A method for preparing an electron transport layer and a perovskite solar cell

Abstract

The present invention relates to the field of solar cells, and specifically to a method for preparing an electron transport layer and a perovskite solar cell. The method comprises: uniformly mixing stannous chloride dihydrate, an organic ligand / heterogeneous growth linker, and a hydrolysis rate controller in deionized water to obtain a tin dioxide precursor solution; immersing a conductive glass substrate in the tin dioxide precursor solution, and performing in-situ growth in a sealed environment below the water evaporation temperature, followed by ultrasonic cleaning and annealing to obtain the electron transport layer. The in-situ chemical growth control strategy proposed in the present invention achieves control of bulk self-doping defects in tin dioxide n-type thin films, controllable energy band regulation, and optimization of conductivity and carrier extraction behavior. This strategy can be used to prepare a series of tin dioxide electron transport layers that are compatible with the preparation scheme and application of perovskite active layers of any component, minimizing energy loss, optimizing interfacial non-radiative recombination, and optimizing carrier transport behavior.

Description

Technical Field

[0001] The present invention relates to the field of solar cells, and in particular to a method for preparing an electron transport layer and a perovskite solar cell. Background Art

[0002] Tin dioxide (SnO2) thin films, n-type semiconductors with wide band gaps and high conductivity, are widely used in the field of solar cells. Due to its excellent carrier extraction ability and high electron mobility, SnO2 is often used as an outstanding electron transport layer material in ortho-perovskite solar cells. It is one of the necessary means to achieve high power conversion efficiency (PCE) and good device stability in perovskite photovoltaic device stacks. However, in device stack construction, because the energy band position of the perovskite active layer varies with composition and stress, a single SnO2 electron transport layer preparation method cannot achieve a good match with different perovskite active layers, which seriously restricts the device efficiency, stability, and large-area module preparation of perovskite solar cells. By modifying the in-situ chemical growth of SnO2, the SnO2 energy level position can be adjusted and the band alignment of the SnO-perovskite layer interface can be optimized. This allows the development of SnO2 n-type transport layers that are compatible with perovskites of arbitrary composition and structure. The high-quality SnO2 / perovskite heterointerface greatly improves device performance.

[0003] Achieving controllable energy and carrier transport behavior at the SnO2 electron transport layer / perovskite active layer heterointerface in perovskite solar cell devices is a pressing challenge. Due to the layer-by-layer nature of the device, the properties of this interface are significantly affected by the properties of the SnO2 electron transport layer. Currently, the most widely used method for preparing SnO2 electron transport layers is spin-coating a commercial SnO2 nanoparticle sol-gel. However, the bulk photoelectric properties of SnO2 films prepared by this method have limited tunability, and their electrical properties can usually only be altered by doping with other impurities, resulting in limited and ineffective control. Furthermore, the sol-gel method is difficult to prepare in large quantities and over large areas, making it unsuitable for commercial production. Chemical water bath deposition, however, is a recently discovered method for effectively controlling the SnO2 electron transport layer. During the preparation process, a precursor solution containing divalent tin first forms a divalent tin hydrate under acidic conditions. The hydrate is then oxidized and dehydrated by the combined action of temperature and an acid-base pair, and finally annealed to form a film. However, the bulk composition, defect control, and large-area preparation uniformity of tin dioxide films prepared by this method remain huge challenges. Summary of the Invention

[0004] The present invention focuses on solving the problem of uncontrolled self-doping of tin dioxide n-type thin film components during in-situ chemical growth, so as to construct non-radiative recombination of low tin dioxide / perovskite buried heterogeneous interface and realize a uniform tin dioxide electron transport layer with controllable photoelectric properties.

[0005] To achieve the above object, the present invention provides an electron transport layer for a perovskite solar cell, which comprises the following steps:

[0006] S1. Mixing stannous chloride dihydrate, an organic ligand / heterogeneous growth linker, and a hydrolysis rate controller in deionized water to obtain a tin dioxide precursor solution, wherein the organic ligand / heterogeneous growth linker is phosphoacetic acid or sulfoacetic acid, and the hydrolysis rate controller comprises an acidic substance and an alkaline substance, wherein the acidic substance is at least one of hydrochloric acid, citric acid, and acetic acid, and the alkaline substance is at least one of urea and ammonia solution;

[0007] S2. Using a chemical water bath deposition method, the conductive glass is used as a substrate and immersed in a tin dioxide precursor solution. The substrate is grown in situ in a closed environment below the evaporation temperature of water. The substrate is then ultrasonically cleaned and annealed to obtain an electron transport layer formed on the conductive glass.

[0008] As a further preferred technical solution of the present invention, the molar ratio of stannous chloride dihydrate to the organic ligand / heterogeneous growth linker is 200:1-50:1.

[0009] As a further preferred technical solution of the present invention, the hydrolysis rate controller includes an acidic substance and an alkaline substance. The acidic substance and the alkaline substance jointly control the hydrolysis rate. The acidic substance provides a strong acid environment to inhibit tin hydrolysis, while the alkaline substance continuously increases the pH of the solution under an elevated temperature environment to promote tin hydrolysis, thereby initiating growth. Preferably, the molar ratio of the acidic substance to the alkaline substance is 1:3-2:3.

[0010] As a further preferred technical solution of the present invention, in step S2, the temperature is 50-95°C lower than the water evaporation temperature.

[0011] As a further preferred technical solution of the present invention, in step S2, the annealing temperature is 150-180°C.

[0012] As a further preferred technical solution of the present invention, step S2 further includes the following steps:

[0013] After annealing, the surface is first treated by immersing in an aqueous amine solution, and then subjected to secondary annealing at 100-150°C.

[0014] According to another aspect of the present invention, the present invention also provides a perovskite solar cell, which includes a conductive glass, an electron transport layer, a perovskite active layer, an organic passivation layer, a hole transport layer and a metal electrode compounded in sequence along the thickness direction.

[0015] As a further preferred technical solution of the present invention, the conductive glass is fluorine-doped tin oxide glass or indium tin oxide glass;

[0016] And / or, the perovskite active layer material includes MAPbI3, FAPbI3, CsPbI3, MA x FA 1-x PbI3、MA x Cs y FA 1-x-y PbI3、Cs x FA 1-x At least one of PbI3, wherein x and y are both less than 1;

[0017] And / or, the organic passivation layer material includes at least one of phenethylamine iodine, n-octylamine bromide, phenethylamine bromide, phenpropylamine iodine / bromide, and phenbutylamine iodine / bromide;

[0018] and / or, the hole transport layer material comprises Spiro-OMeTAD;

[0019] And / or, the metal electrode material includes a conductive metal or a conductive metal alloy.

[0020] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0021] The present invention uses chemical ligand design to regulate the electron density around tin after the introduced chemical ligand interacts with divalent tin, thereby increasing the oxidation potential of induced divalent tin, adjusting the concentration of divalent tin ions self-doped into the tin dioxide bulk film, and adjusting the concentration of oxygen vacancies induced as key shallow donor energy level defects, thereby achieving controllable conductivity, energy band position, and carrier transport behavior of the tin dioxide electron transport layer film. Ultimately, it is applied to perovskite solar cells to effectively solve the energy mismatch and carrier extraction disorder problems of the buried heterogeneous interface between the tin oxide electron transport layer and the perovskite interface. Ultimately, the open circuit voltage and fill factor of the solar cell device are greatly improved, and high-efficiency small-area and large-area (1cm2) films are obtained. 2 )Perovskite solar cell devices.

[0022] The tin in the tin dioxide of the present invention is tetravalent, and the divalent tin chloride dihydrate is used as a reactant to undergo hydrolysis, oxidation, and dehydration to form tetravalent tin dioxide. By designing ligands, the electron density around the divalent tin is regulated, thereby changing the oxidation barrier from divalent tin to tetravalent tin. This reduces the amount of divalent tin oxidized, allowing more divalent tin to be doped into the tin dioxide lattice. Because the lattice maintains electrical neutrality, the incorporation of divalent tin into the lattice induces the generation of positively charged oxygen vacancies. These oxygen vacancies are key to tin dioxide's use as an N-type semiconductor and have important practical value and guiding significance for the industrialization of perovskite batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 This is the SEM image of SnO2-1;

[0025] Figure 2 This is the SEM image of SnO2-2;

[0026] Figure 3 This is the SEM image of SnO2-3

[0027] Figure 4 This is the SEM image of SnO2-4;

[0028] Figure 5 is the ultraviolet photoelectron spectrum of SnO2-1,2,3,4, from which the Fermi level, valence band top and conduction band bottom positions of tin dioxide are obtained;

[0029] Figure 6 Schematic diagram of the energy band arrangement of SnO2-1,2,3,4 and perovskite;

[0030] Figure 7 This is the photoluminescence spectrum of the SnO2-1,2,3,4 / perovskite half-device stack. The lower the peak intensity at 820nm, the stronger the electron extraction ability of the tin dioxide electron transport layer.

[0031] Figure 8 The photoelectric conversion efficiency comparison curves of (a) Comparative Example 1 and (b) Example 2 are shown.

[0032] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0033] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0034] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental methods described, unless otherwise specified, are conventional methods.

[0035] Comparative Example 1

[0036] The method for preparing an electron transport layer by chemical bath deposition of SnO2 using thioglycolic acid as an organic ligand specifically comprises the following steps:

[0037] 1) Raw material preparation:

[0038] Dissolve 2.5 g of urea in 200 mL of water, add 2.5 mL of concentrated hydrochloric acid (mass fraction 37%), 0.274 g of stannous chloride dihydrate, and 25 μL of thioglycolic acid (98 wt %), mix thoroughly, and use as a mother solution.

[0039] 2) Response growth regulation:

[0040] Take the freshly prepared mother liquor and dilute it with deionized water at a volume ratio of 1:5. Place the cleaned FTO glass substrate in the reaction solution, seal the reaction vessel, and oven-dry it at 90°C for 3 hours, resulting in a final solution pH of 1.5. After the reaction, rinse the substrate surface with deionized water and sonicate for 5 minutes. Then, anneal at 180°C for 1 hour. Then, soak it in an aqueous amine solution for 3 minutes, followed by annealing at 150°C for 10 minutes.

[0041] The sample obtained in Comparative Example 1 is labeled SnO2-1, and its surface morphology is as follows Figure 1 As shown in the scanning electron microscope (SEM), it can be seen that the tin oxide film is densely covered.

[0042] The sample was tested under a vacuum instrument, using He I to provide photon energy. The energy of the photons was sufficient to excite the valence band electrons or conduction band electrons in the electron transport layer. After being absorbed by the photons, the electrons gained enough energy to escape from the surface of the electron transport layer, thereby collecting the spectrum. The Fermi level position or work function was obtained by using the high energy edge of the spectrum and 21.22-high energy edge position. The low energy edge position corresponds to the position from the valence band top to the Fermi level. The ultraviolet photoelectron spectrum of this sample and the inferred band position are shown in Figure 2. Figure 5 、 6 shown.

[0043] Comparative Example 2

[0044] The method for preparing an electron transport layer by chemical bath deposition of SnO2 using malonic acid as an organic ligand specifically comprises the following steps:

[0045] Raw material preparation: Dissolve 2.5 g of urea in 200 mL of water, add 2.5 mL of concentrated hydrochloric acid (mass fraction 37%), 0.274 g of stannous chloride dihydrate, and 100 μL of malonic acid (500 mg / mL), mix thoroughly and set aside.

[0046] Reaction growth regulation: same as Comparative Example 1.

[0047] The sample obtained in Comparative Example 2 is labeled SnO2-2, and its surface morphology is as follows Figure 2 The electron scanning microscope SEM shows that the tin oxide film is densely covered. The ultraviolet photoelectron spectrum of this sample and the inferred energy band position are shown in Figure 5 、 6 As shown, the energy difference of the band mismatch is smaller than that of Comparative Example 1.

[0048] Example 1

[0049] The method for preparing an electron transport layer by chemical bath deposition of SnO2 using phosphoacetic acid as an organic ligand specifically comprises the following steps:

[0050] Raw material preparation: Dissolve 2.5 g of urea in 200 mL of water, add 2.5 mL of concentrated hydrochloric acid (mass fraction 37%), 0.274 g of stannous chloride dihydrate, and 100 μL of phosphoacetic acid (500 mg / mL), mix thoroughly and set aside.

[0051] Reaction growth regulation: same as Comparative Example 1.

[0052] The sample obtained in Example 1 is labeled as SnO2-3, and its surface morphology is as follows Figure 3 The electron scanning microscope SEM shows that the tin oxide film is densely covered. The ultraviolet photoelectron spectrum of this sample and the inferred energy band position are shown in Figure 5 、 6 As shown, the energy difference of the band mismatch is smaller than that of Comparative Examples 1 and 2.

[0053] Example 2

[0054] The method for preparing an electron transport layer by chemical bath deposition of SnO2 using sulfoacetic acid as an organic ligand specifically comprises the following steps:

[0055] Raw material preparation: Dissolve 2.5 g of urea in 200 mL of water, add 2.5 mL of concentrated hydrochloric acid (37% by mass), 0.274 g of stannous chloride dihydrate, and 100 μL of sulfoacetic acid (500 mg / mL), mix thoroughly and set aside.

[0056] Reaction growth regulation: same as Comparative Example 1.

[0057] The sample obtained in Example 2 is labeled as SnO2-3, and its surface morphology is as follows Figure 4 The electron scanning microscope SEM shows that the tin oxide film is densely covered. The ultraviolet photoelectron spectrum of this sample and the inferred energy band position are shown in Figure 5 、 6 As shown in Figure 2, the tin oxide exhibits the smallest energy difference with the perovskite, further proving that the electron-withdrawing ability of the ligand effectively changes the energy band position of tin dioxide; and as shown in Figure 2 Figure 7As shown in the photoluminescence spectra, based on the photoluminescence data of the tin dioxide / perovskite semiconductor devices of Examples 1 and 2 and Comparative Examples 1 and 2, it can be observed that tin dioxide exhibits increasingly efficient electron extraction capabilities. As the acid dissociation constants from malonic acid, phosphoacetic acid, to sulfoacetic acid decrease, the electron-binding ability becomes stronger. Consequently, after Sn interacts with the oxygen of the acid radical, the oxygen donates fewer electrons to Sn, lowering the electron density around Sn and making it more difficult to oxidize divalent tin to tetravalent tin. Consequently, the higher the divalent tin content in the tin dioxide, the more oxygen vacancies are induced, leading to an upward shift in the conductivity and Fermi level of the tin dioxide, and a smaller mismatch with the perovskite.

[0058] In order to further demonstrate the beneficial technical effects of the present invention, the above-synthesized samples with tin dioxide electron transport layers (SnO2-1, SnO2-2, SnO2-3, SnO2-4) were prepared into solar cell devices and tested in the following manner, as follows:

[0059] 1. Preparation of the Perovskite Active Layer: 25 μL of the prepared perovskite precursor solution was dropwise applied to the substrate. Spin coating was performed at an acceleration of 1000 rpm / s, then accelerated to 5000 rpm for 30 seconds. In the 10th second before the spin cycle, 150 μL of ethyl acetate antisolvent was added. After the spin cycle was stopped, the wet film was annealed on a 110°C hotplate for 20 minutes to obtain the perovskite active layer on the electron transport layer.

[0060] 2. Passivation layer deposition: After the substrate cools, a quasi-two-dimensional passivation layer is applied. Specifically, 100 μL of a 5 mg / ml solution of phenylethylamine bromide in isopropanol is added to the cooled substrate. Spin coating is performed at 5000 rpm for 30 seconds at an acceleration of 5000 rpm / s to obtain an organic passivation layer on the perovskite active layer.

[0061] 3. Preparation of the Hole Transport Layer: Dissolve 72.3 mg of 2,2',7,7'-tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD), 36 μL of a 260 mg / mL solution of lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) in acetonitrile, and 30 μL of a solution of butyl benzoyl peroxide (t-BP) in 1 mL of chlorobenzene. Spin-coat this mixture at 4000 rpm for 30 seconds onto the substrate where the passivation layer had been deposited, forming a hole transport layer on top of the organic passivation layer.

[0062] 4. Metal electrode deposition: Vacuum evaporation is used to deposit 80nm gold electrodes to complete the preparation of thin-film battery devices.

[0063] 5. Performance and stability test: Custom perforation area is 0.064cm 2A 0.1mm thick metal sheet was used as a light shielding template. The current-voltage characteristic curve of the battery device was tested under the AM 1.5G light provided by a 3A-level solar simulator. The results are as follows: Figure 8 shown.

[0064] In addition, AM 1.5G simulated sunlight was used as the light source to be incident from the bottom of the cell device. The light intensity was calibrated using a silicon cell and measured using a 2400 Keithley digital source meter. The test data is shown in Table 1.

[0065] Table 1

[0066]

[0067] As shown in Table 1, the devices based on the ligands thioglycolic acid, malonic acid, phosphoroacetic acid, and sulfoacetic acid (SnO2-1, SnO2-2, SnO2-3, and SnO2-4, in that order) exhibit progressively higher open-circuit voltages and fill factors, consistent with the ligand design and experimental data. Because sulfoacetic acid has the strongest electron-withdrawing ability for tin, the increased content of divalent tin and oxygen vacancies within the tin dioxide film leads to an upward shift in the Fermi level, optimally matching the perovskite Fermi level and minimizing energy loss. This results in the highest open-circuit voltage, and the enhanced carrier extraction improves the fill factor.

[0068] Combined with Table 1 and Figure 8 By comparison, the SnO2-4 sample of Example 2 has the lowest energy difference with the perovskite, significantly reducing the non-radiative loss of the device. The device ultimately achieves the highest open-circuit voltage, with the open-circuit voltage loss reduced by 90 meV, achieving optimal performance. While the above describes specific embodiments of the present invention, those skilled in the art will appreciate that these are merely illustrative, and that various changes or modifications may be made to the present embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined solely by the appended claims.

Claims

1. A method for preparing an electron transport layer of a perovskite solar cell, characterized in that: The following steps are involved: S1. Mixing stannous chloride dihydrate, an organic ligand / heterogeneous growth linker, and a hydrolysis rate controller in deionized water to obtain a tin dioxide precursor solution, wherein the organic ligand / heterogeneous growth linker is phosphoacetic acid or sulfoacetic acid, and the hydrolysis rate controller comprises an acidic substance and an alkaline substance, wherein the acidic substance is at least one of hydrochloric acid, citric acid, and acetic acid, and the alkaline substance is at least one of urea and ammonia solution; S2. Using a chemical water bath deposition method, the conductive glass is used as a substrate and immersed in a tin dioxide precursor solution. The substrate is grown in situ in a closed environment below the evaporation temperature of water. The substrate is then ultrasonically cleaned and annealed to obtain an electron transport layer formed on the conductive glass.

2. The method for preparing an electron transport layer of a perovskite solar cell according to claim 1, wherein: The molar ratio of stannous chloride dihydrate to the organic ligand / heterogeneous growth linker is 200:1-50:

1.

3. The method for preparing an electron transport layer of a perovskite solar cell according to claim 1, wherein: The molar ratio of the acidic substance to the alkaline substance is 1:3-2:

3.

4. The method for preparing an electron transport layer of a perovskite solar cell according to claim 1, wherein: In step S2, the temperature is 50-95°C lower than the water evaporation temperature.

5. The method for preparing an electron transport layer of a perovskite solar cell according to claim 1, wherein: In step S2, the annealing temperature is 150-180°C.

6. The method for preparing an electron transport layer of a perovskite solar cell according to any one of claims 1 to 5, characterized in that: Step S2 also includes the following steps: After annealing, the surface is first treated by immersing in an aqueous amine solution, and then a secondary annealing is performed at 100-150°C.

7. A perovskite solar cell, characterized in that: The invention comprises a conductive glass, an electron transport layer, a perovskite active layer, an organic passivation layer, a hole transport layer and a metal electrode which are compounded in sequence along the thickness direction, wherein the electron transport layer is prepared by the method according to any one of claims 1 to 6.

8. The perovskite solar cell according to claim 7, characterized in that The conductive glass is fluorine-doped tin oxide glass or indium tin oxide glass; And / or, the perovskite active layer material includes MAPbI3, FAPbI3, CsPbI3, MA x FA 1-x PbI3、MA x Cs y FA 1-x- y PbI3、Cs x FA 1-x At least one of PbI3, wherein x and y are both less than 1; And / or, the organic passivation layer material includes at least one of phenethylamine iodine, n-octylamine bromide, phenethylamine bromide, phenpropylamine iodine / bromide, and phenbutylamine iodine / bromide; and / or, the hole transport layer material comprises Spiro-OMeTAD; And / or, the metal electrode material includes a conductive metal or a conductive metal alloy.

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