Bi-based perovskite thin film crystal phase preparation method and application

Abstract

The application relates to the technical field of photoelectric materials, in particular to a Bi-based perovskite thin film crystal phase preparation method and application. The Bi-based perovskite thin film crystal phase comprises a BiI3 layer, an ammonium salt with a melting point below 200 DEG C is gasified, the BiI3 layer is placed in a gas phase environment formed by the ammonium salt, a uniform and dense non-lead bismuth-based perovskite thin film can be obtained, and the gas phase environment is used for changing the lattice direction and morphology of the Bi-based perovskite thin film. The method can solve the problem of the traditional Bi-based perovskite layered structure and the non-dense thin film, and the thin film has an important role in the research of non-toxic green perovskite materials and the development of photoelectric devices.

Description

Technical Field

[0001] This application relates to the field of optoelectronic materials technology, and more specifically, to a method for preparing Bi-based perovskite thin film crystal phases and its application. Background Technology

[0002] Organic-inorganic hybrid lead halide perovskites have become revolutionary light-absorbing layers for solar cells, with their photoelectric conversion efficiency increasing from 3.8% in 2009 to 25.5%. The outstanding photoelectric performance of these materials is attributed to their unique photoelectric properties, such as a suitable band gap, high absorption coefficient, high and balanced carrier mobility, good defect tolerance, and low exciton binding energy. These properties are fundamentally derived from Pb6s… 2 The chemical properties of lone pairs of electrons and the mixed ionic-covalent bonds in the perovskite lattice are crucial factors. However, the environmental toxicity of lead (Pb) limits the large-scale commercialization of perovskite solar cells. Therefore, there is a strong desire to find new lead-free perovskite materials with equally good photoelectric properties.

[0003] Replace Pb with other equivalent ions 2+ Lead in halide perovskites is a straightforward strategy. The first consideration is lead from the same main group with ns... 2 Sn of electrons 2+ / Ge 2+ Currently, the performance of two-dimensional / three-dimensional hybrid tin-based perovskite devices has exceeded 10%. However, due to Sn... 2+ It is very easy to be oxidized to Sn 4+ When the device is exposed to air, its performance degrades rapidly, a problem that remains unresolved. Similarly, germanium-based halide perovskites have been proven to be non-ideal light-absorbing layers for solar cells due to the easy oxidation of divalent germanium and the presence of deep defect states.

[0004] In order to maintain ns 2 The lone pair electrons enable the material to maintain good photoelectric properties; Group 5 cations (M 3+ =Bi 3+ and Sb 3+ It has been studied to replace Pb 2+ Because of M 3+ Due to their high oxidation state, they cannot form ordinary AMX3 perovskites, but instead form stable A3M2X9 perovskites.

[0005] Generally, the electronic dimension of A3Bi2X9 structure is 0D and 2D, and the bulk phase shows a layered morphology. This material has a natural indirect band gap, and the lower carrier hopping transport problem limits its application in the field of photovoltaics. In the field of solar cells, a high-quality, uniform and dense light-absorbing layer is one of the necessary conditions to obtain high performance. Therefore, the layered structure is difficult to meet the above conditions. Compared with the layered structure, the bulk uniform and dense film can have good carrier transport. However, since the crystal growth always extends along the preferred crystal direction, it has been a challenge in the field to prepare a bulk 3D dense film. Therefore, it is a major challenge in the field to synthesize a high-quality dense film at low temperature by a simple method and apply it to perovskite solar cells. SUMMARY

[0006] The present disclosure provides a Bi-based perovskite thin film crystal phase preparation method and application. To solve the problem of non-dense film of traditional Bi-based perovskite layered structure, the film has an important role in the research of non-toxic green perovskite materials and the development of optoelectronic devices.

[0007] In a first aspect, the present disclosure provides a Bi-based perovskite thin film crystal phase preparation method, comprising the following processes:

[0008] The Bi-based perovskite thin film crystal phase includes a BiI3 layer. The ammonium salt with a melting point below 200℃ is gasified, and the BiI3 layer is placed in the gas phase environment formed by the ammonium salt to obtain a uniform and dense non-lead bismuth-based perovskite thin film. The gas phase environment is used to change the lattice direction and morphology of the Bi-based perovskite thin film.

[0009] The Bi-based perovskite has excellent chemical stability, and the outermost atomic electrons are similar to Pb, which is a potential material for green and environmentally friendly photovoltaics. However, most of the Bi-based perovskites prepared by existing processes are layered structures, the lattice orientation is single, the film morphology is uneven, the charge transport is limited when preparing photovoltaic devices, and the device performance is low. In view of the above problems, the present application uses a two-step gas phase deposition method to prepare MA3Bi2I9 perovskite. The BiI3 layer is placed in the atmosphere of ammonium salt, and the crystal nucleus growth mode is changed through gas phase reaction to generate MA3Bi2X9 thin film. Compared with existing methods, this method has the advantages of high repeatability, simple preparation process, and low-temperature lattice orientation control.

[0010] This method successfully prepares a uniform and dense granular thin film. Compared with the traditional layered thin film, the carrier transport of the MA3Bi2X9 thin film is improved, the visible light absorption intensity is enhanced, and the film morphology is more uniform and flat. As an absorbing layer for preparing photovoltaic devices, the device performance can be greatly improved, and the stability of the thin film is optimized.

[0011] Preferably, the non-lead perovskite thin film has a chemical formula of A3M2X9, wherein A is an organic macromolecule, M is a fifth main group element, and X is a halogen element.

[0012] Preferably, the method for preparing the Bi-based perovskite thin film comprises the following steps:

[0013] S1: Dissolve 0.1 g-0.3 g of BiI3 powder in an organic solvent, keep the solution temperature at 50-60℃ in an inert atmosphere, and the BiI3 powder is completely dissolved to obtain a precursor solution;

[0014] S2: Spin-coat the obtained precursor solution on the surface of the electron transport layer to form a thin film, and then perform annealing treatment on the thin film to obtain a flat BiI3 thin film;

[0015] S3: Place the obtained BiI3 thin film in a culture dish, and place the culture dish upside down on a hot stage, the temperature of the hot stage is 150-180℃, and MAX is placed on the hot stage to make the MAX gasify, the MAX reacts with the BiI3 thin film for 3-5 min, and then the thin film in the culture dish is taken out, and a Bi-based perovskite thin film with a chemical formula of MA3Bi2X9 can be obtained.

[0016] Preferably, the concentration of the BiI3 solution in S1 is 0.8-1.2 mol / L.

[0017] Preferably, the organic solvent in S1 is one or more of DMF, DMSO, and formamide, and the organic solvents are mixed with each other at a ratio of 4:1.

[0018] Preferably, the annealing temperature of the annealing treatment in S2 is 100-150℃.

[0019] Preferably, the spin-coating of the BiI3 solution in S2 is performed in a spin coater, and the rotation speed of the spin coater is greater than 5000 rpm, and the spin-coating time is greater than 30 s.

[0020] Preferably, the bulk phase of the A3BiX3 perovskite thin film is a dense granular shape.

[0021] Preferably, the preparation of the Bi-based perovskite thin film crystal phase has no requirement for the atmosphere, and can be prepared in an inert gas and air.

[0022] In a second aspect, the present disclosure provides an application of a Bi-based perovskite thin film crystal phase, which is used to manufacture a light-absorbing layer of a planar perovskite solar cell, the planar perovskite solar cell comprising an electron transport layer, a light-absorbing layer and a hole transport layer, the electron transport layer being a tin dioxide thin film, and the solar cell structure can be spin-coating SnO2 on an FTO glass substrate, then spin-coating or two-step vapor deposition of the Bi-based perovskite thin film on the electron transport layer, and spin-coating Spiro-OMeTD on the light-absorbing layer, and then evaporating gold / silver electrodes as a counter electrode.

[0023] The preparation of the perovskite material needs to be in a glove box, and the preparation conditions are relatively strict. The method is not limited to the glove box, and can be prepared at low temperature, has low requirements on the preparation environment, and is suitable for large-scale production.

[0024] The prepared perovskite thin film has excellent stability. The unsealed thin film is stored in air with a humidity of 50% for 30 days, and does not degrade. The perovskite thin film prepared by the new method has a high solar energy light absorption coefficient, which is conducive to improving the photoelectric conversion efficiency of the device.

[0025] In summary, the present application has the following beneficial effects:

[0026] 1. In the present application, the Bi-based perovskite prepared by the general method is a layered structure, and the crystal lattice orientation is single, so that the charge transport of the prepared photovoltaic device is limited. The two-step vapor deposition method is creatively used to prepare MA3Bi2I9 perovskite, the crystal nucleus growth mode is changed, and the crystal lattice orientation is controlled at low temperature. The prepared granular thin film is uniform and dense, and compared with the traditional layered thin film, the charge transport is greatly improved.

[0027] 2. In the present application, the traditional preparation of the perovskite material needs to be in a glove box, and the preparation conditions are relatively strict. The method is not limited to the glove box, and can be prepared at low temperature, has low requirements on the preparation environment, and is suitable for large-scale production.

[0028] 3. The perovskite thin film prepared in the present application has excellent stability. The unsealed thin film is stored in air with a humidity of 50% for 30 days, and does not degrade.

[0029] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the protection scope of the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0030] 1, Figure 1 is a schematic diagram of preparing the MA3Bi2I9 thin film according to Embodiment 1 of the present application;

[0031] 2, Figure 2is the ultraviolet-visible absorption spectrum of BiI3, layered MA3Bi2I9 thin film, bulk MA3Bi2I9 thin film prepared in Example 1 of the present application;

[0032] 3、 Figure 3 is the XRD spectrum of BiI3 thin film, layered MA3Bi2I9, bulk granular MA3Bi2I9 thin film prepared in Example 1;

[0033] 4、 Figure 4 are SEM images of (a) BiI3 thin film prepared in Example 1, (b) MA3Bi2I9 thin film prepared in Example 3, (c) MA3Bi2I9 thin film prepared in Example 2, and (d) MA3Bi2I9 thin film prepared in Example 1, respectively;

[0034] 5、 Figure 5 is the IV curve of the photovoltaic device prepared by using MA3Bi2I9 prepared by different methods as the light-absorbing layer. Among them, two-step method MBI-1: BiI3 thin film is prepared by solution method; two-step method MBI-2: BiI3 thin film is prepared by thermal evaporation. One-step method MBI is prepared by one-step solution method;

[0035] 6、 Figure 6 is the X-ray diffraction spectrum comparison chart of the MA3Bi2I9 thin film obtained by two-step method before and after being placed in air with humidity of 50% for 30 days. DETAILED DESCRIPTION

[0036] The present application will be further described in detail in conjunction with the following examples, and it is particularly pointed out that: in the following examples, the specific conditions not specified are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the raw materials used in the following examples can be sourced from ordinary market sales unless otherwise specified.

[0037] Example

[0038] Example 1

[0039] A method for preparing a Bi-based perovskite thin film by a two-step method, as shown in Figure 1 , comprises the following steps:

[0040] (1) Selecting conductive glass FTO as electrode substrate, the FTO glass is ultrasonically cleaned.

[0041] (2) The electron transport layer is selected to be SnO2, SnO2 sol is diluted with deionized water at a ratio of 1:4, and the solution is spin-coated on the FTO substrate at a spin-coating speed of 6000 r / min, and then annealed at 180°C for 30 min.

[0042] (3) Preparation of light-absorbing layer:

[0043] First step, in the glove box, 1.0 mmol BiI3 was added into 1 ml DMF / DMSO (4 / 1, vol) mixed solution, stirred for 30 min to make it completely dissolved. Then the resulting solution was filtered using a polytetrafluoroethylene filter head with a pore size of 0.45 μm. The filtered solution was spin-coated on the O3 treated SnO2 substrate. The spin-coating time was 60 s and the rotation speed was 4000 rpm. The prepared film was annealed at 100 °C.

[0044] Second step, the BiI3 film was fixed on the inner wall of a petri dish, the petri dish was inverted on a hot stage, the BiI3 film faced downward, a certain amount of MAI was placed under the petri dish, and the temperature of the hot stage was heated to 150 °C for 60 min.

[0045] (4) Preparation of the counter electrode, a certain thickness of silver was thermally evaporated on the light-absorbing layer as the electrode.

[0046] The photoelectric conversion efficiency of the Bi-based perovskite solar cell device prepared using this process was 0.13%.

[0047] Example 2

[0048] The preparation method was different from step 3, and the process preparation method of each layer was the same as that of example 1. In example 2, the BiI3 layer was prepared by thermal evaporation: 0.1 mg of BiI3 was weighed and placed in an evaporation boat, and was thermally evaporated to prepare a SnO2 substrate. The vacuum degree was set to 5.0 x 10 -4 Pa, the evaporation temperature was 450 °C, and the evaporation time was 4 min. Then the BiI3 film prepared by thermal evaporation was fixed on the inner wall of a petri dish, the petri dish was inverted on a hot stage, the BiI3 film faced downward, a certain amount of MAI was placed under the petri dish, and the temperature of the hot stage was heated to 150 °C for 60 min.

[0049] The photoelectric conversion efficiency of the perovskite solar cell device prepared using this process was 0.12%.

[0050] Example 3

[0051] The preparation method was different from step 3, and the process preparation method of each layer was the same as that of example 1. In example 3, the preparation of the light-absorbing layer: 1.0 mmol MAI and 0.66 mmol BiI3 powders were weighed in a nitrogen-protected glove box, and were added into a mixed solution of DMF and DMSO (the volume ratio of DMF and DMSO was V DMF :V HCl= 4:1) under vigorous stirring for 1 h until it was completely dissolved. The resulting solution was then filtered using a polytetrafluoroethylene filter head with a pore size of 0.22 μιη. The filtered solution was spin-coated on an O3-treated Sn02substrate. The spin-coating time was 60 s at a rotation speed of 5000 rpm. After 10 s of spin-coating the solution, chlorobenzene was added dropwise to the substrate while it was still rotating. Finally, the prepared thin film was annealed at 100 °C. The photovoltaic conversion efficiency of the perovskite solar cell device prepared using the light-absorbing layer was 0.01%.

[0052] Figure 2 are the UV-Vis absorption spectra of BiI3thin film, layered MA3Bi2I9, bulk granular MA3Bi2I9 thin film, from which Figure 2 It can be seen from the above that BiI3is completely converted into MA3Bi2I9, and granular MA3Bi2I9 exhibits more excellent absorption characteristics, but the absorption spectral range is consistent.

[0053] Figure 3 are the XRD spectra of BiI3thin film, layered MA3Bi2I9, bulk granular MA3Bi2I9 thin film, from which Figure 3 It can be clearly seen from the above that after the two-step vapor deposition, the crystallinity is obviously improved, and the crystal direction also changes accordingly.

[0054] Figure 4 are SEM images of (a) spin-coated BiI3thin film, (b) one-step prepared MA3Bi2I9 thin film, (c) hot vacuum prepared BiI3, vapor deposited MA3Bi2I9 thin film, (d) solution prepared BiI3, vapor deposited MA3Bi2I9 thin film, from which Figure 4 It can be seen from the above that the one-step prepared MA3Bi2I9 thin film is a layered structure, and the surface roughness is large. After vapor deposition, it is converted into a granular structure, making the thin film surface flat and dense.

[0055] Figure 5 are IV curves of photovoltaic devices prepared using different light-absorbing layers. Two-step MBI-1: BiI3thin film is prepared by a solution method; two-step MBI-2: BiI3thin film is prepared by a thermal evaporation method. One-step MBI is prepared by a one-step solution method.

[0056] Figure 6 is the X-ray diffraction spectrum of the MA3Bi2I9 thin film obtained by the two-step method and placed in air with a humidity of 50% for 30 days. Figure 6 It shows that the layered phase MA3Bi2I9 thin film prepared according to the present patent has good air and humidity stability.

[0057] Example 4

[0058] Except for step 3, the preparation methods for each layer are the same as in Example 1. Preparation of the light-absorbing layer in Example 4: First, in a glove box, 1.0 mmol BiI3 was added to 1 ml of a DMF / DMSO (4 / 1, vol) mixed solution and stirred for 30 min to completely dissolve the solvent. The resulting solution was then filtered using a 0.45 μm PTFE filter. The filtered solution was spin-coated onto an O3-treated SnO2 substrate. The spin-coating time was 60 s and the rotation speed was 4000 rpm. The prepared film was annealed at 100 °C.

[0059] The second step is to fix the BiI3 film onto the inner wall of the culture dish, invert the culture dish onto the hot plate with the BiI3 film facing down, place a certain amount of MAI under the culture dish, and heat the hot plate to 150℃ for 90 minutes.

[0060] The photoelectric conversion efficiency of the perovskite solar cell device fabricated using the P-type layer in this process is 0.07%.

[0061] Example 5

[0062] Except for step 3, the preparation methods for each layer are the same as in Example 1. Preparation of the light-absorbing layer in Example 5:

[0063] First, in a glove box, 1.0 mmol BiI3 was added to 1 ml of a DMF / DMSO (4 / 1, vol) mixture and stirred for 30 min to completely dissolve the solvent. The resulting solution was then filtered through a 0.45 μm PTFE filter. The filtered solution was spin-coated onto an O3-treated SnO2 substrate. The spin-coating time was 60 s and the spin speed was 4000 rpm. The prepared film was annealed at 100 °C.

[0064] The second step is to fix the BiI3 film onto the inner wall of the culture dish, invert the culture dish onto the hot plate with the BiI3 film facing down, place a certain amount of MAI under the culture dish, and heat the hot plate to 150℃ for 30 minutes.

[0065] The photoelectric conversion efficiency of the perovskite solar cell device fabricated using the P-type layer in this process is 0.02%.

[0066] Application examples

[0067] Application Example 1

[0068] A method for fabricating a planar perovskite solar cell is as follows:

[0069] Step 1: Fluorine-doped SnO2 transparent conductive glass FTO is continuously immersed in ultrapure water, ethanol, and isopropanol solutions as an electrode substrate and then ultrasonically cleaned in an ultrasonic cleaner.

[0070] Step 2: The electron transport layer is prepared by spin coating. Specifically, the source solution of SnO2 is diluted at a ratio of 1:4, and is spin-coated on a cleaned glass substrate at a spin-coating speed of 6000 r / min, and is annealed at a temperature of 180°C for 30 min.

[0071] Step 3: Preparation of the light-absorbing layer. One-step method: in a nitrogen-protected glove box, the BiI3 / MAX precursor solution prepared in Example 1 is spin-coated on the TiO2 / FTO substrate to form a thin film of a certain thickness, the spin-coating time is 20-40 s, and the spin-coating speed is 3000-6000 rpm. Then the thin film is annealed; the annealing temperature is 100°C, and the specific annealing process can be carried out according to the above method for preparing the light-absorbing layer.

[0072] Step 4: Two-step method for preparing the light-absorbing layer, BiI3 thin film is prepared by solution method or thermal evaporation, and the specific preparation method can be carried out according to the above method. The prepared BiI3 thin film is pasted upside down on the cover of a culture dish, the culture dish is inverted on a hot stage, a certain amount of MAX is placed below the culture dish, the surface of BiI3 is opposite to the MAX, and the distance between the BiI3 thin film and the MAX is controlled to be 3-5 cm. The temperature of the hot stage is controlled to be 150-180°C, until the MAX is gasified, and the reaction is carried out for a certain time, so that the BiI3 is completely converted into MA3Bi2X9.

[0073] Step 5: Preparation of the counter electrode. A certain thickness of silver is thermally evaporated on the light-absorbing layer as the electrode.

[0074] The structure of the perovskite solar cell is that the electron transport layer, the light-absorbing layer, the hole transport layer and the counter electrode are sequentially arranged on the FTO transparent conductive glass substrate; the electron transport layer is SnO2, the light-absorbing layer is MA3Bi2I9, the hole transport layer is Spiro, and the counter electrode is a silver electrode. The solar cell device is constructed by using a planar structure. In the present application, a new MA3Bi2I9 is used as the light-absorbing layer. In the preparation process of the light-absorbing layer, by changing the preparation method, the crystal direction of the thin film is changed by vapor deposition, and a granular, uniform and dense Bi-based perovskite thin film is prepared.

[0075] The perovskite thin film prepared by the new method has a high solar light absorption coefficient, which is conducive to improving the photoelectric conversion efficiency of the device.

[0076] The above is only an exemplary specific embodiment of the present disclosure, but the protection scope of the present disclosure is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present disclosure, which should be covered within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.

Claims

1. A method for preparing a Bi-based perovskite thin film crystalline phase, characterized in that, The method for preparing the Bi-based perovskite thin film includes the following steps: S1: Dissolve 0.1g-0.3g of BiI3 powder in an organic solvent, and maintain the solution temperature at 50-60℃ in an inert atmosphere until the BiI3 powder is completely dissolved to obtain a precursor solution; S2: The obtained precursor solution is spin-coated onto the surface of the electron transport layer to form a thin film, and then the thin film is annealed to obtain a smooth BiI3 thin film. S3: The obtained BiI3 film is upside down and attached to a petri dish. The petri dish is then placed upside down on a hot plate at a temperature of 150°C. MAX is placed on the hot plate and vaporized. The MAX reacts with the BiI3 film for 60 minutes. Then the film is removed from the petri dish to obtain a Bi-based perovskite film with the chemical formula MA3Bi2X9. The MAX is CH3NH3I. The gaseous environment formed after CH3NH3I vaporization is used to change the lattice orientation and morphology of Bi-based perovskite thin films.

2. The method for preparing a Bi-based perovskite thin film crystalline phase according to claim 1, characterized in that, The concentration of the BiI3 solution in S1 is 0.8-1.2 mol / L.

3. The method for preparing a Bi-based perovskite thin film crystalline phase according to claim 1, characterized in that, The organic solvent in S1 is DMF and DMSO, and the DMF and DMSO are mixed together in a volume ratio of 4:

1.

4. The method for preparing a Bi-based perovskite thin film crystalline phase according to claim 1, characterized in that, The annealing temperature in S2 is 100-150℃.

5. The method for preparing a Bi-based perovskite thin film crystalline phase according to claim 1, characterized in that, In step S2, the BiI3 solution is spin-coated in a spin coater with a rotation speed greater than 5000 rpm and a spin-coating time greater than 30 s.

6. The method for preparing a Bi-based perovskite thin film crystalline phase according to claim 1, characterized in that, The bulk phase of the MA3Bi2X9 perovskite thin film is dense and granular.

7. The method for preparing a Bi-based perovskite thin film crystalline phase according to claim 1, characterized in that, In S3, the preparation of the Bi-based perovskite thin film is not required by the atmosphere and can be prepared in either inert gas or air.

8. The application of a Bi-based perovskite thin film crystalline phase prepared according to any one of claims 1-7, characterized in that, The Bi-based perovskite thin film crystal phase is used to manufacture the light-absorbing layer of a planar perovskite solar cell. The planar perovskite solar cell includes an electron transport layer, a light-absorbing layer, and a hole transport layer. The electron transport layer is a tin dioxide thin film. The solar cell structure can be achieved by spin-coating SnO2 onto an FTO glass substrate, then spin-coating or performing a two-step vapor deposition of the Bi-based perovskite thin film onto the electron transport layer, spin-coating Spiro-OMeTD onto the light-absorbing layer, and then evaporating a gold / silver electrode as the counter electrode.

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