A method for controlling the orientation of a polycrystalline thin film using an antisolvent

Abstract

This invention relates to the field of nanomaterial preparation and polycrystalline thin film preparation technology, specifically providing a method for controlling the orientation of polycrystalline thin films using antisolvents. This aims to solve the problems of existing preparation methods, such as cumbersome implementation, incompatibility with industrial production, and potential negative impacts on the integrity of the polycrystalline thin film. To this end, the method for controlling the orientation of polycrystalline thin films using antisolvents includes: coating a pre-prepared precursor solution onto a substrate; coating an antisolvent corresponding to a specific target orientation onto the substrate containing the precursor solution; and subjecting the coated substrate containing the precursor solution and antisolvent to low-temperature annealing to obtain a polycrystalline thin film with the specific target orientation. The annealing time is negatively correlated with the annealing temperature. The polycrystalline thin films prepared by the method of this invention exhibit high orientation consistency, low defect density, high carrier mobility, and a more compact and flat film morphology.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial preparation and polycrystalline thin film preparation technology, specifically a method for controlling the orientation of polycrystalline thin films using antisolvents. Background Technology

[0002] Polycrystalline thin films with specific orientations play a crucial role in the optoelectronic and photovoltaic fields. Specifically, polycrystalline thin films with specific orientations offer the following advantages in optoelectronic and photovoltaic device applications:

[0003] 1. Polycrystalline thin films with the same orientation have less lattice mismatch at the interface, resulting in lower film defect density and higher carrier mobility, which improves the photogenerated carrier transfer efficiency and thus improves device performance.

[0004] 2. Reduce efficiency loss of thin films under continuous operation and decrease potential defect sites at the interface that can be activated by photoaging due to lattice mismatch. In particular, in organic optoelectronic / photovoltaic devices and perovskite optoelectronic / photovoltaic devices, devices based on polycrystalline thin films with the same orientation can effectively solve the problems of phase separation and increased defect density caused by photoaging, thereby greatly improving the stability of devices under continuous operation conditions and providing effective technical support for the industrialization of optoelectronic devices based on organic or perovskite photoactive layers;

[0005] 3. Polycrystalline thin films with the same orientation can also reduce the gaps between crystals, thereby inhibiting the erosion of the photosensitive layer by water, oxygen and other substances through the gaps at the grain boundaries, and improving the device lifespan.

[0006] Currently, methods for obtaining polycrystalline thin films with consistent orientation mainly include controlling the thermal gradient, adjusting intermediates, adjusting phase composition, and applying external forces. However, these methods have problems such as cumbersome implementation, difficulty in compatibility of preparation processes with industrial production, and potential negative impacts on the integrity of polycrystalline thin films.

[0007] Taking the control of thermal gradient and the application of external force to regulate crystal orientation as an example, the preparation process of polycrystalline thin films with uniform orientation using thermal gradient is as follows: Pre-prepared MAFa (which requires stirring at -16℃ for two hours) is dissolved with methylamine iodine and lead iodide at a mass ratio of 25% and then coated onto the substrate surface by a scraping method. Subsequently, a heat source at 85℃ is applied to one side of the substrate to crystallize and obtain a polycrystalline thin film with relatively uniform orientation. This heating process often requires more than 2 hours. The thin film obtained by this method is sensitive to the preparation environment and also suffers from small crystal size, resulting in significant time and energy consumption. The preparation process of regulating crystal orientation by applying external force involves physically pressurizing the pre-prepared polycrystalline thin film using an organic thin film material with a specific structure. Utilizing the strong plasticity of the perovskite structure, secondary crystallization is achieved, thereby regrowth of the crystal into a structure with uniform orientation. Although this method is relatively simple to obtain orientation, the presence of columnar lower surfaces of the organic thin film material often leaves numerous pores on the film surface, affecting the film morphology and long-term stability, and potentially introducing new defects.

[0008] Therefore, there is a need in the field for a new method for preparing polycrystalline thin films to solve the above-mentioned technical problems. Summary of the Invention

[0009] The present invention aims to solve the above-mentioned technical problems, namely, to solve the problems that existing preparation methods are cumbersome to implement, difficult to be compatible with industrial production, and may have a negative impact on the integrity of polycrystalline thin films.

[0010] This invention provides a method for controlling the orientation of polycrystalline thin films using antisolvents, the method comprising:

[0011] S1: Apply the pre-prepared precursor solution onto the substrate;

[0012] S2: Apply the antisolvent corresponding to the target specific orientation onto the substrate where the precursor liquid is located;

[0013] S3: The substrate having been coated with the precursor liquid and the antisolvent is subjected to low-temperature annealing to obtain the polycrystalline thin film with the target specific orientation, wherein the annealing time of the low-temperature annealing is negatively correlated with the annealing temperature.

[0014] In the preferred embodiment of the above method, step S1 specifically includes:

[0015] The pre-prepared perovskite precursor solution is coated onto the substrate;

[0016] The steps in S2 specifically include:

[0017] An antisolvent corresponding to a specific target orientation is applied to the substrate containing the perovskite precursor solution, wherein the antisolvent contains isopropanol.

[0018] In the preferred embodiment of the above method, the step of "coating the pre-prepared perovskite precursor solution onto the substrate" further includes:

[0019] The pre-prepared perovskite precursor solution was coated onto the substrate by spin coating at 2000 rpm for 5 seconds followed by 4000 rpm for 20 seconds.

[0020] The step of “coating the antisolvent corresponding to the target specific orientation onto the substrate where the perovskite precursor solution is located” further includes:

[0021] The antisolvent corresponding to the target specific orientation is applied to the substrate during the last 10 seconds of spin-coating the perovskite precursor solution at 4000 rpm.

[0022] In the preferred embodiment of the above method, the target specific orientation is 111 orientation, and the antisolvent is pure isopropanol solvent.

[0023] In the preferred embodiment of the above method, the target specific orientation is the 001 orientation, and the antisolvent is a mixed solution of formamidinium iodine, methylamine iodine and methylamine chloride as solutes and isopropanol as solvent.

[0024] In the preferred embodiment of the above method, the mixed solution of formamidinium iodine, methylamine iodine and methylamine chloride as solute and isopropanol as solvent is prepared by adding formamidinium iodine, methylamine iodine and methylamine chloride to pure isopropanol solvent in a ratio of 10:1:1.

[0025] In the preferred embodiment of the above method, the concentration of formamidinium in the mixed solvent of isopropanol, formamidinium, methylamine iodine and methylamine chloride is 5 mg / mL, and the concentrations of methylamine iodine and methylamine chloride are both 0.5 mg / mL.

[0026] In the preferred embodiment of the above method, the perovskite precursor solution has the following composition: (FA0.85MA0.10Cs0.05)Pb(I2.85Br0.15) with a concentration of 1.2 mol / mL.

[0027] In a preferred embodiment of the above method, the perovskite precursor solution is prepared by dissolving 175.44 mg formamidinium iodide, 553.2 mg lead iodide, 12.77 mg cesium bromide and 13.44 mg methylamine bromide in a mixed solution of 800 uLDMF + 200 uLDMSO and stirring until homogeneous.

[0028] In the preferred embodiment of the above method, the annealing temperature is 100 to 150°C, and the annealing time is 6 to 25 minutes.

[0029] In the preferred embodiment of the above method, the annealing temperature is 150°C and the annealing time is 6 minutes.

[0030] In the preferred embodiment of the above method, the annealing temperature is 130°C and the annealing time is 15 minutes.

[0031] In the preferred embodiment of the above method, the annealing temperature is 100°C and the annealing time is 25 minutes.

[0032] When using the above technical solution, the polycrystalline thin film prepared by the method of the present invention has high orientation uniformity, low defect density, high carrier mobility and a more compact and flat film morphology. This film has the following advantages in applications (taking perovskite thin films as an example):

[0033] 1. Perovskite films with uniform orientation have a lower intrinsic defect density, which in turn increases the open-circuit voltage of the device during operation, reduces electrical density loss, improves the fill factor, and thus improves the overall efficiency of the device.

[0034] 2. Due to its low lattice mismatch at the grain boundaries, it avoids the generation of new defect states (including phase separation, lead elementalization, etc.) caused by the high grain boundary energy in the photosensitive layer during continuous operation, which can effectively improve the stability of the device during continuous operation.

[0035] 3. Through antisolvent engineering, without the need for complicated de-firing and pressurization processes, only simple control of the antisolvent is required to prepare perovskite films with completely different orientations such as 111 or 001 under the same process conditions, which can meet a variety of control requirements. Attached Figure Description

[0036] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0037] Figure 1 This is a flowchart of the method for controlling the orientation of polycrystalline thin films using antisolvents according to the present invention;

[0038] Figure 2 This is a three-dimensional schematic diagram of perovskite;

[0039] Figure 3 This is a planar schematic diagram of the 001 orientation of perovskite;

[0040] Figure 4 This is a planar schematic diagram of the 111 orientation of perovskite.

[0041] Figure 5This is a data comparison chart of the existing controlled thermal gradient preparation method (10.1038 / ncomms13407), component-controlled preparation method (10.1038 / s41467-018-05076-w), top-bottom growth preparation method (10.1002 / adma.201606831), and the preparation method of the present invention;

[0042] Figure 6 These are microscopic morphology diagrams of polycrystalline thin films prepared using the method of this invention;

[0043] Figure 7 These are microscopic morphology diagrams of polycrystalline thin films prepared using existing component control methods;

[0044] Figure 8 These are microscopic morphology diagrams of polycrystalline thin films prepared using existing methods for controlling thermal gradients.

[0045] Figure 9 This is a microscopic morphology diagram of a polycrystalline thin film prepared using existing methods of applying external force.

[0046] Figure 10 These are data graphs showing the signal intensity of thin films prepared using the method of this invention at different annealing temperatures. Detailed Implementation

[0047] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0048] Based on the problems pointed out in the background art, the existing preparation methods have the disadvantages of being cumbersome to implement, difficult to be compatible with industrial production, and may have a negative impact on the integrity of polycrystalline thin films. The present invention provides a method for preparing polycrystalline thin films by using antisolvent to control specific orientations. The aim is to make the polycrystalline thin films prepared by the preparation method of the present invention have high orientation consistency, low defect density, high carrier mobility and more compact and flat film morphology.

[0049] like Figure 1 As shown, the method of controlling polycrystalline thin film orientation using antisolvents according to the present invention includes:

[0050] S1: Apply the pre-prepared precursor solution onto the substrate;

[0051] S2: Apply the antisolvent corresponding to the specific orientation of the target onto the substrate where the precursor solution is located;

[0052] S3: The coated substrate containing the precursor liquid and antisolvent is subjected to low-temperature annealing to obtain a polycrystalline thin film with a specific orientation. The annealing time is negatively correlated with the annealing temperature.

[0053] In step S3 above, the annealing temperature during the low-temperature annealing process can be 100 to 150°C, the annealing time can be 6 to 25 minutes, and the coating method can be spin coating, scraping coating or spraying, among which spin coating has the best effect.

[0054] It should be noted that polycrystalline thin films are a common type of thin film crystal, including organic polycrystalline thin films such as hydrochloric acid carboxylase polycrystalline thin films, inorganic polycrystalline thin films such as zinc oxide polycrystalline thin films, and organic-inorganic hybrid polycrystalline thin films such as organic-inorganic hybrid perovskite polycrystalline thin films. Through repeated research, experiments, and comparative analysis, the inventors discovered that common thin film crystals can be prepared using the method of this invention. Specifically, by utilizing an antisolvent and controlling the ratio of its components, polycrystalline thin films with different specific orientations can be obtained. Furthermore, low-temperature annealing maintains a high degree of consistency in their orientation. The application of this antisolvent engineering will contribute to the development of devices with long-term stability.

[0055] The following describes in detail the implementation of the present invention using polycrystalline perovskite thin films as an example. These films are widely used in solar cells, photodetectors, and light-emitting devices.

[0056] Preferably, step S1 specifically includes: coating the pre-prepared perovskite precursor solution onto the substrate; step S2 specifically includes: coating an antisolvent corresponding to the target specific orientation onto the substrate where the perovskite precursor solution is located, wherein the antisolvent contains isopropanol.

[0057] In one specific scenario, the step of "coating the pre-prepared perovskite precursor solution onto the substrate" further includes: spin-coating the pre-prepared perovskite precursor solution onto the substrate using a spin-coating method of first at 2000 rpm for 5 seconds and then at 4000 rpm for 20 seconds; the step of "coating the antisolvent corresponding to the target specific orientation onto the substrate containing the perovskite precursor solution" further includes: coating the antisolvent corresponding to the target specific orientation onto the substrate before the last 10 seconds of spin-coating the perovskite precursor solution at 4000 rpm. That is, step S2 can begin during the execution of step S1. Of course, in some embodiments, step S2 can also be executed after step S1 is completed. Those skilled in the art can flexibly set the execution timing of step S2 without affecting the result. Such changes in the execution timing of step S2 do not constitute a limitation of the present invention.

[0058] In the above, the perovskite precursor solution consists of (FA0.85MA0.10Cs0.05)Pb(I2.85Br0.15) with a concentration of 1.2 mol / mL. Specifically, the perovskite precursor solution with the above components is prepared by dissolving 175.44 mg formamidinium iodide, 553.2 mg lead iodide, 12.77 mg cesium bromide, and 13.44 mg methylamine bromide in a mixed solution of 800 μL LDMF + 200 μL LDMSO and stirring until homogeneous.

[0059] The composition of the antisolvent varies depending on the specific orientation. For example, when the target orientation is 111, the inventors have repeatedly experimented, analyzed and compared the results to find that the antisolvent is pure isopropanol. It utilizes the close molecular size of isopropanol and formamidine (FA), the solubility of formamidine, and the interaction mechanism between hydroxyl groups and lead iodide hexahedrons to allow perovskite to precipitate in a specific 111 orientation under its control, and obtain a highly consistent perovskite film after annealing.

[0060] For the target orientation of 001, the inventors, through repeated experiments, analysis and comparison, determined that the antisolvent is a mixed solvent of isopropanol, formamidinium iodide (FAI), methylamine iodide (MAI), and methylamine chloride (MACl). Specifically, the mixed solvent of isopropanol, formamidinium iodide, methylamine iodide and methylamine chloride is prepared by adding formamidinium iodide, methylamine iodide and methylamine chloride to pure isopropanol solvent in a ratio of 10:1:1. In the above mixed solvent of isopropanol, formamidinium iodide, methylamine iodide and methylamine chloride, the concentration of formamidinium iodide is 5 mg / mL, and the concentrations of methylamine iodide and methylamine chloride are both 0.5 mg / mL. Adding different concentrations of FAI, MAI, and MACl to isopropanol can correspondingly inhibit the solubility of formamidin (FA) and the number of hydroxyl vacancies in isopropanol, causing the initial precipitation orientation to change from 111 to 001, and then use the 001 orientation as a template for growth during the subsequent annealing process.

[0061] Figures 2 to 4 A three-dimensional schematic diagram, a planar schematic diagram of the 001 orientation, and a planar schematic diagram of the 111 orientation of perovskite are shown respectively.

[0062] like Figure 10As shown, in the process of preparing polycrystalline perovskite thin films using the method of the present invention, the annealing temperature and annealing time in step S3 are negatively correlated. In one possible scenario, the annealing temperature is 150°C and the annealing time is 6 minutes; in another possible scenario, the annealing temperature is 130°C and the annealing time is 15 minutes; in yet another possible scenario, the annealing temperature is 100°C and the annealing time is 25 minutes. Through repeated experiments and comparisons, the inventors found that for a perovskite precursor solution with a concentration of 1.2 mol / mL, the above three annealing methods have the same effect. For a perovskite precursor solution with a concentration of 1.5 mol / mL, the preferred method is an annealing temperature of 100°C and a annealing time of 25 minutes. It is preferable to gradually decrease the annealing temperature as the concentration increases. The concentration of different perovskite precursor solutions affects the final film thickness.

[0063] like Figure 5 As shown, by controlling the thermal gradient, which requires a continuous heating process of more than 2 hours, the overall preparation process of the present invention only takes 8 to 10 minutes. At the same time, by controlling the thermal gradient to regulate the orientation, the carrier mobility is similar to that of the antisolvent engineering method in only one direction, specifically 5×10-3 cm2V-1s-1. However, in the vertical direction, there is an order of magnitude difference compared with the present invention, specifically 5×10-6 cm2V-1s-1. By comparison, it can be seen that the present invention achieves better overall performance in terms of carrier mobility and defect density than other preparation methods, realizing high carrier mobility and low defect density in polycrystalline thin films.

[0064] Furthermore, it is generally difficult to obtain highly uniformly oriented films by adjusting intermediates, relative components, and applying external forces. Often, a single main peak coexists with several secondary peaks whose intensity is approximately 10-25% of the main peak's intensity. However, the film prepared by the method of this invention exhibits highly uniform orientation, with almost no obvious secondary peaks except for a single, extremely strong main peak. It should be noted that the intensity of the secondary peaks is approximately 0-3% of the main peak's intensity. See also... Figures 6 to 9 , Figure 6 These are polymorphic images prepared using the method of this invention. Figure 7 This is a polymorphism diagram using a component-controlled method (from 10.1038 / s41467-018-05076-w). Figure 8 The polycrystalline morphology diagram is obtained using a temperature gradient method (from 10.1038 / ncomms13407). Figure 9 The polymorphism diagram is obtained using a pressure-consistent method (from 10.1002 / aenm.201702369). Figures 6 to 9 From the shape, it can be seen that, combined with Figure 6 and 7 The advantage of this invention is that it has a more consistent crystal orientation, combined with Figure 6 and 8 The advantage of this invention is that the preparation method is simpler and faster, reducing the overall film preparation time from several hours to a dozen minutes. Figure 6 and 9 The advantage of this invention is that it does not cause destructive damage to the film. Figure 9 The pores generated during this fabrication process can reduce the overall stability of the device.

[0065] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for controlling the orientation of polycrystalline thin films using antisolvents, characterized in that, The method includes: S1: The pre-prepared perovskite precursor solution is coated onto the substrate; S2: Apply an antisolvent corresponding to the target specific orientation to the substrate where the perovskite precursor solution is located, wherein when the target specific orientation is 111 orientation, the antisolvent is pure isopropanol solvent, and when the target specific orientation is 001 orientation, the antisolvent is a mixed solution of formamidinium iodine, methylamine iodine and methylamine chloride as solutes and isopropanol as solvent. S3: The substrate coated with the perovskite precursor solution and the antisolvent is subjected to low-temperature annealing to obtain the polycrystalline thin film with the target specific orientation, wherein the annealing time of the low-temperature annealing is negatively correlated with the annealing temperature. The components of the perovskite precursor solution are (FA) 0.85 MA 0.10 Cs 0.05 )Pb(I 2.85 Br 0.15 The concentration was 1.2 mol / mL.

2. The method according to claim 1, characterized in that, The step of coating the pre-prepared perovskite precursor solution onto the substrate further includes: coating the pre-prepared perovskite precursor solution onto the substrate by spin coating at 2000 rpm for 5 seconds and then at 4000 rpm for 20 seconds. The step of applying an antisolvent corresponding to the target specific orientation to the substrate on which the perovskite precursor liquid is located further includes: applying an antisolvent corresponding to the target specific orientation to the substrate in the last 10 seconds before spin-coating the perovskite precursor liquid at 4000 rpm.

3. The method according to claim 1, characterized in that, The mixed solution of formamidinium, methylamine iodine and methylamine chloride as solutes and isopropanol as solvent is prepared by adding formamidinium, methylamine iodine and methylamine chloride in a ratio of 10:1:1 to pure isopropanol solvent.

4. The method according to claim 3, characterized in that, The concentration of formamidinium in the mixed solvent of isopropanol, formamidinium, methylamine iodine, and methylamine chloride is 5 mg / mL, and the concentrations of methylamine iodine and methylamine chloride are both 0.5 mg / mL.

5. The method according to claim 1, characterized in that, The perovskite precursor solution is prepared by dissolving 175.44 mg formamidinium iodide, 553.2 mg lead iodide, 12.77 mg cesium bromide and 13.44 mg methylamine bromide in a mixed solution of 800 u LDMF + 200 u LDMSO and stirring until homogeneous.

6. The method according to any one of claims 1 to 5, characterized in that, The annealing temperature is 100 to 150°C, and the annealing time is 6 to 25 minutes.

7. The method according to claim 6, characterized in that, The annealing temperature is 150°C and the annealing time is 6 minutes.

8. The method according to claim 6, characterized in that, The annealing temperature is 130°C and the annealing time is 15 minutes.

9. The method according to claim 6, characterized in that, The annealing temperature is 100°C and the annealing time is 25 minutes.

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