Heterojunction for improving charge transport, its preparation method, and perovskite solar cell

Abstract

The present invention discloses a heterojunction for improving charge transport, a preparation method thereof, and a perovskite solar cell, relating to the field of perovskite solar cells. The heterojunction for improving charge transport includes: an SnO2 electron transport layer and a perovskite light-absorbing layer, and a dipole layer is compounded between the SnO2 electron transport layer and the perovskite light-absorbing layer, and the material of the dipole layer is 4-methylsulfonylphenylamidine. The present invention successfully realizes the synchronous increase of the dielectric constant of the heterojunction by using 4-methylsulfonylphenylamidine (SPA) dipole molecules, and adjusts the dielectric properties of the heterojunction to an equilibrium state; effectively reduces the exciton dissociation energy of the perovskite photoactive layer, and promotes the dissociation of excitons to generate free electrons and holes; successfully shields the capture of electrons by interface state traps and inhibits the recombination loss; effectively reduces the interfacial charge transport barrier and promotes the energy level alignment; effectively solves the problem of low efficiency of interfacial charge transport performance and improves the photoelectric conversion efficiency of the device during long-term operation.

Description

Technical Field

[0001] The present invention relates to the field of perovskite solar cells, and particularly to a heterojunction for improving charge transport, a preparation method thereof, and a perovskite solar cell. Background Art

[0002] Among many solar cells, perovskite solar cells (PVSCs) have important application prospects in the optoelectronic field due to their good light absorption, excellent charge transport rate, and adjustable bandgap. Among them, single-junction perovskite solar cells have achieved a power conversion efficiency (PCE) of 26.7%, and are the most promising to replace relatively expensive polycrystalline silicon, copper indium gallium selenide (CIGS), and cadmium telluride (CdTe) solar cells in the market. However, restricted by the interface between the perovskite photoactive layer (abbreviated as perovskite light absorption layer) and the charge transport layer in the heterostructure of perovskite solar cells, the improvement of charge transport efficiency is severely restricted, and more directly leads to low photoelectric conversion efficiency, which is a key problem that must be solved in practical applications.

[0003] In perovskite solar cells, the perovskite light absorption layer and the charge transport layer are the main parts for the generation and collection of photo-generated charge carriers. Their charge dynamics (including charge extraction, charge transfer, and charge recombination) occur at the heterojunction interface formed between the perovskite light absorption layer and the charge transport layer. It should be noted that the charge transfer efficiency from perovskite to the interface depends on maximizing the extraction rate while minimizing the recombination caused by interface defects. However, the complex interfacial chemical environment at the contact between the perovskite light absorption layer and the charge transport layer (such as high defect density and low perovskite crystallinity) results in more serious charge transport loss at the bottom surface of perovskite than at the top surface. In addition, interface defects lead to charge accumulation and recombination losses, further resulting in a decline in device performance and having an adverse impact on the stability of the device. Current strategies mainly focus on interface modification (such as using passivators) to reduce recombination losses caused by interface defects and control energy level alignment to improve charge transport efficiency. However, these strategies are usually accompanied by many side effects, such as passivator degradation, interfacial reaction, induced ion migration, etc., resulting in effective actual effects and seriously affecting the photovoltaic performance and long-term operation stability of perovskite solar cell devices.

[0004] Therefore, how to avoid the disadvantages of interface modification and effectively break through the interface limitation between heterojunctions to construct an efficient charge transport channel is of great significance for improving the efficiency of perovskite solar cells. Summary of the Invention

[0005] The object of the present invention is to provide a method for regulating the dielectric constant to prepare a perovskite solar cell with high charge transport performance for the high defect density barrier and low charge transport efficiency at the interface of a heterojunction (perovskite light-absorbing layer and tin dioxide (SnO₂) electron transport layer). Before pre-depositing the perovskite light-absorbing layer, a dipole-like molecule 4-methylsulfonylphenylamidine (SPA) containing methylsulfonyl and amidino functional groups with different polarities is used to be uniformly deposited on the surface of the prepared SnO₂ electron transport layer to form an interfacial dipole layer, and then the perovskite light-absorbing layer is deposited on the dipole layer. Under the condition that the dielectric constants of the perovskite light-absorbing layer and the SnO₂ layer are synchronously regulated bidirectionally by the SPA dipole layer, an increase in the dielectric constant is achieved and the dielectric properties compatible with the perovskite light-absorbing layer and the SnO₂ layer are balanced, thereby achieving a perovskite solar cell with improved charge transport performance at the heterojunction interface and high photoelectric conversion efficiency.

[0006] To achieve the above object, on the one hand, the present invention provides a heterojunction for improving charge transport, which includes: a SnO₂ electron transport layer and a perovskite light-absorbing layer, and a dipole layer is compounded between the SnO₂ electron transport layer and the perovskite light-absorbing layer; the material of the dipole layer is 4-methylsulfonylphenylamidine (SPA), which has a molecular structure shown in formula (1):

[0007] Formula (1).

[0008] As a further preferred technical solution of the present invention, the thickness of the SnO₂ electron transport layer is 50 nm to 400 nm; and / or, the thickness of the dipole layer is 10 nm to 200 nm; and / or, the thickness of the perovskite light-absorbing layer is 400 nm to 800 nm.

[0009] On the other hand, according to the present invention, a method for preparing a heterojunction for improving charge transport is also provided, including the following steps:

[0010] S1. Deposit a SnO₂ electron transport layer on a transparent conductive substrate;

[0011] S2. Deposit a dipole layer made of 4-methylsulfonylphenylamidine on the surface of the obtained SnO₂ electron transport layer;

[0012] S3. Deposit the perovskite light-absorbing layer on the surface of the obtained dipole layer.

[0013] As a further preferred technical solution of the present invention, the transparent conductive substrate is FTO glass or ITO glass; and / or, the thickness of the transparent conductive substrate is 10 nm to 500 nm.

[0014] As a further preferred technical solution of the present invention, step S1 specifically includes: mixing a 15% (aqueous dispersion system) SnO2 solution with water in a ratio of 1:3, and then using spin coating deposition. The specific deposition process is: rotation speed of 2000 - 3000 rpm, time of 10 - 30 s, deposition annealing temperature of 130 - 150 °C, and time of ≤30 min.

[0015] As a further preferred technical solution of the present invention, step S2 specifically includes: dissolving 4-methylsulfonylphenylamidine in an alcohol solvent at a concentration of 0.10 - 2.00 mg / mL, and then using spin coating deposition. The specific deposition process is: rotation speed of 1000 - 3000 rpm, time of 10 - 30 s, deposition annealing temperature of 100 °C (specifically adjusted according to the boiling point properties of the selected alcohol solvent), and time of ≤30 min. More preferably, the purity of 4-methylsulfonylphenylamidine is above 98%.

[0016] As a further preferred technical solution of the present invention, in step S2, the preparation method of the perovskite light-absorbing layer includes but is not limited to one-step method, two-step method, etc. More preferably, the perovskite light-absorbing layer is a FA, FAMA or FAMACs system. The preparation process of the perovskite light-absorbing layer includes but is not limited to spin coating, blade coating, spraying, slot die coating or any combination of processes.

[0017] According to another aspect of the present invention, the present invention also provides a perovskite solar cell, which employs the above-mentioned heterojunction.

[0018] As a further preferred technical solution of the present invention, the perovskite solar cell further includes a transparent conductive substrate, a hole transport layer and a metal electrode, and the heterojunction is disposed between the transparent conductive substrate and the hole transport layer. More preferably, the hole transport layer includes but is not limited to 2,2',7,7'-tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA), poly(3-hexylthiophene) (P3HT), nickel oxide, and combinations thereof. The thickness of the hole transport layer is 10 nm - 400 nm; the metal electrode can be selected from gold or silver; the transparent conductive substrate is FTO glass or ITO glass.

[0019] As a further preferred technical solution of the present invention, the structure of the perovskite solar cell is an n-i-p normal structure or a p-i-n inverted structure.

[0020] Principle of the present invention: In the preparation process of the heterojunction (perovskite light-absorbing layer and SnO2 electron transport layer) that improves charge transport, a dipole layer is introduced at the heterojunction interface by using 4-methylsulfonylphenylamidine (SPA) dipole molecules. Due to the influence of the self-polarity size of the SPA dipole layer and the adsorption difference of the group orientation, the amidine group is adsorbed orientationally on the perovskite light-absorbing layer and the methylsulfonyl group is adsorbed orientationally on the SnO2 layer. Thus, the polarizabilities of both the perovskite light-absorbing layer and the SnO2 layer are changed simultaneously, resulting in an increase effect in the dielectric constant and the generation of compatible dielectric properties. The prepared heterojunction dielectric properties with a high dielectric constant of the perovskite light-absorbing layer and the SnO2 electron transport layer and compatibility directly enhance the directional charge transport efficiency from the perovskite light-absorbing layer to the SnO2 electron transport layer, avoid the side effects of interface modification, and effectively improve the long-term operation stability of perovskite solar cell devices.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The present invention successfully realizes the synchronous increase of the dielectric constant of the heterojunction for the first time by using 4-methylsulfonylphenylamidine (SPA) dipole molecules, and adjusts the dielectric properties of the heterojunction to an equilibrium state; effectively reduces the exciton dissociation energy of the perovskite photoactive layer, promotes the dissociation of excitons to generate free electrons and holes; successfully shields the capture of electrons by interface state traps and inhibits the recombination loss; effectively reduces the interfacial charge transport barrier and promotes the energy level alignment; effectively solves the problem of low efficiency of interfacial charge transport performance and improves the photoelectric conversion efficiency of the device during long-term operation.

[0023] (2) The preparation method involved in the present invention is relatively simple, easy to operate, and has low energy consumption. It is applicable to various perovskite systems and various perovskite preparation methods, and is suitable for popularization and application. Description of the Drawings

[0024] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0025] Figure 1 It is a schematic diagram of the structure of the perovskite solar cell device prepared in Example 6 of the present invention.

[0026] Figure 2 It is a schematic diagram of the device structure for obtaining the dielectric constants of the perovskite layer and the SnO2 layer prepared in Examples 4 - 5 of the present invention. (a) is the device structure of Example 4, and (b) is the device structure of Example 5.

[0027] Figure 3 It is a dielectric constant diagram of the thin film. Among them, (a) is the dielectric constant diagram of the perovskite thin film obtained in Example 4 and Comparative Example 1; (b) is the dielectric constant diagram of the SnO2 thin film obtained in Example 5 and Comparative Example 2.

[0028] Figure 4 Steady-state photoluminescence (PL) spectra of the heterojunctions (perovskite layer and SnO2 layer) for Example 3 and Comparative Example 3.

[0029] Figure 5 Current-voltage characteristic curves of the perovskite solar cells prepared in Example 6 and Comparative Examples 4, 5, 6, and 7.

[0030] The realization of the object, functional features, and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Detailed Description of the Invention

[0031] The following is a detailed description of the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining and illustrating the present invention and are not used to limit the present invention.

[0032] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0033] In all the following examples and comparative examples, the thicknesses of the SnO2 electron transport layer and the dipole layer are both 100 nm, and the thickness of the perovskite absorption layer is 700 nm.

[0034] Example 1

[0035] A preparation method of a heterojunction that regulates the dielectric constants of a perovskite light-absorbing layer and an SnO2 electron transport layer by a 4-methylsulfonylphenylamidine (SPA) dipole layer to improve charge transport performance, comprising the following steps:

[0036] (1) Dissolve 4-methylsulfonylphenylamidine (SPA) powder uniformly in a methanol solvent at a ratio of 0.15 mg / mL, and continuously shake and disperse it in a shaker for dissolution, and set aside.

[0037] (2) Dissolve 15% (aqueous dispersion system) of SnO2 in deionized water at a ratio of 1:3, and use spin coating deposition (2000 rpm) for 30 s, and the deposition annealing temperature is 150 °C for ≤15 min to obtain an SnO2 thin film.

[0038] (3) Deposit the SPA dipole molecule solution obtained in step (1) on the surface of the SnO2 thin film by spin coating, use spin coating deposition (2000 rpm) for 20 s, and the deposition annealing temperature is 100 °C for ≤10 min to form a deposited SPA dipole layer.

[0039] (4) On the SPA dipole layer obtained in step (3), a perovskite precursor solution prepared by dissolving 1.5 mmol PbI2 in 1 mL of DMF:DMSO = 95:5 and dissolving 90 mg of FAI, 6.9 mg of MAI, and 9 mg of MACl in 1 mL of IPA was deposited on the SPA dipole layer by spin coating. Using spin coating deposition (2000 rpm), the time was 30 s, the deposition annealing temperature was 150 °C, and the time was ≤10 min to obtain a perovskite light-absorbing layer, and finally a heterojunction that simultaneously increases the dielectric constants of the perovskite layer and the SnO2 electron transport layer was formed.

[0040] Example 2

[0041] A method for preparing a heterojunction that regulates the dielectric constants of a perovskite light-absorbing layer and an SnO2 electron transport layer by a 4-methylsulfonylphenylamidine (SPA) dipole layer to improve charge transport performance, comprising the following steps:

[0042] (1) According to a ratio of 0.15 mg / mL, 4-methylsulfonylphenylamidine (SPA) powder was uniformly dissolved in an ethanol solvent and continuously shaken and dispersed in a shaker for dissolution, and then reserved.

[0043] (2) According to a ratio of 1:3, 15% (aqueous dispersion system) of SnO2 was dissolved in deionized water. Using spin coating deposition (2000 rpm), the time was 30 s, the deposition annealing temperature was 150 °C, and the time was ≤15 min to obtain an SnO2 thin film.

[0044] (3) The SPA dipole molecule solution obtained in step (1) was deposited on the surface of the SnO2 thin film by spin coating. Using spin coating deposition (2000 rpm), the time was 20 s, the deposition annealing temperature was 110 °C, and the time was ≤10 min to obtain a deposited SPA dipole layer.

[0045] (4) On the SPA dipole layer obtained in step (3), a perovskite precursor solution prepared by dissolving 1.5 mmol PbI2 in 1 mL of DMF:DMSO = 95:5 and dissolving 90 mg of FAI, 6.9 mg of MAI, and 9 mg of MACl in 1 mL of IPA was deposited on the SPA dipole layer by spin coating. Using spin coating deposition (2000 rpm), the time was 30 s, the deposition annealing temperature was 150 °C, and the time was ≤10 min to obtain a perovskite light-absorbing layer, and finally a heterojunction that simultaneously increases the dielectric constants of the perovskite layer and the SnO2 electron transport layer was formed.

[0046] Example 3

[0047] A method for preparing a heterojunction that regulates the dielectric constants of a perovskite light-absorbing layer and an SnO2 electron transport layer by a 4-methylsulfonylphenylamidine (SPA) dipole layer to improve charge transport performance, comprising the following steps.

[0048] (1) Dissolve 4-methylsulfonylphenylamidine (SPA) powder uniformly in an isopropanol (IPA) solvent at a ratio of 0.15 mg / mL, and continuously shake and disperse it in a shaker for dissolution, and set aside.

[0049] (2) Dissolve 15% (aqueous dispersion system) of SnO2 in deionized water at a ratio of 1:3, and use spin coating deposition (2000 rpm) for 30 s, with a deposition annealing temperature of 150 °C and a time of ≤15 min to obtain an SnO2 thin film.

[0050] (3) Deposit the SPA dipole molecule solvent obtained in step (1) on the surface of the SnO2 thin film by spin coating, using spin coating deposition (2000 rpm) for 20 s, with a deposition annealing temperature of 100 °C and a time of ≤15 min to obtain the deposited SPA dipole layer.

[0051] (4) For the deposited SPA dipole layer obtained in step (3), dissolve 1.5 mmol of PbI2 in 1 mL of DMF:DMSO = 95:5 and dissolve 90 mg of FAI, 6.9 mg of MAI, and 9 mg of MACl in 1 mL of IPA to prepare a perovskite precursor solution, and deposit it on the SPA dipole layer by spin coating, using spin coating deposition (2000 rpm) for 30 s, with a deposition annealing temperature of 150 °C and a time of ≤10 min to obtain a perovskite light-absorbing layer, and finally form a heterojunction that simultaneously increases the dielectric constants of the perovskite layer and the SnO2 electron transport layer.

[0052] It is concluded from Examples 1-3 that the solubility of SPA dipole molecules does not depend on the selection of special alcohol solvents and has a preparation process that meets the requirements of conventional general alcohol solvents.

[0053] Example 4

[0054] A method for preparing a device that increases the dielectric constant of a perovskite layer by a 4-methylsulfonylphenylamidine (SPA) dipole layer, comprising the following steps.

[0055] (1) Preparation of a transparent conductive substrate: Ultrasonically clean a 2.5 cm × 2.5 cm etched ITO conductive glass substrate in detergent, acetone, deionized water, and isopropanol for 15 min. Then dry it with N2 and place it in a plasma cleaner to treat the ITO substrate with UV-ozone for 10 min.

[0056] (2) Dissolve 4-methylsulfonylphenylamidine (SPA) powder uniformly in isopropanol (IPA) solvent at a ratio of 0.15 mg / mL, and continuously shake and disperse it in a shaker for dissolution, and set aside.

[0057] (3) Deposit the SPA dipole molecular solvent obtained in step (2) on the surface of the ITO conductive glass substrate by spin coating. Use spin coating deposition (2000 rpm) for 15 s, and the deposition annealing temperature is 100 °C for ≤10 min to obtain the deposited SPA dipole layer.

[0058] (4) Prepare a lead iodide precursor solution: Weigh 1.5 mmol PbI2 and dissolve it in 1 mL of a solvent with DMF:DMSO = 95:5, and leave it overnight at 60 °C on a hot stage, and set aside. Prepare an organic ammonium salt solution: Dissolve 90 mg of FAI, 6.9 mg of MAI, and 9 mg of MACl in 1 mL of IPA, and then place it in a shaker to fully dissolve, and set aside.

[0059] (5) Take an appropriate amount of the lead iodide precursor solution obtained in step (4) and spin coat it onto the annealed and cooled SPA dipole layer at a speed of 1500 rpm for 30 s. After the first annealing treatment, a lead iodide thin film is obtained. Take an appropriate amount of the organic ammonium salt solution obtained in step (4) and spin coat it on the lead iodide thin film at a speed of 2000 rpm for 30 s. After the second annealing treatment, a perovskite light-absorbing layer is obtained.

[0060] (6) Evaporation of the metal electrode: Place the product obtained in step (5) in an evaporator, and evaporate Ag on the surface of the hole transport layer under high vacuum to obtain the metal electrode Ag, and prepare a perovskite layer device with an increased dielectric constant, and its structure is as shown in Figure 2 (a) in.

[0061] Example 5

[0062] A method for preparing a device with an increased dielectric constant of the SnO2 layer by a 4-methylsulfonylphenylamidine (SPA) dipole layer, including the following steps.

[0063] (1) Preparation of a transparent conductive substrate: Ultrasonically treat a 2.5 cm × 2.5 cm etched ITO conductive glass substrate in detergent, acetone, deionized water, and isopropanol for 15 min for cleaning. Then blow it dry with N2 and place it in a plasma cleaner to treat the ITO substrate with UV-ozone for 10 min.

[0064] (2) Dissolve 4-methylsulfonylphenylamidine (SPA) powder uniformly in isopropanol (IPA) solvent at a ratio of 0.15 mg / mL, and continuously shake and disperse it in a shaker for dissolution, and set aside.

[0065] (3) Dissolve SnO2 in the form of 15% (aqueous dispersion) in deionized water at a ratio of 1:3 to form a SnO2 solvent, and continuously shake it evenly for standby.

[0066] (4) Take an appropriate amount of the SnO2 solvent in step (3) and deposit it on the ITO conductive glass substrate. Use spin coating deposition (2000 rpm) for 30 s, and the deposition annealing temperature is 150 °C for ≤15 min to obtain a SnO2 thin film.

[0067] (5) Deposit the SPA dipole molecule solvent obtained in step (2) on the surface of the SnO2 thin film by spin coating. Use spin coating deposition (2000 rpm) for 15 s, and the deposition annealing temperature is 100 °C for ≤10 min to obtain the deposited SPA dipole layer.

[0068] (6) Evaporation of the metal electrode: Place the product obtained in step (5) in an evaporation instrument, and evaporate Ag on the surface of the hole transport layer under high vacuum to obtain the metal electrode Ag, and prepare a SnO2 layer device with an increased dielectric constant, and its structure is as Figure 2 shown in (b) of

[0069] Example 6

[0070] A preparation method of a perovskite solar cell in which a 4-methylsulfonylphenylamidine (SPA) dipole layer regulates the dielectric constants of a perovskite light-absorbing layer and a SnO2 electron transport layer, and the specific steps are as follows.

[0071] (1) Preparation of the transparent conductive substrate: Ultrasonically treat a 2.5 cm × 2.5 cm etched ITO conductive glass substrate in detergent, acetone, deionized water, and isopropyl alcohol for 15 min for cleaning. Then blow it dry with N2 and place it in a plasma cleaner to treat the ITO substrate with UV-ozone for 10 min.

[0072] (2) Preparation of the SnO2 electron transport layer: Spin coat SnO2 (an aqueous solution of 2.67 wt%) on the surface of the ITO conductive glass substrate at a speed of 3000 rpm for 30 s, and thermally anneal it at 150 °C in air for 30 min.

[0073] (3) Preparation of the 4-methylsulfonylphenylamidine (SPA) dipole layer: Dissolve 4-methylsulfonylphenylamidine (SPA) powder evenly in isopropyl alcohol (IPA) solvent according to a ratio of 0.15 mg / mL, and continuously heat and disperse it in a shaker at 50 °C for 10 min for dissolution for standby.

[0074] Take an appropriate amount of the obtained SPA dipole molecular solution and drop it on the surface of the annealed and cooled SnO2 thin film. Spin-coat it at a speed of 2000 rpm for 30 s, and then perform thermal annealing at 100 °C in air for 15 min to complete the preparation of the SPA dipole layer.

[0075] (4)Preparation of the perovskite light-absorbing layer

[0076] Prepare the lead iodide precursor solution: Weigh 1.5 mmol of PbI2 and dissolve it in 1 mL of a solvent with DMF:DMSO = 95:5. Keep it overnight on a hot stage at 60 °C for later use.

[0077] Prepare the organic ammonium salt solution: Dissolve 90 mg of FAI, 6.9 mg of MAI, and 9 mg of MACl in 1 mL of IPA, and then place it in a shaker to fully dissolve for later use.

[0078] Prepare the lead iodide thin film: Spin-coat an appropriate amount of the lead iodide precursor solution onto the annealed and cooled SPA dipole layer at a speed of 1500 rpm for 30 s. After the first annealing treatment, obtain the lead iodide thin film.

[0079] Prepare the perovskite thin film: Spin-coat the organic ammonium salt solution on the lead iodide thin film at a speed of 2000 rpm for 30 s. After the second annealing treatment, obtain the perovskite light-absorbing layer.

[0080] (5)Preparation of the Spiro-OMeTAD hole transport layer: Dissolve 72.3 mg of Spiro-OMeTAD powder in 1 mL of chlorobenzene, then add 28.85 μL of tert-butylpyridine and 17.5 μL of a 520 mg / mL lithium bis(trifluoromethanesulfonyl)imide / acetonitrile solution. After mixing, place it in a shaker to fully dissolve for later use.

[0081] Take an appropriate amount of the obtained Spiro-OMeTAD solution and drop it on the surface of the annealed and cooled perovskite thin film. Spin-coat it at a speed of 4000 rpm for 30 s to complete the preparation of the hole transport layer.

[0082] (6)Evaporation of the metal electrode: Place the product obtained in step (5) in an evaporation instrument, and evaporate Ag on the surface of the hole transport layer under high vacuum to obtain the metal electrode Ag, thereby obtaining a perovskite solar cell with the structure as Figure 1 shown.

[0083] Comparative Example 1

[0084] The preparation method in Comparative Example 1 is generally the same as that in Example 4. The difference is that it is not necessary to deposit the 4-methylsulfonylphenylamidine (SPA) dipole layer, that is, steps (2) and (3) in Example 4 are not required, and the perovskite light-absorbing layer is deposited on the surface of the ITO conductive glass substrate.

[0085] The perovskite thin films obtained in step (6) of Example 4 and Comparative Example 1 were subjected to dielectric constant test and analysis, and the results are shown in Figure 3 In (a) of, it can be seen that the dielectric constant of the obtained perovskite thin film has been greatly improved. Figure 3 In (a) of, it shows that the dielectric constant of the perovskite light-absorbing layer regulated by the 4-methylsulfonylphenylamidine (SPA) dipole layer has increased significantly, proving that the amidino orientation of the dipole molecule SPA in the perovskite light-absorbing layer changes the polarizability, thus significantly increasing the dielectric constant value.

[0086] Comparative Example 2

[0087] The preparation method in Comparative Example 2 is generally the same as that in Example 5. The difference is that there is no need to deposit the 4-methylsulfonylphenylamidine (SPA) dipole layer, that is, steps (2) and (5) in Example 5 are not required, and the SnO2 layer is deposited on the surface of the ITO conductive glass substrate.

[0088] The SnO2 thin films obtained in step (6) of this Example 5 and Comparative Example 2 were subjected to dielectric constant test and analysis, and the results are shown in Figure 3 In (b) of, it can be seen that the dielectric constant of the obtained SnO2 thin film has been greatly improved. Figure 3 In (b) of, it shows that the dielectric constant of the SnO2 layer regulated by the 4-methylsulfonylphenylamidine (SPA) dipole layer has increased significantly, proving that the methylsulfonyl orientation of the dipole molecule SPA in the SnO2 layer changes the polarizability, thus significantly increasing the dielectric constant value.

[0089] Based on Figure 3 It can be known that the significant synchronous increase in the dielectric constant indicates that 4-methylsulfonylphenylamidine (SPA) can effectively and bidirectionally affect the dielectric properties of the perovskite light-absorbing layer and the SnO2 layer, thereby improving the compatibility of the dielectric properties of the heterojunction.

[0090] Comparative Example 3

[0091] The preparation method in Comparative Example 3 is generally the same as that in Example 3. The difference is that there is no need to deposit the 4-methylsulfonylphenylamidine (SPA) dipole layer, that is, step (3) in Example 3 is not required.

[0092] The heterojunctions (perovskite light-absorbing layer and SnO2 layer) obtained in step (4) of Example 3 and Comparative Example 3 were subjected to steady-state photoluminescence (PL) spectrum analysis, and the results are shown in Figure 4 . From Figure 4 It can be known that the PL spectrum intensity tested by the technical solution provided by the present invention has been greatly reduced, proving the reduction of the efficient interfacial charge transfer performance and interfacial recombination between the perovskite light-absorbing layer and the SnO2 layer.

[0093] Comparative Example 4

[0094] The preparation method in Comparative Example 4 is generally the same as that in Example 6. The difference is that it is not necessary to deposit the 4-methylsulfonylphenylamidine (SPA) dipole layer, that is, step (3) in Example 6 is omitted to serve as a blank control group.

[0095] Comparative Example 5

[0096] The preparation method in Comparative Example 4 is generally the same as that in Example 6. The difference is that step (3) in Example 6 is replaced by depositing 4-fluoroaniline (FPN) as the dipole layer. FPN has the molecular structure shown in Formula (2):

[0097] Formula (2).

[0098] Comparative Example 6

[0099] The preparation method in Comparative Example 5 is generally the same as that in Example 6. The difference is that step (3) in Example 6 is replaced by depositing p-tolylamidine (MPA) as the dipole layer. MPA has the molecular structure shown in Formula (3):

[0100] Formula (3).

[0101] Comparative Example 7

[0102] The preparation method in Comparative Example 6 is generally the same as that in Example 6. The difference is that step (3) in Example 6 is replaced by depositing p-methylsulfonyltoluene (MPS) as the dipole layer. MPS has the molecular structure shown in Formula (4):

[0103] Formula (4).

[0104] In Comparative Example 5, Comparative Example 6, and Comparative Example 7, the preparation method of each dipole layer is the same as step (3) in Example 6.

[0105] The perovskite solar cells obtained in the above Example 6 and Comparative Examples 4-7 were tested for their photoelectric conversion efficiency. Under a solar simulator, under standard one sun (AM 1.5G, 100 mW / cm 2 ), the area of the test mask was 1.01 cm 2 , the scanning speed was 20 mV / s, and the I-V results obtained through forward and reverse scans were as follows: The device conversion efficiency of the perovskite solar cell prepared by regulating the dielectric constants of the perovskite light-absorbing layer and the SnO2 electron transport layer by the 4-methylsulfonylphenylamidine (SPA) dipole layer could reach 26.26% (see Figure 5 ), which was significantly beneficial compared to Comparative Examples 4, 5, and 6.

[0106] Table 1. Performance parameters of perovskite solar cells prepared by dipole layer modulation.

[0107]

[0108] As can be seen from Table 1, when the dielectric constants of the perovskite light-absorbing layer and the SnO2 layer are synchronously regulated by the 4-methylsulfonylphenylamidine (SPA) dipole layer, the performance such as the photoelectric conversion efficiency of the fabricated normal perovskite solar cells is significantly improved. On the contrary, the photoelectric conversion efficiency of the normal perovskite solar cells fabricated with 4-fluoroaniline (FPN) which also has the properties of a dipole layer is much lower than that using the 4-methylsulfonylphenylamidine (SPA) dipole layer, showing the uniqueness of the 4-methylsulfonylphenylamidine (SPA) dipole layer preparation method rather than a random choice. In addition, the efficiency of the normal perovskite solar cells fabricated with the p-tolylamidine (MPA) dipole layer and the methylsulfonyltoluene (MPS) dipole layer with amidino or methylsulfonyl group is lower than that of the 4-methylsulfonylphenylamidine (SPA) dipole layer with both amidino and methylsulfonyl group, showing the specific property of the 4-methylsulfonylphenylamidine (SPA) dipole layer.

[0109] Figure 5 Current-voltage characteristic curves of the perovskite solar cells of Example 6 and Comparative Examples 4, 5, 6, and 7 of the present disclosure. The open-circuit voltage of the device fabricated with the 4-methylsulfonylphenylamidine (SPA) dipole layer can be significantly increased to 1.18 V. This is the result of the two-way dielectric constant regulation of the dipole layer, which improves the dielectric matching environment and promotes the charge transport performance, showing that the dielectric regulation of the 4-methylsulfonylphenylamidine (SPA) dipole layer can greatly improve the photoelectric conversion efficiency of the device.

[0110] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A heterojunction for improving charge transport, characterized in that: include: A SnO2 electron transport layer and a perovskite light absorbing layer, wherein a dipole layer is compounded between the SnO2 electron transport layer and the perovskite light absorbing layer, wherein the material of the dipole layer is 4-methylsulfonylphenylamidine, and the perovskite light absorbing layer is a FA, FAMA or FAMACs system.

2. The heterojunction for improving charge transport according to claim 1, characterized in that: The thickness of the SnO2 electron transport layer is 50 nm to 400 nm; and / or the thickness of the dipole layer is 10 nm to 200 nm; and / or the thickness of the perovskite light absorption layer is 400 nm to 800 nm.

3. The method for preparing a heterojunction for improving charge transport according to claim 1 or 2, characterized in that: The following steps are involved: S1, depositing a SnO2 electron transport layer on a transparent conductive substrate; S2, depositing a dipole layer made of 4-methylsulfonylphenylamidine on the surface of the obtained SnO2 electron transport layer; S3. Depositing a perovskite light absorbing layer on the surface of the obtained dipole layer.

4. The preparation method according to claim 3, characterized in that: The transparent conductive substrate is FTO glass or ITO glass; and / or the transparent conductive substrate has a thickness of 10 nm to 500 nm.

5. The preparation method according to claim 3, characterized in that: Step S2 specifically includes: 4-Methylsulfonylbenzeneamidine was dissolved in an alcohol solvent at a concentration of 0.10-2.00 mg / mL and then deposited by spin coating to obtain a dipole layer.

6. A perovskite solar cell, characterized in that: The heterojunction according to claim 1 or 2 is used.

7. The perovskite solar cell according to claim 6, characterized in that: It also includes a transparent conductive substrate, a hole transport layer and a metal electrode.

8. The perovskite solar cell according to claim 6, characterized in that: The structure of perovskite solar cells is either a nip formal structure or a pin trans structure.

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