A tin dioxide colloid and a preparation method thereof, a perovskite solar cell electron transport layer and application

Abstract

The application relates to the technical field of photoelectric devices, in particular to a tin dioxide colloid and a preparation method thereof, a perovskite solar cell electron transport layer and application. The method comprises the following steps: heating a tin salt solution, then adding an inorganic alkali solution drop by drop, standing after the dropping is completed, obtaining a hydrated tin dioxide precipitate; washing the hydrated tin dioxide precipitate with water to obtain a gelatinous precipitate, adding a gel breaker, and obtaining a tin dioxide precursor colloid through ultrasonic dispersion; carrying out hydrothermal reaction on the tin dioxide precursor colloid, centrifugal separation, dispersing the obtained precipitate in water, and obtaining a light blue transparent tin dioxide colloid with a stability of more than 3 months. The colloidal particles of the prepared high-transparency tin dioxide colloid are a mixture of spherical nanocrystals and nanorods, and the oxygen defect concentration is low; no surfactant needs to be added to stabilize the colloid or promote film formation; the prepared high-transparency tin dioxide colloid is suitable for the electron transport layer of a perovskite solar cell, and the efficiency and stability of the device are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic device technology, and in particular to a tin dioxide colloid, its preparation method, an electron transport layer for perovskite solar cells, and its applications. Background Technology

[0002] Tin dioxide (SnO2), as an important n-type wide bandgap semiconductor, possesses high electron mobility, good optical transmittance, and a band structure that matches perovskite materials. It exhibits excellent performance and great application potential as an electron transport layer in perovskite solar cells. However, when traditional spherical SnO2 nanoparticles are used to prepare thin films, the particles often have point contacts, easily forming pores and resulting in poor film density. These interparticle pore defects not only affect the longitudinal charge transport efficiency, but more seriously, during subsequent spin-coating of the perovskite precursor solution, the solution can penetrate along these pore defects, directly contacting the underlying conductive electrode (such as ITO or FTO). This penetration behavior leads to multiple adverse consequences: on the one hand, the perovskite precursor cannot form uniform crystals in the pore region, easily resulting in incomplete crystallization or pinhole defects; on the other hand, the direct contact between the perovskite layer and the conductive electrode creates a high concentration of defect states at the interface, exacerbating nonradiative recombination losses and causing interface energy level mismatch problems, ultimately severely limiting the photoelectric conversion efficiency and long-term operational stability of the device.

[0003] To improve the density of electron transport layer films, methods such as high-temperature annealing or the introduction of organic additives are commonly used. While high-temperature annealing can improve the crystallinity and density of SnO2 films, this process is energy-intensive and contradicts the low-temperature fabrication requirements of flexible devices. Introducing organic additives or polymers (such as polyethylene glycol) into SnO2 colloids can improve the dispersibility of nanoparticles and the wettability of the film, but the introduction of organic additives may introduce impurity residues: if not completely removed, the residual organic matter can become interfacial impurities, affecting the crystallinity quality and interfacial charge transport characteristics of subsequent perovskite layers.

[0004] Therefore, how to obtain a tin dioxide colloid capable of spontaneously forming a dense electron transport layer film while avoiding high-temperature annealing processes and organic additive residues has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a tin dioxide colloid, its preparation method, an electron transport layer for perovskite solar cells, and its application, in order to solve the problem in the prior art that it is difficult to obtain a tin dioxide colloid capable of spontaneously forming a dense electron transport layer film while avoiding high-temperature annealing processes and organic additive residues.

[0006] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0007] The first aspect of this invention is to provide a method for preparing tin dioxide colloid, the method comprising the following steps:

[0008] (1) Heat the tin salt solution, then add an inorganic alkali solution dropwise. After the addition is complete, let it stand to obtain hydrated tin dioxide precipitate; the molar ratio of the inorganic alkali to the tin salt is 1-5:1.

[0009] (2) Wash the hydrated tin dioxide precipitate with water to obtain a gel-like precipitate, add a desiccant, and disperse by ultrasonication to obtain tin dioxide precursor colloid;

[0010] (3) The tin dioxide precursor colloid is subjected to hydrothermal reaction, centrifuged and separated, and the resulting precipitate is dispersed in water to obtain tin dioxide colloid.

[0011] A second aspect of the present invention is to provide a tin dioxide colloid, which is prepared by the method for preparing tin dioxide colloid as described above using hydrogen peroxide hydrolysis.

[0012] A third aspect of the present invention provides a method for preparing an electron transport layer, comprising the following steps: spin-coating the tin dioxide colloid described above or the tin dioxide colloid obtained by the method described above onto a substrate, followed by heat treatment to obtain an electron transport layer.

[0013] A fourth aspect of the present invention is to provide an electron transport layer prepared by the preparation method described above.

[0014] A fifth aspect of the present invention provides a perovskite optoelectronic device, comprising a substrate, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and an electrode arranged sequentially; wherein the electron transport layer is an electron transport layer prepared by the above-described preparation method or an electron transport layer described above.

[0015] The sixth aspect of the present invention is to provide tin dioxide colloid prepared by the preparation method described above, and / or electron transport layer prepared by the preparation method described above, and / or perovskite optoelectronic devices as described above, for use in photovoltaic cells, light-emitting diodes, photodetectors or lasers.

[0016] As described above, the tin dioxide colloid, its preparation method, the electron transport layer of a perovskite solar cell, and its application of the present invention have the following beneficial effects:

[0017] (1) The entire preparation process of this invention uses water as a medium and hydrogen peroxide as a desiccant. The desiccant process optimizes the dispersibility of the colloid, so that it can maintain high dispersibility without adding any organic surfactants or soft stencils. The process is simple and environmentally friendly, and the product is easy to purify, making it suitable for commercial-scale preparation and application.

[0018] (2) By controlling the hydrothermal reaction conditions, the present invention can simultaneously generate nanospheres and nanorods in a single system. During film formation, the nanorods can overlap to form a conductive network, while the nanospheres can effectively fill the gaps between the nanorods, significantly improving the compactness of the film and reducing interface defects.

[0019] (3) In the prior art, SnO2 colloids without surfactants usually settle within a few days. The present invention achieves higher stability through H2O2 surface modification and hydrothermal crystallization optimization. It can be stored stably for more than 3 months at room temperature without significant aggregation or sedimentation, and the SnO2 grain size is less than 20nm.

[0020] (4) In the prior art, the electron transport layer formed by spin-coating spherical SnO2 nanoparticles generally has a large number of pinholes and intergranular voids, which usually require multi-layer coating or post-treatment (such as high-temperature annealing, additive assistance) to improve the density. The present invention breaks through the limitations of using single-morphology nanoparticles and innovatively adopts a colloidal system of nanorods and nanospheres: the nanorods are used to form a conductive network by overlapping each other, and the nanospheres are used to effectively fill the voids between the rods, so that a dense and flat electron transport layer can be obtained by spin-coating in one step. This composite structure not only overcomes the dual technical defects of "poor density of simple spherical particles" and "wedge-shaped voids in simple nanorods", but also achieves synergistic effect between the two. The electron transport layer prepared by this colloidal method provides an excellent crystalline substrate for the perovskite layer, which can induce the formation of large-sized grains of perovskite, significantly reduce the interfacial charge recombination loss, and ultimately improve the photoelectric conversion efficiency and long-term stability of perovskite solar cells. Compared to existing technologies that require complex processes or multiple steps to barely improve film quality, this invention achieves superior film density and device performance with a simplified process and lower energy consumption. Attached Figure Description

[0021] Figure 1 A digital photograph of the colloid prepared in Example 1.

[0022] Figure 2 The image shows the X-ray diffraction (XRD) pattern of the colloid prepared in Example 1 after vacuum drying at room temperature.

[0023] Figure 3 The image shows a comparison curve of the hydrated particle size distribution of the colloid prepared in Example 1 before and after 3 months of storage. The inset is a digital photograph of the colloid.

[0024] Figure 4 Transmission electron microscopy (TEM) image of the hydrothermal tin dioxide colloid prepared in Example 1.

[0025] Figure 5 Another transmission electron microscope (TEM) image of the hydrothermal tin dioxide colloid prepared in Example 1.

[0026] Figure 6 Transmission electron microscopy (TEM) image of the hydrothermal tin dioxide colloid prepared in Example 2.

[0027] Figure 7 XPS spectra (O 1s and Sn 3d) of the tin dioxide colloid prepared in Example 2 and the commercial tin dioxide colloid after being formed into films.

[0028] Figure 8 The image shows the transmittance spectrum of the tin dioxide colloid prepared in Example 2 after spin coating. The inset is a digital photograph of the colloid.

[0029] Figure 9 The image shows a scanning electron microscope (SEM) image of the tin dioxide thin film prepared in Example 2.

[0030] Figure 10 The water contact angle test results are for the tin dioxide thin film deposited on FTO glass prepared in Example 2.

[0031] Figure 11 An atomic force microscope (AFM) image of the tin dioxide thin film deposited on FTO glass prepared in Example 2.

[0032] Figure 12 for Figure 11 The corresponding 3D AFM image.

[0033] Figure 13 Transmission electron microscopy (TEM) image of the hydrothermal tin dioxide colloid prepared in Example 3.

[0034] Figure 14 The electron paramagnetic resonance spectra of the tin dioxide colloid prepared in Example 3 and the commercial tin dioxide colloid spin-coated into thin films are shown.

[0035] Figure 15 The current-voltage (IV) curves of the tin dioxide colloid prepared in Example 3 and the commercial tin dioxide colloid spin-coated into thin films are shown.

[0036] Figure 16 The image shows a scanning electron microscope (SEM) image of the perovskite thin film prepared in Example 3.

[0037] Figure 17The image shows a scanning electron microscope (SEM) image of the cross-section of the perovskite optoelectronic device prepared in Example 3.

[0038] Figure 18 This is a comparison of the positive JV curves of perovskite optoelectronic devices prepared with tin dioxide colloid in Example 3 and commercial tin dioxide colloid, respectively.

[0039] Figure 19 The results show the stability test results of perovskite solar cells prepared by the tin dioxide colloid of Example 3 and commercial tin dioxide colloid, respectively, at room temperature (about 27°C), without encapsulation, and with a relative humidity of about 30%. Detailed Implementation

[0040] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. Those skilled in the art can easily understand other advantages and effects of this invention from the content disclosed in this specification.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0042] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0043] In this invention, the terms "preferredly," "more preferably," "better," and "even better" refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of the invention. That is, in this invention, "preferredly," "more preferably," "better," and "even better" are merely descriptions of more effective implementations or examples, but do not constitute a limitation on the scope of protection of the invention.

[0044] In this invention, terms such as "further," "even more," and "particularly" are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0045] In this invention, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this invention, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0046] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0047] Unless otherwise specified, all steps of this invention may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0048] Unless otherwise stated, a singular term may include a plural term and should not be understood as having a quantity of one.

[0049] In this invention, "above" or "below" both include the number itself. For example, "below 1" includes 1.

[0050] In this invention, room temperature refers to 0~40°C, including but not limited to 10~40°C, or further to 20~30°C.

[0051] To overcome the drawbacks of existing methods, such as high energy consumption during high-temperature annealing and easy residue of organic additives, optimizing the quality of electron transport layer films by controlling the morphology of SnO2 nanocrystals has become an important research direction in this field. SnO2 nanorods with one-dimensional structures can overlap after film formation to form an effective electron transport network, which is beneficial for improving the longitudinal charge transport efficiency. However, in films composed solely of nanorods, the wedge-shaped gaps between the rods are difficult to completely fill, and using nanorods alone cannot achieve a completely dense film coverage. Theoretically, if zero-dimensional spherical nanocrystals can be combined with one-dimensional nanorods, it is hoped that the filling effect of spherical particles and the bridging effect of rod-shaped structures can achieve synergistic effects: nanorods can construct a fast electron transport framework, while smaller nanospheres can effectively fill the gaps between nanorods, thereby obtaining a denser composite film with fewer defects.

[0052] Regarding the preparation of SnO2 nanocrystals, various synthetic routes have been reported in the existing technology. Paik et al. proposed a method for preparing ultrafine SnO2 nanocrystals using SnCl4·5H2O and H2O2, which can obtain uniformly dispersed nanoparticles with a size of approximately 4–6 nm. However, this method uses KOH to stabilize the colloid after degellation, and the residual K⁺ may migrate into the perovskite layer, leading to perovskite lattice structure distortion and introducing additional defect states. In addition, the preparation of SnO2 nanorods often requires the addition of soft template agents (such as various surfactants) to control the anisotropic growth of crystals. Surfactants such as polyvinylpyrrolidone and hexadecyltrimethylammonium bromide can effectively control the morphology of SnO2 nanocrystals in hydrothermal reactions, but soft template agents are usually insulating organic materials that need to be removed by high-temperature treatment in subsequent processes. If the removal is incomplete, the residual organic matter will become interfacial impurities, which will lead to abnormal subsequent perovskite crystallization, thereby offsetting the performance gains brought by morphology control.

[0053] Therefore, current technologies still lack a simple, surfactant-free method for preparing SnO2 nanomaterials that allows for morphological control and the production of highly stable colloids. It is also difficult to obtain SnO2 colloids with nanorod and nanosphere composite structures. Therefore, developing a novel SnO2 colloid preparation method that overcomes these shortcomings is of significant research and application value for promoting the development of high-performance perovskite solar cells.

[0054] The first aspect of this invention is to provide a method for preparing tin dioxide colloid, the method comprising the following steps:

[0055] (1) Heat the tin salt solution, then add an inorganic alkali solution dropwise. After the addition is complete, let it stand to obtain hydrated tin dioxide precipitate; the molar ratio of the inorganic alkali to the tin salt is 1-5:1.

[0056] (2) Wash the hydrated tin dioxide precipitate with water to obtain a gel-like precipitate, add a desiccant, and disperse by ultrasonication to obtain tin dioxide precursor colloid;

[0057] (3) The tin dioxide precursor colloid is subjected to hydrothermal reaction, centrifuged and separated, and the resulting precipitate is dispersed in water to obtain tin dioxide colloid.

[0058] This invention obtains hydrated tin dioxide by hydrolysis of tin salt, and then reacts the hydrated tin dioxide with the descaling agent hydrogen peroxide to obtain a peroxide complex. The peroxide complex is then decomposed by heating to saturate and generate tin dioxide colloid.

[0059] In some embodiments of the present invention, in step (1), the molar ratio of the inorganic alkali to the tin salt is 1-5:1; for example, 1-3:1 or 3-5:1. If the concentration of the alkali is too high, it will be difficult to remove the precipitate completely during subsequent washing, and the pH of the overall colloid is weakly acidic. Excessive alkali will leave residual hydroxide ions that will affect the stability of the colloid.

[0060] In some embodiments of the present invention, in step (1), the concentration of the tin salt solution is 0.5-3 mol / L; for example, 0.5-1.1 mol / L, 1.1-1.8 mol / L, 1.8-2.4 mol / L, 2.4-3.0 mol / L. When the concentration of tin salt is too low, the number of crystal nuclei generated is small and the particles are easy to grow, which is not conducive to obtaining nanoscale colloids in the future. When the concentration is too high, the viscosity of the reaction system increases, the hydrolysis rate is too fast, and it is easy to cause local supersaturation and generate agglomerates.

[0061] In some embodiments of the present invention, in step (1), the tin salt is selected from one or more of tin tetrachloride, stannous chloride, or tin nitrate;

[0062] In some embodiments of the present invention, in step (1), the heating temperature is 50-70°C; for example, 50-55°C, 55-60°C, 60-65°C, 65-70°C; when the temperature is below 50°C, the hydrolysis reaction rate is slow, the required reaction time is too long, and the hydrolysis is incomplete; when the temperature is above 70°C, the hydrolysis is too violent, and the generated precipitate is large and easily agglomerates.

[0063] In some embodiments of the present invention, in step (1), the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide or ammonia water;

[0064] In some embodiments of the present invention, in step (1), the concentration of the inorganic alkaline solution is 1-6 mol / L; for example, 1-2 mol / L, 2-3 mol / L, 3-4 mol / L, or 4-6 mol / L. If the concentration of the alkaline solution is too low, the added volume will be too large, which will dilute the reaction system and affect the morphology of the hydrolysis products. If the concentration is too high, the local alkalinity will be too strong, making subsequent washing difficult and potentially introducing too many ionic impurities.

[0065] In some embodiments of the present invention, in step (1), the settling temperature is 50-70°C; for example, 50-55°C, 55-60°C, 60-65°C, 65-70°C; the settling time is 0.5-5h; for example, 0.5-2h, 2-3h, 3-4h, 4-5h. If the settling temperature is too high or the time is too long, the precipitate will be further matured, the particles will grow larger or even settle tightly, which is not conducive to subsequent degelling. If the temperature is too low or the time is too short, the aging will be insufficient, the precipitate structure will be loose, and it will be easily lost during washing.

[0066] In some embodiments of the present invention, in step (2), the number of washing cycles is ≥1; preferably 1-5 times; for example, 1-2 times, 2-3 times, 3-4 times, or 4-5 times. If the number of washing cycles is too few, the residual ions will interfere with the stability of the colloid, and if the number of washing cycles is too many, some of the colloidal precipitate may be lost due to repeated dispersion.

[0067] In some embodiments of the present invention, in step (2), the desiccant is a hydrogen peroxide aqueous solution; preferably, the concentration of the hydrogen peroxide aqueous solution is 0.05-2 mol / L; for example, 0.05-0.5 mol / L, 0.5-1.0 mol / L, 1.0-1.5 mol / L, 1.5-2.0 mol / L; if the concentration of hydrogen peroxide is too low, it will not be able to effectively desiccate the precipitate to form a stable colloid, and if the concentration is too high, it may cause the colloid particle size to be too small or to form soluble peroxide coordination compounds, which will reduce the yield.

[0068] In some embodiments of the present invention, in step (2), the temperature of the ultrasound is 0-30℃, for example, 0-8℃, 8-15℃, 15-23℃, 23-30℃; the frequency of the ultrasound is 35-45KHz, for example, 35-38kHz, 38-42kHz, 42-45kHz; and the duration of the ultrasound is 2-48h, for example, 2-14h, 14-25h, 25-37h, 37-48h.

[0069] In some embodiments of the present invention, in step (2), the molar ratio of hydrated tin dioxide to the descaling agent is 1:4-10; for example, 1:4-6, 1:6-8, or 1:8-10. If the proportion of the descaling agent is too low, it cannot be fully descaled, and the precipitate remains in lumps. If the proportion is too high, the excess hydrogen peroxide will cause the pH of the colloid to be too low, which will damage the stability of the colloid, and an additional step is required to remove the excess hydrogen peroxide.

[0070] In some embodiments of the present invention, in step (2), the mass fraction of tin dioxide in the gel-like precipitate is 8-20 wt%, with the remainder being water; for example, 8-11 wt%, 11-14 wt%, 14-17 wt%, 17-20 wt%.

[0071] In some embodiments of the present invention, in step (3), the temperature of the hydrothermal reaction is 100-200℃, for example, 100-200℃; the reaction time is 12-48h, for example, 12-21h, 21-30h, 30-39h, 39-48h. When the hydrothermal temperature is below 100℃, the driving force for crystal growth is insufficient, the crystallinity of the product is poor, and it may still be amorphous or semi-crystalline. When the temperature is above 200℃, the energy consumption is high and the equipment requirements are high, and it is easy to cause excessive particle growth and agglomeration. When the reaction time is too short, crystallization is incomplete; when the time is too long, the particles will continue to grow, causing the particle size distribution to become wider.

[0072] In some embodiments of the present invention, in step (3), the centrifugation speed is 7000-9000 rpm, for example, 7000-7500 rpm, 7500-8000 rpm, 8000-8500 rpm, 8500-9000 rpm; the centrifugation time is 8-12 min; for example, 8-9 min, 9-10 min, 10-11 min, 11-12 min;

[0073] In some embodiments of the present invention, in step (3), the mass ratio of the precipitate to water is 1-4:1. For example, 1-2:1, 2-3:1, or 3-4:1.

[0074] A second aspect of the present invention is to provide a tin dioxide colloid, which is prepared by the method for preparing tin dioxide colloid as described above using hydrogen peroxide hydrolysis.

[0075] In some embodiments of the present invention, the tin dioxide colloid contains two morphologies: nanorods and spherical nanocrystals.

[0076] In some embodiments of the present invention, the grain size in the tin dioxide colloid is 2-20 nm. For example, it is 2-7 nm, 7-12 nm, 12-17 nm, or 17-20 nm.

[0077] In some embodiments of the present invention, the weight ratio of nanorods to spherical nanocrystals in the tin dioxide colloid is 1-5:10; for example, 1-3:10 or 3-5:10.

[0078] In some embodiments of the present invention, the aspect ratio of the nanorod is 2-5:1, for example, 2-3:1 or 3-5:1, and the diameter of the nanorod is 3-5 nm, for example, 3-4 nm or 4-5 nm; the diameter is the size of the cross-section of the nanorod, and more specifically, the diameter here is the size of the longest crystal plane.

[0079] In some embodiments of the present invention, the particle size of the spherical nanocrystals is 2-4 nm. For example, 2-2.5 nm, 2.5-3 nm, 3-3.5 nm, or 3.5-4 nm.

[0080] A third aspect of the present invention provides a method for preparing an electron transport layer, comprising the following steps: spin-coating the tin dioxide colloid described above or the tin dioxide colloid obtained by the method described above onto a substrate, followed by heat treatment to obtain an electron transport layer.

[0081] In some embodiments of the present invention, the substrate is FTO glass;

[0082] In some embodiments of the present invention, the substrate undergoes the following pretreatment operation before spin coating: the substrate is ultrasonically cleaned sequentially with glass cleaner, ethanol, and acetone, dried, and then subjected to ultraviolet ozone treatment; preferably, the ultrasonic treatment time is 20-40 min; for example, 20-25 min, 25-30 min, 30-35 min, or 35-40 min; the ultrasonic frequency is 35-45 kHz; for example, 35-38 kHz, 38-42 kHz, or 42-45 kHz; the ultrasonic temperature is 35-45 °C; for example, 35-38 °C, 38-42 °C, or 42-45 °C; and / or, the ultraviolet ozone treatment time is 1100-1300 s; for example, 1100-1150 s, 1150-1200 s, 1200-1250 s, or 1250-1300 s;

[0083] In some embodiments of the present invention, the spin coating speed is 2800-3200 rpm; for example, 2800-2900 rpm, 2900-3000 rpm, 3000-3100 rpm, 3100-3200 rpm; and the spin coating time is 10-30 s; for example, 10-15 s, 15-20 s, 20-25 s, 25-30 s.

[0084] In some embodiments of the present invention, the temperature of the heat treatment is 130-170°C, for example, 130-140°C, 140-150°C, 150-160°C, or 160-170°C; and the time of the heat treatment is 15-30 min, for example, 15-19 min, 19-23 min, 23-27 min, or 27-30 min.

[0085] In some embodiments of the present invention, the thickness of the electron transport layer is 10-20 nm. For example, it is 10-13 nm, 13-16 nm, 16-18 nm, or 18-20 nm.

[0086] A fourth aspect of the present invention is to provide an electron transport layer prepared by the preparation method described above.

[0087] A fifth aspect of the present invention provides a perovskite optoelectronic device, comprising a substrate, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and an electrode arranged sequentially; wherein the electron transport layer is an electron transport layer prepared by the above-described preparation method or an electron transport layer described above.

[0088] In some embodiments of the present invention, the fabrication method of the perovskite optoelectronic device is well known in the art and can be operated by methods known in the art. Specifically, the operation is as follows: an electron transport layer is fabricated on a substrate; a perovskite light-absorbing layer is formed on the electron transport layer; a hole transport layer is formed on the perovskite light-absorbing layer; and an electrode is formed on the hole transport layer to obtain the perovskite optoelectronic device.

[0089] The sixth aspect of the present invention is to provide tin dioxide colloid prepared by the preparation method described above, and / or an electron transport layer prepared by the preparation method described above, and / or the perovskite optoelectronic device described above, in photovoltaic cells, light-emitting diodes, photodetectors or lasers.

[0090] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0091] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, equipment, and materials similar to or equivalent to those described, used, and materials in the embodiments of this invention may be used to implement this invention.

[0092] The commercial SnO2 colloidal dispersion of this invention was purchased from Alfa Aesar, CAS 18282-10-5.

[0093] Example

[0094] Example 1

[0095] This embodiment provides a method for preparing tin dioxide colloid, including the following steps:

[0096] (1) Place 200 mL of 0.5 mol / L tin tetrachloride solution in a flask, heat to 70 °C and maintain the temperature. Under constant stirring, slowly add 200 mL of 2 mol / L ammonia solution, controlling the dropping rate to keep the reaction system homogeneous. After the addition is complete, continue to keep the reaction at 70 °C for 2 hours to obtain a white precipitate (i.e., hydrated tin dioxide precipitate). After the reaction is complete, stop heating and allow the system to cool naturally to room temperature.

[0097] (2) Discard the supernatant, and wash the resulting precipitate three times with deionized water to obtain a hydrous tin dioxide gel solid (tin dioxide mass fraction of 15wt%). Weigh 50g of the above gel solid and transfer it to a beaker containing 100mL of 2.0mol / L hydrogen peroxide solution. Maintain the temperature of the mixture at 25℃ and disperse it for 12 hours under the combined action of mechanical stirring (300rpm) and ultrasound to obtain a transparent tin dioxide precursor colloid; wherein the frequency of ultrasound is 40KHz.

[0098] (3) Measure 50 mL of the tin dioxide precursor colloid and transfer it to an 80 mL hydrothermal reactor lined with polytetrafluoroethylene. Place the hydrothermal reactor in an oven and react at 200 °C for 24 hours. After the reaction is complete, allow it to cool naturally to room temperature and open the reactor to obtain a white gel-like product. After centrifugation (8000 rpm, 10 min), discard the supernatant, redisperse the precipitate in an appropriate amount of distilled water, and bring the volume to 50 mL to obtain a light blue, highly transparent spherical-bar mixed tin dioxide colloid.

[0099] The prepared tin dioxide colloid was characterized and tested, and the results are as follows: Figure 1-5 As shown.

[0100] Figure 1 Digital photographs of the colloid prepared in this example are shown. A clear light path can be seen when the colloid is irradiated with a laser, further confirming the Tyndall effect.

[0101] Figure 2 The X-ray diffraction (XRD) patterns of the colloid prepared for this example after vacuum drying at room temperature show that the diffraction peaks at approximately 26.5°, 33.8°, 37.9°, and 51.8° are consistent with the standard card (JCPDS No. 41-1445) for the rutile phase of SnO2.

[0102] Figure 3 The accompanying curves show the hydrated particle size distribution of the colloid prepared in this embodiment after 3 months of storage. The hydrated particle sizes exhibit a concentrated distribution, with the main peak around 70 nm. Furthermore, the particle size did not change significantly due to aging and sedimentation after 3 months, indicating good stability of the colloid. This particle size level is slightly higher than the grain size, mainly because the high temperature and pressure environment provided by the hydrothermal reaction accelerates grain growth. The hydration film coating the surface of the colloidal particles introduces testing errors, leading to a higher measured hydrated particle size value. The digital photograph in the inset is a digital photograph of the 0.047 mol / L tin dioxide colloid prepared in this example after 3 months of storage. The photograph shows that the colloid remains pale blue and transparent, indicating good stability, and there is no significant change between the photographs before and after storage.

[0103] Figure 4 , 5 Transmission electron microscopy (TEM) images of the hydrothermal tin dioxide colloid prepared in this embodiment fully confirm that the method can successfully obtain a stable tin dioxide colloid with good crystallinity and uniform particle size (approximately 5-10 nm). The morphology of the nanoparticles consists of a mixture of rod-shaped and spherical particles. The diameter of the spherical particles is distributed between 2-4 nm, and the aspect ratio of the rod-shaped particles is concentrated at 3:1. The average diameter of the nanorods is 5 nm. The weight ratio of the nanorods to the spherical nanocrystals is 1:2.

[0104] Example 2

[0105] This embodiment provides a method for preparing tin dioxide colloid, which differs from Example 1 in that it includes the following steps:

[0106] A 200 mL solution of 1.0 mol / L tin tetrachloride was heated to 60 °C and maintained at this temperature. While stirring continuously, 100 mL of a 4 mol / L sodium hydroxide solution was added dropwise. After the addition was complete, the mixture was aged at 60 °C for another hour. The reaction mixture was washed with deionized water to obtain a hydrated tin dioxide precipitate (containing approximately 90 wt% water; the water content could be determined by vacuum drying the hydrated precipitate at 110 °C). The precipitate, equivalent to 5 g of tin dioxide, was dispersed in 100 mL of a 1.0 mol / L hydrogen peroxide solution. The dispersion was carried out at room temperature with stirring and ultrasonication for 24 hours to obtain a precursor colloid. 60 mL of this colloid was subjected to a hydrothermal reaction at 180 °C for 48 hours. After centrifugation, the reaction product was redispersed in water and the volume was adjusted to 60 mL to obtain a stable tin dioxide colloid, wherein the tin dioxide nanorods had a diameter of 4-5 nm and an aspect ratio of 4:1, and the spherical tin dioxide nanocrystals had a diameter of 3 nm; the weight ratio of the nanorods to the spherical nanocrystals was 3:10.

[0107] The prepared tin dioxide colloid was characterized and tested, and the results are as follows: Figure 6 As shown.

[0108] Figure 6 The transmission electron microscope (TEM) image of the hydrothermal colloid prepared for this example clearly shows obvious lattice fringes, indicating that the colloidal particles have a high degree of crystallinity.

[0109] Example 3

[0110] This embodiment provides a method for preparing tin dioxide colloid, which differs from Example 1 in that it includes the following steps:

[0111] A 200 mL solution of 1.5 mol / L stannous chloride was heated to 50 °C. 300 mL of a 2 mol / L ammonia-potassium hydroxide mixture (molar ratio 1:1) was added dropwise. After addition, the solution was allowed to stand at 50 °C for 3 hours to age. A precipitate was obtained after washing. 5 g of the precipitate containing stannous dioxide was weighed and added to 100 mL of a 0.1 mol / L hydrogen peroxide solution. The precipitate was ultrasonically dispersed at 25 °C for 6 hours to obtain a precursor colloid. 40 mL of the colloid was placed in a 100 mL hydrothermal reactor and reacted at 160 °C for 48 hours. The reaction product was centrifuged, washed with water, and then redispersed in water to a final volume, yielding a light blue stannous dioxide colloid. The stannous dioxide nanorods had a diameter of 3-5 nm and an aspect ratio of 3:1, while the spherical stannous dioxide nanocrystals had a diameter of 2-3 nm; the weight ratio of the nanorods to the spherical nanocrystals was 1:5.

[0112] The prepared tin dioxide colloid was characterized and tested, and the results are as follows: Figure 13 As shown.

[0113] Figure 13 The transmission electron microscope image of the hydrothermal colloid prepared in this example also shows clear lattice fringes, but due to the lower hydrothermal temperature, the grain size is 2-3 nm, which is lower than that in Examples 1 and 2.

[0114] Application examples

[0115] Application Example 1

[0116] This application example provides a method for fabricating an electron transport layer, including the following steps:

[0117] The FTO glass was sequentially cleaned with glass cleaner, ethanol, and acetone, with each cleaning agent followed by ultrasonic treatment for 30 minutes, and then dried. The ultrasonic frequency was 40 kHz, and the ultrasonic temperature was 40°C. The drying method was oven drying at 60°C for 24 hours. The dried substrate was then subjected to 1200 seconds of ultraviolet ozone treatment. The tin dioxide colloid prepared in Example 2 was spin-coated onto the cleaned FTO glass substrate at 3000 rpm for 20 seconds, followed by heat treatment at 150°C in air for 20 minutes to obtain a tin dioxide electron transport layer film with a thickness of approximately 15 nm.

[0118] The prepared tin dioxide electron transport layer thin film was characterized, and the results are as follows: Figure 7-12 As shown.

[0119] Figure 7 XPS analysis of O 1s and Sn 3d in the films prepared from the colloidal and commercially available tin dioxide colloids in this example shows that the Sn 3d core energy level of the SnO2 film of this invention shifts to higher binding energies, making it closer to standard Sn. 4+ The SnO2 prepared by this method exhibits an oxidized state, and the binding energy of hydroxyl oxygen in its O 1s spectrum is reduced. This indicates that the SnO2 prepared by this method has a lower oxygen vacancy density, effectively suppressing the interfacial trap state and thus improving the charge extraction efficiency at the electron transport layer / perovskite junction.

[0120] Figure 8 The transmittance spectrum of the tin dioxide colloid prepared in this example after spin-coating shows a high visible light transmittance (>80%). The inset is a digital photograph of the colloid prepared in Example 2, which is light blue and transparent.

[0121] Figure 9The scanning electron microscope image of the tin dioxide thin film prepared for this example shows that the film is dense and has no obvious pore defects because the rod-shaped nanocrystals fill the gaps of the spherical stack.

[0122] Figure 10 The water contact angle of the tin dioxide thin film deposited on FTO glass prepared in this example is shown. A small contact angle indicates good wettability, which effectively reduces the heterogeneous nucleation energy barrier on the electron transport layer surface. This improves the spreadability of the perovskite precursor solution, promotes uniform nucleation, and is conducive to obtaining a perovskite thin film with higher crystal quality in the end.

[0123] Figure 11 An atomic force microscope image of the tin dioxide thin film deposited on FTO glass prepared in this example. Figure 12 for Figure 11 The corresponding three-dimensional image shows that the average roughness of the film is 1.11 nm, and it has a smooth morphology with certain nanoscale undulations, which is suitable for forming perovskite films with high coverage and low defects.

[0124] Application Example 2

[0125] This application example provides a perovskite optoelectronic device, comprising, sequentially arranged, an FTO glass, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and an electrode, namely, FTO glass / SnO2 / perovskite / Spiro-OMeTAD / gold electrode, wherein the perovskite composition is FTO. 0.85 MA 0.15 Pb(I 0.85 Br 0.15 3. The specific preparation method is as follows:

[0126] (1) The FTO glass (2.5 cm × 2.5 cm) was cleaned sequentially with glass cleaner, ethanol, and acetone. Each cleaning agent was followed by ultrasonic treatment for 30 minutes, and then dried. The ultrasonic frequency was 40 kHz and the ultrasonic temperature was 40 °C. The drying method was oven drying at 60 °C for 24 h. The dried substrate was further subjected to ultraviolet ozone treatment for 1200 seconds. The tin dioxide colloid prepared in Example 3 was spin-coated onto the cleaned FTO glass substrate at 3000 rpm for 20 seconds, and then heat-treated at 150 °C in air for 20 minutes to obtain a tin dioxide electron transport layer film with a thickness of about 15 nm.

[0127] (2) PbI2 was dissolved in a mixed solvent of dimethyl sulfoxide and N,N-dimethylformamide to prepare a precursor solution with a concentration of 1.5 M, wherein the volume ratio of dimethyl sulfoxide to N,N-dimethylformamide was 1:9. The solution was then spin-coated at 5000 rpm onto the tin dioxide electron transport layer film obtained in step (1) for 30 seconds. Subsequently, the solution was heat-annealed at 70 °C for 30 minutes to form a PbI2 film. Formamidinium iodide (FAI, 180 mg), methylamine bromide (MABr, 18 mg), and methylamine chloride (MACl, 18 mg) were dissolved in 2 mL of isopropanol (IPA) to prepare a mixed organic ammonium salt solution. The mixed organic ammonium salt solution was spin-coated onto the surface of the lead iodide film at a spin speed of 4000 rpm for 30 seconds. Subsequently, the solution was heat-treated at 150 °C for 30 minutes to obtain a perovskite film with a thickness of approximately 800 nm.

[0128] (3) Spin-coating a Spiro-OMeTAD solution (concentration of 69.3 mg / mL) onto the surface of the perovskite film obtained in step (2) to form a hole transport layer; the thickness of the hole transport layer is approximately 5 nm.

[0129] (4) A gold electrode layer is deposited on the surface of the hole transport layer obtained in step (3) using a thermal evaporation method to obtain a perovskite optoelectronic device. The thickness of the gold electrode layer is approximately 100 nm.

[0130] Perovskite optoelectronic devices were prepared using commercially available SnO2 colloidal dispersions in accordance with the aforementioned method.

[0131] The performance of the prepared tin dioxide electron transport layer thin film and the perovskite optoelectronic device was tested, and the results are as follows: Figure 14-19 As shown in Table 1.

[0132] Figure 14 The electron paramagnetic resonance spectra of the tin dioxide thin film prepared in this example are compared with those of commercial SnO2. The SnO2 material provided by this invention is characterized by having a lower oxygen vacancy concentration, and the signal intensity at g≈2.003 is significantly lower than that of commercial SnO2.

[0133] Figure 15 The current-voltage curves of the tin dioxide film prepared in this example are compared with those of commercially available films. The SnO2 film of the present invention has higher conductivity than that of commercially prepared films, indicating that it has lower internal resistance and better conductivity, thereby improving its electron mobility as an electron transport layer.

[0134] Figure 16 This is a scanning electron microscope image of the perovskite prepared in this example. The perovskite film prepared based on SnO2 of this invention has a high-quality polycrystalline structure with uniform density, good crystallinity and clear grain boundaries.

[0135] Figure 17 The scanning electron microscope (SEM) images of the cross-section of the device prepared for this example further demonstrate the clear cross-sectional structure of the device, showing a clear and continuous interface between the tin dioxide layer and the perovskite layer. This good interfacial contact lays the foundation for reducing defects and improving charge extraction efficiency.

[0136] Figure 18 This table shows a comparison of the positive JV curves of the battery device fabricated in this example and those fabricated commercially. The device fabricated based on this invention has an efficiency close to 24%, which is higher than that of the device fabricated under the same conditions using commercially available tin dioxide. Figure 18 The relevant efficiency parameters of the corresponding devices.

[0137] Table 1 shows the relevant efficiency parameters of the perovskite optoelectronic device obtained from Application Example 2.

[0138]

[0139] Figure 19 The stability of the perovskite solar cell prepared in this example at room temperature (~27°C), without encapsulation, and with a relative humidity of about 30% was compared with that of a device prepared with commercial tin dioxide colloid. The device prepared in this invention can still maintain an initial efficiency of 93.5% after 30 days of exposure, and its stability is significantly better than that of the commercial reference device (84.5%).

[0140] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing tin dioxide colloid, characterized in that, The method includes the following steps: (1) Heat the tin salt solution, then add an inorganic alkali solution dropwise. After the addition is complete, let it stand to obtain hydrated tin dioxide precipitate; the molar ratio of the inorganic alkali to the tin salt is 1-5:

1. (2) Wash the hydrated tin dioxide precipitate with water to obtain a gel-like precipitate, add a desiccant, and disperse by ultrasonication to obtain tin dioxide precursor colloid; (3) The tin dioxide precursor colloid is subjected to hydrothermal reaction, centrifuged and separated, and the resulting precipitate is dispersed in water to obtain tin dioxide colloid.

2. The method for preparing tin dioxide colloid according to claim 1, characterized in that: It also includes one or more of the following features: 11) In step (1), the concentration of the tin salt solution is 0.5-3 mol / L; 12) In step (1), the tin salt is selected from one or more of tin tetrachloride, stannous chloride, or tin nitrate; 13) In step (1), the heating temperature is raised to 50-70℃; 14) In step (1), the inorganic base is selected from one or more of sodium hydroxide, potassium hydroxide, or ammonia water; 15) In step (1), the concentration of the inorganic alkaline solution is 1-6 mol / L; 16) In step (1), the temperature for standing is 50-70℃; the standing time is 0.5-5h; 21) In step (2), the number of washing cycles is ≥ 1 time; preferably 1-5 times; 22) In step (2), the degumming agent is a hydrogen peroxide solution; preferably, the concentration of the hydrogen peroxide solution is 0.05-2 mol / L; 23) In step (2), the temperature of the ultrasound is 0-30℃, the frequency of the ultrasound is 35-45KHz, and the duration of the ultrasound is 2-48h; 24) In step (2), the molar ratio of hydrated tin dioxide to the descaling agent is 1:4-10; 25) In step (2), the mass fraction of tin dioxide in the gel-like precipitate is 8-20 wt%, and the remainder is water; 31) In step (3), the temperature of the hydrothermal reaction is 100-200℃ and the reaction time is 12-48h; 32) In step (3), the centrifugation speed is 7000-9000 rpm and the centrifugation time is 8-12 min; 33) In step (3), the mass ratio of the precipitate to water is 1-4:

1.

3. A tin dioxide colloid, characterized in that: The tin dioxide colloid was prepared by the method for preparing tin dioxide colloid using hydrogen peroxide hydrolysis gel as described in any one of claims 1-2.

4. The tin dioxide colloid according to claim 3, characterized in that: The tin dioxide colloid contains two morphologies of grains: nanorods and spherical nanocrystals; and / or, the grain size of the tin dioxide colloid is 2-20 nm.

5. The tin dioxide colloid according to claim 4, characterized in that: In the tin dioxide colloid, the weight ratio of nanorods to spherical nanocrystals is 1-5:10; and / or, the aspect ratio of the nanorods is 2-5:1, and the diameter of the nanorods is 3-5 nm; and / or, the particle size of the spherical nanocrystals is 2-4 nm.

6. A method for preparing an electron transport layer, characterized in that: The method includes the following steps: spin-coating the tin dioxide colloid according to any one of claims 3-5 or the tin dioxide colloid obtained by the method according to any one of claims 1-2 onto a substrate, followed by heat treatment to obtain an electron transport layer.

7. The preparation method according to claim 6, characterized in that: It also includes one or more of the following features: A1) The substrate is FTO glass; A2) The substrate is pretreated before spin coating as follows: the substrate is ultrasonically cleaned sequentially with glass cleaner, ethanol, and acetone, dried, and then subjected to ultraviolet ozone treatment; preferably, the ultrasonic treatment time is 20-40 min; the ultrasonic frequency is 35-45 kHz; the ultrasonic temperature is 35-45 °C; and / or, the ultraviolet ozone treatment time is 1100-1300 s; A3) The spin coating speed is 2800-3200 rpm; the spin coating time is 10-30 s; A4) The heat treatment temperature is 130-170℃, and the heat treatment time is 15-30 min; A5) The thickness of the electron transport layer is 10-20 nm.

8. An electron transport layer, characterized in that: It is prepared by the preparation method described in any one of claims 6-7.

9. A perovskite optoelectronic device, characterized in that: It includes a substrate, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and an electrode arranged sequentially; the electron transport layer is an electron transport layer prepared by the preparation method according to any one of claims 6-7 or an electron transport layer according to claim 8.

10. The application of the tin dioxide colloid prepared by the preparation method of any one of claims 1-2, and / or the electron transport layer prepared by the preparation method of any one of claims 6-7, and / or the perovskite optoelectronic device as described in claim 9 in photovoltaic cells, light-emitting diodes, photodetectors, or lasers.

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