Method for improving water and oxygen stability of perovskite solar cell by in-situ polymerization internal packaging technology

Abstract

The invention discloses a method for improving water and oxygen stability of a perovskite solar cell, and belongs to the technical field of perovskite solar cell preparation. According to the technical scheme, monomer alpha-ethyl cyanoacrylate (ECA) is introduced into a perovskite crystal boundary and an interface of the perovskite solar cell, polymerization is completed under triggering of water molecules, and a poly (alpha-ethyl cyanoacrylate) (PECA) packaging layer with a certain thickness is formed. The PECA packaging layer prevents environmental water and oxygen from eroding perovskite crystals and does not block transmission and collection of carriers, and has a certain defect passivation effect, so that the water and oxygen stability of the perovskite solar cell is improved. PECA internal packaging is a simple, feasible and efficient method for improving the water and oxygen stability of the perovskite solar cell, and the popularization and application prospects are wide.

Description

Technical Field

[0001] The invention belongs to the technical field of perovskite solar cell preparation, and in particular relates to a method for improving the water-oxygen stability of a perovskite solar cell. Background Art

[0002] Perovskite solar cells (PSCs) have attracted the interest of many researchers due to their long carrier transport range, adjustable band gap, low preparation cost and all-solid-state structure. In less than a decade, their photoelectric conversion efficiency has exceeded 26%, and they are expected to replace single-crystal silicon solar cells for large-scale commercial production and become the next generation of new high-efficiency thin-film solar cells.

[0003] However, the light-absorbing layer of PSCs is mostly a hybrid perovskite polycrystalline film, which is extremely susceptible to corrosion by water and oxygen, and decomposes rapidly, greatly reducing the expected service life. At the same time, the solution method brings the advantages of simple preparation process and low cost to PSCs, but it also leads to the uncontrolled crystallization rate of perovskite films and the generation of a large number of grain boundaries. Under harsh environmental conditions, these widely distributed grain boundaries provide a fast channel for the invasion of external water and oxygen and the escape of internal ions, and a large number of defects at the grain boundaries will also cause serious non-radiative carrier recombination. Therefore, it is crucial to develop a simple, practical and compatible with existing processes for grain boundary encapsulation strategy to improve the efficiency and stability of PSCs. From the current research results, the device's resistance to water and oxygen is often enhanced by adding encapsulation technology in actual production, but this will undoubtedly increase the complexity and cost of the preparation process. At present, there is no literature report on the application of PECA encapsulation technology compatible with existing processes in perovskite solar cells. Summary of the invention

[0004] The object of the present invention is to provide a method for improving the water and oxygen stability of perovskite solar cells, which improves the water and oxygen stability by blocking water and oxygen through a PECA inner encapsulation layer while reducing defect sites.

[0005] To achieve the above object, the present invention adopts the following technical solution: A method for improving the water and oxygen stability of perovskite solar cells by in-situ polymerization inner encapsulation technology: a poly (ethyl α-cyanoacrylate) encapsulation layer is prepared at the bulk grain boundary and interface of the perovskite light absorbing layer of the perovskite solar cell.

[0006] The thickness of the poly(ethyl α-cyanoacrylate) encapsulation layer is 3-10 nm.

[0007] The ethyl α-cyanoacrylate ECA encapsulation layer is prepared into a 3-10 mg / mL solution, and the poly(ethyl α-cyanoacrylate) encapsulation layer is prepared by spin coating, dipping or drop coating. The solvent is any one or more of chlorobenzene, toluene and ethyl acetate.

[0008] The beneficial effects of the present invention are: blocking harmful water and oxygen is achieved through the poly(ethyl α-cyanoacrylate) encapsulation layer, while passivating defects at the grain boundaries and interfaces, thereby greatly improving its water and oxygen stability. The maximum efficiency of perovskite solar cells based on the poly(ethyl α-cyanoacrylate) encapsulation layer exceeds 23%, and it shows significantly improved stability in water immersion aging tests. Unencapsulated devices can still retain 90% of the initial PCE after being stored in humid air for nearly 1,600 hours. Therefore, poly(ethyl α-cyanoacrylate) internal encapsulation is a simple, feasible and efficient method to improve the water and oxygen stability of perovskite solar cells, and it has broad prospects for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is the structural formula of ECA monomer and the process diagram of its polymerization reaction triggered by water molecules; Figure 2 This is a comparison of the changes of ECA monomers after being stored in dry and humid air for 6 hours; Figure 3 The FTIR spectra of fully polymerized PECA and PECA after washing with CB and IPA, respectively; Figure 4 This is the TEM image of the perovskite film encapsulated in 5 mg mL-1 PECA; Figure 5 This is a graph of the photoelectric conversion efficiency based on different thicknesses of the PECA inner encapsulation layer; Figure 6 It is the contact angle test of the perovskite film with or without PECA encapsulation; Figure 7 It is the water immersion test of perovskite film with or without PECA encapsulation at room temperature; Figure 8 It is the PCE decay curve of the two groups of devices under continuous storage conditions. DETAILED DESCRIPTION

[0010] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0011] Example 1 In the glove box, the ECA monomer was dissolved in the anti-solvent and evenly added to the perovskite light-absorbing layer by spin coating to prepare a 3 nm thick PECA. The specific steps were as follows: 30 mg of ECA was taken and dissolved in 10 mL of chlorobenzene, toluene, and ethyl acetate (mixed in any ratio of the three), stirred evenly and filtered to prepare a solution with a concentration of 3 mg / mL, which was then added dropwise to the perovskite wet film at a speed of 5000 rpm, and then transferred to the air and annealed on a heating plate at 120 °C to form a 3 nm PECA layer, and then taken back to the glove box to continue depositing the transport layer and electrodes on the perovskite absorption layer to complete the preparation of the perovskite solar cell.

[0012] Example 2 In the glove box, the ECA monomer was dissolved in the anti-solvent and evenly added to the perovskite light-absorbing layer by spin coating to prepare a 5 nm thick PECA. The specific steps were as follows: 30 mg of ECA was taken and dissolved in 6 mL of chlorobenzene, toluene, and ethyl acetate (mixed in any ratio of the three), stirred evenly and filtered to prepare a solution with a concentration of 5 mg / mL, which was then added dropwise to the perovskite wet film at a speed of 5000 rpm, and then transferred to the air and annealed on a heating plate at 120 °C to form a 5 nm PECA layer, and then taken back to the glove box to continue depositing the transport layer and electrodes on the perovskite absorption layer to complete the preparation of the perovskite solar cell.

[0013] Example 3 In the glove box, the ECA monomer was dissolved in the anti-solvent and evenly added to the perovskite light-absorbing layer by spin coating to prepare a 10 nm thick PECA. The specific steps were as follows: 30 mg of ECA was taken and dissolved in 3 mL of chlorobenzene, toluene, and ethyl acetate (mixed in any ratio of the three), stirred evenly and filtered to prepare a solution with a concentration of 10 mg / mL. The solution was then added dropwise to the perovskite wet film at a speed of 5000 rpm, and then transferred to the air and annealed on a heating plate at 120 °C to form a 10 nm PECA layer. The transport layer and electrodes were then taken back to the glove box to continue depositing the perovskite absorption layer to complete the preparation of the perovskite solar cell.

[0014] Example 4 In a glove box, the ECA monomer was dissolved in an anti-solvent and added dropwise to the perovskite light-absorbing layer after spin coating to prepare a 5 nm thick PECA. The specific steps were as follows: 20 mg of ECA was taken and dissolved in 20 mL of chlorobenzene, toluene, and ethyl acetate (mixed in any ratio of the three), stirred evenly and filtered to prepare a solution with a concentration of 1 mg / mL, which was then slowly and evenly added dropwise to the perovskite wet film that had been spin-coated but not annealed, the excess solution was removed, and then the film was transferred to the air and annealed on a heating plate at 120 °C to form a 5 nm PECA layer, and then the glove box was taken back to continue depositing the transport layer and electrodes on the perovskite absorption layer to complete the preparation of the perovskite solar cell.

[0015] Example 5 In a glove box, the ECA monomer was dissolved in an anti-solvent and added dropwise to the perovskite light-absorbing layer after spin coating by an immersion method to prepare a 5 nm thick PECA. The specific steps were as follows: 20 mg of ECA was taken and dissolved in 20 mL of chlorobenzene, toluene, and ethyl acetate (mixed in any ratio of the three), stirred evenly and filtered to prepare a solution with a concentration of 1 mg / mL. The spin-coated but unannealed perovskite wet film was then slowly immersed in the prepared solution for 2 seconds and then quickly taken out to remove excess solution at the edge. The film was then transferred to the air and annealed on a heating plate at 120 °C to form a 5 nm PECA layer. The film was then taken back to the glove box to continue depositing the transport layer and electrodes on the perovskite absorption layer to complete the preparation of the perovskite solar cell.

[0016] Photoelectric performance test: Test the photoelectric conversion performance under the AM 1.5G standard solar simulator; Figure 1 The structural formula of the ECA monomer and its polymerization reaction process triggered by water molecules are shown in Figure 2. In this diagram, strong electron-withdrawing groups (-C≡N and -COOR) are covalently connected to unsaturated carbon atoms, and the strong induction effect makes the C=C double bond highly activated. Therefore, no additional initiator or heating conditions are required, and only a trace amount of water molecules can cause a rapid polymerization reaction. The specific process is as follows: Figure 1 As shown in (b), water molecules attack the β-unsaturated carbon in the ECA molecule, undergo a nucleophilic addition reaction with it, and generate a carbon anion intermediate. The generated carbon anion can continue to induce the next addition reaction, allowing the carbon anions from different monomers to form bonds with each other and complete a rapid addition polymerization reaction.

[0017] Figure 2 The following is a comparison of the changes of ECA monomer after being stored in dry and humid air for 6 hours. Two bottles of ECA monomer liquid with the same volume are sealed in glass bottles and filled with dry and humid air respectively. Figure 2As shown in the figure, after 6 hours, ECA in humid air completely polymerized into a solid, while ECA in dry air remained in a liquid state. Obviously, this fact verifies that ECA monomers can undergo rapid polymerization under the action of water molecules.

[0018] Figure 3 The FTIR spectra of fully polymerized PECA and its rinsing with CB and IPA were recorded to verify the tolerance of PECA to solvent rinsing. The results are shown in Figure 2. Figure 3 By comparison, it was found that the signals of each group were basically consistent before and after washing, indicating that after PECA was completely self-polymerized, it was almost unaffected by the subsequent preparation process and had excellent solvent resistance and process compatibility.

[0019] Figure 4 Based on 5 mg mL -1 TEM image of the perovskite film encapsulated in PECA; TEM was used to characterize the thickness and distribution of the encapsulation layer in PECA. The results are as follows Figure 4 As shown in the figure. The area with a lattice fringe spacing of about 0.22 nm corresponds to the (224) crystal plane of the 3-perovskite. At the same time, a dense polymer layer of about 4-5 nm thick can be seen uniformly coated on the outer surface of the perovskite grains. Thanks to the quantum tunneling effect, the thinner PECA polymer layer does not hinder the transport of carriers.

[0020] Figure 5 This is a diagram of the photoelectric conversion efficiency based on different thicknesses of the PECA inner encapsulation layer. It can be seen that the device prepared in Example 2 achieved a maximum efficiency of up to 23.6%, achieving a balance between stability and performance.

[0021] Figure 6 This is the contact angle test of the perovskite film with or without PECA encapsulation. It can be clearly seen that the water contact angle of the perovskite after PECA modification increased significantly from 54° to 87°, which is mainly due to the strong hydrophobicity brought by the PECA polymer layer at the upper interface of the perovskite, indicating that the perovskite film has greatly improved its resistance to water erosion.

[0022] Figure 7 The water immersion test of the perovskite film with or without PECA encapsulation at room temperature. At room temperature, two groups of perovskite films were immersed in deionized water at the same time, and the changes of the perovskite film in the process were recorded. Figure 7As shown in the figure, after immersion in water for 3 seconds, the blank perovskite film turned grayish yellow, indicating that it was severely decomposed, while the experimental group remained completely black at this time; after immersion for 5 seconds, the blank film completely turned bright yellow, indicating that it was completely decomposed, and it was not until the 15th second of immersion that the experimental group film began to gradually decompose, and was basically completely decomposed at the 40th second. The test results intuitively confirmed that the perovskite film encapsulated in PECA has acquired extremely strong water resistance, which is mainly due to the PECA layer's ability to completely and densely cover the grain boundaries and upper interfaces, acting as a solid and comprehensive space barrier, effectively blocking the erosion of water molecules on the perovskite lattice.

[0023] Figure 8 The PCE decay curves of the two groups of devices under continuous storage conditions. After storing the two groups of devices in air (15±5%RH, 25℃) for about 1600 hours, the PECA encapsulated device retained 90% of its initial PCE, while the PCE of the blank device was only 34%. Therefore, PECA encapsulation is a feasible and process-compatible strategy to improve the water and oxygen stability of perovskite solar cells.

[0024] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for improving the water and oxygen stability of perovskite solar cells by in-situ polymerization and encapsulation technology, characterized in that: A poly(ethyl α-cyanoacrylate) encapsulation layer is prepared at the bulk grain boundary and interface of the perovskite light absorbing layer of the perovskite solar cell.

2. The method according to claim 1, characterized in that: The thickness of the poly(ethyl α-cyanoacrylate) encapsulation layer is 3-10 nm.

3. The method according to claim 1, characterized in that: The monomer α-ethyl cyanoacrylate (ECA) of poly(ethyl α-cyanoacrylate) is prepared into a 3-10 mg / mL solution, and the poly(ethyl α-cyanoacrylate) PECA encapsulation layer is prepared by spin coating, dipping or drop coating.

4. The method according to claim 3, characterized in that: The PECA layer was drop-coated on the perovskite wet film at a speed of 5000 rpm and then transferred to a hot plate in air for annealing.

5. The method according to claim 4, characterized in that: The temperature on the hot plate was 120°C.

6. The method according to claim 4, characterized in that: The thickness of the PECA layer is 3-10 nm.

7. The method according to claim 3, characterized in that: The solvent is any one of chlorobenzene, toluene or ethyl acetate or a mixture thereof.

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