Perovskite solar cell based on lithium bis (oxalate) borate interface modification

Abstract

The invention relates to the technical field of solar photovoltaics, in particular to a perovskite solar cell based on lithium bis (oxalate) borate interface modification. The method comprises the following steps: 1, cleaning an FTO glass substrate; step 2, preparing a lithium bis (oxalate) borate aqueous solution; step 3, preparing a lithium bis (oxalate) borate / TiO2 electron transport layer; step 3, preparing a perovskite absorption layer; 4, preparing a hole transport layer; 5, Au electrode evaporation is carried out; and step 6, testing the photoelectric conversion efficiency of the battery device. According to the invention, the surface of TiO2 is modified by using a lithium bis (oxalate) borate aqueous solution, and the electron transport layer which is low in price and environment-friendly is prepared. Meanwhile, the conductivity of TiO2 is improved, the charge extraction rate of carriers at a TiO2 interface is improved, the photoelectric conversion efficiency of a perovskite solar cell device is effectively improved, and an effective way is provided for preparing an efficient and stable perovskite solar cell.

Description

Technical Field

[0001] The present invention relates to the technical field of solar photovoltaics, and specifically to a perovskite solar cell based on the interfacial modification of lithium bis(oxalato)borate. Background Art

[0002] The perovskite light-absorbing layer has many excellent optoelectronic properties such as a high absorption coefficient, a low exciton binding energy, and an almost ideal bandgap. In the past decade, it has become a research hotspot in the photovoltaic industry. Currently, the certified efficiency of perovskite solar cells has reached 26.1%.

[0003] In a perovskite solar cell device, the electron transport layer is located under the perovskite light-absorbing layer, which can effectively improve the carrier transport efficiency. By modifying the surface of the electron transport layer, the conductivity of the electron transport layer can be greatly improved, the non-radiative recombination of carriers between the perovskite layer and the electron transport layer can be reduced, and the open-circuit voltage of the perovskite solar cell device can be increased. In addition, the modified electron transport layer can reduce the defects at the bottom of the perovskite layer, improve the crystallization effect of the perovskite transport layer, and improve the film quality of the perovskite light-absorbing layer.

[0004] In recent years, researchers have developed electron transport layer materials such as mesoporous TiO2, SnO2, C 60 、planar TiO2, etc. However, there are still a large number of difficulties and challenges in the industrial application of these electron transport layer materials. The SnO2 electron transport layer has problems such as complex preparation conditions, poor crystallization quality, and low fill factor of the final device, which is not conducive to industrial production; C 60 The problems of its own stability and high cost of the electron transport layer seriously hinder the large-scale industrial production; the mesoporous TiO2 electron transport layer has problems such as complex preparation process, high preparation temperature, and serious hysteresis phenomenon of the final device; The most promising planar TiO2 electron transport layer for industrialization has problems such as poor conductivity and mismatch of energy levels with high-performance perovskite light-absorbing layers. The TiO2 thin film prepared by the traditional spin coating method and chemical bath deposition method has a large number of defects due to the residual solvent on its surface, which results in poor conductivity on the surface of the TiO2 thin film and interfacial recombination loss during charge transport.

[0005] Therefore, finding a green, stable, and low-cost additive to modify the planar TiO2 electron transport layer is one of the key topics for accelerating the large-scale production of perovskite solar cells. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the present invention provides a perovskite solar cell based on lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof. By utilizing the advantages of good film-forming property, high conductivity and high solubility of lithium bis(oxalato)borate, lithium bis(oxalato)borate is used as an intermediate modification material between the perovskite light-absorbing layer and the TiO2 electron transport layer. The lithium bis(oxalato)borate / TiO2 electron transport layer greatly improves the surface conductivity and energy level structure of the TiO2 thin film, thereby reducing the non-radiative recombination of carrier transport between the perovskite layer and the electron transport layer. At the same time, the modified TiO2 electron transport layer can effectively improve the crystallization of the perovskite thin film, greatly reducing the defects at the bottom of the perovskite light-absorbing layer, so that the final perovskite solar cell device has more excellent optoelectronic performance and operation stability. The present invention provides an effective design idea and method for the industrial large-scale preparation of high-performance and low-cost formal perovskite solar cell electron transport layer materials.

[0007] The present invention is realized through the following technical solutions: A perovskite solar cell based on lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof, including the following steps, Step 1, cleaning the FTO glass substrate: Select FTO transparent conductive glass (2.45*2.45 cm 2 ), wipe the surface impurities with a dust-free paper, and then ultrasonically treat with a cleaner, ultrapure water, ethanol and isopropanol for 18 minutes each in turn. After drying with a nitrogen gun, it is treated with ultraviolet ozone for later use; Step 2, preparing an aqueous solution of lithium bis(oxalato)borate: First, prepare aqueous solutions of lithium bis(oxalato)borate with different concentrations; Mix different weights of lithium bis(oxalato)borate and ultrapure water, and stir at 10~50°C for 5~10 hours to obtain an aqueous solution of lithium bis(oxalato)borate; Step 3, preparing the lithium bis(oxalato)borate / TiO2 electron transport layer; Leave a common electrode of 0.45*2.45 cm on the FTO substrate with a polyimide tape, and treat it with ultraviolet ozone for 6~36 minutes; use the chemical bath method to grow at a constant temperature for 60 minutes to obtain a uniform and dense planar TiO2 electron transport layer. 2 Spin-coat the aqueous solution of lithium bis(oxalato)borate onto the surface of TiO2, and perform high-temperature annealing and ultraviolet ozone treatment;

[0008] Spin-coat the aqueous solution of lithium bis(oxalato)borate onto the surface of TiO2, and perform high-temperature annealing and ultraviolet ozone treatment; Step 4, preparing the perovskite absorption layer thin film; First, weigh three solutes with a molar ratio of PbI2:CH(NH2)2I:MACl = 1:0.92:0.08, and dissolve them in a mixed solvent with a ratio of DMSO:DMF = 1:1.5, 1:3.5 or GBL:DMSO = 7.2:2.8; drop the perovskite precursor solution onto the surface of lithium bis(oxalato)borate / TiO2; The spin-coating process includes two stages, namely 800 rpm for 8 s and 4900 rpm for 25 s; at the same time, quickly drop anhydrous ether onto the surface of the perovskite wet film during spin-coating, and quickly anneal the obtained perovskite wet film.

[0009] Step 5, prepare the hole transport layer; Blow the surface of the annealed perovskite film clean, and spin-coat the prepared Spiro-OMeTAD solution onto the surface of the perovskite film to obtain the hole transport layer.

[0010] Step 6, evaporate electrodes on the above-prepared film to obtain a complete perovskite solar cell device.

[0011] Step 7, use a standard solar simulator to test the battery efficiency.

[0012] Preferably, in step 1, the cleaned and dried FTO is treated with ultraviolet ozone for 6 - 36 minutes to remove surface contamination and increase the surface wettability of FTO.

[0013] Preferably, in step 2, the concentration of the aqueous solution of lithium bis(oxalato)borate configured is 0.3 - 13 mg / mL.

[0014] Mix lithium bis(oxalato)borate and ultrapure water, and stir at 10 - 50 °C for 5 - 10 hours to obtain an aqueous solution of lithium bis(oxalato)borate.

[0015] Preferably, in step 3, the spin-coating process of the aqueous solution of lithium bis(oxalato)borate is 300 - 6300 rpm for 33 - 70 s.

[0016] Preferably, in step 3, the annealing temperature after spin-coating lithium bis(oxalato)borate is 80 - 160 °C for 12 - 62 minutes; the ultraviolet ozone treatment is 8 - 25 minutes.

[0017] Preferably, in step 3, the thickness of the lithium bis(oxalato)borate / TiO2 electron transport layer is 33 - 53 nm.

[0018] Preferably, in step 4, the molar ratio of solutes in the perovskite precursor solution is three solutes of PbI2:CH(NH2)2I:MACl = 1:0.92:0.08, and they are dissolved in a mixed solvent with a ratio of DMSO:DMF = 1:1.5, 1:3.5 or GBL:DMSO = 7.2:2.8; Preferably, in step 4, the relationship between the volume of the perovskite solution to be dropped and the area of the FTO substrate is 8.5~13.5 μL / cm 2 .

[0019] Preferably, in step 4, the time for dropping the antisolvent anhydrous diethyl ether is 10~25 s remaining until the end of the second section, and the amount of the antisolvent anhydrous diethyl ether dropped is 300~1200 mL on the surface of the perovskite wet film.

[0020] Preferably, in step 5, the perovskite film prepared by the one-step spin-coating method is rapidly annealed, and the annealing conditions are 110~190 °C for 12~65 minutes.

[0021] Preferably, in step 5, the thickness of the perovskite light-absorbing layer is 390~650 nm.

[0022] Preferably, in step 6, when preparing the hole transport layer solution, 21.5 μL of a pre-prepared Li-TFSI solution (510 mg / mL) and 37.5 μL of a tBP solution need to be added to a chlorobenzene solution of 90 mg / mL Spiro-OMeTAD, stirred at room temperature in the dark for 3~7 hours, and then filtered with a polytetrafluoroethylene filter membrane with a pore size of 0.22 μm for standby.

[0023] Preferably, in step 6, the relationship between the volume of the hole transport layer solution to be dropped and the area of the FTO substrate is 6.7~9.3 μL / cm 2 .

[0024] Preferably, in step 6, the spin-coating process of the hole transport layer is 4900 rpm, 28 s.

[0025] Preferably, in step 6, the thickness of the Spiro hole transport layer is 160~260 nm.

[0026] Preferably, in step 7, the scanning rate of the solar simulator is 0.1~0.8 V / s, the delay time is 10~200 ms, and the scanning step width is 0.01~0.04 V.

[0027] A perovskite solar cell device based on a lithium bis(oxalato)borate / TiO2 electron transport layer is prepared by the preparation method described in the present invention.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects: Taking advantage of the good film-forming property, high conductivity and high solubility of lithium bis(oxalato)borate, lithium bis(oxalato)borate is used as an intermediate modification material between the perovskite light-absorbing layer and the TiO2 electron transport layer. The lithium bis(oxalato)borate / TiO2 electron transport layer has strong surface conductivity, and its LUMO energy level is more matched with the conduction band of the perovskite absorption layer, greatly reducing the non-radiative recombination of carrier transport between the perovskite layer and the electron transport layer. At the same time, the modified TiO2 electron transport layer can effectively improve the crystallization of the perovskite film, significantly reducing the defects at the bottom of the perovskite light-absorbing layer, so that the final perovskite solar cell device obtains a maximum photoelectric conversion efficiency of 24.30% under the test conditions of one standard sunlight (AM1.5G). The modification process is low-cost, simple, green and has excellent optoelectronic properties, which will help to accelerate the large-scale industrial production of perovskite solar cells. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of a high-efficiency formal perovskite solar cell prepared in Example 2 of the present invention; Figure 2 It is a schematic flow chart of preparing the lithium bis(oxalato)borate / TiO2 electron transport layer and the perovskite absorption layer film in Example 2 of the present invention; Figure 3 It is a comparative X-ray diffraction (XRD) diagram of the perovskite film on the lithium bis(oxalato)borate / TiO2 prepared by the method described in Example 2 of the present invention and the traditional TiO2 substrate.

[0030] Figure 4 It is a comparative steady-state fluorescence diagram of the perovskite film on the lithium bis(oxalato)borate / TiO2 prepared by the method described in Example 2 of the present invention and the traditional TiO2 substrate.

[0031] Figure 5 It is a comparative photoelectric conversion efficiency diagram of the perovskite film on the lithium bis(oxalato)borate / TiO2 prepared by the method described in Example 2 of the present invention and the traditional TiO2 substrate. Detailed Description of the Invention

[0032] To make the technical route and advantages of the present invention clearer, the following specific embodiments are used to further elaborate the present invention in detail. The following is an explanation rather than a limitation of the present invention.

[0033] The present invention is a perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof, including the following steps: Step 1, cleaning the FTO glass substrate: Select an FTO transparent conductive glass (2.45 * 2.45 cm 2), wipe the surface impurities with lint-free paper, then ultrasonically clean with detergent, ultrapure water, ethanol, and isopropyl alcohol for 18 minutes each in sequence. After drying with a nitrogen gun, treat with ultraviolet ozone for later use; Step 2, prepare an aqueous solution of lithium bis(oxalato)borate: First, prepare aqueous solutions of lithium bis(oxalato)borate with different concentrations; Mix different weights of lithium bis(oxalato)borate and ultrapure water, and stir at 10 - 50 °C for 5 - 10 hours to obtain an aqueous solution of lithium bis(oxalato)borate; Step 3, prepare a lithium bis(oxalato)borate / TiO₂ electron transport layer; Leave a 0.45 * 2.45 cm 2 common electrode on the FTO substrate, and treat with ultraviolet ozone for 6 - 36 minutes; Use the chemical bath method to grow at a constant temperature for 60 minutes to obtain a uniform and dense planar TiO₂ electron transport layer.

[0034] Spin-coat the lithium bis(oxalato)borate aqueous solution onto the TiO₂ surface with a spin-coating process of 300 - 6300 rpm for 33 - 70 s, anneal at 80 - 160 °C for 12 - 62 minutes, and treat with ultraviolet ozone for 8 - 25 minutes; Step 4, prepare a perovskite absorption layer film; First, weigh three solutes with a solute molar ratio of PbI₂:CH(NH₂)₂I:MACl = 1:0.92:0.08, and dissolve them in a mixed solvent with a ratio of DMSO:DMF = 1:1.5, 1:3.5 or GBL:DMSO = 7.2:2.8; Drop the perovskite precursor solution onto the surface of lithium bis(oxalato)borate / TiO₂; The spin-coating process includes two stages, which are 800 rpm for 8 s and 4900 rpm for 25 s respectively; At the same time, quickly drop anhydrous ether on the surface of the perovskite wet film during the spin-coating process, and quickly anneal the obtained perovskite wet film at 110 - 190 °C for 12 - 65 minutes.

[0035] Step 5, prepare a hole transport layer; Blow the surface of the annealed perovskite film clean, and spin-coat the prepared Spiro-OMeTAD solution onto the perovskite film surface at a process of 4900 rpm for 28 s to obtain a hole transport layer.

[0036] Step 6, evaporate an electrode with a thickness of 65 - 135 nm on the above-prepared film to obtain a complete perovskite solar cell device.

[0037] Step 7, use a standard solar light simulator at a light intensity of 100 mW / cm 2The photoelectric conversion efficiency of the battery was tested under the condition of

[0038] In the present invention, the structure of the perovskite solar cell device is successively an FTO substrate, a lithium bis(oxalato)borate / TiO2 electron transport layer, a perovskite absorption layer, Spiro-OMeTAD and an Au electrode. The surface of TiO2 is modified with lithium bis(oxalato)borate to prepare an electron transport layer with good conductivity and more matching energy levels with the perovskite absorption layer. At the same time, the crystallization process of the perovskite light-absorbing layer is effectively improved, the non-radiative recombination of carriers at the interface is inhibited, and the photoelectric conversion efficiency of the perovskite solar cell device is improved. Example 1

[0039] A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to the present invention include the following preparation steps: Preparation of perovskite precursor solution: Prepare a perovskite precursor solution with a concentration of 1.28 M, a solute molar ratio of PbI2:CH(NH2)2I:MACl = 1:0.92:0.08; and a solvent ratio of DMSO:DMF = 1:3.5 for 0.92 MA 0.08 PbI3 perovskite precursor solution.

[0040] Preparation of lithium bis(oxalato)borate aqueous solution: First, prepare a lithium bis(oxalato)borate solution with a concentration of 0.7 mg / mL and stir it at 30 °C for 5 hours.

[0041] Preparation of lithium bis(oxalato)borate / TiO2 electron transport layer: Leave a common electrode of 0.45 * 2.45 cm on the FTO substrate with polyimide tape, and perform ultraviolet ozone treatment for 15 minutes; a uniform and dense planar TiO2 electron transport layer is obtained by chemical bath method at a constant temperature for 60 minutes. 2 The common electrode of 0.45 * 2.45 cm is left on the FTO substrate with polyimide tape, and ultraviolet ozone treatment is carried out for 15 minutes; a uniform and dense planar TiO2 electron transport layer is obtained by chemical bath method at a constant temperature for 60 minutes.

[0042] Spin-coat the lithium bis(oxalato)borate aqueous solution onto the TiO2 surface with a spin-coating process of 4000 rpm for 40 s, anneal it at 100 °C for 15 minutes and perform ultraviolet ozone treatment for 10 minutes; Preparation of perovskite absorption layer: Pipette 50 μL of 1.28 M 0.92 MA 0.08 PbI3 perovskite precursor solution is uniformly dropped onto the electron transport layer; a perovskite light-absorbing layer is obtained by spin-coating with a spin-coating process of 800 rpm for 8 s and 3900 rpm for 25 s; at the same time, when there are still 10 - 25 s left at the end of the second section, 800 mL of anti-solvent anhydrous ether is dropped onto the surface of the perovskite wet film, and then the obtained perovskite wet film is annealed and treated on a hot plate at 150 °C for 15 minutes.​

[0043] Preparation of hole transport layer: Pipette 36 μL of 90 mg / mL Spiro-OMeTAD hole transport layer solution and evenly drop it on the perovskite transport layer; obtain the hole transport layer by a spin coating process at 4900 rpm for 28 s, and store the prepared hole transport layer in the dark and dry for 5 hours.

[0044] Preparation of metal electrode: Evaporate a 100-nm-thick gold electrode on the above-prepared film by thermal evaporation method, and the effective area of the battery of the mask is 0.085 cm 2 , and a complete perovskite solar cell device is obtained. Example 2

[0045] A perovskite solar cell based on lithium bis(oxalato)borate / TiO2 electron transport layer and its preparation method according to the present invention include the following preparation steps: Prepare an aqueous solution of lithium bis(oxalato)borate: First, prepare a 0.3 mg / mL lithium bis(oxalato)borate solution and stir it at 30 °C for 5 hours.

[0046] Other steps are the same as those in Example 1.

[0047] Comparative Example 1 In this comparative example, the titanium dioxide electron transport layer was prepared according to the steps of Example 1. The difference from Example 1 is that: during the preparation of the titanium dioxide electron transport layer in step 2, the 0.3 mg / mL lithium bis(oxalato)borate solution was not prepared and spin-coated; the remaining steps remained unchanged. Finally, a perovskite solar cell device was obtained.

[0048] The steady-state fluorescence tests were respectively carried out on the electron transport layers prepared in Example 1 and Comparative Example 1, and the results are as Figure 4 shown. It can be seen that the steady-state fluorescence signal of the perovskite film in Example 1 weakened, indicating that the modified electron transport layer more effectively extracts carriers from the perovskite absorption layer.

[0049] The photoelectric conversion efficiency tests were respectively carried out on the perovskite absorption layers prepared in Example 1 and Comparative Example 1, and the results are as Figure 5 shown. It can be seen that the photoelectric conversion efficiency of the perovskite solar cell device in Example 1 increased from 21.13% in Comparative Example 1 to 24.30%.

Claims

1. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and its preparation method, the characteristics of which include the following steps: Step 1, cleaning the FTO glass substrate: Select an FTO transparent conductive glass (2.45 * 2.45 cm 2 ), wipe the surface impurities with lint-free paper, then ultrasonically treat with a cleaning agent, ultrapure water, ethanol, and isopropanol for 18 minutes each in turn. After drying with a nitrogen gun and ultraviolet ozone treatment, it is ready for use; Step 2, prepare an aqueous solution of lithium bis(oxalato)borate: First, prepare aqueous solutions of lithium bis(oxalato)borate with different concentrations; Mix different weights of lithium bis(oxalato)borate and ultrapure water, and stir at 10 - 50 °C for 5 - 10 hours to obtain an aqueous solution of lithium bis(oxalato)borate; Step 3, prepare a lithium bis(oxalato)borate / TiO2 electron transport layer; Leave a 0.45 * 2.45 cm area of the FTO substrate with polyimide tape 2 for the common electrode, and perform ultraviolet ozone treatment for 6 - 36 minutes; use the chemical bath method to grow a uniform and dense planar TiO2 electron transport layer at a constant temperature; Spin-coat the aqueous solution of lithium bis(oxalato)borate onto the surface of TiO2, and perform high-temperature annealing and ultraviolet ozone treatment; Step 4, prepare a perovskite absorption layer film; First, weigh three solutes with a solute molar ratio of PbI2:CH(NH2)2I:MACl = 1:0.92:0.08, and dissolve them in a mixed solvent with a ratio of DMSO:DMF = 1:1.5, 1:3.5 or GBL:DMSO = 7.2:2.8; drop the perovskite precursor solution onto the surface of lithium bis(oxalato)borate / TiO2; The spin-coating process includes two sections, which are 800 rpm for 8 s and 4900 rpm for 25 s respectively; at the same time, quickly drop anhydrous ether onto the surface of the perovskite wet film during spin-coating, and quickly anneal the obtained perovskite wet film; Step 5, prepare a hole transport layer; Blow the surface of the annealed perovskite film clean, and spin-coat the prepared Spiro-OMeTAD solution onto the surface of the perovskite film to obtain a hole transport layer; Step 6, evaporate electrodes on the above-prepared film to obtain a complete perovskite solar cell device; Step 7, use a standard solar simulator to test the battery efficiency.

2. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to claim 1, characterized in that, In step 1, the prepared FTO substrate is treated with ultraviolet ozone for 6 - 36 minutes to remove surface contamination and increase the surface wettability of FTO.

3. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to claim 1, characterized in that, In step 2, the concentration of the prepared aqueous solution of lithium bis(oxalato)borate is 0.3 - 13 mg / mL.

4. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to claim 1, characterized in that, In step 2, the stirring temperature of the aqueous solution of lithium bis(oxalato)borate is 10 - 50 °C to obtain a clear aqueous solution of lithium bis(oxalato)borate.

5. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to claim 1, characterized in that, In step 2, the stirring time of the aqueous solution of lithium bis(oxalato)borate is 5 - 10 hours.

6. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to claim 1, characterized in that, In step 3, the spin-coating process of the aqueous solution of lithium bis(oxalato)borate is 300 - 6300 rpm for 33 - 70 s.

7. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to claim 1, characterized in that, In step 3, the annealing temperature after spin-coating lithium bis(oxalato)borate is 80 - 160 °C for 12 - 62 minutes; the ultraviolet ozone treatment is 8 - 25 minutes.

8. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to claim 1, characterized in that, In step 4, prepare a 1.28 M perovskite precursor solution; Weigh three solutes with a solute molar ratio of PbI2:CH(NH2)2I:MACl = 1:0.92:0.08, and dissolve them in a mixed solvent with a ratio of DMSO:DMF = 1:1.5, 1:3.5 or GBL:DMSO = 7.2:2.8; stir the mixed solution at room temperature for more than 3 - 7 hours, and filter it with a 0.22 μm pore size polytetrafluoroethylene filter membrane to obtain a perovskite solution.

9. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof according to claim 1, characterized in that, In step 4, when there are still 10 - 25 s left until the end of the second section, 300 - 1200 mL of anhydrous ether is added dropwise onto the surface of the perovskite wet film.

10. A perovskite solar cell based on a lithium bis(oxalato)borate / TiO2 electron transport layer and a preparation method thereof, characterized in that, Prepared by the preparation method according to any one of claims 1 - 7.

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