Heterojunction for improving charge transfer, preparation method thereof and perovskite solar cell

Abstract

The invention discloses a heterojunction for improving charge transfer, a preparation method of the heterojunction and a perovskite solar cell, and relates to the field of perovskite solar cells. The heterojunction for improving charge transfer comprises a SnO2 electron transfer layer and a perovskite light absorption layer, a dipole layer is compounded between the SnO2 electron transfer layer and the perovskite light absorption layer, and the material of the dipole layer is 4-methylsulfonyl phenylamidine. According to the invention, 4-methylsulfonyl phenylamidine (SPA) dipole molecules are adopted to successfully realize the increase of the synchronous dielectric constant of the heterojunction, and the dielectric property of the heterojunction is adjusted to a balanced state; the photogenerated exciton dissociation energy of the perovskite photoactive layer is effectively reduced, and exciton dissociation is promoted to generate free electrons and holes; capturing of electrons by interface state traps is successfully shielded, and recombination loss is inhibited; the interface charge transfer barrier is effectively reduced, and the energy level arrangement is promoted; the problem that the charge transmission performance of a heterogeneous interface is low is effectively solved, and the photoelectric conversion efficiency of long-term operation of the device is improved.

Description

Technical Field

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

[0002] Among many solar cells, perovskite solar cells (PVSC) have important application prospects in the optoelectronic field due to their good light absorption, excellent charge transfer rate, and adjustable band gap. Among them, single-junction perovskite solar cells have achieved a power conversion efficiency (PCE) of 26.7%, and are the most promising alternatives to relatively expensive polysilicon, copper indium gallium selenide (CIGS), and cadmium telluride (CdTe) solar cells on the market. However, due to the interface limitations of the perovskite photoactive layer (referred to as the perovskite light absorption layer) and the charge transport layer of the heterogeneous structure of perovskite solar cells, the improvement of charge transfer 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 absorber and charge transport layer are the main generating and collecting parts of photogenerated charge carriers. Its charge dynamics (including charge extraction, charge transfer and charge recombination) occur at the heterojunction interface formed by the perovskite absorber and the charge transport layer. It is worth noting 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 between the perovskite absorber and the charge transport layer (such as high defect density and low perovskite crystallinity) causes the charge transfer loss on the bottom surface of the perovskite to be more serious than that on the top surface of the perovskite. In addition, the defects at the interface lead to charge accumulation and recombination losses, which further lead to the degradation of device performance and have an adverse effect on the stability of the device. Current strategies mainly focus on interface modification (such as the use of passivators) to reduce the recombination losses caused by defects at the interface and control the energy level arrangement to improve the charge transfer efficiency. However, these strategies are usually accompanied by numerous side effects, such as passivator degradation, interfacial reactions, induced ion migration, etc., which result in ineffective actual effects and seriously affect the photovoltaic performance and long-term operating stability of perovskite solar cell devices.

[0004] Therefore, how to avoid the disadvantages of interface modification and effectively break through the interface limitations between heterojunctions to construct efficient charge transfer channels is of great significance to improving the efficiency of perovskite solar cells. Summary of the invention

[0005] The purpose of the present invention is to provide a method for regulating dielectric constant to prepare a perovskite solar cell with high charge transfer performance, aiming at the high defect density barrier and low charge transfer efficiency at the interface of the heterojunction (perovskite light absorbing layer and tin dioxide (SnO2) electron transport layer). Before pre-depositing the perovskite light absorbing layer, a dipole molecule 4-methylsulfonylphenylamidine (SPA) containing methylsulfonyl and amidine functional groups with different polarities is used to uniformly deposit on the surface of the prepared SnO2 electron transport layer to form an interface dipole layer, and then the perovskite light absorbing layer is deposited on the dipole layer. Under the bidirectional synchronous regulation of the dielectric constants of the perovskite light absorbing layer and the SnO2 layer by the SPA dipole layer, the dielectric constant is increased and the dielectric properties compatible with the perovskite light absorbing layer and the SnO2 layer are balanced, thereby achieving the improvement of the charge transfer performance of the heterojunction interface and realizing a perovskite solar cell with 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 comprises: a SnO2 electron transport layer and a perovskite light absorption layer, wherein a dipole layer is composited between the SnO2 electron transport layer and the perovskite light absorption 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~400 nm; and / or the thickness of the dipole layer is 10 nm~200 nm; and / or the thickness of the perovskite light absorption layer is 400 nm~800 nm.

[0009] According to another aspect of the present invention, the present invention also provides a method for preparing a heterojunction for improving charge transport, comprising the following steps:

[0010] S1, depositing a SnO2 electron transport layer on a transparent conductive substrate;

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

[0012] S3. Depositing a 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 transparent conductive substrate has a thickness of 10 nm to 500 nm.

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

[0015] As a further preferred technical solution of the present invention, step S2 specifically comprises: dissolving 4-methylsulfonylbenzeneamidine in an alcohol solvent at a concentration of 0.10-2.00 mg / mL, and then depositing by spin coating, wherein the specific deposition process is: a rotation speed of 1000-3000 rpm, a time of 10-30 s, a deposition annealing temperature of 100 °C (specifically adjusted according to the boiling point properties of the selected alcohol solvent), and a time of ≤30 min. It is further preferred that the purity of 4-methylsulfonylbenzeneamidine 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 a one-step method, a two-step method, etc. It is further preferred that 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, spray coating, slit 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 adopts 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 arranged 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-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA), polytrihexylthiophenol (P3HT), nickel oxide and a combination thereof, and the thickness of the hole transport layer is 10nm~400nm; the metal electrode can be selected from gold or silver; and 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 a nip formal structure or a pin trans structure.

[0020] The principle of the present invention is that in the preparation process of a heterojunction (perovskite light absorbing layer and SnO2 electron transport layer) for improving charge transport, a dipole layer is introduced into the heterojunction interface by using 4-methylsulfonylphenylamidine (SPA) dipole molecules. Due to the influence of the polarity of the SPA dipole layer itself and the difference in the orientation adsorption of the groups, the amidine groups are oriented to be adsorbed on the perovskite light absorbing layer and the methylsulfonyl groups are oriented to be adsorbed on the SnO2 layer, thereby simultaneously changing the polarizability of the perovskite light absorbing layer and the SnO2 layer, resulting in an increase effect of the dielectric constant and compatibility of dielectric properties. The prepared heterojunction dielectric properties of the perovskite light absorbing layer and the SnO2 electron transport layer with high dielectric constant and compatibility directly enhance the directional charge transfer 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 the perovskite solar cell device.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention uses 4-methylsulfonylphenylamidine (SPA) dipole molecules for the first time to successfully achieve a synchronous increase in the dielectric constant of the heterojunction and adjust the dielectric properties of the heterojunction to an equilibrium state; effectively reduce the dissociation energy of photogenerated excitons in the perovskite photoactive layer, promote the dissociation of excitons to generate free electrons and holes; successfully shield the capture of electrons by interface state traps and inhibit recombination losses; effectively reduce the interface charge transfer barrier and promote energy level arrangement; effectively solve the problem of inefficient charge transfer performance at the heterojunction interface and improve 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 a variety of perovskite systems and various perovskite preparation methods and is suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below in conjunction with the accompanying 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 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 The dielectric constant diagrams of the films are shown in FIG. 1 , wherein (a) is the dielectric constant diagram of the perovskite films obtained in Example 4 and Comparative Example 1; and (b) is the dielectric constant diagram of the SnO2 films obtained in Example 5 and Comparative Example 2.

[0028] Figure 4 2 are steady-state photoluminescence (PL) spectra of the heterojunctions (perovskite layer and SnO2 layer) of Example 3 and Comparative Example 3.

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

[0030] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

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

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

[0034] Example 1

[0035] A method for preparing a heterojunction in which the dielectric constants of a perovskite light absorption layer and a SnO2 electron transport layer are regulated by a 4-methylsulfonylphenylamidine (SPA) dipole layer to improve charge transport performance comprises the following steps:

[0036] (1) Dissolve 4-methylsulfonylphenylamidine (SPA) powder evenly in methanol solvent at a ratio of 0.15 mg / mL. Shake the solution on a shaker to disperse and dissolve it. Set aside.

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

[0038] (3) The SPA dipole molecule solution obtained in step (1) is deposited on the surface of the SnO2 film by spin coating. The spin coating deposition is performed at 2000 rpm for 20 s, and the deposition annealing temperature is 100 °C for ≤10 min to form a 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 DMF:DMSO=95:5 and 90 mg FAI, 6.9 mg MAI and 9 mg MACl in 1 mL IPA was deposited on the SPA dipole layer by spin coating. Spin coating deposition (2000 rpm) was performed for 30 s. The deposition annealing temperature was 150°C for ≤10 min to obtain a perovskite light absorbing layer, and finally a heterojunction was formed that simultaneously increased the dielectric constants of the perovskite layer and the SnO2 electron transport layer.

[0040] Example 2

[0041] A method for preparing a heterojunction in which the dielectric constants of a perovskite light absorption layer and a SnO2 electron transport layer are regulated by a 4-methylsulfonylphenylamidine (SPA) dipole layer to improve charge transport performance comprises the following steps:

[0042] (1) Dissolve 4-methylsulfonylphenylamidine (SPA) powder evenly in ethanol solvent at a ratio of 0.15 mg / mL. Shake the mixture on a shaker to disperse and dissolve it. Set aside.

[0043] (2) Dissolve 15% (water dispersion system) SnO2 in deionized water at a ratio of 1:3, and obtain SnO2 thin film by spin coating deposition (2000 rpm) for 30 s. The deposition annealing temperature is 150 °C for ≤15 min.

[0044] (3) The SPA dipole molecule solution obtained in step (1) is deposited on the surface of the SnO2 film by spin coating. The spin coating deposition is performed at 2000 rpm for 20 s, and the deposition annealing temperature is 110 °C for ≤10 min to form a 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 DMF:DMSO=95:5 and 90 mg FAI, 6.9 mg MAI and 9 mg MACl in 1 mL IPA was deposited on the SPA dipole layer by spin coating. Spin coating deposition (2000 rpm) was performed for 30 s. The deposition annealing temperature was 150°C for ≤10 min to obtain a perovskite light absorbing layer, and finally a heterojunction was formed that simultaneously increased the dielectric constants of the perovskite layer and the SnO2 electron transport layer.

[0046] Example 3

[0047] A method for preparing a heterojunction by regulating the dielectric constants of a perovskite light absorption layer and a SnO2 electron transport layer by a 4-methylsulfonylphenylamidine (SPA) dipole layer to improve charge transport performance comprises the following steps.

[0048] (1) Dissolve 4-methylsulfonylphenylamidine (SPA) powder evenly in isopropyl alcohol (IPA) solvent at a ratio of 0.15 mg / mL. Shake the mixture on a shaker to disperse and dissolve it. Set aside.

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

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

[0051] (4) The SPA dipole layer deposited in step (3) was deposited on the SPA dipole layer by spin coating using a perovskite precursor solution prepared by dissolving 1.5 mmol PbI2 in 1 mL DMF:DMSO=95:5 and 90 mg FAI, 6.9 mg MAI and 9 mg MACl in 1 mL IPA. The solution was deposited by spin coating (2000 rpm) for 30 s and annealing at 150°C for ≤10 min to obtain a perovskite light absorbing layer, thereby finally forming a heterojunction that simultaneously increases the dielectric constant of the perovskite layer and the SnO2 electron transport layer.

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

[0053] Example 4

[0054] A method for preparing a device for increasing the dielectric constant of a perovskite layer by using a 4-methylsulfonylphenylamidine (SPA) dipole layer comprises the following steps.

[0055] (1) Preparation of transparent conductive substrate: A 2.5 cm × 2.5 cm etched ITO conductive glass substrate was cleaned in detergent, acetone, deionized water and isopropanol by ultrasonic treatment for 15 min in sequence. It was then blown dry with N2 and placed in a plasma cleaner to treat the ITO substrate with UV-ozone for 10 min.

[0056] (2) Dissolve 4-methylsulfonylphenylamidine (SPA) powder evenly in isopropyl alcohol (IPA) solvent at a ratio of 0.15 mg / mL. Shake the mixture on a shaker to disperse and dissolve it. Set aside.

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

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

[0059] (5) Take an appropriate amount of the lead iodide precursor solution in step (4) and spin-coat it on the annealed and cooled SPA dipole layer at a speed of 1500 rpm for 30 s. After the first annealing treatment, a lead iodide film is obtained. Take an appropriate amount of the organic ammonium salt solution in step (4) and spin-coat it on the lead iodide 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 metal electrode: The product obtained in step (5) is placed in an evaporator, and Ag is evaporated on the surface of the hole transport layer under high vacuum to obtain a metal electrode Ag, thereby preparing a perovskite layer device with an increased dielectric constant, the structure of which is as follows: Figure 2 As shown in (a) in .

[0061] Example 5

[0062] A method for preparing a device for increasing the dielectric constant of a SnO2 layer by using a 4-methylsulfonylphenylamidine (SPA) dipole layer comprises the following steps.

[0063] (1) Preparation of transparent conductive substrate: A 2.5 cm × 2.5 cm etched ITO conductive glass substrate was cleaned in detergent, acetone, deionized water and isopropanol by ultrasonic treatment for 15 min in sequence. It was then blown dry with N2 and placed in a plasma cleaner to treat the ITO substrate with UV-ozone for 10 min.

[0064] (2) Dissolve 4-methylsulfonylphenylamidine (SPA) powder evenly in isopropyl alcohol (IPA) solvent at a ratio of 0.15 mg / mL. Shake the mixture on a shaker to disperse and dissolve it. Set aside.

[0065] (3) Dissolve 15% (water dispersion system) SnO2 in deionized water in a ratio of 1:3 to form a SnO2 solvent. Shake continuously to mix well and set aside.

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

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

[0068] (6) Evaporation of metal electrode: The product obtained in step (5) is placed in an evaporator, and Ag is evaporated on the surface of the hole transport layer under high vacuum to obtain a metal electrode Ag, thereby preparing a SnO2 layer device with an increased dielectric constant, the structure of which is as follows: Figure 2 As shown in (b) in .

[0069] Example 6

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

[0071] (1) Preparation of transparent conductive substrate: A 2.5 cm × 2.5 cm etched ITO conductive glass substrate was cleaned in detergent, acetone, deionized water and isopropanol by ultrasonic treatment for 15 min in sequence. It was then blown dry with N2 and placed in a plasma cleaner to treat the ITO substrate with UV-ozone for 10 min.

[0072] (2) Preparation of SnO2 electron transport layer: SnO2 (2.67 wt% aqueous solution) was spin coated on the surface of ITO conductive glass substrate at 3000 rpm for 30 s and thermally annealed at 150 °C in air for 30 min.

[0073] (3) Preparation of 4-methylsulfonylbenzeneamidine (SPA) dipole layer: Dissolve 4-methylsulfonylbenzeneamidine (SPA) powder evenly in isopropyl alcohol (IPA) solvent at a ratio of 0.15 mg / mL, and heat on a shaker at 50 °C for 10 min to disperse and dissolve the mixture for later use.

[0074] Take an appropriate amount of the obtained SPA dipole molecule solution and drop it on the surface of the annealed and cooled SnO2 film. Spin coating is performed at a speed of 2000 rpm for 30 seconds. Thermal annealing is performed at 100 °C in air for 15 minutes to complete the preparation of the SPA dipole layer.

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

[0076] Prepare lead iodide precursor solution: weigh 1.5 mmol PbI2 and dissolve it in 1 mL DMF:DMSO=95:5 solvent, heat on a hot plate at 60 °C overnight and set aside.

[0077] Prepare organic ammonium salt solution: dissolve 90 mg FAI, 6.9 mg MAI and 9 mg MACl in 1 mL IPA, then place on a shaker to fully dissolve and set aside.

[0078] Preparation of lead iodide film: spin-coat an appropriate amount of 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, a lead iodide film is obtained.

[0079] Preparation of perovskite film: spin coating an organic ammonium salt solution on the lead iodide film at a speed of 2000 rpm for 30 seconds, and after a second annealing treatment, a perovskite light-absorbing layer is obtained.

[0080] (5) Preparation of Spiro-OMeTAD hole transport layer: Dissolve 72.3 mg of Spiro-OMeTAD powder in 1 mL of chlorobenzene, add 28.85 μL of tert-butylpyridine and 17.5 μL of 520 mg / mL lithium bis(trifluoromethanesulfonyl)imide / acetonitrile solution, mix and place 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 film. The spin coating speed is 4000 rpm and the spin coating time is 30 s to complete the preparation of the hole transport layer.

[0082] (6) Evaporation of metal electrode: The product obtained in step (5) is placed in an evaporator, and Ag is evaporated on the surface of the hole transport layer under high vacuum to obtain a metal electrode Ag, thereby obtaining Figure 1 Perovskite solar cell with the shown structure.

[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 there is no need to deposit a 4-methylsulfonylphenylamidine (SPA) dipole layer, that is, there is no need to perform steps (2) and (3) in Example 4 to deposit a perovskite light absorbing layer on the surface of the ITO conductive glass substrate.

[0085] The dielectric constant of the perovskite film obtained in step (6) of Example 4 and Comparative Example 1 was tested and analyzed. The results are shown in Figure 3 In (a), it can be seen that the dielectric constant of the obtained perovskite film is greatly improved. Figure 3 (a) in the figure shows that the dielectric constant of the perovskite light absorbing layer regulated by the 4-methylsulfonylphenylamidine (SPA) dipole layer increases significantly, proving that the amidine group orientation of the dipole molecule SPA in the perovskite light absorbing layer changes the polarizability and thus significantly increases 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 a 4-methylsulfonylphenylamidine (SPA) dipole layer, that is, there is no need to perform steps (2) and (5) in Example 5 to deposit a SnO2 layer on the surface of the ITO conductive glass substrate.

[0088] The dielectric constant of the SnO2 film obtained in step (6) of Example 5 and Comparative Example 2 was tested and analyzed. The results are shown in Figure 3 In (b), it can be seen that the dielectric constant of the obtained SnO2 film is greatly improved. Figure 3 (b) in the figure shows that the dielectric constant of the SnO2 layer regulated by the 4-methylsulfonylphenylamidine (SPA) dipole layer is significantly increased, proving that the methylsulfonyl group orientation of the dipole molecule SPA in the SnO2 layer changes the polarizability and thus significantly increases the dielectric constant value.

[0089] based on Figure 3 It can be seen 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 it is not necessary to deposit a 4-methylsulfonylphenylamidine (SPA) dipole layer, that is, step (3) in Example 3 is not required.

[0092] The heterojunction (perovskite light absorbing layer and SnO2 layer) obtained in step (4) of Example 3 and Comparative Example 3 was subjected to steady-state photoluminescence (PL) spectroscopy analysis. The results are shown in Figure 4 .Depend on Figure 4 It can be seen that the PL spectrum intensity tested by the technical solution provided by the present invention is greatly reduced, which proves the reduction of interface recombination of efficient interface charge transfer performance 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 a 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 a dipole layer. FPN has a 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 para-amidinotoluene (MPA) as a dipole layer. MPA has a 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 a dipole layer. MPS has a molecular structure shown in formula (4):

[0103] Formula (4).

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

[0105] The perovskite solar cells obtained in Example 6 and Comparative Examples 4-7 were tested for photoelectric conversion efficiency under a solar simulator with a standard one-sun light (AM 1.5G, 100 mW / cm 2 ), test mask area 1.01 cm 2 , scanning speed 20 mV / s, the IV results of the forward and reverse scan tests are: the device conversion efficiency of the perovskite solar cell prepared by regulating the dielectric constants of the perovskite light absorption layer and the SnO2 electron transport layer by the 4-methylsulfonylphenylamidine (SPA) dipole layer can reach 26.26% (see Figure 5 ), which is obviously beneficial to Comparative Examples 4, 5 and 6.

[0106] Table 1. Device performance parameters of perovskite solar cells prepared by dipole layer regulation.

[0107]

[0108] As can be seen from Table 1, when the 4-methylsulfonylbenzeneamidine (SPA) dipole layer is used to synchronously regulate the dielectric constant of the perovskite light-absorbing layer and the SnO2 layer, the photoelectric conversion efficiency and other properties of the prepared formal perovskite solar cell are significantly improved. On the contrary, the photoelectric conversion efficiency of the formal perovskite solar cell prepared by 4-fluoroaniline (FPN), which also has the properties of a dipole layer, is much lower than that using the 4-methylsulfonylbenzeneamidine (SPA) dipole layer, showing the uniqueness of the 4-methylsulfonylbenzeneamidine (SPA) dipole layer preparation method, rather than a random choice. In addition, the efficiency of the formal perovskite solar cell prepared by the para-amidinotoluene (MPA) dipole layer and the methylsulfonyltoluene (MPS) dipole layer with an amidine group or a methylsulfone group is lower than that of the 4-methylsulfonylbenzeneamidine (SPA) dipole layer with both an amidine group and a methylsulfone group, showing the specific properties of the 4-methylsulfonylbenzeneamidine (SPA) dipole layer.

[0109] Figure 5 The current-voltage characteristic curves of the perovskite solar cells of Example 6 of the present disclosure and Comparative Examples 4, 5, 6, and 7. The open circuit voltage of the device prepared by the 4-methylsulfonylphenylamidine (SPA) dipole layer can be significantly increased to 1.18V, which is the result of the bidirectional dielectric constant regulation of the dipole layer, and the improvement of the dielectric adaptation environment promotes the charge transfer 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 specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only 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 absorption layer, wherein a dipole layer is compounded between the SnO2 electron transport layer and the perovskite light absorption layer, and the material of the dipole layer is 4-methylsulfonylbenzeneamidine.

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 S1 specifically includes: A 15% (water dispersion system) SnO2 solution was mixed with water in a ratio of 1:3, and then spin coating was used for deposition to obtain a SnO2 electron transport layer.

6. 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.

7. The preparation method according to claim 3, characterized in that: The perovskite light-absorbing layer is a FA, FAMA or FAMACs system.

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

9. The perovskite solar cell according to claim 8, characterized in that: It also includes a transparent conductive substrate, a hole transport layer and a metal electrode.

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

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