Hole transport layer based on photo-thermal synergistic crosslinking and self-assembly and preparation method and application thereof

Abstract

The invention discloses a hole transport layer based on photo-thermal synergistic crosslinking and self-assembly and a preparation method and application thereof, and belongs to the technical field of hole transport materials.The preparation method comprises the steps that center plane molecules, a photoinitiator and crosslinking micromolecules are dissolved with an organic solvent to obtain a mixed solution; and spin-coating the mixed solution on a substrate or a thin film, finally carrying out a photo-thermal synergistic crosslinking process, and annealing and cooling to obtain the hole transport layer. According to the invention, a photo-thermal synergistic crosslinking process is established, columnar phase arrangement of self-assembled micromolecules and a three-dimensional network structure of crosslinkable micromolecules are strengthened, the crosslinking density is effectively improved, the crosslinking temperature is reduced, and damage to molecular orderliness and perovskite caused by a single curing mode is avoided. The open-circuit voltage (VOC) of the perovskite solar cell prepared by using the hole transport layer disclosed by the invention reaches 1.044 V, the short-circuit current (JSC) reaches 21.90 mA.cm <-2 >, and the photoelectric conversion efficiency (PCE) reaches 18.61%.

Description

Technical Field

[0001] The present invention belongs to the technical field of hole transport materials, and specifically is a hole transport layer based on photothermal synergistic crosslinking and self-assembly and a preparation method thereof. Background Art

[0002] With the continuous deepening of research on perovskite solar cells (PSCs) in recent years, the photoelectric conversion efficiency (PCE) of the cells has been greatly improved. The stability problem at high operating efficiency has become the key to restricting its practical application. The classic hole transport material (HTM) 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD) needs to be doped to improve mobility. The strong hygroscopicity of the dopant will cause the hole transport layer (HTL) and perovskite to form corrosion micropores, thereby reducing the environmental stability of the cell, which has become a core issue restricting its commercial application. The development of environmentally stable HTL and its material system is an important scientific issue in the field of PSCs.

[0003] In response to the stability problem of perovskite solar cells, researchers have proposed cross-linked hole transport materials. Cross-linked HTM can undergo cross-linking polymerization reactions through ultraviolet light or heat to form new covalent bonds. In the prior art, the cross-linked hole transport layer for perovskite solar cells is mainly achieved through single thermal cross-linking or photocross-linking, which has the following limitations: thermal cross-linking requires high temperature and long-term treatment (>200°C, 1h), which is easy to cause thermal expansion or degradation of flexible substrates (such as PET, PEN) or temperature-sensitive functional layers (such as perovskite pre-deposition layers). The high cross-linking temperature limits its application in PSCs with mesoporous structures and conventional planar structures, because introducing high temperature into PSCs will exceed the tolerance of perovskite and damage the perovskite. Chinese patent CN114597322A uses thermal cross-linking to prepare a hole transport layer, and the thermal cross-linking temperature is 200-250 degrees Celsius, which is much higher than the 150 degrees Celsius of the flexible substrate, and the scope of application is limited.

[0004] Photocrosslinking has the advantages of rapid reaction and no need for high temperature, but the addition and residue of some photocrosslinking reaction photoinitiators will cause defects in the film and exciton quenching, which will affect the performance and stability of the device. Patent CN101058616B uses quinoline metal complex monomers and uses ultraviolet light to prepare crosslinked polymers. Its HOMO energy level (-4.5~-5.0 eV) is mismatched with the energy level of the perovskite layer (-5.5 eV), resulting in serious interface recombination, which is not suitable for the preparation of hole transport layers of perovskite solar cells. Patent US20170184986A1 relates to "an improved outer coating of an organic photoconductor drum and its manufacturing method." Using crosslinkable hole transport molecules containing 4 free radical polymerizable functional groups, crosslinking is achieved by photocrosslinking, and post-baking is used to anneal and release stress in the coating. This method is still a traditional single photocrosslinking method, and post-baking is only used for annealing and stress release, and does not participate in the crosslinking reaction.

[0005] The existing single thermal crosslinking or photocrosslinking method cannot meet the high mobility and stability requirements of the hole transport layer of perovskite solar cells. At present, the development demand for perovskite solar cells still lacks a hole transport layer with both high mobility and excellent stability and its preparation method. Summary of the invention

[0006] The purpose of the present invention is to solve the problem that existing perovskite solar cell devices lack a hole transport layer with both high mobility and excellent stability, and propose a hole transport layer based on photothermal synergistic crosslinking and self-assembly and a preparation method thereof. The prepared hole transport layer has a higher hole mobility, improves the crosslinking density of the crosslinked hole transport layer, reduces the crosslinking temperature, expands the application range of the crosslinked transport layer, and improves the stability of the hole transport layer.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solution: a hole transport layer based on photothermal synergistic crosslinking and self-assembly and a preparation method thereof, comprising the following steps: (1) dissolving the central plane molecule, the cross-linking small molecule and the photoinitiator in an organic solvent to obtain a mixed solution; (2) spin coating the mixed solution obtained in step (1) on a substrate or a film to form a uniform liquid film; (3) treating the liquid film with light to cause the cross-linked small molecules to undergo a photo-cross-linking reaction and form a preliminary cross-linked structure; (4) The light-treated liquid film is heat-treated to strengthen the self-assembled columnar phase arrangement of the central plane molecules and the three-dimensional network structure of the cross-linked small molecules, and finally a hole transport layer is obtained.

[0008] Preferably, the central plane molecule is at least one of perylene, triphenylene, hexaphenylene or anthraquinone; Preferably, the central plane molecule in step (1) has a structure as shown in Formula I, Formula II, Formula III or Formula IV: R in Formula I to Formula IV is independently an alkyl group, an alkoxy group, an ester group, an alkynyl group, a carbonyl group or an amide group.

[0009] Preferably, the alkyl group is a straight chain or branched chain alkyl group having 1 to 12 carbon atoms.

[0010] More preferably, the central plane molecule has a structure as shown in Formula II-1: .

[0011] Preferably, the photoinitiator in step (1) is OPPI (4-octyloxydiphenyliodonium hexafluoroantimonate), and the cross-linking small molecule is Vp-TPD (N,N′-di-p-tolyl-N,N′-bis(4-vinylphenyl)-4,4′-benzidine).

[0012] Preferably, the mass of the central plane molecule in step (1) is 5-30% of the mass of the cross-linked small molecule; and the mass of the photoinitiator is 8-10% of the mass of the cross-linked small molecule.

[0013] Specifically, the organic solvent in step (1) is at least one of toluene, chlorobenzene, chloroform, dichloromethane, tetrahydrofuran, N-methylpyrrolidone or o-dichlorobenzene.

[0014] Specifically, the light source of the light treatment in step (3) is 365 nm, 4 W, and the illumination time of the light treatment is 20 to 40 seconds; the temperature of the heat treatment in step (4) is 100 to 120°C, and the insulation time of the heat treatment is 20 to 40 minutes.

[0015] The present invention also provides a hole transport layer prepared by the above preparation method. The hole transport layer of the present invention has excellent hole transport ability, and applying it to a device can improve the performance of the device.

[0016] The present invention also provides the application of the hole transport layer described in the above technical solution in a perovskite solar cell. There is no special limitation on the application operation of the hole transport layer in the perovskite solar cell, and the application operation familiar to those skilled in the art can be adopted.

[0017] The present invention dissolves and mixes the central plane molecules, photoinitiators and cross-linked small molecules with an organic solvent. During the coating process, the central plane molecules have a large plane conjugated structure and can be assembled into a one-dimensional columnar structure driven by π-π interaction. This structure can be used as a building block to expand laterally under the interaction between molecules to form a hexagonal columnar phase with a one-dimensional transmission channel. Through the photothermal synergistic cross-linking process, the cross-linked small molecules are first pre-polymerized by photoinitiation, and then the columnar phase arrangement and three-dimensional network cross-linking are strengthened by heat treatment to avoid the destruction of molecular order by a single curing method. The cross-linked small molecules are introduced to form a three-dimensional cross-structure during the heat treatment process, thereby enhancing the mechanical strength, solvent resistance and thermal stability of the film. The cross-linked small molecules work synergistically with the central plane molecules to smooth the energy level difference and reduce the interface composite loss. Thereby, the hole transport capacity of the hole transport layer is improved, and then the performance of the solar cell device is improved. Experimental results show that the hole mobility of the hole transport layer prepared by the preparation method of the present invention reaches 2.58×10 -2 cm -2 V -1 s -1 .

[0018] The photothermal synergistic crosslinking process established by the present invention first quickly fixes the pre-self-assembled molecular arrangement through photocrosslinking, effectively avoiding the damage to the molecular orientation caused by thermal disturbance, and then triggers the secondary crosslinking of the unreacted groups through heat treatment, further improving the crosslinking density. The combination of the two breaks through the limitations of single energy input. The present invention not only retains the orderliness of molecular preassembly, but also improves the crosslinking density through the synergistic effect of light first and heat later, so that the crosslinking temperature is significantly reduced, avoiding the damage to the perovskite. This effect cannot be achieved by simple superposition of conventional means.

[0019] The introduction of photoinitiators into the cross-linking system allows the cross-linking molecules to reduce the cross-linking temperature under the synergistic effect of ultraviolet light and heat, and the cross-linking temperature is controlled below 120 ° C. The cross-linked 3D spatial network can inhibit the movement range of ions, avoid the hygroscopicity of ions, and protect the perovskite.

[0020] The present invention utilizes the self-assembly behavior of central plane molecules to construct a one-dimensional transmission channel in the cross-linked film, uses cross-linked small molecules as the cross-linking skeleton, and prepares a mixed hole transport layer through a photothermal synergistic cross-linking process, which effectively reduces the cross-linking temperature, thereby improving the hole transport capacity of the hole transport layer, balancing the energy level, and improving the device performance. The photoelectric conversion efficiency PCE is increased to 18.61%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the structural formula of the photoinitiator OPPI and the cross-linking small molecule Vp-TPD used in the examples and comparative examples; Figure 2TEM images of the hole transport layers prepared in Example 1 and Comparative Example; Figure 3 The three-dimensional TEM images of the hole transport layers prepared in Example 1 and the comparative example; Figure 4 The voltage-current curves of the hole transport layers prepared in Example 4 and the comparative example; Figure 5 The perovskite solar cell devices prepared in Application Examples 1 to 6 and Comparative Examples are J - V curve. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0023] Example 1 A method for preparing a hole transport layer based on photothermal synergistic crosslinking and self-assembly comprises the following steps: (1) dissolving the central plane molecule T6TE, the photoinitiator OPPI, and the cross-linking small molecule Vp-TPD in chlorobenzene to prepare a mixed solution; the central plane molecule has a structural formula as shown in formula II-1, the central plane molecule accounts for 5% of the cross-linking small molecule mass, and the photoinitiator accounts for 10% of the cross-linking small molecule mass; (2) The mixed solution obtained in step (1) was spin-coated on a glass substrate ITO, and then irradiated with ultraviolet light for 30 seconds (365 nm, 4 W) in a glove box and heat treated at 100 °C for 30 minutes to obtain a hole transport layer.

[0024] .

[0025] The preparation method of the central plane molecule T6TE shown in formula II-1 comprises the following steps: 1) Add catechol (11.01 g, 0.1 mol), 75 mL acetone, and hexadecyltrimethylammonium bromide (1% of the amount of catechol) in turn into a reaction apparatus equipped with a stirrer, a spherical condenser, and a 250 mL three-necked flask; after the temperature is raised to 60°C and refluxed, add an aqueous solution of sodium carbonate (15.9 g, 0.15 mol) and KI (1% of the amount of catechol) and then add n-hexyl bromide (33.01 g, 0.2 mol) and heat to 80°C and continue to reflux for 24 h. After the reaction is complete, pour the reactants into a Buchner funnel for suction filtration, remove the solvent by vacuum rotary evaporation, and separate by column chromatography to obtain colorless and transparent liquid o-hexyloxyphenol (11.658 g, 0.06 mol); 2) The colorless transparent liquid o-hexyloxyphenol (6.99 g, 0.036 mol) and anhydrous dichloromethane (DCM) (35 mL) obtained in step 1) were added to a four-necked flask, and the reaction device was ventilated three times to maintain a nitrogen environment. Concentrated sulfuric acid (98%, 0.5 mL) was added under magnetic stirring and stirring in an ice-water bath, and then anhydrous ferric chloride (17.51 ​​g, 0.108 mol) was slowly added. The reaction was carried out at room temperature for 2 to 3 hours, and the nitrogen environment was maintained throughout the process. After the raw materials reacted completely, the substrate in the three-necked flask was poured into 350 mL of ice methanol, filtered, evaporated under reduced pressure to remove the solvent, and separated by column chromatography to obtain an off-white solid 3,7,10-tri(hexyloxy)-2,6,11-trihydroxybenzophenone (2.46 g, 0.012 mol); 3) Under the protection of nitrogen, 3,7,10-tri(hexyloxy)-2,6,11-trihydroxybenzophenanthrene (0.5 g, 8.7×10 -4 mol), anhydrous dichloromethane (DCM) (30 mL), dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), after magnetic stirring for 15 minutes, valeric acid (0.889 g, 8.7×10 -3 mol) was injected into a three-necked flask and immediately immersed in an oil bath at 45 °C for 24 h. After the reaction was completed, the reaction substrate was poured into a Buchner funnel and filtered to remove N,N-dicyclohexylurea (DCU). The product was concentrated by vacuum rotary evaporation, purified by column chromatography, and recrystallized by methanol to obtain 0.57 g of a white product central planar molecule T6TE; wherein the molar ratio of 3,7,10-tri(hexyloxy)-2,6,11-trihydroxybenzophenone to dicyclohexylcarbodiimide and 4-dimethylaminopyridine was 1:2.5:0.2; The synthetic route of the central planar molecule T6TE is as follows: .

[0026] Example 2 A method for preparing a hole transport layer based on photothermal synergistic crosslinking and self-assembly comprises the following steps: (1) dissolving the central plane molecule T6TE, the photoinitiator OPPI, and the cross-linking small molecule Vp-TPD in chlorobenzene to prepare a mixed solution; the central plane molecule has a structural formula as shown in formula II-1, the central plane molecule accounts for 10% of the cross-linking small molecule weight, and the photoinitiator accounts for 10% of the cross-linking small molecule weight; (2) Spin-coat the mixed solution obtained in step (1) onto a substrate or a film, then irradiate with ultraviolet light for 30 seconds (365 nm, 4 W) in a glove box, and heat-treat at 100 °C for 30 minutes to obtain a hole transport layer.

[0027] Example 3 A method for preparing a hole transport layer based on photothermal synergistic crosslinking and self-assembly comprises the following steps: (1) dissolving the central plane molecule T6TE, the photoinitiator OPPI, and the cross-linking small molecule Vp-TPD in chlorobenzene to prepare a mixed solution; the central plane molecule has a structural formula as shown in formula II-1, the central plane molecule accounts for 15% of the weight of the cross-linking small molecule, and the photoinitiator accounts for 10% of the weight of the cross-linking small molecule; (2) Spin-coat the mixed solution obtained in step (1) onto a substrate or a film, then irradiate with ultraviolet light for 30 seconds (365 nm, 4 W) in a glove box, and heat-treat at 100 °C for 30 minutes to obtain a hole transport layer.

[0028] Example 4 A method for preparing a hole transport layer based on photothermal synergistic crosslinking and self-assembly comprises the following steps: (1) dissolving the central plane molecule T6TE, the photoinitiator OPPI, and the cross-linking small molecule Vp-TPD in chlorobenzene to prepare a mixed solution; the central plane molecule has a structural formula as shown in formula II-1, the central plane molecule accounts for 20% of the cross-linking small molecule weight, and the photoinitiator accounts for 10% of the cross-linking small molecule weight; (2) Spin-coat the mixed solution obtained in step (1) onto a substrate or a film, then irradiate with ultraviolet light for 30 seconds (365 nm, 4 W) in a glove box, and heat-treat at 100 °C for 30 minutes to obtain a hole transport layer.

[0029] Example 5 A method for preparing a hole transport layer based on photothermal synergistic crosslinking and self-assembly comprises the following steps: (1) dissolving the central plane molecule T6TE, the photoinitiator OPPI, and the cross-linking small molecule Vp-TPD in chlorobenzene to prepare a mixed solution; the central plane molecule has a structural formula as shown in formula II-1, the central plane molecule accounts for 25% of the weight of the cross-linking small molecule, and the photoinitiator accounts for 10% of the weight of the cross-linking small molecule; (2) Spin-coat the mixed solution obtained in step (1) onto a substrate or a film, then irradiate with ultraviolet light for 30 seconds (365 nm, 4 W) in a glove box, and heat-treat at 100 °C for 30 minutes to obtain a hole transport layer.

[0030] Example 6 A method for preparing a hole transport layer based on photothermal synergistic crosslinking and self-assembly comprises the following steps: (1) dissolving the central plane molecule T6TE, the photoinitiator OPPI, and the cross-linking small molecule Vp-TPD in chlorobenzene to prepare a mixed solution; the central plane molecule has a structural formula as shown in formula II-1, the central plane molecule accounts for 30% of the cross-linking small molecule weight, and the photoinitiator accounts for 10% of the cross-linking small molecule weight; (2) Spin-coat the mixed solution obtained in step (1) onto a substrate or a film, then irradiate with ultraviolet light for 30 seconds (365 nm, 4 W) in a glove box, and heat-treat at 100 °C for 30 minutes to obtain a hole transport layer.

[0031] Comparative Example A method for preparing a hole transport layer comprises the following steps: (1) Mixing a cross-linking small molecule Vp-TPD, a photoinitiator OPPI and an organic solvent chlorobenzene to obtain a mixed solution; wherein the amounts of the cross-linking small molecule Vp-TPD, the photoinitiator OPPI and the organic solvent are the same as those in Example 1 (i.e., only the central plane molecule is omitted compared to Example 1); (2) The mixed solution obtained in step (1) was spin-coated on a glass substrate, and then exposed to ultraviolet light for 30 s (365 nm, 4 W) in a glove box and heat treated at 100 °C for 30 min to obtain a hole transport layer.

[0032] The planar TEM images and three-dimensional TEM images of the hole transport layer prepared in Example 1 and the comparative example are as follows: Figure 2 and Figure 3 As shown, from Figure 2 and Figure 3 It can be seen that the hole transport layer prepared after doping the central planar molecule T6TE does not produce obvious voids, and the average roughness is reduced from 2.50 nm to 1.87 nm, indicating that the film-forming performance of the hole transport layer is improved, and the performance of the prepared hole transport layer film is better.

[0033] The performance of the hole transport layer prepared in Example 4 and the comparative example was tested, and the hole carrier mobility was tested using the space charge limited current method (SCLC). The voltage-current curve is as follows: Figure 4 As shown, from Figure 4 It can be seen that the introduction of the central plane molecule T6TE can increase the carrier mobility of Vp-TPD from 6.96×10 -3 cm -2 V -1 s -1 Increased to 2.58×10 -2 cm -2 V -1 s -1 .

[0034] Application Example 1 The hole transport layer prepared in Example 1 is applied to a perovskite solar cell device, and the specific steps are as follows: (1) The central plane molecule T6TE, the cross-linking small molecule Vp-TPD, the photoinitiator OPPI and the organic solvent chlorobenzene are mixed to obtain a mixed solution; wherein the central plane molecule accounts for 5% of the cross-linking small molecule weight; the photoinitiator OPPI accounts for 10% of the cross-linking small molecule weight; (2) Spin-coating the mixed solution obtained in step (1) on a glass substrate ITO, irradiating the mixture with ultraviolet light for 30 seconds (365 nm, 4 W) in a glove box, and heat treating the mixture at 100 °C for 30 minutes to obtain a hole transport layer; (3) dispersing nano-alumina with isopropanol, and spin-coating the nano-alumina film on the hole transport layer obtained in step (2) in a glove box; (4) In a glove box, a perovskite film is spin-coated on the alumina film obtained in step (3) in a one-step manner, and then exposed to ultraviolet light for 30 seconds and annealed at 100° C. for 30 minutes in the glove box to obtain a perovskite film; wherein the structure of the perovskite film is Cs 0.05 (FA 5 / 6 MA 1 / 6 ) 0.95 Pb(I 0.85 Br 0.15 )3; (5) using chlorobenzene to disperse the interface modification material 1,3-propane-diammonium iodide, spin-coating the modification layer on the perovskite film obtained in step (4) in a glove box, and then annealing at 100 °C for 5 min to obtain an interface modification layer on the perovskite; (6) At a vacuum degree of 6×10 -4 The electron transport layer C was deposited under the conditions of Pa. 60 (thickness of 20 nm) and an electron blocking layer BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, thickness of 6 nm) are formed on the modified layer obtained in step (5) to obtain a perovskite solar cell device.

[0035] Figure 5 A perovskite solar cell device comprising the perovskite solar cell device prepared in Application Example 1 J - V Curve. Figure 5 It can be seen that the open circuit voltage (V OC ) is 1.023V, the short-circuit current (J SC ) is 20.94 mA cm -2 The filling factor FF is 82.34% and the photoelectric conversion efficiency PCE is 16.45%.

[0036] Application Examples 2~6 On the basis of Application Example 1, the dosage of the central plane molecule T6TE was changed, and the central plane molecule T6TE was 10%, 15%, 20%, 25% and 30% of the total mass of the central plane molecule and the cross-linked small molecules, respectively, to obtain a perovskite solar cell device.

[0037] Application comparison On the basis of the application example, the amount of the central plane molecule T6TE is changed, and the central plane molecule is 0% of the total mass of the cross-linked small molecules to obtain a perovskite solar cell device.

[0038] The perovskite solar cell devices prepared in Examples 1 to 6 and the comparative examples were subjected to performance tests, and the current-voltage characteristics were recorded using a Keithley 2400 SourceMeter, where: Figure 5 The perovskite solar cell devices prepared in Application Examples 1 to 6 and Comparative Examples are J - V curve; from Figure 5 It can be seen that when the amount of the central plane molecule is 25% of the total mass of the cross-linked small molecules, the PCE of the perovskite solar cell device is optimal, and the open circuit voltage (V OC ) increases from 1.023 V to 1.044 V, the short-circuit current (J SC ) from 20.94 mA·cm -2 Increased to 21.90 mA·cm -2 , the photoelectric conversion efficiency (PCE) increased from 16.45% to 18.61%.

[0039] It can be seen from the above embodiments and application examples that the hole transport layer prepared by the preparation method provided by the present invention has a higher hole mobility.

[0040] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0041] The above is only the best embodiment of the present invention. It should be pointed out that, for ordinary technicians in this field, without departing from the principle of the present invention, the technical solution of the present invention can be modified or replaced by equivalents, which can also achieve the technical effect of the present invention and should also be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing a hole transport layer based on photothermal synergistic crosslinking and self-assembly, characterized in that: The following steps are involved: (1) dissolving the central plane molecule, the cross-linking small molecule and the photoinitiator in an organic solvent to obtain a mixed solution; (2) spin coating the mixed solution obtained in step (1) on a substrate or a film to form a uniform liquid film; (3) treating the liquid film with light to cause the cross-linked small molecules to undergo a photo-cross-linking reaction and form a preliminary cross-linked structure; (4) The light-treated liquid film is heat-treated to strengthen the self-assembled columnar phase arrangement of the central plane molecules and the three-dimensional network structure of the cross-linked small molecules, and finally a hole transport layer is obtained.

2. The preparation method according to claim 1, characterized in that: The central plane molecule is at least one of perylene, triphenylene, hexaphenylene or anthraquinone.

3. The preparation method according to claim 1, characterized in that: The central plane molecule in step (1) has a structural formula as shown in Formula I, Formula II, Formula III or Formula IV: In Formula I to Formula IV, R is independently an alkyl group, an alkoxy group, an ester group, an alkynyl group, a carbonyl group or an amide; the alkyl group is a straight chain or branched chain alkyl group having 1 to 12 carbon atoms.

4. The preparation method according to claim 2 or 3, characterized in that: The central plane molecule has a structural formula as shown in formula II-1: 。 5. The preparation method according to claim 1, characterized in that: The photoinitiator is OPPI (4-octyloxydiphenyliodonium hexafluoroantimonate); the cross-linking small molecule is Vp-TPD (N,N'-di-p-tolyl-N,N'-bis(4-vinylphenyl)-4,4'-benzidine).

6. The preparation method according to claim 1, characterized in that: The mass of the central plane molecule described in step (1) is 5-30% of the mass of the cross-linked small molecule, and the mass of the photoinitiator is 8-10% of the mass of the cross-linked small molecule.

7. The preparation method according to claim 1, characterized in that: The organic solvent in step (1) is one of toluene, chlorobenzene, chloroform, dichloromethane, tetrahydrofuran, N-methylpyrrolidone or o-dichlorobenzene.

8. The preparation method according to claim 1, characterized in that: The wavelength of the light source for the light treatment in step (3) is 365 nm, the power is 4 W, and the illumination time of the light treatment is 20 to 40 s; the temperature of the heat treatment in step (4) is 100 to 120° C., and the insulation time of the heat treatment is 20 to 40 min.

9. The hole transport layer prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the hole transport layer according to claim 9 in perovskite solar cells.

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