Solar cell and preparation method thereof

Abstract

The invention relates to the technical field of cells, in particular to a solar cell and a preparation method thereof, and the preparation method comprises the following steps: adding a hole transport material and a first perovskite material into a solvent to prepare a mixed solution; coating a substrate with the mixed solution, and performing annealing treatment to obtain a composite hole transport layer; coating the composite hole transport layer with a perovskite precursor solution, and performing annealing treatment to obtain a perovskite layer; the perovskite precursor solution comprises a second perovskite material, and the second perovskite material is the same as the first perovskite material. According to the preparation method of the solar cell provided by the invention, the perovskite seed crystal with the same components as the perovskite layer is pre-buried in the composite hole transport layer, and the perovskite seed crystal is used as a nucleation site to induce the perovskite layer to crystallize from bottom to top, so that the generation of bottom holes is inhibited.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to solar cells and methods for their fabrication. Background Technology

[0002] Solution processing is one of the key processes for preparing low-cost photovoltaic modules. However, due to the large thickness of the perovskite layer, when using solution processing to prepare the perovskite layer, after the formation of a thick perovskite wet film, crystal nuclei are randomly formed throughout the liquid phase wet film. During solvent evaporation, the crystal nuclei preferentially accumulate at the gas-liquid interface (top), where the evaporation rate is fastest. The crystal nuclei at the top rapidly crystallize to form a dense and continuous crystalline layer. This crystalline layer hinders the continued evaporation of the solvent below, causing the residual solvent at the bottom of the perovskite wet film to evaporate rapidly during subsequent annealing. The residual solvent cannot be discharged smoothly, resulting in a large number of bottom pore structures at the interface between the perovskite layer and the hole transport layer, which reduces the quality of the perovskite layer. Summary of the Invention

[0003] Based on this, this application provides a solar cell and its fabrication method. By pre-embedding perovskite seeds with the same composition as the perovskite layer in the composite hole transport layer, the perovskite seeds act as nucleation sites to induce the perovskite layer to crystallize from bottom to top (in the direction away from the composite hole transport layer), thereby suppressing the generation of bottom holes.

[0004] The first aspect of this application provides a method for preparing a solar cell, comprising the following steps:

[0005] Hole transport material and first perovskite material are added to a solvent to prepare a mixture;

[0006] The mixture was coated onto a substrate and annealed to obtain a composite hole transport layer.

[0007] A perovskite precursor solution was coated onto a composite hole transport layer and then annealed to obtain a perovskite layer.

[0008] The perovskite precursor solution includes a second perovskite material, which is the same as the first perovskite material.

[0009] In some embodiments, the mass concentration of the hole transport material in the mixture is 0.1 mg / mL to 5 mg / mL, and the molar concentration of the first perovskite material is 0.001 M to 0.5 M.

[0010] In some embodiments, the solvent includes a first solvent and a second solvent in a volume ratio of (3~20):1;

[0011] The first solvent is N,N-dimethylformamide;

[0012] The second solvent includes one or more of dimethyl sulfoxide, N-methyl-2-pyrrolidone, γ-butyrolactone, γ-valerolactone, cerium ammonium nitrate, 2-mercaptoethanol, 2-methylpentane, ethylene glycol monobutyl ether, and triethyl phosphate.

[0013] In some implementations, the thickness of the composite hole transport layer is 5 nm to 100 nm.

[0014] In some embodiments, the molar concentration of the second perovskite material in the perovskite precursor solution is 1.2M to 2M.

[0015] In some embodiments, the hole transport material includes one or more of phosphonic acid self-assembled monomolecule materials, small molecule hole transport materials, and polymeric hole transport materials.

[0016] In some embodiments, the general structural formula of the first perovskite material is ABX3, where A is FA. + MA + DMA + Cs + and Rb + One or more of them, where B is Pb 2+ and Sn 2+ At least one of them, X is Br - I - and CI - One or more of them.

[0017] In some implementations, the annealing process satisfies at least one of the following conditions:

[0018] (1) The annealing temperature is 80℃~150℃;

[0019] (2) The annealing time is 1 min to 30 min.

[0020] In some embodiments, the coating method for applying the mixture to the substrate includes one or more of spin coating, blade coating, slot coating, inkjet printing, spraying, and immersion.

[0021] In some implementations, the following steps are also included:

[0022] An electron transport layer is formed on the perovskite layer;

[0023] An electrode layer is formed on the electron transport layer.

[0024] The second aspect of this application provides a solar cell prepared using the method for preparing a solar cell as provided in the first aspect of this application.

[0025] Compared with traditional technologies, this application has the following advantages:

[0026] This application pre-embeds perovskite seed crystals identical to those in the perovskite layer within the hole transport layer. During deposition, the hole transport material preferentially anchors to the substrate, while the seed crystals are uniformly distributed on the surface of the hole transport material, serving as nucleation sites to induce subsequent perovskite layer growth. Utilizing the superior lattice matching, extremely low interface energy, and low heterogeneous nucleation barrier between the seed crystals and the epitaxial growth (perovskite material in the perovskite layer), the crystallization process of the perovskite layer begins with the seed crystals. The crystals extend outward, connecting at the interface with the hole transport layer to form a continuous bottom crystalline layer. Subsequently, the solvent evaporates from bottom to top (along the direction away from the hole transport layer), and the crystallization process also begins from the bottom crystalline layer, gradually advancing into the interior of the perovskite liquid film. Crystallization proceeds from bottom to top, ensuring that the solvent evaporates from the bottom upward throughout the entire crystallization process, preventing premature formation of a closed layer at the top. This fundamentally eliminates bottom voids caused by solvent trapping, thereby obtaining a dense, high-quality perovskite layer thick film. Attached Figure Description

[0027] To better describe and illustrate embodiments or examples of the applications disclosed herein, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the embodiments or examples currently described, or the best mode of conduct of these applications as currently understood. Furthermore, throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0028] Figure 1 This is a schematic flowchart of a method for preparing a solar cell according to one embodiment of this application.

[0029] Figure 2 This is a schematic diagram of the structure of a solar cell in one embodiment of this application.

[0030] Figure 3 This is a schematic diagram of the structure of a solar cell in another embodiment of this application.

[0031] Figure 4 This is a scanning electron microscope (SEM) image of the surface of the composite hole transport layer in Embodiment 1 of this application.

[0032] Figure 5 This is a cross-sectional scanning electron microscope (SEM) image of the composite hole transport layer in Embodiment 1 of this application.

[0033] Figure 6 This is a scanning electron microscope (SEM) image of the perovskite layer in Example 1 of this application.

[0034] Figure 7 This is a cross-sectional scanning electron microscope (SEM) image of the perovskite layer in Example 1 of this application.

[0035] Figure 8 This is a scanning electron microscope (SEM) image of the hole transport layer in Comparative Example 1 of this application.

[0036] Figure 9 This is a cross-sectional scanning electron microscope (SEM) image of the hole transport layer in Comparative Example 1 of this application.

[0037] Figure 10 This is a scanning electron microscope (SEM) image of the perovskite layer in Comparative Example 1 of this application.

[0038] Figure 11 This is a cross-sectional scanning electron microscope (SEM) image of the perovskite layer in Comparative Example 1 of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 101. Crystalline silicon bottom cell; 102. Tunneling composite layer; 103. Composite hole transport layer; 104. Perovskite layer; 105. Electron transport layer; 106. Buffer layer; 107. Transparent conductive oxide layer; 108. Metal electrode layer. Detailed Implementation

[0041] A detailed reference is now provided to embodiments of this application, one or more of which are described below. Each embodiment is provided for explanation and not for limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this application without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this document; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, stating that a parameter is an integer ≥ 2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, stating that a parameter is an integer selected from "2-10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. 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 mention that the method may also include step (c) indicates 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.

[0045] Unless otherwise specified, the terms "comprising," "containing," and "including" as used in this application can be open-ended or closed-ended. In open-ended cases, for example, "comprising," "containing," and "including" can mean that other members, elements, or method steps not listed can also be included, or that only the listed members, elements, or method steps can be included.

[0046] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0047] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0048] In this application, if the unit of a data range is only followed by the right endpoint, it means that the units of the left and right endpoints are the same. For example, "30~120min" means "30min~120min".

[0049] like Figure 1 As shown, the first aspect of this application provides a method for preparing a solar cell, comprising the following steps:

[0050] S1. Add the hole transport material and the first perovskite material to a solvent to prepare a mixture.

[0051] S2. The mixture is coated onto the substrate and annealed to obtain the composite hole transport layer 103.

[0052] S3. Coat the composite hole transport layer 103 with a perovskite precursor solution and anneal it to obtain the perovskite layer 104.

[0053] The perovskite precursor solution includes a second perovskite material, which is identical to the first perovskite material. This application pre-embeds perovskite seed crystals identical to those in the perovskite layer 104 within the hole transport layer. During deposition, the hole transport material preferentially anchors to the substrate, and the seed crystals are uniformly distributed on the surface of the hole transport material, serving as nucleation sites to induce the subsequent growth of the perovskite layer 104. Utilizing the superior lattice matching, extremely low interface energy, and low heterogeneous nucleation barrier between the seed crystals and the epitaxial growth (the perovskite material in the perovskite layer 104), the crystallization process of the perovskite layer 104 is facilitated. First, starting with the seed material, the crystal extends outward and connects with the hole transport layer to form a continuous bottom crystalline layer. Then, the solvent evaporates from bottom to top (in the direction away from the hole transport layer), and the crystallization process also starts from the bottom crystalline layer and gradually advances into the interior of the perovskite liquid film. The entire crystallization process ensures that the solvent evaporates from bottom to top, avoiding the premature formation of a closed layer at the top. This fundamentally eliminates the bottom pores caused by the solvent being trapped, thereby obtaining a dense and high-quality perovskite layer 104 thick film.

[0054] The preparation method provided in this application is universal because the seed crystals pre-embedded in the hole transport layer are the same as the active components of the perovskite in the perovskite layer 104, and therefore does not depend on a specific chemical system.

[0055] The preparation method provided in this application integrates the induced nucleation function into the hole transport layer preparation step, which simplifies the process, reduces costs, avoids the inherent interface charge transport barrier and stability risks of introducing heterogeneous components, solves the defects of introducing insulating regions and high performance degradation risks at the interface, and simultaneously improves the interface charge transport efficiency and long-term stability of the device.

[0056] It should be noted that the "perovskite seed crystal" in this application refers to a nanoscale crystal with the exact same chemical composition and crystal structure as the target perovskite layer 104, introduced onto the surface of the hole transport layer. Its function is to provide a ready-made, lattice-matched heterogeneous nucleation template for subsequent crystallization of perovskite materials from solution, thereby significantly reducing the nucleation barrier and actively guiding and controlling the entire crystallization process from the substrate interface upwards.

[0057] In some embodiments, the mass concentration of the hole transport material in the mixture is 0.1 mg / mL to 5 mg / mL, and the molar concentration of the first perovskite material is 0.001 M to 0.5 M.

[0058] It is understood that the mass concentration of the hole transport material in the mixture is 0.1 mg / mL to 5 mg / mL, including but not limited to 0.1 mg / mL, 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, and 5 mg / mL. The molar concentration of the first perovskite material in the mixture is 0.001 M to 0.5 M, including but not limited to 0.001 M, 0.1 M, 0.2 M, 0.3 M, 0.4 M, and 0.5 M.

[0059] The mass concentration of the hole transport material in the mixture was set at 0.1 mg / mL to 5 mg / mL, and the molar concentration of the perovskite material was set at 0.001 M to 0.5 M, aiming to achieve a synergistic balance between hole transport and crystallization induction functions. Specifically, on the one hand, the concentration of the hole transport material ensures that the thickness of the hole transport layer is moderate, which can both firmly anchor the substrate and not hinder the contact between the perovskite seed crystal and the subsequent perovskite precursor solution, so that the perovskite seed crystal can play a good role in inducing heterogeneous nucleation; on the other hand, the moderate concentration of the perovskite seed crystal ensures that it forms sufficient nucleation sites on the surface of the hole transport layer without crowding out the anchoring points between the hole transport material and the substrate, ensuring that the perovskite layer 104 can initiate a bottom-up, uniform and dense crystallization process from the bottom interface (the surface of the hole transport layer).

[0060] In some embodiments, the solvent in S1 above includes a first solvent and a second solvent with a volume ratio of (3~20):1. The volume ratio of the first solvent and the second solvent includes, but is not limited to, 3:1, 8:1, 11:1, 14:1, and 20:1.

[0061] For example, the first solvent is N,N-dimethylformamide (DMF).

[0062] For example, the second solvent includes one or more of dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), γ-butyrolactone (GBL), γ-valerolactone (GVL), cerium ammonium nitrate (CAN), 2-mercaptoethanol (2-ME), 2-methylpentane (2-MP), ethylene glycol monobutyl ether (2-BE), and triethyl phosphate (TEP).

[0063] In some embodiments, after adding the hole transport material and the first perovskite material to the solvent in S1 above, the mixture is stirred at a temperature of 20°C to 100°C for 1 to 12 hours to obtain a mixture.

[0064] In some embodiments, the hole transport material includes one or more of phosphonic acid self-assembled monomolecule materials, small molecule hole transport materials, and polymeric hole transport materials.

[0065] For example, phosphoric acid self-assembled monomolecule materials include, but are not limited to, [2-(9H-carbazole-9-yl)ethyl]phosphonic acid (2PACz), [2-(3,6-dimethyl-9H-carbazole-9-yl)ethyl]phosphonic acid (Me-2PACz), [2-(3,6-dimethoxy-9H-carbazole-9-yl)ethyl]phosphonic acid (MeO-2PACz), [4-(9H-carbazole-9-yl)butyl]phosphonic acid (4PACz), [4-(3,6-dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid (Me-4PACz), [4-(3,6-dimethoxy-9H-carbazole-9-yl)butyl]phosphonic acid (MeO-4PACz), and [4-(7H-dibenzocarbazole-7-yl)... [Butyl]phosphonic acid (4PADCB), [2-(3,6-dibromo-9H-carbazole-9-yl)ethyl]phosphonic acid (Br-2PACz), [4-(3,6-dibromo-9H-carbazole-9-yl)butyl]phosphonic acid (Br-4PACz), [4-(3,6-diphenyl-9H-carbazole-9-yl)hexyl]phosphonic acid (Ph-4PACz), [2-(7H-dibenzocarbazole-7-yl)ethyl]phosphonic acid (2PADCB), (4-(2,7-dibromo-9,9-dimethylacridin-10(9H)yl)butyl)phosphonic acid (DMAcPA), [4-(3,7-dibromo-10H-phenthiazin-10-yl)butyl]phosphonic acid (Br-4PAPT) or one or more of these.

[0066] For example, small molecule hole transport materials include, but are not limited to, one or more of 2,2',7,7'-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9'-spirobifluorene (spiro-OMeTAD) and 2,2',7,7'-tetrakis(N,N-di-p-tolyl)amino-9,9-spirobifluorene (spiro-TTB).

[0067] For example, polymer hole transport materials include, but are not limited to, one or more of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)biphenyldiamine] (poly-TPD), and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS).

[0068] In some embodiments, the general structural formula of the first perovskite material is ABX3, where A is FA. + MA + DMA + Cs + and Rb + One or more of them, where B is Pb 2+ and Sn 2+At least one of them, X is Br - I - and CI - One or more of them.

[0069] In some embodiments, the first perovskite material is composed of at least one of DMAI, DMABr, DMACl, RbI, RbBr, RbCl, FAI, FABr, MAI, MABr, MACl, CsI, and CsBr, and at least one of PbI2, SnI2, PbBr2, and PbCl2, with a band gap of 1.48 eV to 1.85 eV.

[0070] In some implementations, the solar cell can be a single-junction perovskite solar cell, a crystalline silicon-perovskite tandem solar cell, or an all-perovskite tandem cell.

[0071] For example, when the solar cell is a single-junction perovskite solar cell, the substrate in S2 above is a transparent conductive oxide layer 107 (TCO), including but not limited to one or more of ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine-doped tin oxide), AZO (aluminum-doped zinc oxide), IWO (tungsten-doped indium oxide), and IZrO (indium zirconium oxide).

[0072] For example, when the solar cell is a crystalline silicon-perovskite tandem solar cell, the substrate in S2 above includes, but is not limited to, a transparent conductive oxide layer 107 (TCO) loaded on the crystalline silicon base cell 101. The transparent conductive oxide layer 107 (TCO) acts as a tunneling recombination layer 102 in the crystalline silicon-perovskite tandem solar cell, used to recombine electrons and holes from the crystalline silicon base cell 101 and the hole transport layer.

[0073] For example, the crystalline silicon base cell 101 includes, but is not limited to, one of PERC, TOPCon, HJT, IBC, HBC and TBC, for absorbing long-wavelength sunlight.

[0074] In some embodiments, the coating method for coating the mixture onto the substrate in S2 above includes one or more of spin coating, blade coating, slot coating, inkjet printing, spraying, and immersion.

[0075] In one specific embodiment, the mixture is coated onto the substrate by spin coating, with a spin coating speed of 1000 rpm to 8000 rpm and a spin coating time of 10 s to 50 s.

[0076] After spin coating, annealing is performed at a temperature of 80℃~150℃ for 1min~30min.

[0077] In one specific embodiment, the mixture is coated onto the substrate using a slit coating method. The slit coating moving speed is 5 mm / s to 30 mm / s, the liquid supply speed is 5 μL / s to 50 μL / s, and the distance from the coating port to the substrate is 20 μm to 150 μm.

[0078] After the slot coating is completed, annealing is performed at a temperature of 100℃~150℃ for 5min~30min.

[0079] In some embodiments, the thickness of the composite hole transport layer 103 is 5nm to 100nm, including 5nm, 20nm, 40nm, 60nm, 80nm, and 100nm.

[0080] In some embodiments, the molar concentration of the second perovskite material in the perovskite precursor solution is 1.2M to 2M, including but not limited to 1.2M, 1.4M, 1.6M, 1.8M, and 2M.

[0081] In some embodiments, the coating method for coating the perovskite precursor solution onto the composite hole transport layer 103 in S3 above includes one or more of spin coating, blade coating, slot coating, inkjet printing, spraying, and immersion.

[0082] In one specific embodiment, a perovskite precursor solution is coated onto the composite hole transport layer 103 by spin coating. The spin coating speed is successively 300 rpm to 1000 rpm and the spin coating time is 1s to 10s, 1000 rpm to 5000 rpm and the time is 10s to 50s, and 5000 rpm to 8000 rpm and the time is 10s to 50s. 50uL to 500uL of ethyl acetate is added dropwise within 1s to 20s before the end of spin coating.

[0083] After spin coating, annealing is performed to remove residual solvent. The annealing temperature is 100℃~150℃ and the time is 5min~30min.

[0084] In one specific embodiment, a perovskite precursor solution is coated on the composite hole transport layer 103 using a slit coating method. The slit coating moving speed is 5 mm / s to 40 mm / s, the liquid supply speed is 5 μL / s to 60 μL / s, and the distance from the coating port to the substrate is 10 μm to 200 μm.

[0085] After the slot coating is completed, annealing is performed at a temperature of 100℃~150℃ for 5min~30min.

[0086] In some embodiments, the coating method of coating the mixture onto the substrate may be the same as or different from the coating method of coating the perovskite precursor solution onto the composite hole transport layer 103.

[0087] In some embodiments, the solvent in the perovskite precursor solution includes DMF and a third solvent, the third solvent including but not limited to one or more of dimethyl sulfoxide, N-methyl-2-pyrrolidone, γ-butyrolactone, γ-valerolactone, cerium ammonium nitrate, 2-mercaptoethanol, 2-methylpentane, ethylene glycol monobutyl ether, and triethyl phosphate.

[0088] In some embodiments, the method for fabricating a solar cell further includes the following steps:

[0089] S4. An electron transport layer 105 is formed on the perovskite layer 104.

[0090] S5. An electrode layer is formed on the electron transport layer 105.

[0091] In some embodiments, in S4 above, the electron transport material in the electron transport layer 105 includes, but is not limited to, one or more of PCBM, C60 and C60 derivatives, for collecting electrons from the perovskite layer 104 and blocking the transport of holes.

[0092] In one specific embodiment, the electron transport material is coated onto the perovskite layer 104 by means of spin coating, blade coating, slot coating, inkjet printing, spraying or immersion.

[0093] In one embodiment, the electrode layer in S5 above can be a metal electrode layer 108, or a composite structure of a transparent conductive oxide layer 107 (TCO) and a metal electrode layer 108, with the transparent conductive oxide layer 107 disposed between the electron transport layer 105 and the metal electrode layer 108.

[0094] For example, the metal electrode layer 108 includes, but is not limited to, one or more of Ag, Cu, Al, Au, Ni and Cr, for transferring charge to an external circuit.

[0095] For example, the metal electrode layer 108 can be prepared by one or more of the following methods: screen printing, electroplating, inkjet printing, and vapor deposition.

[0096] Exemplarily, the transparent conductive oxide layer 107 (TCO) includes, but is not limited to, one or more of ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine-doped tin oxide), AZO (aluminum-doped zinc oxide), IWO (tungsten-doped indium oxide), and IZrO (indium zirconium oxide) for collecting charge and laterally transporting it to the metal electrode layer 108.

[0097] For example, the transparent conductive oxide layer 107 can be prepared by one or more of magnetron sputtering, pulsed laser deposition, chemical vapor deposition, atomic layer deposition, and reactive plasma deposition.

[0098] In some embodiments, the step of forming the electron transport layer 105 is followed by the step of forming a buffer layer 106 on the electron transport layer 105.

[0099] For example, the buffer layer 106 includes, but is not limited to, one or more of SnOx and BCP. This is used to improve the direct contact between the electron transport layer 105 and the electrode layer, and to prevent damage to the electron transport layer 105 during electrode layer fabrication.

[0100] For example, the buffer layer 106 can be prepared by one or more of atomic layer deposition, vapor deposition, spin coating, blade coating and slot coating.

[0101] The second aspect of this application provides a solar cell prepared using the method for preparing a solar cell as provided in the first aspect of this application.

[0102] In one specific embodiment, the solar cell is a single-junction perovskite cell, with the structure as follows: Figure 2 As shown, it includes a transparent conductive oxide layer 107, a composite hole transport layer 103, a perovskite layer 104, an electron transport layer 105, a buffer layer 106, a transparent conductive oxide layer 107, and a metal electrode layer 108, which are stacked sequentially.

[0103] In one specific embodiment, the solar cell is a crystalline silicon-perovskite tandem solar cell, with the structure as follows: Figure 3 As shown, it includes a crystalline silicon bottom cell 101, a tunneling composite layer 102, a composite hole transport layer 103, a perovskite layer 104, an electron transport layer 105, a buffer layer 106, a transparent conductive oxide layer 107, and a metal electrode layer 108, which are stacked sequentially.

[0104] The present application will be further described below with reference to specific embodiments and comparative examples.

[0105] Example 1

[0106] (1) Preparation of tunneling composite layer 102: On a crystalline silicon heterojunction bottom cell, an ITO tunneling composite layer 102 with a thickness of 13 nm was prepared by magnetron sputtering. The magnetron sputtering process adopted DC sputtering mode, the target material was In2O3:SnO2 (94wt%:6wt%), and the sputtering power was 70W.

[0107] (2) Preparation of composite hole transport layer 103: hole transport material MeO-2PACz and first perovskite material Cs are prepared. 0.23FA 0.77 Pb (I 0.77 Br 0.23 3) was dissolved in a DMF:DMSO mixed solvent with a volume ratio of 4:1, and heated and stirred at 30°C for 6 hours to obtain a mixed solution. The mixed solution was then coated onto the tunneling composite layer 102 by spin coating, and annealed at 100°C for 15 minutes to obtain a composite hole transport layer 103 with a thickness of 50 nm. The concentration of the hole transport material in the mixed solution was 0.4 mg / mL, and the concentration of the first perovskite material was 0.05 M; the spin coating speed was 3000 rpm, and the time was 25 s.

[0108] Surface scanning electron microscope (SEM) image of the composite hole transport layer as follows: Figure 4 As shown, the cross-sectional scanning electron microscope (SEM) image is as follows: Figure 5 As shown, the first perovskite material has been well covered on the substrate and the hole transport layer.

[0109] (3) Preparation of perovskite layer 104: A perovskite precursor solution was coated onto the composite hole transport layer 103 by spin coating. The second perovskite material in the perovskite precursor solution was Cs. 0.23 FA 0.77 Pb (I 0.77 Br 0.23 3. The solvent was a DMF:DMSO mixed solvent with a volume ratio of 4:1. The concentration of the second perovskite material was 1.8 M. Annealing was performed at 100℃ for 20 min to obtain a perovskite layer 104 with a thickness of 750 nm. During spin coating, the spin coating speeds were 500 rpm for 5 s, 2500 rpm for 20 s, and 7000 rpm for 35 s. 10 s before the end of spin coating, 200 μL of ethyl acetate was added dropwise.

[0110] The surface scanning electron microscope (SEM) image of the perovskite layer 104 is shown below. Figure 6 As shown, the cross-sectional scanning electron microscope (SEM) image is as follows: Figure 7 As shown in the figure, no bottom holes are generated at the interface between the perovskite layer 104 and the composite hole transport layer 103, the contact is good, and the perovskite surface is uniform and dense.

[0111] (4) Fabrication of electron transport layer 105: A C60 electron transport layer 105 with a thickness of 10 nm was fabricated on the perovskite layer 104 by vapor deposition. The vapor deposition process was carried out under high vacuum conditions (10 nm). -6 The deposition was carried out under Torr conditions at a rate of 0.1 nm / s.

[0112] (5) Preparation of buffer layer 106: A SnOx buffer layer 106 with a thickness of 25 nm was prepared on electron transport layer 105 by atomic layer deposition process. The atomic layer deposition process used tin tetrachloride and ozone as tin source and oxygen source, respectively, and performed alternating pulse deposition at 90 °C to complete 100 ALD cycles.

[0113] (6) Preparation of transparent conductive oxide layer 107: A transparent conductive oxide layer 107 with a thickness of 40 nm was prepared on buffer layer 106 by magnetron sputtering. The magnetron sputtering process adopted DC sputtering mode, the target material was In2O3:ZnO (90wt%:10wt%), and the sputtering power was 500W.

[0114] (7) Preparation of metal electrode layer 108: An Ag metal electrode layer 108 with a thickness of 120 nm was prepared on the transparent conductive oxide layer 107 by vacuum thermal evaporation. The evaporation process was carried out under high vacuum conditions (10 nm). -6 The deposition process was carried out using a Torr evaporation method at a rate of 0.3 nm / s, with the metal electrode pattern defined by a metal mask.

[0115] Example 2

[0116] This embodiment adopts a technical solution that is basically the same as that of Embodiment 1. The difference between this embodiment and Embodiment 1 lies in steps (2) and (3), specifically:

[0117] (2) Preparation of composite hole transport layer 103: hole transport material 2PACz and first perovskite material Cs are prepared. 0.22 FA 0.78 Pb (I 0.8 Br 0.2 3 mol% MAPbCl3 was dissolved in a DMF:NMP mixed solvent with a volume ratio of 9:1, and heated and stirred at 30°C for 6 h to obtain a mixed solution. The mixed solution was coated onto the tunneling composite layer 102 using a slot coating method, and annealed at 100°C for 10 min to obtain a composite hole transport layer 103 with a thickness of 50 nm. The concentration of the hole transport material in the mixed solution was 0.4 mg / mL, and the concentration of the first perovskite material was 0.05 M; the coating speed was 12 mm / s, the liquid supply rate was 10 μL / s, and the distance from the coating port to the substrate was 50 μm.

[0118] (3) Preparation of perovskite layer 104: A perovskite precursor solution is coated on the composite hole transport layer 103 by slit coating. The second perovskite material in the perovskite precursor solution is Cs. 0.22 FA 0.78 Pb (I 0.8 Br 0.2A perovskite layer 104 with a thickness of 800 nm was prepared by annealing at 150 °C for 10 min with 3 mol% MAPbCl3 in a DMF:NMP mixed solvent at a volume ratio of 9:1. The concentration of the second perovskite material was 1.8 M. The coating process was carried out at 150 °C for 10 min. The coating speed was 15 mm / s, the liquid supply rate was 15 μL / s, and the distance from the coating port to the substrate was 80 μm.

[0119] Example 3

[0120] This embodiment adopts the same technical solution as Embodiment 1. The difference between this embodiment and Embodiment 1 is that the concentration of the hole transport material in step (2) is 0.1 mg / mL and the concentration of the first perovskite material is 0.05 M.

[0121] Example 4

[0122] This embodiment adopts the same technical solution as Embodiment 1. The difference between this embodiment and Embodiment 1 is that the concentration of the hole transport material in step (2) is 5 mg / mL and the concentration of the first perovskite material is 0.05 M.

[0123] Example 5

[0124] This embodiment adopts the same technical solution as Embodiment 1. The difference between this embodiment and Embodiment 1 is that the concentration of the hole transport material in step (2) is 0.4 mg / mL and the concentration of the first perovskite material is 0.001 M.

[0125] Example 6

[0126] This embodiment adopts the same technical solution as Embodiment 1. The difference between this embodiment and Embodiment 1 is that the concentration of the hole transport material in step (2) is 0.4 mg / mL and the concentration of the first perovskite material is 0.5 M.

[0127] Example 7

[0128] This embodiment adopts the same technical solution as Embodiment 1, except that in step (2) of this embodiment, a DMF:DMSO mixed solvent with a volume ratio of 3:1 is used.

[0129] Example 8

[0130] This embodiment adopts the same technical solution as Embodiment 1, except that in step (2) of this embodiment, a DMF:DMSO mixed solvent with a volume ratio of 20:1 is used.

[0131] Example 9

[0132] This embodiment adopts the same technical solution as Embodiment 1, but differs from Embodiment 1 in that a composite hole transport layer 103 with a thickness of 5 nm is prepared in step (2) of this embodiment.

[0133] Example 10

[0134] This embodiment adopts the same technical solution as Embodiment 1, but differs from Embodiment 1 in that a composite hole transport layer 103 with a thickness of 100 nm is prepared in step (2) of this embodiment.

[0135] Example 11

[0136] This embodiment adopts the same technical solution as Embodiment 1. The main difference between this embodiment and Embodiment 1 is that the concentration of the second perovskite material in step (3) is 1.2M.

[0137] Comparative Example 1

[0138] This comparative example uses essentially the same technical solution as Example 1, except that step (2) in this comparative example involves the preparation of a hole transport layer: the hole transport material MeO-2PACz is dissolved in a DMF:DMSO mixed solvent with a volume ratio of 4:1, and heated and stirred at 30°C for 6 hours to obtain a hole transport solution. The hole transport solution is then coated onto the tunneling composite layer 102 using spin coating, and annealed at 100°C for 15 minutes to obtain a hole transport layer with a thickness of 2 nm. The concentration of the hole transport material in the mixed solution is 0.4 mg / mL; the spin coating speed is 3000 rpm, and the time is 25 s.

[0139] Surface scanning electron microscope (SEM) image of the hole transport layer as follows Figure 8 As shown, the cross-sectional scanning electron microscope (SEM) image is as follows: Figure 9 As shown. A scanning electron microscope (SEM) image of the surface of perovskite layer 104 is shown below. Figure 10 As shown, the cross-sectional scanning electron microscope (SEM) image is as follows: Figure 11 As shown in the figure, the perovskite layer 104 prepared in this comparative example has a large number of bottom pores at the interface with the hole transport layer, and the surface of the perovskite layer 104 has poor compactness.

[0140] Comparative Example 2

[0141] The comparative example uses the same technical solution as Example 2. The difference between the comparative example and Example 2 is that the first perovskite material was not added to the mixture in step (2) of the comparative example, and the thickness of the hole transport layer prepared is 2nm.

[0142] Comparative Example 3

[0143] The comparative example uses the same technical solution as Example 3. The difference between the comparative example and Example 3 is that the first perovskite material was not added to the mixture in step (2) of the comparative example, and the thickness of the hole transport layer prepared is 2nm.

[0144] Test case

[0145] (1) Photovoltaic conversion performance test: The solar cells prepared in the above examples and comparative examples were placed in a solar simulator (manufacturer: Wavelabs). Under the illumination of a certain solar intensity, a bias voltage (Vp, bias voltage range of -0.1 V to 2.1 V) was applied to the device using a test source meter and the output current of the device was tested to obtain the bias voltage-current density curve.

[0146] Open-circuit voltage (Voc): The terminal voltage of the solar cell when no load is connected, i.e., when the current density in the bias-current density curve is 0 mA·cm. -2 The bias voltage value at that time.

[0147] Short-circuit current density (Jsc): The output current per unit area of ​​the solar cell when it is short-circuited, i.e., the current density when the bias voltage is 0V in the bias voltage-current density curve.

[0148] Fill factor (FF): FF = max(Vp × Jsc), where Vp is the bias voltage and Jsc is the short-circuit current density.

[0149] Photovoltaic cell efficiency (PCE): PCE = Voc × Jsc × FF. The test results are shown in Table 1.

[0150] (2) Long-term stability test: After the solar cells prepared in the above examples and comparative examples were placed for 1000 hours, the PCE retention rate was tested. The test results are shown in Table 1.

[0151] (3) Contact angle test: The perovskite precursor solution used in the above examples and comparative examples was dropped onto the corresponding composite hole transport layer / hole transport layer, and the contact angle was tested. The smaller the contact angle, the lower the interfacial energy. The test results are shown in Table 1.

[0152] Table 1

[0153]

[0154] According to the data in Table 1, compared with Comparative Examples 1-3, in Examples 1-3, by pre-embedding perovskite seed crystals (first perovskite material) with the same composition as the perovskite layer in the composite hole transport layer, a dense and high-quality perovskite layer thick film was obtained, which improved the photoelectric conversion efficiency of the solar cell.

[0155] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0156] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a solar cell, characterized in that, Includes the following steps: Hole transport material and first perovskite material are added to a solvent to prepare a mixture; The mixture is coated onto a substrate and annealed to obtain a composite hole transport layer. A perovskite precursor solution was coated onto the composite hole transport layer, followed by annealing to obtain a perovskite layer. The perovskite precursor solution includes a second perovskite material, which is the same as the first perovskite material.

2. The method for preparing a solar cell according to claim 1, characterized in that, In the mixture, the mass concentration of the hole transport material is 0.1 mg / mL to 5 mg / mL, and the molar concentration of the first perovskite material is 0.001 M to 0.5 M.

3. The method for preparing a solar cell according to claim 1, characterized in that, The solvent comprises a first solvent and a second solvent in a volume ratio of (3~20):1; The first solvent is N,N-dimethylformamide; The second solvent includes one or more of dimethyl sulfoxide, N-methyl-2-pyrrolidone, γ-butyrolactone, γ-valerolactone, cerium ammonium nitrate, 2-mercaptoethanol, 2-methylpentane, ethylene glycol monobutyl ether, and triethyl phosphate.

4. The method for preparing a solar cell according to claim 1, characterized in that, The thickness of the composite hole transport layer is 5nm~100nm.

5. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, In the perovskite precursor solution, the molar concentration of the second perovskite material is 1.2M~2M.

6. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, The method for preparing the solar cell satisfies at least one of the following conditions: (1) The hole transport material includes one or more of the following: phosphonic acid self-assembled monomolecule materials, small molecule hole transport materials, and polymer hole transport materials; (2) The general structural formula of the first perovskite material is ABX3, where A is FA. + MA + DMA + Cs + and Rb + One or more of them, where B is Pb 2+ and Sn 2+ At least one of them, X is Br - I - and CI - One or more of them.

7. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, Annealing treatment must meet at least one of the following conditions: (1) The annealing temperature is 80℃~150℃; (2) The annealing time is 1 min to 30 min.

8. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, The coating method for applying the mixture to the substrate includes one or more of spin coating, blade coating, slot coating, inkjet printing, spraying, and immersion.

9. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, It also includes the following steps: An electron transport layer is formed on the perovskite layer; An electrode layer is formed on the electron transport layer.

10. A solar cell, characterized in that, The solar cell is prepared using the method described in any one of claims 1 to 9.

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