Ferroelectric photovoltaic film with layered structure as well as preparation method and application of ferroelectric photovoltaic film

Abstract

The invention discloses a layered structure ferroelectric photovoltaic film and a preparation method and application thereof, the preparation method comprises the following steps: S1, preparing a precursor solution which contains one or more of bismuth salt, lanthanum salt and barium salt; and S2, preparing the thin film by adopting a spin-coating method. The rare earth La-doped BLTO ferroelectric film is prepared, the ferroelectric property of the rare earth La-doped BLTO film is obviously improved, meanwhile, the anti-fatigue property of the rare earth La-doped BLTO film is also obviously improved, and the energy storage property of the film is improved through rare earth element doping. The BLBT film is deposited on the Pt / Ti / SiO2 / Si bottom electrode, the prepared film has the characteristics of high maximum polarizability, low residual polarizability and low leakage current density, and the energy storage performance is greatly improved compared with that of a BBT film. The ferroelectric photovoltaic film with the layered structure prepared by the method can be applied to a dielectric energy storage capacitor.

Description

Technical Field

[0001] The invention belongs to the technical field of ferroelectric thin films, and in particular relates to a layered ferroelectric photovoltaic thin film and a preparation method and application thereof. Background Art

[0002] Aurivillius-type layered ferroelectrics have attracted increasing research interest as new high-temperature lead-free dielectric materials with good electrical properties; Bi4Ti3O 12 (BTO)-based environmentally friendly lead-free ferroelectric material is a three-layer ('m'=3) Aurivillius phase compound, and its structural formula is [(Bi2O2) 2+ (Bi2Ti3O 10 ) 2- ], and has been widely used in the electronics industry, capacitors, sensors, nonvolatile FE memories, piezoelectric sensors, and optical devices. At the same time, the shortcomings of BTO films, such as small residual polarization and poor fatigue performance, cannot be ignored, which limits its further application in ferroelectric memory devices.

[0003] BaBi4Ti4O 15 (BBT) is a four-layer ('m' = 4) Aurivillius phase compound with the structural formula [(Bi2O2) 2+ ((BaBi2)Ti4O 13 ) 2- ], where Ba and Bi ions are located at the A site and Ti ions are located at the B site. Their intrinsic electrical properties are anisotropic, with the maximum value of conductivity and the main component of spontaneous polarization parallel to (Bi2O2) 2+ layer. BBT-based materials exhibit excellent ferroelectric properties at room temperature. The presence of spontaneous polarization leads to the formation of hysteresis loops in high-intensity alternating fields. BBT belongs to a class of relaxor ferroelectrics. For BBT ferroelectric films, large Ba 2+ Substituting Bi in perovskite-like structural layers 3+ , which leads to Ba 2+ The uneven distribution and local charge imbalance of the ferroelectrics cause the long-range dipole interactions to be destroyed, forming local polar nanoregions (PNRs), which lead to relaxor behavior. Relaxor ferroelectrics have many applications in electronic devices, such as multilayer ceramic capacitors, optoelectronic devices, and medical imaging devices. At high temperatures, they exist in a non-polar paraelectric phase, which is similar to the paraelectric phase of normal ferroelectrics in many aspects. Upon cooling, they transform into an ergodic relaxation state, with nanoscale polar regions with randomly distributed dipole moment directions. A general feature of relaxation is that the temperature dependence of the dielectric constant has a broad maximum, whose location T mThe ferroelectric behavior of relaxors is explained by the shift to lower temperatures as the probe field frequency decreases. Different models have been proposed to explain the ferroelectric behavior of relaxors, but it is usually difficult to simulate and understand these dynamic relaxations in solid materials.

[0004] BBT-based materials also exhibit excellent dielectric properties. The dielectric properties of dielectric materials are one of the important indicators for characterizing energy storage performance. Generally speaking, dielectric properties can be divided into two aspects: dielectric constant and dielectric loss. The dielectric constant reflects the ability of dielectric materials to store electrostatic energy in an electrostatic field. Often, the higher the dielectric constant, the better the energy storage performance of the material itself. The dielectric constant is an intrinsic property of dielectric materials. Dielectric loss is closely related to the breakdown electric field strength of dielectric materials, so the dielectric loss of materials often indirectly affects their energy storage density and energy storage efficiency. According to existing reports, the dielectric loss (tanδ) of BBT is very low at room temperature (about 0.03). When the temperature changes from room temperature to 200°C, the size of the dielectric loss of BBT is almost constant, and then as the temperature increases, the dielectric loss gradually increases with the increase in temperature. This is because the temperature enhances the electronic activity inside the material, thereby enhancing the conductivity of the material itself.

[0005] The energy storage density and breakdown field strength of BBT film are low, and the energy storage performance needs to be improved. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a layered ferroelectric photovoltaic film, comprising the following steps:

[0007] S1. preparing a precursor solution, wherein the precursor solution contains one or more of a bismuth salt, a lanthanum salt, and a barium salt;

[0008] S2. Prepare the thin film by spin coating using a coating machine.

[0009] Preferably, the step S2 specifically includes the following steps:

[0010] A. Place the Pt / Ti / SiO2 / Si substrate into a coating machine, use a pipette to draw 10 μL of the precursor solution and drop it onto the substrate. Set the coating machine parameters to a speed of 5000 rpm and a spin coating time of 20 s. Then start the coating machine and evenly spin coat the solution onto the substrate.

[0011] B. Place the spin-coated sample on a heating platform, set the temperature of the heating platform to 120°C, and heat for 2 minutes;

[0012] C. Place the heated sample in a tube furnace for pyrolysis. The temperature of the tube furnace is set to 400°C and the heating time is 10 minutes.

[0013] D. Repeat steps AC 10 times;

[0014] E. Place the sample in a tubular furnace for annealing at a temperature of 650°C and an annealing time of 30 minutes.

[0015] Preferably, the step S1 is: press Bi 3.25 La 0.75 Ti3O 12 The chemical formulas are bismuth acetate, lanthanum acetate, tetrabutyl phthalate, and propionic acid, and are prepared according to a colloid concentration of 0.1 mol / L.

[0016] Preferably, Bi is in excess of 5%, and the reagent is weighed according to the amount and dissolved in the propionic acid solution, and stirred for 6 hours at room temperature and pressure to obtain a clear and transparent colorless liquid, which is left to stand for 72 hours for use.

[0017] Preferably, the step S1 is: press Bi 3.25 La 0.75 Ti3O 12 The chemical formulas are bismuth nitrate, lanthanum nitrate, tetrabutyl phthalate, glacial acetic acid, and ethylene glycol methyl ether, and the colloid concentration is 0.1 mol / L.

[0018] Preferably, Bi is in excess of 5%, reagents are weighed according to the measurement, glacial acetic acid and ethylene glycol methyl ether are selected as solvents, and the content ratio is 3:1. The weighed reagents are dissolved in the solvent, and stirred for 6 hours under normal pressure and 40°C water bath heating to obtain a clear and transparent colorless liquid, which is left to stand for 24 hours for use.

[0019] Preferably, the step S1 is: press BaLa 0.2 Bi 3.8 Ti4O 15 The chemical formulas are bismuth acetate, barium acetate, lanthanum acetate, tetrabutyl phthalate, and propionic acid, and the colloid concentration is 0.1 mol / L.

[0020] Preferably, Bi is in excess of 5%, and the reagents are weighed and dissolved in a propionic acid solution, stirred for 6 hours at room temperature and pressure to obtain a clear, transparent, colorless liquid, which is then left to stand for 72 hours for use.

[0021] The layered ferroelectric photovoltaic film prepared by the above preparation method.

[0022] Application of layered ferroelectric photovoltaic films in dielectric energy storage capacitors.

[0023] Beneficial effects:

[0024] 1. The present invention prepares rare earth La-doped Bi 3.25 La 0.75 Ti3O 12(BLTO) ferroelectric film, and studied its morphological characteristics and energy storage performance. The results showed that the ferroelectric properties of the BLTO film were significantly improved after doping with the rare earth element La. At the same time, its fatigue resistance was also significantly improved. The energy storage performance of the film was improved by doping with rare earth elements.

[0025] 2. In order to optimize the energy storage performance of BBT film, the present invention deposits Bi on the Pt / SiO2 / Si bottom electrode. 3.25 La 0.75 BaTi4O 15 (BLBT) film, through analysis and research, it was found that the prepared film has the characteristics of high maximum polarization, small residual polarization, and low leakage current density, and the energy storage performance has been greatly improved compared with BBT film. The energy storage density and breakdown field strength of BBT film are relatively low. After doping with rare earth element La, these two indicators have been greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings:

[0027] Figure 1 This is the morphology analysis of the BTO ferroelectric film in a preferred embodiment of the present invention: (a) XRD graph and (b) SEM graph.

[0028] Figure 2 This is a diagram of the BTO cross section and energy storage performance in a preferred embodiment of the present invention: (a) cross section diagram (b) PE loop under maximum field.

[0029] Figure 3 This is the morphology analysis of the BLTO (AC) ferroelectric film in a preferred embodiment of the present invention: (a) XRD graph and (b) SEM graph.

[0030] Figure 4 This is a comparison diagram of the energy storage performance of BTO and BLTO (AC) in a preferred embodiment of the present invention: (a) PE loop comparison under approximate field (b) PE loop comparison under maximum field.

[0031] Figure 5 The energy storage performance of the BLTO (AC) film in a preferred embodiment of the present invention varies with the electric field: (a) PE loop measured under different electric fields; (b) U, U r Relationship diagram with electric field change; (c) P max , P r , (a) Relationship between ΔP and electric field; (d) Relationship between efficiency η and electric field.

[0032] Figure 6 The relationship between the energy storage performance of the BLTO (AC) film and the frequency in a preferred embodiment of the present invention is as follows: (a) PE loop measured at different frequencies; (b) Pmax , P r , ΔP vs. frequency; (c) U, U r , η varies with frequency.

[0033] Figure 7 The relationship between the energy storage performance of the BLTO (AC) film and the temperature in a preferred embodiment of the present invention is as follows: (a) PE loop measured at different temperatures; (b) P max , P r , ΔP versus temperature; (c) U, U r , graph showing the relationship between η and temperature.

[0034] Figure 8 The diagram of energy storage performance change of BLTO (AC) film in fatigue test in a preferred embodiment of the present invention is as follows: (a) PE loop in fatigue test; (b) P max , P r , ΔP versus charge and discharge times; (c) U, U r , η changes with the number of charge and discharge times.

[0035] Fig. 9 This is the morphology analysis of the BLTO (HN) ferroelectric film in a preferred embodiment of the present invention: (a) XRD diagram and (b) SEM diagram.

[0036] Fig.10 This is a comparison diagram of the energy storage performance of BLTO (AC) and BLTO (HN) in a preferred embodiment of the present invention: (a) PE loop comparison under approximate field; (b) PE loop comparison measured under maximum field; (c) leakage current comparison.

[0037] Fig.11 The relationship between energy storage performance and electric field in a preferred embodiment of the present invention is as follows: (a) PE loop measured under different electric fields; (b) P max , P r , ΔP versus electric field; (c) recoverable energy density U r And the relationship between efficiency η and electric field.

[0038] Fig.12 This is the morphology analysis of the BBT ferroelectric film in a preferred embodiment of the present invention: (a) XRD graph and (b) SEM graph.

[0039] Fig.13 The relationship between the energy storage performance of the BBT ferroelectric film and the electric field in a preferred embodiment of the present invention is as follows: (a) PE loop measured under different electric fields; (b) U, U r Relationship diagram with electric field change; (c) P max , P r, (a) Relationship between ΔP and electric field; (d) Relationship between efficiency η and electric field.

[0040] Fig.14 The relationship between the energy storage performance of the BBT ferroelectric film and the frequency in a preferred embodiment of the present invention is as follows: (a) PE loop measured at different frequencies; (b) P max , P r , ΔP vs. frequency; (c) U, U r , η varies with frequency.

[0041] Fig.15 The following is a diagram showing the relationship between energy storage performance and temperature in a preferred embodiment of the present invention: (a) PE loop measured at different temperatures; (b) P max , P r , ΔP versus temperature; (c) U, U r , graph showing the relationship between η and temperature.

[0042] Fig.16 The diagram of the energy storage performance change of the BBT ferroelectric film in the fatigue test of a preferred embodiment of the present invention is as follows: (a) PE loop in the fatigue test; (b) P in the fatigue test max , P r , ΔP changes; (c) U, U in fatigue test r ,η changes.

[0043] Fig.17 This is the morphology analysis of the BLBT ferroelectric film in a preferred embodiment of the present invention: (a) XRD graph and (b) SEM graph.

[0044] Fig.18 The following are the relationship diagrams of energy storage performance as a function of electric field in a preferred embodiment of the present invention: (a) PE loops of BLBT and BBT measured at maximum field; (b) relationship diagram of leakage current density of BLBT and BBT as a function of electric field; (c) PE loops measured at different electric fields at a measurement frequency of 5 kHz; (d) relationship diagram of Pmax, Pr, ΔP as a function of electric field; (e) relationship diagram of U, Ur, η as a function of electric field.

[0045] Fig.19 The following are the relationship diagrams of energy storage performance with frequency in a preferred embodiment of the present invention: (a) PE loop measured at different frequencies (b) Pm, Pr, ΔP with frequency (c) U, Ur, η with frequency.

[0046] Fig. 20 The following is a diagram showing the relationship between energy storage performance and temperature in a preferred embodiment of the present invention: (a) PE loop measured at different temperatures; (b) P max , P r, ΔP versus temperature; (c) U, U r , graph showing the relationship between η and temperature.

[0047] Fig.21 The diagram of energy storage performance change in fatigue test of a preferred embodiment of the present invention is as follows: (a) PE loop in fatigue test (b) P max , P r , ΔP versus charge and discharge times; (c) U, U r , η changes with the number of charge and discharge times. DETAILED DESCRIPTION

[0048] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0049] Example 1

[0050] Bi 3.25 La 0.75 Ti3O 12 (AC) Thin film preparation

[0051] 1. Preparation of Precursor Solution

[0052] Table 1 Precursor salts required for the preparation of BLTO (AC) ferroelectric thin films

[0053]

[0054] The reagents used to prepare the precursor solution of the BLTO film are shown in Table 1. The solution is prepared according to a colloidal concentration of 0.1 mol / L, wherein an excess of 5% Bi is used to compensate for volatilization during heat treatment. The reagents are weighed and dissolved in a propionic acid solution, stirred at room temperature and pressure for 6 hours to obtain a clear, transparent, colorless liquid, which is then left to stand for 72 hours for use.

[0055] 2. Thin film preparation: BLBT thin film is prepared by spin coating at room temperature and pressure. The environment should be as dust-free and clean as possible. Spin coating is performed according to the following steps:

[0056] Step 1: Place the Pt / Ti / SiO2 / Si substrate into a coating machine, use a pipette to draw 10 μL of the precursor solution and drop it onto the substrate. Set the coating machine parameters to 5000 rpm and 20 s of spin coating time. Then start the coating machine and evenly spin coat the solution onto the substrate.

[0057] Step 2: Place the spin-coated sample on a heating table. Set the temperature of the heating table to 120°C and the heating time to 2 minutes to remove the organic solvent.

[0058] Step 3: Place the heated sample in a tubular furnace for pyrolysis. The temperature of the tubular furnace is set to 400°C and the heating time is 10 minutes.

[0059] Step 4: Repeat steps 1-3 10 times to increase the thickness of the film.

[0060] Step 5: Place the sample in a tube furnace for annealing at a temperature of 650°C for 30 minutes.

[0061] In order to improve the energy storage performance of BTO film, the present invention uses chemical solution deposition method to prepare rare earth La doped Bi on Pt / Ti / SiO2 / Si substrate. 3.25 La 0.75 Ti3O 12 (BLTO) ferroelectric thin film.

[0062] Example 2

[0063] Bi 3.25 La 0.75 Ti3O 12 Preparation of (HN) thin films

[0064] 1. Preparation of Precursor Solution

[0065] Table 2 Precursor salts required for the preparation of BLTO (HN) ferroelectric thin films

[0066]

[0067] The reagents used to prepare the precursor solution of BLTO (HN) film are shown in Table 2. The solution is prepared according to a colloidal concentration of 0.1 mol / L, wherein an excess of 5% Bi is used to compensate for volatilization during heat treatment. The reagents are weighed according to the measurement, and glacial acetic acid and ethylene glycol methyl ether are selected as solvents with a content ratio of 3:1. The weighed reagents are dissolved in the solvent and stirred for 6 hours under normal pressure and 40°C water bath heating to obtain a clear and transparent colorless liquid, which is then left to stand for 24 hours for use.

[0068] 2. Thin film preparation: BLTO (HN) thin film is prepared by spin coating at room temperature and pressure. The environment is as dust-free and clean as possible. Spin coating is performed according to the following steps:

[0069] Step 1: Place the Pt / Ti / SiO2 / Si substrate into a coating machine, use a pipette to draw 10 μL of the precursor solution and drop it onto the substrate. Set the coating machine parameters to 5000 rpm and 20 s of spin coating time. Then start the coating machine and evenly spin coat the solution onto the substrate.

[0070] Step 2: Place the spin-coated sample on a heating table, set the temperature of the heating table to 120°C, and heat for 2 minutes to remove the solvent.

[0071] Step 3: Place the heated sample in a tubular furnace for pyrolysis. The temperature of the tubular furnace is set to 400°C and the heating time is 10 minutes.

[0072] Step 4: Repeat steps 1-3 10 times to increase the thickness of the film.

[0073] Step 5: Place the sample in a tube furnace for annealing at a temperature of 650°C for 30 minutes.

[0074] Example 3

[0075] BaBi4Ti4O 15 (BBT) film preparation

[0076] 1. Preparation of Precursor Solution

[0077] Table 3 Precursor salts required for the preparation of BBT ferroelectric thin films

[0078]

[0079] The reagents used to prepare the precursor solution of BBT film are shown in Table 3. The solution was prepared according to the colloidal concentration of 0.1 mol / L, in which Bi was excessive by 5% to compensate for the volatilization during the heat treatment.

[67] The reagent is weighed according to the measurement and dissolved in the propionic acid solution. The mixture is stirred for 6 hours at room temperature and pressure to obtain a clear, transparent, colorless liquid, which is then allowed to stand for 72 hours for use.

[0080] 2. Thin film preparation: The BBT thin film is prepared by spin coating at room temperature and pressure. The environment is as dust-free and clean as possible. The spin coating is performed according to the following steps.

[0081] Step 1: Place the Pt / Ti / SiO2 / Si substrate into a coating machine, use a pipette to draw 10 μL of the precursor solution and drop it onto the substrate. Set the coating machine parameters to 5000 rpm and 20 s of spin coating time. Then start the coating machine and evenly spin coat the solution onto the substrate.

[0082] Step 2: Place the spin-coated sample on a heating table. Set the temperature of the heating table to 120°C and the heating time to 2 minutes to remove the organic solvent.

[0083] Step 3: Place the heated sample in a tubular furnace for pyrolysis. The temperature of the tubular furnace is set to 400°C and the heating time is 10 minutes.

[0084] Step 4: Repeat steps 1-3 10 times to increase the thickness of the film.

[0085] Step 5: Place the sample in a tube furnace for annealing at a temperature of 650°C for 30 minutes.

[0086] Example 4

[0087] BaLa 0.2 Bi 3.8 Ti4O 15 Preparation of (BLBT) films

[0088] 1. Preparation of precursor solution

[0089] Table 4 Precursor salts required for preparing BLBT ferroelectric thin films

[0090]

[0091] The reagents used to prepare the precursor solution of the BLBT film are shown in Table 4. They are prepared according to a colloid concentration of 0.1 mol / L, wherein an excess of 5% Bi is used to compensate for volatilization during heat treatment. The reagents are weighed and dissolved in a propionic acid solution, stirred at room temperature and pressure for 6 hours to obtain a clear, transparent, colorless liquid, which is then left to stand for 72 hours for use.

[0092] 2. Thin film preparation: The BLBT thin film was prepared by spin coating at room temperature and pressure. The environment was kept as dust-free and clean as possible. The spin coating was performed according to the following steps.

[0093] Step 1: Place the Pt / Ti / SiO2 / Si substrate into a coating machine, use a pipette to draw 10 μL of the precursor solution and drop it onto the substrate. Set the coating machine parameters to 5000 rpm and 20 s of spin coating time. Then start the coating machine and evenly spin coat the solution onto the substrate.

[0094] Step 2: Place the spin-coated sample on a heating table. Set the temperature of the heating table to 120°C and the heating time to 2 minutes to remove the organic solvent.

[0095] Step 3: Place the heated sample in a tubular furnace for pyrolysis. The temperature of the tubular furnace is set to 400°C and the heating time is 10 minutes.

[0096] Step 4: Repeat steps 1-3 10 times to increase the thickness of the film.

[0097] Step 5: Place the sample in a tube furnace for annealing at a temperature of 650°C for 30 minutes.

[0098] Experimental Example 1

[0099] Bi 3.25 La 0.75 Ti3O 12 (AC) Microstructure and performance characterization of thin films

[0100] 1. Experimental methods

[0101] (a) The crystal structure of the obtained film was characterized using a Philips XPert PRO X-ray diffractometer (XRD, A Philips XPert PRO diffractometer, The Netherlands);

[0102] (b) The microstructure and thickness of the film were scanned using a Japanese FEI Sirion 200 field emission scanning electron microscope (FE-SEM);

[0103] (c) To measure the electrical properties, a circular Au top electrode with a diameter of about 0.2 mm was deposited on the film surface using a sputtering instrument (SCB-12 Miriam Mini Ion Sputtering Instrument, China) through a stainless steel shadow mask;

[0104] (d) Ferroelectric and leakage current characteristics were tested using a Sawyer-Tower circuit connected to a computer-controlled standardized ferroelectric test system (Precision Premier II, Radiant Technologies, USA).

[0105] 2. Microstructure and crystal structure analysis

[0106] Figure 3 (a) shows the XRD spectra of BLTO film and BTO film deposited on Pt / Ti / SiO2 / Si substrate at an annealing temperature of 650°C. The results show that the prepared BLTO (AC) film is a single-phase polycrystalline and can be refracted according to an orthorhombic lattice with a space group of A21am. It can be seen that as the BTO film is doped with La ions, the peak intensity of the diffraction peak decreases, indicating that the amorphous state of BLTO is improved and the grain size becomes smaller. In order to further study the effect of La ion doping on the micromorphology and electrical properties of the film, the SEM was used to scan the morphological characteristics of the film, and the corresponding results are shown in Figure 2. Figure 3 (b) As shown, it can be seen that the surface morphology of the prepared film is dense, the degree of crystallization is good, the grain size is small, the connectivity between the grains is large, and the grain boundaries are clear and obvious, which is consistent with the characteristics of the XRD spectrum. Figure 3 (b) The upper right corner is a cross-sectional view of the film. By measuring the cross-sectional view of the film, it was found that the thickness of the film was about 270nm.

[0107] Electrical performance analysis

[0108] Figure 4 (a) BTO thin film and rare earth La-doped Bi4Ti3O 12 The comparison of the hysteresis loops of the (BLTO) film under an electric field of about 0.5 MV / cm shows that both films exhibit large polarization and obvious hysteresis, and have typical ferroelectric properties. Figure 4 As shown in (a), compared with the BTO film, the BLTO film has a slender and elongated hysteresis loop, suggesting that the film has high energy storage density and energy storage efficiency. In addition, by comparison, it is found that the polarization value of BLTO is lower than that of BTO under the same field. This is because BLTO shows a smaller grain size and a denser microstructure than the BTO film. According to previous reports, due to the enhanced clamping effect of adjacent grains and the absence of domain walls, the movement and switching of domain walls in small grain samples will become relatively difficult. In addition, the grain size is small, the pore density is large, and the grain boundaries and pores are paraelectric regions, which will lead to low polarization.

[0109] Figure 4 (b) is a comparison of the hysteresis loops of BTO film and rare earth La-doped BLTO film at their respective maximum field strengths. From the shape of the hysteresis loops, it can be clearly seen that the BLTO film is better than the BTO film in terms of breakdown field strength, energy storage density, and energy storage efficiency. Through calculation, it is found that the breakdown field strength of BLTO can be as high as 3.14MV / cm. In terms of energy storage density, the maximum recoverable energy storage density U of BTO is r Only 2.49J / cm 3 , and the maximum recoverable energy storage density of BLTO is U r Up to 50.31J / cm 3 The above results may be due to the fact that the doping of rare earth element La changes the grain size and morphology of the film, effectively suppressing oxygen vacancies, while the concentration of oxygen vacancies decreases, the insulation properties of the material are improved, and the leakage current of the material is reduced, which ultimately leads to a significant improvement in the energy storage performance of the BLTO film.

[0110] Figure 5 (a) is the room temperature PE hysteresis loop of BLTO film under different applied electric fields when the measurement frequency is 5kHz. The results show that all PE loops are thin in shape. m Larger, Pr smaller, coercive field E c The BLTO(AC) film can withstand an electric field greater than 3MV / cm. Figure 5 (b) Given U,U r The dependence of U,U r It gradually increases with the increase of the external electric field. The efficiency η first decreases and then tends to be stable, and finally decreases slightly. Figure 5 (c) is the polarization Pmax , P r As well as the relationship between ΔP and the change of electric field, we can see that as the electric field increases, P max increased rapidly, while P r It is relatively gentle, indicating that the remnant polarization of the BLTO film is low. Generally speaking, the energy storage density of the ferroelectric film is related to the shape of the hysteresis loop. The maximum polarization is high, the remnant polarization is low, and the hysteresis loop is elongated. Such a ferroelectric film is conducive to energy storage. Figure 5 As shown in (d), the BLTO film has excellent energy storage performance. r About 44.7J / cm 3 The BLTO(AC) film has a high energy density and high energy efficiency, which means that the BLTO(AC) film can be used as a candidate material for lead-free ferroelectric film capacitors in energy storage applications.

[0111] Figure 6 (a) is the PE loop measured at room temperature with a field strength of 0.74 MV / cm and different frequencies. It can be seen that when the frequency increases from 1 kHz to 64 kHz, all the loops overlap and the shape hardly changes, indicating that the BLTO (AC) ferroelectric film has good frequency stability. Figure 6 (b) is the polarization P max , P r As well as the relationship between ΔP and frequency, we can see that as the frequency increases, P max There is a slight downward trend, and it decreases significantly after 32kHz. max has the same trend, while P r It is relatively gentle. Through calculation, it is found that P max From 19.7μC / cm 2 Down to 16.7μC / cm 2 , ΔP is from 17.46μC / cm 2 Down to 15.18μC / cm 2 . Figure 6 (c) is U, U r , η vs. frequency, we can see that the energy storage density U and U of BLTO (AC) film r It remains stable, with only a slight drop at a measurement frequency of 64kHz. Interestingly, it can be observed that the energy storage efficiency η increases slightly as the frequency increases, which illustrates the excellent frequency stability of the film.

[0112] The thermal stability of ferroelectric film capacitors is another important factor in the application. Good thermal stability can make film capacitors miniaturized and reduce the overall cost by eliminating the need for a secondary cooling system. Figure 7 (a) shows the PE loops of the BLTO(AC) film measured at different temperatures from room temperature to 180°C under an applied electric field of 0.74 MV / cm and a frequency of 5 kHz. As the measurement temperature increases, the PE loops overlap with each other with little change, indicating that the energy storage performance of the film is less dependent on the measurement temperature. The calculated P max , P r The relationship between the value of ΔP and the measured temperature is as follows: Figure 7 (b) As shown in the figure, the increase in the measurement temperature will lead to higher thermal energy, which will promote the movement and reversal of ferroelectric domains, resulting in P m and P r There is a slight rise, and then tends to be stable. The temperature-related U and U are calculated from the PE loop. re And the efficiency η changes as Figure 7 As shown in (c), as the temperature increases from room temperature to 180°C, U r and efficiency η from 5.38 J / cm 3 and 75.66% decreased to 5.33 J / cm 3 and 74.5%, indicating that the BLTO(AC) film has good thermal stability.

[0113] Figure 8 It shows that at room temperature, under an electric field of 0.74 MV / cm, a frequency of 5 kHz, 10 6 The energy storage performance change diagram before and after the charge and discharge cycle shows that the shape of the PE loop remains basically unchanged. max Only from 18.1μC / cm 2 Down to 17.5μC / cm 2 , so that the recoverable energy density (U r ) from 4.97 J / cm 3 Slightly decreased to 4.92 J / cm 3 , the efficiency η slightly decreased from 74.17% to 73.76%, which indicates that the film has good fatigue resistance. This good fatigue resistance is mainly attributed to (Bi2O2) 2+ The layer effectively blocks leakage current and prevents electrical breakdown during repeated polarization under high electric fields. These results indicate that the BLTO(AC) film has excellent fatigue durability.

[0114] Experimental Example 2

[0115] Bi 3.25 La 0.75 Ti3O12 Microstructure and performance characterization of (HN) thin films

[0116] The experimental method is the same as that of Experimental Example 1.

[0117] Fig. 9 (a) shows the XRD spectra of BLTO (AC) film and BLTO (HN) film deposited on Pt / Ti / SiO2 / Si substrate at an annealing temperature of 650°C. The results show that the prepared BLTO (HN) film is a single-phase polycrystalline and can be refracted according to an orthorhombic lattice with a space group of A21am. It can be seen that compared with the BLTO (AC) film, the peak intensity of the diffraction peak of the BLTO (HN) film is improved, indicating that the degree of crystallization of BLTO (HN) is improved and the grain size is larger. In order to further study the effects of different precursor solutions on the micromorphology and electrical properties of ferroelectric films, SEM was used to scan the morphological features of the film, and the corresponding results are shown in Figure 2. Fig. 9 (b) As shown, it can be seen that the surface morphology of the prepared film is dense, the degree of crystallization is good, the grain size is large, the connectivity between the grains is large, and the grain boundaries are clear and obvious, which is consistent with the characteristics of the XRD spectrum. Fig. 9 (b) The upper right corner is a cross-sectional view of the film. By measuring the cross-sectional view of the film, it was found that the thickness of the film was about 470nm.

[0118] like Fig.10 (a) is a comparison of the hysteresis loops of BLTO films prepared using acetate and nitrate precursor solutions under an electric field of about 2 MV / cm. It can be seen that both films exhibit large polarization and obvious hysteresis, and have typical ferroelectric properties. As shown in the figure, the P of BLTO (AC) film max It is larger than that of BLTO(HN) film, but the hysteresis loop of BLTO(HN) film is fatter, which indicates that it has a large energy loss during the charge and discharge process, which ultimately leads to a low energy storage efficiency of the film. Obviously, compared with BLTO(HN) film, BLTO(AC) film has a slender and long hysteresis loop, which means that the film has high energy storage density and efficiency.

[0119] Fig.10 (b) shows the PE loops of the BLTO(AC) and BLTO(HN) films at the maximum field. It can be seen from the figure that the maximum field of the BLTO(AC) ferroelectric film is 3.14 MV / cm, while the maximum field of the BLTO(HN) ferroelectric film is only 2.1 MV / cm. The recoverable energy density U of the BLTO(AC) film at the maximum field r 50.31 J / cm 3, which is nearly three times that of BLTO(HN) film. The difference in energy storage performance may be caused by the difference in grains, and the size of the grains may affect the energy storage performance of the ferroelectric film. Generally, the smaller the grains, the better the electrical properties of the ferroelectric film may be. This is because smaller grain sizes may lead to more grain boundaries and defects, which may cause the leakage current to decrease, thereby increasing the polarization strength and polarization charge density of the ferroelectric film, thereby improving the energy storage density of the ferroelectric film.

[0120] Fig.10 (c) is a comparison of the leakage current density of BLTO(AC) and BLTO(HN) films. From the figure, we can see that both films have lower leakage current density. BLTO(AC) film has a lower leakage current density, which is about 10 -4 A / cm 2 This is an order of magnitude lower than the leakage current of previously reported BTO films. The low leakage current density may be caused by two reasons: on the one hand, due to La 3+ The ion replaces the Bi at the A position 3+ Ion, Bi 3+ The oxygen vacancies caused by ion volatilization are suppressed, thus reducing the leakage current density. 3+ The addition of ions increases the band gap, which makes it difficult for free electrons to jump to higher energy levels and also reduces the conductivity of the film. The reduction in conductivity ultimately reduces the leakage current density to a good level. Another reason for the low leakage current density is that the prepared film is incompletely crystallized, with fine grains and dense morphology, which is confirmed by our XRD and SEM measurements.

[0121] The SEM micromorphology also confirms that there is a difference in the grain size of the two films, and the difference in grain size may be caused by the use of different precursor solutions and preparation conditions. 3.25 La 0.75 Ti3O 12 In the ferroelectric thin film prepared from the precursor solution, bismuth acetate and lanthanum acetate as solvents and stabilizers may have an inhibitory effect on crystal growth, thus producing a smaller grain size. 3.25 La 0.75 Ti3O 12 In the ferroelectric films prepared from the precursor solutions, bismuth nitrate and lanthanum nitrate may promote the crystal growth, thus producing larger grain size.

[0122] Fig.11(a) shows the electric field-related PE loop of BLTO(HN) at room temperature with a measurement frequency of 5 kHz. As the electric field strength increases, the PE loop remains slender and sharp. By continuously increasing the electric field strength, the breakdown electric field (E b ) reached 2.1MV / cm.

[0123] Fig.11 (b) is the polarization P max , P r As well as the relationship between ΔP and the change of electric field, we can see that as the electric field increases, P max The upward trend is obvious before 0.5MV / cm, and then the trend slows down, and ΔP also has the same trend. r The film maintains a slow growth trend and remains at a low level, indicating that the film has good energy storage efficiency. max From 2.13μC / cm 2 Rising to 30.4μC / cm 2 , ΔP is from 1.895μC / cm 2 Rising to 23.12μC / cm 2 .

[0124] The recoverable energy density (U r ) and energy storage efficiency (η) vary with the electric field as shown in Fig.11 As shown in (c), it can be seen from the figure that no matter the recoverable energy storage density U re In terms of efficiency η, BLTO(HN) is far inferior to BLTO(AC) ferroelectric film. Further observation shows that with the increase of electric field, the recoverable energy density U of BLTO(AC) and BLTO(HN) films increases. re It keeps increasing and finally reaches the maximum value, U r 27.37J / cm 3 and 17.57 J / cm 3 , while the efficiency η decreases significantly with the increase of electric field strength in the range of 0.2MV / cm to 0.6MV / cm, and the downward trend begins to slow down after 0.8MV / cm. When the applied electric field increases from ~0.2MV / cm to ~2MV / cm, the efficiency η values ​​of the two films decrease from 86% to 74% and from 76% to 61%, respectively. The results show that both ferroelectric films have good electric field dependence.

[0125] Example 1 and Example 2 are preparations of three-layer Aurivillius phase thin films. maxIn order to improve the energy storage performance of BTO ferroelectric film, Bi(CH3COO)3, La(CH3COO)3, and Ti(C4H9O)4 were used as precursor salts to deposit Bi on Pt / Ti / SiO2 / Si substrate. 3.25 La 0.75 Ti3O 12 (AC) ferroelectric film, which exhibits a very fine and sharp PE hysteresis loop. At room temperature and an electric field of 3.14 V / cm, its recoverable energy density U r 50.31 J / cm 3 , the energy storage efficiency is 68.03%, at 10 6 The energy storage performance has almost no change after the cyclic charge and discharge test, indicating that the film has excellent fatigue durability. The PE curve does not change much in the temperature range of 20℃ to 180℃, indicating that the film has good thermal stability.

[0126] At the same time, in order to explore the influence of different precursor solutions on the energy storage properties of ferroelectric films, bismuth nitrate (Bi(NO3)3), lanthanum nitrate (La(NO3)3) and tetrabutyl phthalate (Ti(C4H9O)4) were used as precursor salts to prepare BLTO(HN) ferroelectric films. The results obtained were quite different from those of BLTO(AC) ferroelectric films with the same process and different precursor salts. On a microscopic scale, the grain size of BLTO(NO) is larger than that of BLTO(AC). The grain size will affect the energy storage properties of ferroelectric films.

[0127] Experimental Example 3

[0128] BaBi4Ti4O 15 Microstructure and performance characterization of (BBT) films

[0129] Experimental methods:

[0130] (a) The crystal structure of the obtained film was characterized by Philips XPert PRO X-ray diffractometer (XRD, A Philips XPert PRO diffractometer, The Netherlands);

[0131] (b) The microstructure and thickness of the film were scanned using a Japanese FEI Sirion 200 field emission scanning electron microscope (FE-SEM);

[0132] (c) To measure the electrical properties, a circular Au top electrode with a diameter of about 0.2 mm was deposited on the film surface using a sputtering instrument (SCB-12 Miriam Mini Ion Sputtering Instrument, China) through a stainless steel shadow mask;

[0133] (d) Ferroelectric and leakage current characteristics were tested using a Sawyer-Tower circuit connected to a computer-controlled standardized ferroelectric test system (Precision Premier II, Radiant Technologies, USA).

[0134] Microstructure and crystal structure characterization:

[0135] Fig.12 (a) shows the XRD spectrum of the BBT film deposited on the Pt / Ti / SiO2 / Si substrate at an annealing temperature of 650°C. The results show that the prepared film is a single-phase polycrystalline with sharp diffraction peaks, indicating that the film has a good degree of crystallization and can be refracted according to the orthorhombic lattice of the space group A21am. In order to further study the grain size and microstructure of the film, the film was scanned by SEM, and the corresponding results are shown in Figure 2. Fig.12 (b) As shown, it can be seen that the surface morphology of the prepared film is dense, the degree of crystallization is good, the grain size is moderate, and the grain boundary is clear and obvious, which is consistent with the characteristics of the XRD spectrum. Fig.12 (b) The upper right corner is a cross-sectional view of the film. By measuring the cross-sectional view of the film, it was found that the thickness of the film was about 545nm.

[0136] XRD spectrum for electrical performance analysis. The results show that the prepared film is single-phase polycrystalline with sharp diffraction peaks, indicating that the film has a good degree of crystallization and can be refracted according to the orthorhombic lattice of the space group A21am, which is consistent with the previously reported research results. In order to further study the grain size and microstructure of the film, the film was scanned by SEM for morphological characteristics, and the corresponding results are shown in Fig.12 (b) As shown, it can be seen that the surface morphology of the prepared film is dense, the degree of crystallization is good, the grain size is moderate, and the grain boundary is clear and obvious, which is consistent with the characteristics of the XRD spectrum. Fig.12 (b) The upper right corner is a cross-sectional view of the film. By measuring the cross-sectional view of the film, it was found that the thickness of the film was about 545nm.

[0137] Electrical performance analysis:

[0138] Fig.13 (a) is the PE hysteresis loop of the BBT film measured at room temperature under different external electric fields at a measurement frequency of 5kHz. As can be seen from the figure, all PE loops are slender. Slender hysteresis loops usually indicate that the ferroelectric film has a lower leakage current density and better polarization retention performance, and can maintain its polarization state for a long time, thus helping to achieve stable and reliable energy storage and sensor applications. m Moderate, P rThe electric field strength was continuously increased during the test, and it was finally measured that the maximum electric field that the BBT film could withstand was 1.74MV / cm. Fig.13 (b) shows U,U r The dependence of U, U r It gradually increases with the increase of the external electric field. η first decreases and then tends to be stable, and finally decreases slightly. Fig.13 (c) is the polarization P max , P r As well as the relationship between ΔP and the change of electric field, we can see that as the electric field increases, P max increased rapidly, while P r It is relatively flat, indicating that the remnant polarization of the BBT film is low. Generally speaking, the energy storage density of the ferroelectric film is related to the shape of the hysteresis loop. The maximum polarization is high, the remnant polarization is low, and the hysteresis loop is elongated. Such a ferroelectric film is conducive to energy storage. Fig.13 (b) and Fig.13 (d) It can be seen that the U of the BBT ferroelectric film at 1.74 MV / cm r About 28J / cm 3 , the energy storage efficiency η is 89%, which is roughly the same as the results previously reported by our research group. BBT film has excellent energy storage efficiency, which means that BBT-based films can be used as candidate materials for lead-free ferroelectric film capacitors in energy storage applications, but the energy storage density is not ideal, so how to maintain the high energy storage efficiency of BBT ferroelectric films while improving the energy storage density has become the research focus of BBT-based films.

[0139] Fig.14 (a) is the PE loop measured at room temperature with a field strength of 1.1 MV / cm and different frequencies. It can be seen that when the frequency increases from 1 kHz to 50 kHz, the shape of the PE loop hardly changes, and all loops overlap, which indicates that the BBT ferroelectric film has good frequency stability. Fig.14 (b) is the polarization P max , P r As well as the relationship between ΔP and frequency, we can see that as the frequency increases, P max It remains stable at first, then decreases slightly after 8kHz. max has the same trend, while P r It is relatively gentle. Through calculation, it is found that P max From 28.6μC / cm 2 Down to 26.6μC / cm 2 , ΔP is from 27.39μC / cm 2 Down to 25.86μC / cm2 . Fig.14 (c) is U, U r From the relationship between η and frequency, we can see that the energy storage efficiency η of BBT film has almost no change at different frequencies, which can also be explained by Fig.14 It is verified that the shape of the PE loop in (a) has almost no change. r It remains stable at 16kHz and below, and only drops slightly after 16kHz.

[0140] The thermal stability of BBT film is characterized by testing its PE loop at 20℃ to 180℃. The PE loops measured at different temperatures are as follows: Fig.15 As shown in (a), with the increase of temperature, the shape of the PE loop does not change significantly, indicating that it has good thermal stability. Fig.15 (b) shows P max , P r As well as the trend of ΔP changing with increasing temperature, it can be seen from the figure that P max and ΔP remain stable or even increase at 140°C or below, because at high temperatures, higher thermal energy makes it easier for ferroelectric domains to move and reverse, and then decrease after 140°C. Fig.15 (c) is the relationship between energy storage efficiency and energy storage density calculated by the PE loop and temperature. As shown in the figure, under the electric field of 1.1MV / cm, as the temperature rises, U r The values ​​of and η were slightly reduced, which were 12.93 J / cm 3 to 12.37J / cm 3 The energy storage efficiency decreases with increasing temperature, that is, the energy storage loss increases with increasing temperature. This phenomenon is mainly due to the increase in leakage current caused by the increase in electron concentration and ionic conductivity at high temperature. These results show that the degradation of energy storage performance with increasing temperature is almost negligible. Good temperature stability is one of the important performance indicators of ferroelectric films. The above results show that BBT-based films have good temperature stability and can be used normally in relatively harsh environments.

[0141] Fig.16 (a) shows the results of 10 6 charge and discharge cycles. 6 The PE loops before and after the first cycle show almost no change, indicating that the BBT film has good fatigue durability, which is an important consideration for ferroelectric capacitors in energy storage applications. Fig.16 (b) It can be seen that P max Always at 12.5μC / cm3 Floating around, where P max With P r The curves of are almost identical, indicating that the BBT ferroelectric film can maintain a very high energy storage efficiency during repeated charge and discharge. Fig.16 (c) It can be seen that in 10 6 The U of BBT ferroelectric film before and after the first charge and discharge test r Only from 2.25J / cm 3 Down to 2.2 J / cm 3 , which causes the efficiency to drop from 94.82% to 94.12%, indicating that the film has excellent anti-fatigue properties.

[0142] The inventors deposited four layers of Aurivillius structure BBT ferroelectric thin films on Pt / Ti / SiO2 / Si substrates using the CSD method. The morphology and energy storage performance of the BBT thin films were studied. The study found that the PE loop of the BBT thin film was slender, and the P m Moderate, P r Smaller, U r Not high, η is relatively high (87.1%). And BBT film has excellent performance in electric field dependence, frequency stability, temperature stability and anti-fatigue properties. These results show that BBT film has great potential for development and utilization in the field of energy storage. The above research also points out the direction for subsequent work, that is, through certain methods, while retaining the excellent properties of BBT ferroelectric film, the energy storage density of the film can be improved.

[0143] Experimental Example 4

[0144] BaLa 0.2 Bi 3.8 Ti4O 15 Microstructure and performance characterization of (BLBT) films

[0145] Experimental methods:

[0146] (a) The crystal structure of the obtained film was characterized by Philips XPert PRO X-ray diffractometer (XRD, A Philips XPert PRO diffractometer, The Netherlands);

[0147] (b) The microstructure and thickness of the film were scanned using a Japanese FEI Sirion 200 field emission scanning electron microscope (FE-SEM);

[0148] (c) To measure the electrical properties, a circular Au top electrode with a diameter of about 0.2 mm was deposited on the film surface using a sputtering instrument (SCB-12 Miriam Mini Ion Sputtering Instrument, China) through a stainless steel shadow mask;

[0149] (d) Ferroelectric and leakage current characteristics were tested using a Sawyer-Tower circuit connected to a computer-controlled standardized ferroelectric test system (Precision Premier II, Radiant Technologies, USA).

[0150] Microstructure and crystal structure analysis:

[0151] The XRD spectrum of the obtained film is shown in Fig.17 (a) shows the Miller index of the substrate peak. Compared with BBT, the diffraction peak (119) of the La-doped BLBT film at 30° is significantly enhanced, indicating that the crystal quality of the film is improved. Fig.17 (b) This is also confirmed by the SEM surface morphology of the film, from which it can be seen that the BLBT film has obvious particle visibility and large grain size. Nevertheless, the grain size of the BLBT ferroelectric film prepared in this work is still smaller than that of the ceramic or high-temperature annealed films reported previously. It has been confirmed that the domain size is proportional to the square root of the grain size.

[0152] Electrical performance analysis:

[0153] Fig.18 (a) is the PE loop of BBT and BLBT films under the maximum electric field. Due to the ultra-fine grain size, the PE hysteresis loops of the two films have a large P max and a smaller P r , and the shape is thin and sharp. This elongated PE loop also reveals the good relaxor ferroelectric properties of the film, due to the large Ba 2+ Substituting Bi in perovskite-like structural layers 3+ , which leads to Ba 2+ The uneven distribution and local charge imbalance of the ferroelectric film destroy the long-range dipole interaction and form a local polar nanoregion (PNR). The relaxation behavior that ultimately leads to low energy loss and high efficiency in the film during charge and discharge. The elongated hysteresis loop of the ferroelectric film can also indicate that the polarization state of the film has a high stability. In practical applications, ferroelectric materials need to be able to maintain their polarization state for a long time without being affected by external interference and the environment. In addition, compared with the maximum polarization of the BBT film of 46.7μC / cm 2 Compared with the maximum breakdown field of 2.01 MV / cm, the BLBT film has a larger polarization and electric field resistance, which are 55.6 μC / cm 2 and 3.04 MV / cm. This may be due to the volatile Bi in the perovskite layer 3+ La 3+substituted, which suppresses defects in the film, resulting in a decrease in the leakage current of the BLBT film, such as Fig.18 (b) shows that the leakage current density increases from 10 -4 A / cm 2 Reduce to 10 -5 A / cm 2 , which makes the BLBT film have a higher breakdown electric field. According to the PE loop, the recyclable energy storage density of BBT and BLBT is calculated to be 28.27 J / cm 3 and 66.8 J / cm 3 , the energy storage efficiencies are 89.66% and 85.1% respectively. Both films have high energy storage efficiencies. Fig.18 (c) shows the room temperature electric field-dependent PE hysteresis loop at a measurement frequency of 5 kHz. As the electric field strength increases, the PE loop remains thin and sharp, and the breakdown electric field (E b ) reached 3.04MV / cm.

[0154] Fig.18 (d) is the P of BLBT max , P r As well as the relationship between ΔP and the change of electric field, we can see that as the electric field increases, P max The increase was relatively rapid and reached 55.6 μC / cm at the maximum field. 2 , and P r The value is small and the curve is straight, indicating that the residual polarization of the BLBT film is low, the maximum polarization is high, and the hysteresis loop is elongated, which means that the energy storage density and energy storage efficiency of the BLBT film are relatively high.

[0155] Total energy density (U), recoverable energy density (U r ) and energy storage efficiency (η) vary with the electric field as shown in Fig.18 (e) As shown in Figure 2, U and U r It continues to increase and finally reaches the maximum value U=77.3J / cm 3 and Ur=66.8J / cm 3 , which is attributed to the large polarization and high breakdown field strength. When the applied electric field increases from ~0.5MV / cm to ~3MV / cm, the η value decreases from 91.5% to 85.1%. The results show that the film capacitor has good electric field dependence.

[0156] Fig.19(a) is the PE loop of the BLBT ferroelectric film at different frequencies. It can be seen from the figure that as the measurement frequency increases from 0.5kHz to 64kHz, the polarization value decreases slightly, and the PE loop always maintains a slender shape, which illustrates the high energy storage density, high efficiency and excellent frequency stability of the BLBT ferroelectric film. Fig.19 (b) shows the P of BLBT ferroelectric film max , P r As well as the curve of ΔP changing with frequency, we can see that as the frequency increases, P max and ΔP decreased slightly. Finally, P max From 33.5μC / cm 2 to 29.3μC / cm 2 .

[0157] U, U r and η vary with frequency as Fig.19 (c) is shown. Interestingly, the η value first decreases at around 8kHz and then begins to increase. This is mainly due to the time effect of the long-range ferroelectric state induced by the electric field returning to the initial ergodic state. Generally speaking, when a ferroelectric is subjected to an electric field, its ferroelectric polarization changes, resulting in the reconstruction of the ferroelectric domains. When the electric field is removed, the ferroelectric domains return to the initial ergodic state. This process is called the time effect of the ferroelectric domains. Under an electric field of 1.5MV / cm, when the measurement frequency range is 0.5 to 64kHz, U r The value is 21.8J / cm 3 ~17.9J / cm 3 There is a slight change between the two, indicating that the ferroelectric film has excellent frequency stability in the field of energy storage capacitors. Excellent frequency stability is very important for ferroelectric films. Nowadays, ferroelectric films are widely used in wireless communications, microwave electronics, optoelectronics, sensors and other fields. Especially in the field of microwave electronics, ferroelectric films are usually used to make circuit components such as oscillators and filters. The performance reliability of these circuit components depends on the frequency stability of the ferroelectric film. If the frequency stability is poor, these circuit component systems will be difficult to operate reliably.

[0158] In addition to electric field dependence and frequency stability, the temperature stability and fatigue resistance of ferroelectric energy storage films are also key factors for energy storage capacitors. Good thermal stability can ensure that dielectric capacitors can still be used normally in extreme environments, while avoiding additional heat dissipation systems, catering to the trend of miniaturization and intensification of electronic components and saving production costs.

[0159] Fig. 20(a) shows the PE loop of the BLBT film from 20°C to 180°C under an electric field of 1.5 MV / cm. As the temperature increases, the PE loop shape remains elongated without obvious sudden changes, and overlaps with each other, indicating that the BLBT film can still maintain high energy storage efficiency at high temperatures. Fig. 20 (b) is P max , P r And the curve of ΔP changing with temperature. It can be clearly seen from the figure that with the increase of temperature, P max , P r And ΔP remains almost flat before 140℃. After 140℃, the residual polarization P r Starts to rise, after 160℃, P max There is a very small decrease, which is consistent with Fig. 20 This is consistent with the fact that the PE loop shape starts to become slightly fatter after 160°C in (a). What is more interesting is that before 160°C, P max It starts to rise slightly and reaches a maximum value of 32.7μC / cm at 160℃ 2 This is because the increase in temperature promotes the movement and conversion of ferroelectric domains. Ferroelectric domains are polarized areas in ferroelectric materials, which have a certain directionality and arrangement. In ferroelectric films, the size and arrangement of ferroelectric domains directly affect their electrical properties. When the temperature rises, the crystal structure in the ferroelectric film will undergo thermal vibration and thermal disturbance, causing the boundaries of the ferroelectric domains to shift and change, thereby promoting the movement and conversion of ferroelectric domains. In addition, the increase in temperature may cause the polarization direction of the ferroelectric domains to change, thereby changing the shape and size of the ferroelectric domains. This change can also promote the movement and conversion of ferroelectric domains, thereby changing the electrical properties of the ferroelectric film and ultimately leading to P max of the rise.

[0160] The trends of BLBT film energy storage density and energy storage efficiency with temperature are shown in Fig. 20 (c) U is almost constant over the temperature range, and 23.8 J / cm2 is observed at 20°C, 100°C, and 180°C, respectively. 3 , 23.4J / cm 3 and 24.6 J / cm 3 At the same time, U r The temperature shows a similar trend before reaching 160℃. Above 160℃, U r As the temperature rises, it gradually decreases, which is also reflected in the energy storage efficiency. The energy storage efficiency η value is relatively stable in the range of 20℃~140℃, but as the temperature rises, the η value decreases significantly. This phenomenon is mainly caused by the increase of electron concentration and ion conductivity at high temperature.

[72] .

[0161] Fig.21 (a) shows the BLT film under 1MV / cm electric field at 10 8 PE loop before and after the first charge and discharge. It can be seen that the hysteresis loop hardly changes with the increase of the number of charge and discharge cycles. In addition, the U of the BLBT film before and after the fatigue test was calculated based on the PE loop. re The value is 9.78J / cm 3 and 9.69 J / cm 3 The efficiency η value is 90.93% and 89.70% before and after the fatigue test, and the change is very small, indicating that the film has good fatigue resistance. Basically, the (Bi2O2) in the layered structure 2+ The layer can effectively block leakage current and prevent electrical breakdown during repeated polarization under high electric fields, which makes the BLBT film have such excellent fatigue resistance. 8 The effect of the charge-discharge cycle on the energy storage performance is almost negligible, which indicates that the BLBT film has an excellent service life in energy storage capacitors.

[0162] The inventors doped the rare earth element La into BBT to improve the energy storage performance of the film, and prepared BBT and BLBT films on silicon wafers using chemical solution deposition. The electric field dependence, frequency stability, temperature stability and fatigue durability of the BLBT film were studied. The experimental results show that the maximum breakdown field strength of the BLBT film is as high as 3.04MV / cm, which is 50% higher than the breakdown field strength of the BBT film, indicating that rare earth element doping can effectively improve the breakdown field strength of the film. In addition, the crystal quality is also improved. Due to the synergistic effect of these two aspects, the U of the La-doped BBT film is r The value reached 66.8J / cm 3 , U r The value reached 85.1%. These results indicate that BLBT films have broad application prospects in dielectric energy storage capacitors.

[0163] The inventors deposited BaBi4Ti4O on a Pt / Ti / SiO2 / Si substrate using a CSD process. 15 The (BBT) film was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the thickness of the ferroelectric film was measured by analyzing the microstructure of the cross section. The electrical properties were then analyzed by a ferroelectric analyzer, and the results showed that a relatively good energy storage performance was obtained at an annealing temperature of 650°C.

[0164] At the same time, in order to optimize the energy storage performance of the BBT film, the inventors deposited Bi on the Pt / SiO2 / Si bottom electrode using the same process under the same conditions.3.25 La 0.75 BaTi4O 15 (BLBT) film, through analysis and research, it was found that the prepared film has the characteristics of high maximum polarization, small residual polarization, and low leakage current density, and the energy storage performance has been greatly improved compared with BBT film. Specifically, the energy storage density and breakdown field strength of BBT film are relatively low. After doping with rare earth element La, these two indicators have been greatly improved.

[0165] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a layered ferroelectric photovoltaic film, characterized in that: The following steps are involved: S1. preparing a precursor solution, wherein the precursor solution contains one or more of a bismuth salt, a lanthanum salt, and a barium salt; S2. Prepare the thin film by spin coating using a coating machine.

2. The method for preparing the layered ferroelectric photovoltaic thin film according to claim 1, characterized in that: The step S2 specifically includes the following steps: A. Place the Pt / Ti / SiO2 / Si substrate into a coating machine, use a pipette to draw 10 μL of the precursor solution and drop it onto the substrate. Set the coating machine parameters to a speed of 5000 rpm and a spin coating time of 20 s. Then start the coating machine and evenly spin coat the solution onto the substrate. B. Place the spin-coated sample on a heating platform, set the temperature of the heating platform to 120°C, and heat for 2 minutes; C. Place the heated sample in a tube furnace for pyrolysis. The temperature of the tube furnace is set to 400°C and the heating time is 10 minutes. D. Repeat steps AC 10 times; E. Place the sample in a tubular furnace for annealing at a temperature of 650°C and an annealing time of 30 minutes.

3. The method for preparing a layered ferroelectric photovoltaic thin film according to claim 1 or 2, characterized in that: The step S1 is: press Bi 3.25 La 0.75 Ti3O 12 The chemical formulas are bismuth acetate, lanthanum acetate, tetrabutyl phthalate, and propionic acid, and are prepared according to a colloid concentration of 0.1 mol / L.

4. The method for preparing a layered ferroelectric photovoltaic thin film according to claim 3, characterized in that: Bi is in excess of 5%, and the reagents are weighed according to the measurement and dissolved in the propionic acid solution. The mixture is stirred for 6 hours at room temperature and pressure to obtain a clear and transparent colorless liquid, which is then left to stand for 72 hours for use.

5. The method for preparing a layered ferroelectric photovoltaic thin film according to claim 1 or 2, characterized in that: The step S1 is: press Bi 3.25 La 0.75 Ti3O 12 The chemical formulas are bismuth nitrate, lanthanum nitrate, tetrabutyl phthalate, glacial acetic acid, and ethylene glycol methyl ether, and the colloid concentration is 0.1 mol / L.

6. The method for preparing a layered ferroelectric photovoltaic thin film according to claim 5, characterized in that: Bi is in excess of 5%, reagents are weighed according to the measurement, glacial acetic acid and ethylene glycol methyl ether are used as solvents, and the content ratio is 3:

1. The weighed reagents are dissolved in the solvent, and stirred for 6 hours under normal pressure and 40°C water bath heating to obtain a clear and transparent colorless liquid, which is allowed to stand for 24 hours for use.

7. The method for preparing a layered ferroelectric photovoltaic thin film according to claim 1 or 2, characterized in that: The step S1 is: press Bala 0.2 Bi 3.8 Ti4O 15 The chemical formulas are bismuth acetate, barium acetate, lanthanum acetate, tetrabutyl phthalate, and propionic acid, and the colloid concentration is 0.1 mol / L.

8. The method for preparing a layered ferroelectric photovoltaic thin film according to claim 7, characterized in that: Bi is in excess of 5%, and the reagents are weighed according to the measurement. They are dissolved in the propionic acid solution and stirred at room temperature and pressure for 6 hours to obtain a clear and transparent colorless liquid, which is then left to stand for 72 hours for use.

9. The layered ferroelectric photovoltaic film prepared by the preparation method of claim 4, 6 or 8.

10. Application of the layered ferroelectric photovoltaic film according to claim 9 in dielectric energy storage capacitors.

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