric field, and the crystal structure of each layer of BiFeO3 - based ferroelectric thin film is consistent with that of the parent phase BiFeO3;

[0064] The energy conversion efficiency of the bismuth ferrite - based ferroelectric thin film (BSFCO - g) photovoltaic device is 10.3%.

[0065] As Figure 3 shown, Figure 3 are the photovoltaic performance test results of the bismuth ferrite - based ferroelectric thin film photovoltaic device sample. Figure 3 (a) shows the short - circuit current J of the bismuth ferrite - based ferroelectric thin film photovoltaic device SC , Figure 3 (b) shows the open - circuit voltage V of the bismuth ferrite - based ferroelectric thin film photovoltaic device OC . As shown in the figure, the non - gradient - doped bismuth ferrite - based ferroelectric thin film photovoltaic devices (such as BSFCO - 1, BSFCO - 2, BSFCO - 3) lack a gradient electric field, so the short - circuit current J of these devicesSC and the open-circuit voltage V OC are both relatively small. For example, its short-circuit current J SC is all less than 4 mA / cm 2 , and the open-circuit voltage V OC is all less than 0.6 V. However, for the Sm, Co gradient-doped BiFeO3 ferroelectric thin film (BSFCO-g, with the structure of "BSFCO-1 / BSFCO-2 / BSFCO-3"), due to the multi-factor coupling effect of "gradient electric field, LSPR effect, and carrier transport layer", the short-circuit current J SC and the open-circuit voltage V OC of its photovoltaic device are both relatively large. J SC reaches 10.2 mA / cm 2 , and the open-circuit voltage V OC is even as high as 1.9 V. Therefore, the energy conversion efficiency of the gradient-doped bismuth ferrite-based ferroelectric thin film (BSFCO-g) photovoltaic device has been greatly improved, breaking through the important threshold of 10% for the first time. As Figure 3 (c) shows, the energy conversion efficiency of the non-gradient-doped bismuth ferrite-based ferroelectric thin film photovoltaic devices (such as BSFCO-1, BSFCO-2, BSFCO-3) is generally low, generally below 2%. However, for the Sm, Co gradient-doped BiFeO3 ferroelectric thin film (BSFCO-g, with the structure of "BSFCO-1 / BSFCO-2 / BSFCO-3"), the energy conversion efficiency of its photovoltaic device is as high as 10.3%, which is currently the highest energy conversion efficiency of ferroelectric photovoltaic devices at home and abroad. Moreover, breaking through the 10% energy conversion efficiency indicates that the bismuth ferrite-based ferroelectric thin film photovoltaic device has already possessed the value of commercial development, which has a great promoting effect and significance for the large-scale development and application of ferroelectric photovoltaic effect and devices.

[0066] The following further details a bismuth ferrite-based ferroelectric thin film photovoltaic device and its preparation method of the present invention through specific embodiments.

[0067] Example 1

[0068] 1. Prepare the thin film precursor solution:

[0069] (1) Prepare the precursor solution of the electron transport layer (SnO2 thin film): Weigh 0.6767 g of SnCl2 and 0.2233 g of thiourea, add them to 30 ml of pure water, stir at 60 °C for 30 min until it becomes clear, lower the temperature to room temperature, and continue to stir for 3 hours to present a stable colorless, clear and transparent solution. Let it stand and age at room temperature for 20 hours to form a stable sol.

[0070] (2) Prepare Bi 0.975 Sm0.025 Fe 0.95 Co 0.05 Precursor solution of Bi

[0071] Weigh 4.9659 g of Bi(NO3)3·5H2O and add it to a beaker containing 20 ml of acetic acid (labeled as beaker BSFCO - 1). Stir at 60 °C for 50 min until it is completely dissolved into a clear solution, and then cool the solution temperature to room temperature. Then, weigh 0.1111 g of Sm(NO3)3·6H2O, 3.838 g of Fe(NO3)3·9H2O, 0.1455 g of Co(NO3)2·6H2O and 40 ml of ethylene glycol methyl ether, and add them all to beaker BSFCO - 1. Stir at room temperature for 4 hours until a dark red clear solution appears. Finally, let it stand and age at room temperature for 24 hours to form a stable sol.

[0072] (3) Prepare the precursor solution of the hole - transporting layer (NiO thin film): Weigh 1.064 g of Ni(CH3COO)2 and add it to 20 ml of ethylene glycol methyl ether. Stir at 60 °C for 40 min until it becomes clear. Then cool the temperature to room temperature and stir for 5 hours to obtain a stable clear green solution. Let it stand and age at room temperature for 25 hours to form a stable sol.

[0073] 2. Deposit the thin film:

[0074] (1) Sputter the gold (Au) nanoparticle layer:

[0075] First, ultrasonically clean the "glass / FTO" substrate for 20 min for standby. Then, perform gold plating on the surface of the clean FTO substrate. Sputter gold for 1 min under a magnetron sputtering instrument (vacuum degree: 10 Pa, sputtering current: 30 mA) to introduce the surface plasmon resonance effect of gold (Au) nanoparticles in the ferroelectric photovoltaic device.

[0076] (2) Spin - coat to prepare the electron - transporting layer (SnO2 thin film):

[0077] Drop the SnO2 precursor solution onto the FTO substrate after gold plating in step (1) for spin - coating: Set the rotation speed to 600 rpm and the duration to 9 s, then increase the rotation speed to 4000 rpm and the duration to 30 s. Anneal the spin - coated sample at 200 °C for 50 min to form a dense SnO2 thin film.

[0078] (3) Spin - coat to prepare Bi 0.975 Sm 0.025 Fe 0.95 Co 0.05 Sm

[0079] Drop the BSFCO-1 precursor solution onto the sample obtained in step (2) and spin-coat it: set the rotation speed to 600 rpm for 9 seconds, then increase the rotation speed to 4000 rpm for 30 s. Anneal the spin-coated sample at 230 °C for 3 minutes. Repeat the above experimental operation 9 times to obtain the set film thickness. Finally, anneal the obtained sample at 550 °C for 30 minutes to form a dense bismuth ferrite-based (Bi 0.975 Sm 0.025 Fe 0.95 Co 0.05 O3, BSFCO-1) ferroelectric film.

[0080] (4) Spin-coat to prepare the hole transport layer (NiO film):

[0081] Drop the NiO precursor solution onto the sample obtained in step (3) and spin-coat it: set the rotation speed to 600 rpm for 9 seconds, then increase the rotation speed to 4000 rpm for 30 s. Anneal the spin-coated sample at 150 °C for 3 minutes, and then anneal the sample at 450 °C for 40 minutes to form a dense NiO film.

[0082] (5) Finally, use a mask plate in a magnetron sputtering instrument to deposit a gold electrode on the sample obtained in step (4) for 5 minutes (vacuum degree: 10 Pa, sputtering current: 30 mA) for subsequent photovoltaic performance testing.

[0083] Example 2:

[0084] 1. Prepare the film precursor solution:

[0085] (1) Prepare the precursor solution for the electron transport layer (SnO2 film): Weigh 0.6767 g of SnCl2 and 0.2233 g of thiourea, add them to 30 ml of pure water, stir at 60 °C for 50 min until clear, lower the temperature to room temperature, and continue stirring for 5 hours to obtain a stable colorless, clear and transparent solution. Let it stand and age at room temperature for 25 hours to form a stable sol.

[0086] (2) Prepare the precursor solution for the Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O3 film (BSFCO-2):

[0087] Weigh 4.8381 g of Bi(NO3)3·5H2O and add it to a beaker containing 20 ml of acetic acid (marked as beaker BSFCO-2). Stir at 60 °C for 30 min until it is completely dissolved into a clear solution, and then cool the solution temperature to room temperature. Then, weigh 0.2222 g of Sm(NO3)3·6H2O, 3.838 g of Fe(NO3)3·9H2O, 0.1455 g of Co(NO3)2·6H2O and 40 ml of ethylene glycol methyl ether, and add them together to beaker BSFCO-2. Stir at room temperature for 3 hours until a dark red clear solution appears. Finally, let it stand and age at room temperature for 24 hours to form a stable sol.

[0088] (3) Prepare the precursor solution for the hole transport layer (NiO thin film): Weigh 1.064 g of Ni(CH3COO)2 and add it to 20 ml of ethylene glycol methyl ether. Stir at 60 °C for 30 min until it is clear, cool the solution temperature to room temperature, and stir for 3 hours until a stable clear green solution appears. Let it stand and age at room temperature for 24 hours to form a stable sol.

[0089] 2. Deposit the thin film:

[0090] (1) Sputter the gold (Au) nanoparticle layer:

[0091] First, ultrasonically clean the "glass / FTO" substrate for 30 min for standby, and then perform gold plating on the surface of the clean FTO substrate. Sputter gold for 1 min under a magnetron sputtering instrument (vacuum degree: 10 Pa, sputtering current: 30 mA) to introduce the surface plasmon resonance effect of gold (Au) nanoparticles in the ferroelectric photovoltaic device.

[0092] (2) Spin-coat to prepare the electron transport layer (SnO2 thin film):

[0093] Drop the SnO2 precursor solution onto the FTO substrate after gold plating in step (1) for spin-coating: set the rotation speed to 600 rpm for 9 s, and then increase the rotation speed to 4000 rpm for 30 s. Anneal the spin-coated sample at 230 °C for 50 min to form a dense SnO2 thin film.

[0094] (3) Spin-coat to prepare the Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O3 thin film (BSFCO-2):

[0095] Drop the BSFCO-2 precursor solution onto the sample obtained in step (2) and perform spin coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, then increase the rotation speed to 4000 rpm, with a duration of 30 s. Anneal the spin-coated sample at 230 °C for 3 minutes. Repeat the above experimental operation 9 times to obtain the set film thickness. Finally, anneal the obtained sample at 550 °C for 30 minutes to form a dense bismuth ferrite-based (Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O3, BSFCO-2) ferroelectric film.

[0096] (4) Spin coat to prepare the hole transport layer (NiO film):

[0097] Drop the NiO precursor solution onto the sample obtained in step (3) and perform spin coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, then increase the rotation speed to 4000 rpm, with a duration of 30 s. Anneal the spin-coated sample at 130 °C for 3 minutes, and then anneal the sample at 450 °C for 30 minutes to form a dense NiO film.

[0098] (5) Finally, use a mask plate in a magnetron sputtering instrument to deposit a gold electrode on the sample obtained in step (4) for 6 minutes (vacuum degree: 10 Pa, sputtering current: 30 mA) for subsequent photovoltaic performance testing.

[0099] Example 3:

[0100] 1. Prepare the film precursor solution:

[0101] (1) Prepare the precursor solution for the electron transport layer (SnO2 film): Weigh 0.6767 g of SnCl2 and 0.2233 g of thiourea, add them to 30 ml of pure water, stir at 60 °C for 30 min until clear, lower the temperature to room temperature, and continue stirring for 3 hours to obtain a stable colorless, clear and transparent solution. Let it stand and age at room temperature for 24 hours to form a stable sol.

[0102] (2) Prepare the precursor solution for the Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05 O3 film (BSFCO-3):

[0103] Weigh 4.7112 g of Bi(NO3)3·5H2O and add it to a beaker containing 20 ml of acetic acid (marked as beaker BSFCO-3). Stir at 60 °C for 30 min until it is completely dissolved into a clear solution, and then cool the solution temperature to room temperature. Then, weigh 0.3333 g of Sm(NO3)3·6H2O, 3.838 g of Fe(NO3)3·9H2O, 0.1455 g of Co(NO3)2·6H2O and 40 ml of ethylene glycol monomethyl ether, and add them together to beaker BSFCO-3. Stir at room temperature for 5 hours until a dark red clear solution appears. Finally, let it stand and age at room temperature for 24 hours to form a stable sol.

[0104] (3) Prepare the precursor solution of the hole transport layer (NiO thin film): Weigh 1.064 g of Ni(CH3COO)2 and add it to 20 ml of ethylene glycol monomethyl ether. Stir at 60 °C for 30 min until it is clear, cool the solution temperature to room temperature, and stir for 3 hours until a stable clear green solution appears. Let it stand and age at room temperature for 25 hours to form a stable sol.

[0105] 2. Deposit the thin film:

[0106] (1) Sputter the gold (Au) nanoparticle layer:

[0107] First, ultrasonically clean the "glass / FTO" substrate for 30 min for standby, and then perform gold plating on the surface of the clean FTO substrate. Spray gold under a magnetron sputtering instrument for 1 min (vacuum degree: 10 Pa, sputtering current: 30 mA) to introduce the surface plasmon resonance effect of gold (Au) nanoparticles into the ferroelectric photovoltaic device.

[0108] (2) Spin-coat to prepare the electron transport layer (SnO2 thin film):

[0109] Drop the SnO2 precursor solution onto the FTO substrate after gold plating in step (1) for spin-coating: set the rotation speed to 600 rpm, and the duration is 9 s, then increase the rotation speed to 4000 rpm, and the duration is 30 s. Anneal the spin-coated sample at 200 °C for 70 minutes to form a dense SnO2 thin film.

[0110] (3) Spin-coat to prepare Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05 O3 thin film (BSFCO-3):

[0111] Drop the BSFCO-3 precursor solution onto the sample obtained in step (2) and perform spin coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, then increase the rotation speed to 4000 rpm and the duration to 30 s. Anneal the spin-coated sample at 230 °C for 2 minutes. Repeat the above experimental operations 9 times to obtain the set film thickness. Finally, anneal the obtained sample at 550 °C for 30 minutes to form a dense bismuth ferrite-based (Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05 O3, BSFCO-3) ferroelectric film.

[0112] (4) Spin-coat to prepare the hole transport layer (NiO film):

[0113] Drop the NiO precursor solution onto the sample obtained in step (3) and perform spin coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, then increase the rotation speed to 4000 rpm and the duration to 30 s. Anneal the spin-coated sample at 150 °C for 2 minutes, and then anneal the sample at 450 °C for 30 minutes to form a dense NiO film.

[0114] (5) Finally, use a mask under a magnetron sputtering instrument to deposit a gold electrode on the sample obtained in step (4) for 5 minutes (vacuum degree: 10 Pa, sputtering current: 30 mA) for subsequent photovoltaic performance testing.

[0115] Example 4:

[0116] 1. Prepare the film precursor solution:

[0117] (1) Prepare the precursor solution for the electron transport layer (SnO2 film): Weigh 0.6767 g of SnCl2 and 0.2233 g of thiourea, add them to 30 ml of pure water, stir at 60 °C for 30 min until it becomes clear, lower the temperature to room temperature, and continue stirring for 3 hours to obtain a stable colorless, clear and transparent solution. Let it stand and age at room temperature for 24 hours to form a stable sol.

[0118] (2) Prepare Bi 0.975 Sm 0.025 Fe 0.95 Co 0.05 O3 (BSFCO-1), Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O3 (BSFCO-2) and Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05Precursor solutions of three O3(BSFCO-3) thin films:

[0119] Weigh 4.9659 g, 4.838 g, and 4.7112 g of Bi(NO3)3·5H2O and add them to three beakers containing 20 ml of acetic acid (labeled as beakers BSFCO-1, BSFCO-2, and BSFCO-3) respectively. After stirring at 60 °C for 30 min until completely dissolved into a clear solution, cool the solution temperature to room temperature. Then, weigh 0.1111 g, 0.2222 g, and 0.3333 g of Sm(NO3)3·6H2O and add them to beakers BSFCO-1, BSFCO-2, and BSFCO-3 respectively. Then weigh three equal portions of 3.838 g of Fe(NO3)3·9H2O, 0.1455 g of Co(NO3)2·6H2O, and 40 ml of ethylene glycol monomethyl ether, and add them to beakers BSFCO-1, BSFCO-2, and BSFCO-3 respectively. Stir at room temperature for 5 hours until a dark red clear solution appears. Finally, let it stand and age at room temperature for 24 hours to form a stable sol.

[0120] (3) Prepare the precursor solution of the hole transport layer (NiO thin film): Weigh 1.064 g of Ni(CH3COO)2 and add it to 20 ml of ethylene glycol monomethyl ether. Stir at 60 °C for 30 min until clear, then cool the temperature to room temperature and stir for 3 hours until a stable clear green solution appears. Let it stand and age at room temperature for 24 hours to form a stable sol.

[0121] 2. Deposit thin films:

[0122] (1) Sputter the gold (Au) nanoparticle layer:

[0123] First, ultrasonically clean the "glass / FTO" substrate for 30 min and set it aside. Then, perform gold plating on the surface of the clean FTO substrate. Sputter gold for 1 min under a magnetron sputtering instrument (vacuum degree: 10 Pa, sputtering current: 30 mA) to introduce the surface plasmon resonance effect of gold (Au) nanoparticles in the ferroelectric photovoltaic device.

[0124] (2) Spin-coat to prepare the electron transport layer (SnO2 thin film):

[0125] Drop the SnO2 precursor solution on the FTO substrate after gold plating in step (1) and perform spin-coating: set the rotation speed to 600 rpm for 9 s, then increase the rotation speed to 4000 rpm for 30 s. Anneal the spin-coated sample at 230 °C for 50 min to form a dense SnO2 thin film.

[0126] (3) Spin-coat to prepare a gradient-doped multilayer film, denoted as BSFCO-g (Bi 0.975 Sm0.025 Fe 0.95 Co 0.05 O3 / Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O3 / Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05 O3, namely: BSFCO-1 / BSFCO-2 / BSFCO-3):

[0127] Drop the BSFCO-1 precursor solution onto the sample obtained in step (2) and perform spin coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, then increase the rotation speed to 4000 rpm, with a duration of 30 s. Anneal the spin-coated sample at 230 °C for 2 minutes, and repeat the above experimental operation 3 times to obtain the set film thickness. Drop the BSFCO-2 precursor solution onto the sample obtained in the previous step and perform spin coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, then increase the rotation speed to 4000 rpm, with a duration of 30 s. Anneal the spin-coated sample at 230 °C for 2 minutes. Repeat the above experimental operation 3 times to obtain the set film thickness. Drop the BSFCO-3 precursor solution onto the sample obtained in the previous step and perform spin coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, then increase the rotation speed to 4000 rpm, with a duration of 30 s. Anneal the spin-coated sample at 230 °C for 2 minutes. Repeat the above experimental operation 3 times to obtain the set film thickness. Finally, anneal the sample at 550 °C for 30 minutes.

[0128] Through the above construction process, a gradient-doped multi-layer BSFCO-g film (Bi 0.975 Sm 0.025 Fe 0.95 Co 0.05 O3 / Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O3 / Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05 O3, namely: BSFCO-1 / BSFCO-2 / BSFCO-3).

[0129] (4) Spin coat to prepare the hole transport layer (NiO film):

[0130] Drop the NiO precursor solution onto the sample obtained in step (3) and perform spin coating: set the rotation speed to 600 rpm, with a duration of 9 seconds, then increase the rotation speed to 4000 rpm, with a duration of 30 s. Anneal the spin-coated sample at 150 °C for 2 minutes, and then anneal the sample at 450 °C for 30 minutes to form a dense NiO thin film.

[0131] (5) Finally, use a mask under a magnetron sputtering instrument to deposit a gold electrode on the sample obtained in step (4) for 5 minutes (vacuum degree: 10 Pa, sputtering current: 30 mA) for subsequent photovoltaic performance testing.

[0132] As Figure 1 and Figure 3 shown, Figure 1 in, LSPR is the surface plasmon resonance effect introduced by gold nanoparticles, P flexo and E flexo are flexoelectric polarization and flexoelectric electric field respectively, and BSFCO-g is a gradient-doped multilayer film. Figure 3 In, all light sources for photovoltaic performance testing are monochromatic lasers with a wavelength of 405 nm and a maximum output power density of 50 mW / cm 2 ; the light power density irradiated on the surface of the photovoltaic device is 45 mW / cm 2 .

[0133] In the Figure 2 of the present invention, the crystal structures of all doped thin films (BSFCO thin films) are consistent with the parent phase BiFeO3, and all samples contain necessary functional layers such as Au, NiO, and SnO2. The Figure 2 of the present invention is the XRD pattern of all thin films prepared in Examples 1 to 4. As Figure 2 shown: the crystal structures of all (Sm, Co) co-doped BiFeO3 thin films (BSFCO thin films) are consistent with the parent phase BiFeO3, confirming that the doped thin films maintain the ferroelectric properties of the parent phase BiFeO3, that is, ferroelectric photovoltaic devices. Moreover, the diffraction peaks of substances such as Au, NiO, and SnO2 are included in all thin film samples, indicating that the structure form of the photovoltaic device we prepared is as Figure 1 shown: "bottom electrode FTO / Au nanoparticle layer / SnO2 electron transport layer / BSFCO ferroelectric thin film / NiO hole transport layer / Au electrode". The present invention greatly improves the energy conversion efficiency of bismuth ferrite-based ferroelectric thin film photovoltaic devices, making its energy conversion rate greater than 10%, and making it have better application value.

[0134] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and does not impose any formal restrictions on the present invention. Any ordinary technician in the industry can smoothly implement the present invention according to the description in the specification and the above. However, any minor changes, modifications, and equivalent variations made by those skilled in the art within the scope of the technical solution of the present invention by using the technical content disclosed above are equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of a bismuth ferrite-based ferroelectric thin film photovoltaic device, characterized in that, It includes the following steps: S1. Using glass with an FTO thin film on its surface as a substrate, sputtering a gold nanoparticle layer on the surface of the FTO thin film to obtain a first sample; S2. Spin-coating a SnO2 precursor solution on the first sample and annealing it to form a SnO2 thin film to obtain a second sample; S3. Spin-coating a BiFeO3 precursor solution on the second sample, forming a multi-layer BiFeO3-based ferroelectric thin film through gradient doping, and annealing it to form a functional layer with a gradient built-in electric field to obtain a third sample; S4. Spin-coating a NiO precursor solution on the third sample and annealing it to form a NiO layer to obtain a fourth sample; S5. Gold-plating electrodes on the fourth sample in a magnetron sputtering instrument to obtain a bismuth ferrite-based ferroelectric thin film photovoltaic device with a complete structure.

2. The preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device according to claim 1, wherein In the above S1, the parameters for sputtering the gold nanoparticle layer are controlled as follows: The vacuum degree is 10 - 15 Pa, the sputtering current is 25 - 30 mA, and the sputtering time is 0.5 - 2 minutes.

3. The preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device according to claim 1, characterized in that, In the above S2, the preparation of the SnO2 precursor solution includes: dissolving SnCl2 and thiourea in pure water according to a mass ratio of 2.5:1 - 3.5:1, stirring at 60 - 70 °C until clear, and standing and aging for 20 - 25 hours to form a sol; Among them, the molar concentration of SnCl2 in the SnO2 precursor solution is 0.05 - 0.15 mol / L.

4. The preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device according to claim 3, characterized in that, In the above S2, the spin-coating parameters are: an initial rotation speed of 600 - 700 rpm for 7 - 10 seconds, rising to 4000 - 4500 rpm for 30 - 40 seconds, the annealing temperature is 200 - 230 °C, and the annealing time is 50 - 70 minutes.

5. The preparation method of a bismuth ferrite-based ferroelectric thin film photovoltaic device according to claim 1, characterized in that, In the above S3, the functional layer includes: Bi 0.975 Sm 0.025 Fe 0.95 Co 0.05 O3; Bi 0.95 Sm 0.05 Fe 0.95 Co 0.05 O3; and Bi 0.925 Sm 0.075 Fe 0.95 Co 0.05 multilayer BiFeO3-based ferroelectric thin films of BiFeO3 6. The preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device according to claim 1, characterized in that, In the above S3, the annealing conditions for spin-coating the BiFeO3 thin film are: annealing at 200 - 230 °C for 2 - 3 minutes after each layer is spin-coated, and finally annealing at 500 - 550 °C for 30 - 40 minutes.

7. The preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device according to claim 1, characterized in that, In the above S3, the functional layer with a gradient built-in electric field is achieved by repeating spin-coating 9 - 10 times.

8. The preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device according to claim 1, wherein, In the above S4, the preparation of the NiO precursor solution includes: dissolving Ni(CH3COO)2 in ethylene glycol methyl ether, stirring at 60 - 70 °C until clear, and standing and aging for 20 - 25 hours to form a NiO precursor solution; Among them, the mass percentage of Ni(CH3COO)2 in the NiO precursor solution is 5.2% - 5.4%.

9. The preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device according to claim 8, characterized in that, In the above S4, the spin-coating parameters are: an initial rotation speed of 600 - 700 rpm for 7 - 10 seconds, rising to 4000 - 4500 rpm for 30 - 40 seconds, the annealing conditions are pre-annealing at 130 - 150 °C for 2 - 3 minutes, and then annealing at 430 - 460 °C for 30 - 40 minutes.

10. A bismuth ferrite-based ferroelectric thin film photovoltaic device, characterized in that, The bismuth ferrite-based ferroelectric thin film photovoltaic device is prepared by the preparation method of the bismuth ferrite-based ferroelectric thin film photovoltaic device according to any one of claims 1 - 9; Among them, in the bismuth ferrite-based ferroelectric thin film photovoltaic device: the multi-layer BiFeO3-based ferroelectric thin film can introduce a gradient built-in electric field, and the crystal structure of each layer of the BiFeO3-based ferroelectric thin film is the same as that of the parent phase BiFeO3; The energy conversion efficiency of the bismuth ferrite-based ferroelectric thin film photovoltaic device is 10% - 15%.

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