Method for regulating and controlling crystallization of perovskite thin film based on potassium nitrate modified buried interface

Abstract

The invention discloses a method for regulating and controlling crystallization of a perovskite thin film based on a potassium nitrate modified buried interface. The method comprises the following steps: dissolving potassium nitrate in DMSO; coating a DMSO solution of potassium nitrate on the titanium dioxide film by adopting a spin-coating method, and annealing to obtain a potassium nitrate buried interface modification layer; and preparing a perovskite layer on the potassium nitrate buried interface modification layer to obtain the potassium nitrate modified perovskite thin film. The prepared potassium nitrate modified perovskite thin film can be further used for preparing a perovskite photovoltaic device. According to the invention, potassium nitrate is used as a bottom-buried interface modification layer, in the annealing crystallization process of the perovskite film, perovskite crystallization can be delayed, a glossy perovskite film with a large grain size is formed, defects at the grain boundary of the perovskite film and in the crystal are passivated, the transmission capability of charges at the bottom-buried interface is improved, and the performance of a photovoltaic device is improved. The method is low in cost and suitable for large-scale perovskite solar photovoltaic devices, especially for preparation of perovskite cells.

Description

Technical Field

[0001] The present application relates to the technical field of perovskite solar cells, and in particular to a method for regulating the crystallization of perovskite thin films based on potassium nitrate-modified buried interfaces. Background Art

[0002] Perovskite solar cells are a new generation of photovoltaic devices and a leading contender for the next generation of commercial solar cells. As early as 2013, they were recognized by the journal Science as one of the top ten scientific breakthroughs of the year. Defect states, as recombination centers during charge transfer in perovskite solar cells, are a significant factor in reducing the cell's photoelectric conversion efficiency and stability. Defect states are primarily located within perovskite crystals, at grain boundaries in perovskite films, and at the interfaces of various functional layers. Introducing modifying materials at these interfaces can reduce interfacial charge recombination losses, regulate band offsets between functional layers, improve the morphology of the perovskite layer, and ultimately enhance device performance.

[0003] The electron transport layer, as the lower surface of the buried interface, plays an important role in perovskite crystallization and charge transport. Its surface defects and internal defects can be effectively reduced through methods such as doping engineering and interface modification engineering. The perovskite light absorption layer, as the upper surface of the buried interface, plays a key role in the optoelectronic performance of the device. In view of the phenomenon that a large number of defects are generated at the interface and in the crystal during the liquid phase preparation of perovskite, the introduction of metal compounds as interface modification materials can improve the crystallization of perovskite and passivate the defects at the buried interface. Mojtaba Abdi-Jalebi et al. in (Cs, FA, MA) Pb (I 0.85 Br 0.15 )3-type perovskite precursor solution, and found that the potassium ions did not enter the lattice, but formed a potassium-containing passivation layer on the surface of the perovskite film, resulting in a significant alleviation of the light-induced ion migration on the perovskite film and the interface, and the open-circuit voltage loss of the device was only 0.11 V. In addition, the Pb-I bond in the perovskite is easily broken to form halide vacancies or dangling bonds. The introduction of some anions can passivate the Pb 2+ Defects caused by interstitial and halide vacancies due to NO3 − (0.196 Å) has a radius close to I − (0.224 Å), NO3 − Can be with I − The intermediate ion exchange reaction occurs, delaying the crystallization of perovskite, thereby increasing the grain size of perovskite. + and NO3 − It is worth looking forward to using it in perovskites to improve the performance of devices. Summary of the Invention

[0004] Objective: To overcome the shortcomings of the prior art, the present invention provides a method for regulating the crystallization of perovskite films based on potassium nitrate modification of the buried interface. Potassium nitrate is introduced as a buried interface modification layer of perovskite photovoltaic devices to regulate the quality of the perovskite film, while improving the crystallization of the perovskite and passivating interface defects, thereby enhancing the photoelectric conversion performance of the photovoltaic device.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] In a first aspect, the present invention provides a method for regulating the crystallization of perovskite thin films based on potassium nitrate modification of a buried interface, comprising: Dissolve potassium nitrate in DMSO; A DMSO solution of potassium nitrate is coated on the titanium dioxide film by spin coating and annealed to obtain a potassium nitrate buried interface modification layer; A perovskite layer is prepared on the potassium nitrate buried interface modification layer to obtain a potassium nitrate modified perovskite film.

[0007] In some embodiments, the concentration of the potassium nitrate solution in DMSO is 0.1-0.2 M. Preferably, the concentration of the potassium nitrate solution in DMSO is 0.1 M.

[0008] In some embodiments, the spin coating speed of the potassium nitrate DMSO solution is 2500-2800 rpm for 25-30 s. Preferably, the spin coating speed of the potassium nitrate DMSO solution is 2500 rpm for 25 s.

[0009] In some embodiments, the annealing temperature of the potassium nitrate buried interface modification layer is 75-80° C., and the annealing time is 10-15 min. Preferably, the annealing temperature of the potassium nitrate buried interface modification layer is 75° C., and the annealing time is 10 min.

[0010] In some embodiments, the perovskite layer is prepared by a one-step method, that is, a perovskite precursor solution is first prepared and then directly spin-coated on the potassium nitrate buried interface modification layer.

[0011] In a second aspect, the present invention provides a method for preparing a perovskite solar cell, comprising: The anode substrate is surface treated and then an electron transport layer is prepared; A potassium nitrate-modified perovskite film is prepared on the surface of the electron transport layer according to the method of the first aspect to obtain a perovskite active layer; preparing a hole transport layer on the surface of the perovskite active layer; An electrode is prepared on the surface of the hole transport layer.

[0012] In some embodiments, the method for surface treating the anode substrate comprises: using an FTO glass substrate as the anode substrate, etching the FTO glass substrate with zinc powder and a 2-3 M hydrochloric acid solution, sequentially ultrasonicating the FTO glass substrate in acetone, deionized water, and ethanol for 20-30 minutes, washing, drying, and treating with ultraviolet ozone for 20-30 minutes. Preferably, using an FTO glass substrate as the anode substrate, etching the FTO glass substrate with zinc powder and a 2 M hydrochloric acid solution, sequentially ultrasonicating the FTO glass substrate in acetone, deionized water, and ethanol for 20 minutes, washing, drying, and treating with ultraviolet ozone for 20 minutes.

[0013] In some embodiments, the method for preparing an electron transport layer includes: spin coating a TiO2 precursor solution on the surface of a surface-treated anode substrate at a spin coating speed of 2500-3000 rmp for 30-45 s, followed by heating on a 125-130°C heating table for 10-15 min and annealing; the annealing conditions are: heating to 500-550°C within 30-35 min, keeping warm for 30-40 min, and cooling to room temperature.

[0014] Preferably, the TiO2 precursor solution is spin-coated at a speed of 2500 rpm for 30 seconds, followed by heating on a 125°C heating table for 10 minutes for annealing; the annealing conditions are: heating to 500°C within 30 minutes, keeping warm for 30 minutes, and cooling to room temperature.

[0015] The preparation method of the TiO2 precursor solution includes: adding 2 mol / L hydrochloric acid to isopropyl alcohol in a volume ratio to obtain a mixed solution A, wherein the volume ratio of the 2 mol / L hydrochloric acid to the isopropyl alcohol is 1: (72-75); taking another portion of isopropyl alcohol, adding isopropyl titanate, and continuously stirring for 1-2 hours to obtain a mixed solution B, wherein the volume ratio of the isopropyl titanate to the isopropyl alcohol is 1: (6.5-7); adding the mixed solution A dropwise to the mixed solution B in a volume ratio of 1:1-1:2, and letting it stand to obtain the product.

[0016] In some embodiments, the method for preparing the hole transport layer comprises: spin coating 50-60 μL of Spiro-OMeTAD solution on the surface of the perovskite active layer under a nitrogen environment at a spin coating speed of 2500-3000 rpm for 35-40 s. Preferably, spin coating 50 μL of Spiro-OMeTAD solution on the surface of the perovskite active layer at a spin coating speed of 3000 rpm for 35 s.

[0017] In some embodiments, the electrode is a metal electrode, preferably a silver electrode; the electrode is prepared by a thermal evaporation process under a vacuum environment, with an evaporation rate of 0.5-0.8 Å·s -1The thickness of the deposited electrode is 150-180 nm. Preferably, the evaporation rate is 0.8 Å·s -1 , the deposited electrode thickness is 150 nm.

[0018] Beneficial Effects: The method provided by the present invention for regulating the crystallization of perovskite thin films based on potassium nitrate modification of the buried interface uses potassium nitrate as a buried interface modification layer between TiO2 and perovskite in perovskite photovoltaic devices. During the annealing and crystallization process of the perovskite film, the perovskite crystallization is delayed, thereby forming a lustrous perovskite film with large grain size. The method also passivates defects at the grain boundaries and within the crystals of the perovskite film, improves the charge transfer capability at the buried interface, and enhances the performance of the photovoltaic device. This method is low-cost and suitable for the preparation of large-scale perovskite solar photovoltaic devices, especially perovskite cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 3 is the X-ray diffraction pattern of TiO2 / CH3NH3PbI3 and TiO2 / KNO3 / CH3NH3PbI3 thin films in the embodiments of the present invention.

[0020] Figure 2 3 is the SEM top view of TiO2 / CH3NH3PbI3 and TiO2 / KNO3 / CH3NH3PbI3 thin films in the embodiment of the present invention, Figure 2 Figure a is the SEM top view of TiO2 / CH3NH3PbI3 film. Figure 2 Figure b is the SEM top view of TiO2 / KNO3 / CH3NH3PbI3 film.

[0021] Figure 3 3 is the UV-visible absorption spectrum of TiO2 / CH3NH3PbI3 and TiO2 / KNO3 / CH3NH3PbI3 thin films in the embodiments of the present invention.

[0022] Figure 4 It is the steady-state PL spectrum of TiO2 / CH3NH3PbI3 and TiO2 / KNO3 / CH3NH3PbI3 thin films in the embodiment of the present invention.

[0023] Figure 5 Schematic diagram of the color change during the annealing process of TiO2 / CH3NH3PbI3 and TiO2 / KNO3 / CH3NH3PbI3 thin films in an embodiment of the present invention.

[0024] Figure 6 This is the modification mechanism model of the TiO2 / CH3NH3PbI3 buried interface by potassium nitrate in the embodiment of the present invention. Figure 6 a in the middle is K + and NO3 – Schematic diagram of the localization plane in perovskite, Figure 6 b is NO3 – Schematic diagram of motion space in perovskite.

[0025] Figure 7 These are the JV curves and parameters of the control device and the KNO3-based device in the embodiments of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention, its application, or use.

[0027] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to actual proportional relationships. The techniques, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific values ​​should be interpreted as being merely exemplary, not as limitations. Therefore, other examples of the exemplary embodiments may also include different values. It should be noted that similar numbers and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0028] The present invention will be further described below with reference to the examples.

[0029] Example 1:

[0030] This embodiment provides a method for regulating the crystallization of perovskite thin films based on modifying a buried interface with potassium nitrate, comprising: S1. Completely dissolve potassium nitrate in DMSO to prepare a 0.1 M potassium nitrate DMSO solution; S2, 0.1 M potassium nitrate in DMSO solution was applied to the titanium dioxide film by spin coating at a speed of 2500 rpm for 25 s; S3, annealing, the annealing temperature is 75 ° C, the annealing time is 10 min, and the potassium nitrate buried interface modification layer is obtained; S4. A perovskite layer is prepared on the potassium nitrate buried interface modification layer by a one-step method to obtain a potassium nitrate modified perovskite film.

[0031] Example 2:

[0032] This embodiment provides a preparation method of a planar formal perovskite solar cell based on Example 1, wherein the planar formal perovskite solar cell comprises, from bottom to top, an anode substrate (FTO), an electron transport layer (TiO2), an interface modification layer (KNO3), a perovskite layer (CH3NH3PbI3), a hole transport layer (Spiro-OMeTAD), and a back electrode layer (Ag).

[0033] The specific steps include: 1. Solution preparation: 1. Electron transport layer TiO2 precursor solution: take 35 μL, 2 mol·L –1 100 μL of hydrochloric acid was added to 2.53 mL of isopropanol to obtain mixed solution A; 369 μL of isopropyl titanate was added to another 2.53 mL of isopropanol while stirring, and the mixture was stirred continuously at room temperature for 1 h to obtain mixed solution B; mixed solution A was evenly added dropwise to mixed solution B. The addition should be slow to prevent turbidity, and the mixture was allowed to stand for 1 h before use.

[0034] 2. Perovskite precursor solution: Add 159 mg of CH3NH3I and 462 mg of PbI2 to a solvent consisting of 0.16 mL of DMSO and 0.64 mL of DMF. Stir the mixture at 70 ºC for 6 h.

[0035] 3. Hole transport layer: First, take 26 mg of Li-TFSI and dissolve it in 50 μL of acetonitrile. Then weigh 72.3 mg of Spiro-OMeTAD and dissolve it in 1 mL of chlorobenzene. Stir evenly for 1 h. Take 17.5 μL of Li-TFSI solution and 28.8 μL of TBP and add them to the Spiro-OMeTAD solution. Continue stirring for 12 h and set aside.

[0036] 4. Potassium nitrate solution: Dissolve potassium nitrate in DMSO solution until completely dissolved. The concentration of the prepared potassium nitrate solution is 0.1 M.

[0037] 2. Preparation process: 1. Surface treatment of the anode substrate: First, the FTO glass substrate was etched with zinc powder and 2 M hydrochloric acid solution, then ultrasonicated in acetone, deionized water, and ethanol for 20 min, cleaned, dried, and treated with UV ozone for 20 min.

[0038] 2. Preparation of the electron transport layer: Spin-coat the TiO2 precursor of the electron transport layer at a speed of 2500 rpm for 30 seconds, then heat on a heating plate at 125°C for 10 minutes and anneal. The annealing setting is: increase to 500°C over 30 minutes, hold for 30 minutes, and cool to room temperature.

[0039] 3. Preparation of buried interface modification layer: Spin-coat 0.1 M potassium nitrate in DMSO solution at a speed of 2500 rpm for 25 seconds, then heat on a 75 ºC heating table for 10 minutes, cool to room temperature in air, and then treat with UV-ozone for 20 minutes before use.

[0040] 4. Preparation of the perovskite active layer: One-step spin coating preparation. Spin coating of the perovskite precursor solution needs to be carried out in a glove box, and the anti-solvent must be added during the process. The specific parameters are: spin coating speed 4000 rpm, duration 20 s, after 10 seconds, 200 μL of chlorobenzene is added to improve the crystallization quality of the film. Then, it is immediately annealed at 75 ºC and 105 ºC for 10 minutes each, and cooled to room temperature.

[0041] 5. Preparation of hole transport layer: In a nitrogen environment, 50 μL of Spiro-OMeTAD solution was coated on the perovskite film using a spin coating process at 3000 rpm for 35 s.

[0042] 6. Preparation of silver electrode: At a pressure less than 5×10 -4 Pa vacuum environment, using thermal evaporation technology, the evaporation rate is 0.8 Å·s -1 , depositing a 150 nm thick silver electrode.

[0043] That is, a planar formal perovskite solar cell is prepared.

[0044] Comparative Example 1:

[0045] This comparative example provides a preparation method of a planar formal perovskite solar cell based on Example 1, which differs from Example 2 in that the preparation of the buried interface modification layer in step 3 is not performed, and a control planar formal perovskite solar cell is prepared.

[0046] Depend on Figure 1 It can be seen that the XRD peak value of the (110) crystal plane of the perovskite film prepared in Example 1 is significantly higher than that of the control perovskite film prepared in Comparative Example 1, which indicates that potassium nitrate modification of the buried interface has a greater effect on the crystallinity of the perovskite, making it more crystallinity.

[0047] Depend on Figure 2 It can be seen that the cracks of the perovskite film prepared based on potassium nitrate in Example 1 are significantly reduced compared with the control perovskite film prepared in Comparative Example 1, forming a pinhole-free and uniform perovskite film.

[0048] Figure 3The effect of the buried interface modified with potassium nitrate on the optical properties of the perovskite film is demonstrated. As can be seen from the figure, the absorbance of the perovskite film prepared based on the buried interface modified with potassium nitrate is significantly enhanced in the entire area, which indicates that the crystallinity of its perovskite is better.

[0049] Figure 4 The steady-state PL spectra of TiO2 / CH3NH3PbI3 and TiO2 / KNO3 / CH3NH3PbI3 films are shown. From the PL peak intensity, the PL intensity of TiO2 / KNO3 / CH3NH3PbI3 film is significantly improved compared with that of TiO2 / CH3NH3PbI3 film. This is because the crystallinity and surface morphology of the perovskite are improved by modifying the buried interface with potassium nitrate, and the defects in the perovskite body and the surface grain boundaries are reduced, which effectively suppresses the non-radiative recombination of electrons and holes at this location.

[0050] Figure 5 The color changes of TiO2 / CH3NH3PbI3 and TiO2 / KNO3 / CH3NH3PbI3 films during the annealing process are shown. It can be seen from the figure that the color change time of the potassium nitrate-based perovskite film during the annealing process is longer, which means that the crystallization process of the perovskite is slower, making it easy to form a perovskite film with gloss and larger grain size.

[0051] Figure 6 The modification mechanism model of TiO2 / CH3NH3PbI3 buried interface by potassium nitrate is shown. + The radius is 1.33Å, much smaller than CH3NH3 + 1.80 Å, so K + It is impossible to incorporate into the perovskite lattice, but remains at the perovskite grain boundaries, e.g. Figure 6 As shown in Figure a, this can effectively passivate defect states and reduce non-radiative recombination in perovskite films. − For example, its radius is close to I – , NO3 − During the thermal annealing process, it is easy to move in the perovskite lattice and form an intermediate phase with the perovskite precursor solution, which delays the crystallization of the perovskite and is conducive to the formation of a shiny perovskite film with a large grain size. Figure 6 Middle b.

[0052] Figure 7 The JV curves and corresponding parameter data of the control device and the KNO3-based device are shown. It can be seen that the performance of the KNO3-based device is significantly improved and the PCE is significantly improved.

[0053] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A method for regulating the crystallization of perovskite thin films based on potassium nitrate modification of buried interfaces, characterized in that: include: Dissolve potassium nitrate in DMSO; A DMSO solution of potassium nitrate is coated on the titanium dioxide film by spin coating and annealed to obtain a potassium nitrate buried interface modification layer; A perovskite layer is prepared on the potassium nitrate buried interface modification layer to obtain a potassium nitrate modified perovskite film.

2. The method for regulating the crystallization of perovskite thin films based on potassium nitrate modification of buried interfaces according to claim 1, characterized in that: The concentration of the potassium nitrate DMSO solution is 0.1-0.2 M.

3. The method for regulating the crystallization of perovskite thin films based on potassium nitrate modification of buried interfaces according to claim 1, characterized in that: The spin coating speed of the potassium nitrate DMSO solution is 2500-2800 rpm, and the duration is 25-30 s.

4. The method for regulating the crystallization of perovskite thin films based on potassium nitrate modification of buried interfaces according to claim 1, characterized in that: The annealing temperature of the potassium nitrate buried interface modification layer is 75-80° C., and the annealing time is 10-15 minutes.

5. The method for regulating the crystallization of perovskite thin films based on potassium nitrate modification of buried interfaces according to claim 1, characterized in that: The perovskite layer is prepared by a one-step method.

6. A method for preparing a perovskite solar cell, characterized in that: include: The anode substrate is surface treated and then an electron transport layer is prepared; A potassium nitrate-modified perovskite film is prepared on the surface of the electron transport layer according to the method according to any one of claims 1 to 4 to obtain a perovskite active layer; preparing a hole transport layer on the surface of the perovskite active layer; An electrode is prepared on the surface of the hole transport layer.

7. The method for preparing a planar perovskite solar cell according to claim 6, wherein: The method for surface treating the anode substrate comprises: using an FTO glass substrate as the anode substrate, etching the FTO glass substrate with zinc powder and 2-3 M hydrochloric acid solution, ultrasonicating in acetone, deionized water and ethanol for 20-30 minutes, cleaning, drying and ultraviolet ozone treatment for 20-30 minutes.

8. The method for preparing a planar perovskite solar cell according to claim 6, wherein: The method for preparing the electron transport layer comprises: spin coating a TiO2 precursor solution on the surface of the surface-treated anode substrate at a spin coating speed of 2500-3000 rpm for 30-45 seconds, then heating on a heating table at 125-130°C for 10-15 minutes and annealing; the annealing conditions are: heating to 500-550°C within 30-35 minutes, holding the temperature for 30-40 minutes, and cooling to room temperature; The preparation method of the TiO2 precursor solution includes: adding 2 mol / L hydrochloric acid to isopropyl alcohol in a volume ratio to obtain a mixed solution A, wherein the volume ratio of the 2 mol / L hydrochloric acid to the isopropyl alcohol is 1:(72-75); taking another portion of isopropyl alcohol, adding isopropyl titanate, and continuously stirring for 1-2 hours to obtain a mixed solution B, wherein the volume ratio of the isopropyl titanate to the isopropyl alcohol is 1:(6.5-7); and adding the mixed solution A dropwise to the mixed solution B in a volume ratio of 1:1-1:2, and letting it stand to obtain the product.

9. The method for preparing a planar perovskite solar cell according to claim 6, wherein: The method for preparing the hole transport layer includes: spin coating 50-60 μL of Spiro-OMeTAD solution on the surface of the perovskite active layer in a nitrogen environment at a spin coating speed of 2500-3000 rmp for 35-40 s.

10. The method for preparing a planar perovskite solar cell according to claim 6, wherein: The electrode is a metal electrode, preferably a silver electrode; the electrode is prepared by a thermal evaporation process in a vacuum environment, with an evaporation rate of 0.5-0.8 Å·s -1 , the deposited electrode thickness is 150-180 nm.

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