Preparation methods of lead-free perovskite precursor solution, light absorption layer and solar cell

Abstract

The invention discloses a lead-free perovskite precursor solution, a light absorption layer and a preparation method of a solar cell, and belongs to the technical field of novel thin-film solar cells. By adding a trace amount of cerous oxalate into a precursor solution of lead-free perovskite, a carboxyl group can inhibit non-radiative recombination in a perovskite crystal growth process, and the photovoltaic performance of a perovskite device is improved; the carboxyl group can protect the surface of the lead-free perovskite thin film, inhibit oxidation of Sn < 2 + > and increase the stability of the lead-free perovskite thin film; the trace cerium ions can inhibit harmful p-type doping while inhibiting halogen ion migration, and carboxyl and trivalent ions have a coordination effect, so that the crystallization and growth process of perovskite can be delayed, and the defect density can be reduced, thereby improving the efficiency and stability of the lead-free perovskite solar cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel thin-film solar cells, and particularly relates to a method for preparing a lead-free perovskite precursor solution, an absorbing layer, and a solar cell thereof. Background Art

[0002] At present, perovskite solar cells are in a stage of rapid development. Since achieving a certified efficiency of over 25%, their efficiency level has been comparable to that of mature crystalline silicon solar cells. However, the presence of the heavy metal toxic element lead has severely restricted the development scale and application scenarios of lead-based perovskite solar cells. Therefore, finding a suitable lead-free perovskite material is a research direction with good prospects at present. Lead-free perovskite materials have low toxicity and similar optoelectronic properties to lead-based perovskite materials, thus attracting much attention and being expected to replace lead-based perovskite materials. However, lead-free perovskite materials (tin-based) themselves also have some problems. For example, the 2+ characteristic of being easily oxidized makes the device performance vulnerable to environmental factors; the nucleation rate of lead-free perovskite is fast, and the crystallization rate is difficult to control, resulting in unstable film formation quality. These factors cause the efficiency of lead-free perovskite solar cells to be relatively low, and the reproducibility and stability are poor. Therefore, it is of great significance to explore a new method to improve the efficiency and stability of lead-free perovskite solar cells. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for preparing a lead-free perovskite precursor solution, a lead-free perovskite absorbing layer, and a solar cell thereof. The lead-free perovskite absorbing layer has low cost, good film crystallinity, and high reproducibility. The lead-free perovskite solar cell has a high photoelectric conversion efficiency and good stability.

[0004] The present invention provides a lead-free perovskite precursor solution, which contains cerium oxalate.

[0005] Further, the concentration of cerium oxalate in the lead-free perovskite precursor solution is 0.03 - 0.08 mg / mL.

[0006] In an embodiment of the present invention, the lead-free perovskite precursor solution includes cerium oxalate, methylammonium iodide, formamidinium iodide, stannous iodide, stannous fluoride, and tin powder.

[0007] Preferably, the molar ratio of cerium oxalate, methylammonium iodide, formamidinium iodide, stannous iodide, stannous fluoride, and tin powder is 0.03 - 0.08 mg:0.25 mol:0.75 mol:1.00 mol:0.1 mol:0.01 mol.

[0008] Further, the solvent of the lead-free perovskite precursor solution is one or two of N,N-dimethylformamide and dimethyl sulfoxide.

[0009] Preferably, the solvent is composed of N,N-dimethylformamide and dimethyl sulfoxide in a volume ratio of 3:1 to 4:1.

[0010] In an embodiment of the present invention, the solvent is composed of N,N-dimethylformamide and dimethyl sulfoxide in a volume ratio of 4:1.

[0011] The present invention also provides a lead-free perovskite light-absorbing layer, which is prepared by coating the above-mentioned lead-free perovskite precursor solution on a substrate under a protective atmosphere, dropping an anti-solvent, and then performing an annealing treatment.

[0012] Preferably, the spin coating is set to rotate at 1000 rpm for 8 - 10 s first, and then rotate at 3000 - 6000 rpm for 35 - 50 s.

[0013] Preferably, the anti-solvent is dropped at the 10 - 20 s of spin coating; the volume ratio of the anti-solvent to the precursor solution is 100 - 400:50, and the anti-solvent is chlorobenzene.

[0014] Preferably, the annealing is divided into two steps. The temperature of the first annealing treatment is 30 - 50 °C, and the annealing time is 5 - 10 min. The temperature of the second annealing treatment is 70 - 90 °C, and the annealing time is 5 - 10 min.

[0015] Preferably, the thickness of the lead-free perovskite thin film light-absorbing layer is 200 - 400 nm.

[0016] In addition, the present invention also provides a lead-free perovskite solar cell, which includes the above-mentioned lead-free perovskite light-absorbing layer.

[0017] In an embodiment of the present invention, the lead-free perovskite solar cell includes, from bottom to top, a transparent conductive substrate, a hole transport layer, a lead-free perovskite light-absorbing layer, an electron transport layer, a hole blocking layer, and an electrode layer; the preparation method of the lead-free perovskite solar cell is as follows:

[0018] (1) Ultrasonically disperse the filtered hole material evenly at a temperature of 5 - 10 °C, then coat it on the transparent conductive substrate and perform an annealing treatment to form a hole transport layer;

[0019] (2) Prepare a lead-free perovskite light-absorbing layer on the hole transport layer according to the above-mentioned preparation method of the lead-free perovskite light-absorbing layer;

[0020] (3) Place the fully dissolved and filtered electron transport material solution on a hot stage at 30 - 40 °C. After the solution temperature is stable, deposit an electron transport layer on the lead-free perovskite light-absorbing layer by spin coating;

[0021] (4) Filter the saturated isopropanol solution of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), place it at 20-25 °C, and after the solution temperature stabilizes, deposit a hole blocking layer on the electron transport layer by spin coating method.

[0022] (5) After the hole blocking layer is prepared, deposit a metal electrode layer on the hole blocking layer by using a vacuum coating device.

[0023] Compared with the prior art, the lead-free perovskite precursor solution, light-absorbing layer and the preparation method of the solar cell provided by the present invention have the following beneficial effects:

[0024] The lead-free perovskite thin film introduced with cerium oxalate as an additive in the present invention has the following three functions: First, use carboxyl groups to inhibit non-radiative recombination in the thin film; second, use carboxyl groups to interact with the surface of the perovskite thin film to form a passivation layer to inhibit the oxidation of Sn 2+ , and third, use cerium ions in the additive to regulate the offset of halogen ions in the thin film and eliminate some charge defects.

[0025] The efficiency and stability of the lead-free perovskite solar cell prepared by the present invention have been significantly improved. Compared with the lead-free perovskite solar cell without using the additive, its highest photoelectric conversion efficiency has increased from 6.95% to 8.91%, an increase of about 28.2%. After the prepared lead-free perovskite solar cell device is placed in the air with a humidity of 20% for 300 h, it still maintains more than 85% of the initial photoelectric conversion efficiency. Description of the Drawings

[0026] Figure 1 is the ultraviolet absorption diagram of the lead-free perovskite thin film in Example 1 and Comparative Example 1;

[0027] Figure 2 is the X-ray diffraction diagram of the lead-free perovskite thin film in Example 1 and Comparative Example 1;

[0028] Figure 3 is the current density-voltage test curve of the lead-free perovskite solar cell in Example 1 and Comparative Example 1. Detailed Embodiments

[0029] The present invention will be further described below with reference to the drawings and embodiments.

[0030] Example 1

[0031] Step 1): Ultrasonically clean indium tin oxide transparent conductive glass with glass cleaner, deionized water, isopropanol, acetone and alcohol for 20 min each time, and then soak the cleaned indium tin oxide transparent conductive glass in absolute ethanol, seal it with tin foil and store it airtight.

[0032] Step 2): Cerium oxalate, methylamine iodine, formamidine iodine, stannous iodide, stannous fluoride and tin powder are mixed in a molar ratio of 0.05 mg: 0.25 mol: 0.75 mol: 1.0 mol: 0.1 mol: 0.01 mol, dissolved in a solvent of N, N-dimethylformamide and dimethyl sulfoxide in a volume ratio of 4:1, and then stirred at 25-30°C for 5 hours to obtain a lead-free perovskite thin film absorption layer solution, wherein the concentration of cerium oxalate is 0.05 mg / mL.

[0033] Cerium oxalate is an additive (manufacturer: Aladdin, item number: C118872), the structural formula is:

[0034]

[0035] Step 3): The cleaned indium tin oxide transparent conductive glass is blown dry with an air gun, and then subjected to ultraviolet ozone treatment for 20 minutes.

[0036] Step 4): The hole transport layer material PEDOT:PSS is filtered with a filter element with a pore size of 0.45 μm, and then ultrasonicated for 25 minutes at a temperature of 5 to 10°C. The filtered PEDOT:PSS is then dripped onto the treated indium tin oxide transparent conductive glass with a pipette. The spin coating speed is set to 1000 rpm for 8 seconds, and then 4000 rpm for 40 seconds. After the spin coating is completed, it is immediately transferred to a hot stage at 150°C for 20 minutes of annealing.

[0037] Step 5): The transparent conductive glass substrate with a hole transport layer prepared in step 4) is transferred to a glove box, and the lead-free perovskite thin film light absorbing layer solution prepared in step 2) is used to prepare a lead-free perovskite thin film light absorbing layer by a one-step solution method. The spin coating speed is set to 1000 rpm for 8 s, then 5000 rpm for 40 s, and 130 μL of chlorobenzene is added as an anti-solvent in the 13th second. After the spin coating is completed, it is immediately transferred to a hot stage at 40°C for a first step annealing treatment for 5 minutes, and then transferred to a hot stage at 80°C for a second step annealing treatment for 10 minutes.

[0038] Step 6): Spin-coat 30 μL of a chlorobenzene solution of

[60] PCBM (selected according to the energy level matching between the perovskite layer and the electron transport layer) on the lead-free perovskite film light-absorbing layer prepared in step 5), wherein the concentration of

[60] PCBM in chlorobenzene is 20 mg / mL, and place it on a hot stage at 30-40°C for 25 minutes, set the spin coater speed to 2000 rpm for 30 seconds, and then transfer it to a hot stage at 70°C for 10 minutes of annealing to form an electron transport layer.

[0039] Step 7): Spin-coat 30 μL of an isopropanol solution of BCP on the electron transport layer prepared in Step 6), where the concentration of BCP in isopropanol is 0.5 mg / mL, and place it at room temperature (20 - 25 °C) for more than 15 min. The spin-coating is set at 4000 rpm for 40 s, and then transfer it to a hot plate at 60 °C for a 5-min annealing treatment to deposit a hole blocking layer on the electron transport layer.

[0040] Step 8): After leaving the hole blocking layer prepared in Step 7) to stand for 1 - 2 h, evaporate and deposit a 100-nm-thick metal electrode by vacuum evaporation to complete the preparation of the lead-free perovskite solar cell.

[0041] The device prepared in Example 1 was under simulated sunlight with an intensity of 100 mW / cm 2 under AM 1.5G. The measured results are as Figure 3 shown. The best power conversion efficiency is 8.91%. After being placed in air with a humidity of 20% for 300 h, the power conversion efficiency is 7.36%, still maintaining more than 85% of the initial power conversion efficiency.

[0042] Example 2

[0043] Step 1): The same as in Example 1.

[0044] Step 2): Mix cerium oxalate, methylammonium iodide, formamidinium iodide, stannous iodide, stannous fluoride, and tin powder in a ratio of 0.03 mg:0.25 mol:0.75 mol:1.0 mol:0.1 mol:0.01 mol, dissolve them in a solvent of N,N-dimethylformamide and dimethyl sulfoxide with a volume ratio of 4:1, and then stir at 25 - 30 °C for 5 h to prepare a lead-free perovskite thin film light-absorbing layer solution, where the concentration of cerium oxalate is 0.03 mg / mL.

[0045] Step 3): The same as in Example 1.

[0046] Step 4): The same as in Example 1.

[0047] Step 5): The same as in Example 1.

[0048] Step 6): The same as in Example 1.

[0049] Step 7): The same as in Example 1.

[0050] Step 8): The same as in Example 1.

[0051] The device prepared in Example 2 was under simulated sunlight with an intensity of 100 mW / cm 2Under the light intensity of AM 1.5G, the measured best photoelectric conversion efficiency is 8.59%. After being placed in air with a humidity of 20% for 300 h, the photoelectric conversion efficiency is 7.3%, still maintaining more than 85% of the initial efficiency.

[0052] Example 3

[0053] Step 1): The same as Example 1.

[0054] Step 2): Cerium oxalate, methylammonium iodide, formamidinium iodide, stannous iodide, stannous fluoride and tin powder are mixed according to the ratio of 0.08 mg: 0.25 mol: 0.75 mol: 1.0 mol: 0.1 mol: 0.01 mol, dissolved in N,N-dimethylformamide and dimethyl sulfoxide solvents with a volume ratio of 4:1, and then stirred at 25-30 °C for 5 h to prepare a lead-free perovskite thin film light-absorbing layer solution, where the concentration of cerium oxalate is 0.08 mg / mL.

[0055] Step 3): The same as Example 1.

[0056] Step 4): The same as Example 1.

[0057] Step 5): The same as Example 1.

[0058] Step 6): The same as Example 1.

[0059] Step 7): The same as Example 1.

[0060] Step 8): The same as Example 1.

[0061] The device prepared in Example 3 was under simulated sunlight of 100 mW / cm 2 Under the light intensity of AM 1.5G, the measured best photoelectric conversion efficiency is 8.43%. After being placed in air with a humidity of 20% for 300 h, the photoelectric conversion efficiency is 7.17%, still maintaining more than 85% of the initial efficiency.

[0062] Comparative Example 1

[0063] In this comparative example, cerium oxalate is not added, and the dosage of other raw materials and the operation steps are the same as those in Example 1.

[0064] The device prepared in Comparative Example 1 was under simulated sunlight of 100 mW / cm 2 Under the light intensity of AM 1.5G, the measured best photoelectric conversion efficiency is 6.95%. After being placed in air with a humidity of 20% for 300 h, the photoelectric conversion efficiency is 2.78%, only maintaining 40% of the initial efficiency.

[0065] Comparative Example 2

[0066] Step 1): The same as Example 1.

[0067] Step 2): Mix methylammonium iodide, formamidinium iodide, stannous iodide, stannous fluoride and tin powder in a molar ratio of 0.25:0.75:1.0:0.1:0.02, dissolve them in a solvent of N,N-dimethylformamide and dimethyl sulfoxide with a volume ratio of 4:1, and then stir at 25-30 °C for 5 h to obtain a lead-free perovskite thin film light-absorbing layer solution.

[0068] Step 3): The same as Example 1.

[0069] Step 4): The same as Example 1.

[0070] Step 5): The same as Example 1.

[0071] Step 6): The same as Example 1.

[0072] Step 7): The same as Example 1.

[0073] Step 8): The same as Example 1.

[0074] The best power conversion efficiency measured for the device prepared in Comparative Example 2 under the light intensity of simulated sunlight of 100 mW / cm² AM 1.5G was 6.59%, and the power conversion efficiency was 4.28% after being placed in air with a humidity of 20% for 300 h, only maintaining 65% of the initial efficiency.

[0075] Comparative Example 3

[0076] Step 1): The same as Example 1.

[0077] Step 2): Mix neodymium oxalate, methylammonium iodide, formamidinium iodide, stannous iodide, stannous fluoride and tin powder in a ratio of 0.05 mg:0.25 mol:0.75 mol:1.0 mol:0.1 mol:0.01 mol, dissolve them in a solvent of N,N-dimethylformamide and dimethyl sulfoxide with a volume ratio of 4:1, and then stir at 25-30 °C for 4-6 h to obtain a lead-free perovskite thin film light-absorbing layer solution, where the concentration of neodymium oxalate is 0.05 mg / mL.

[0078] Step 3): The same as Example 1.

[0079] Step 4): The same as Example 1.

[0080] Step 5): The same as Example 1.

[0081] Step 6): The same as Example 1.

[0082] Step 7): The same as Example 1.

[0083] Step 8): The same as Example 1.

[0084] The device prepared in Comparative Example 3 was irradiated with simulated sunlight at an intensity of 100 mW / cm 2 under the light intensity of AM 1.5G. The measured best power conversion efficiency was 7.32%. After being placed in air with a humidity of 20% for 300 h, the power conversion efficiency was 4.81%, only maintaining 65.7% of the initial efficiency.

[0085] Comparative Example 4

[0086] Step 1): The same as in Example 1.

[0087] Step 2): Cerium oxalate, methylammonium iodide, formamidinium iodide, stannous iodide, stannous fluoride and tin powder were mixed according to the molar ratio of 0.01 mg: 0.25 mol: 0.75 mol: 1.0 mol: 0.1 mol: 0.01 mol, and dissolved in a solvent of N,N-dimethylformamide and dimethyl sulfoxide with a volume ratio of 4:1. Then, it was stirred at 25-30 °C for 5 h to prepare a lead-free perovskite thin film light-absorbing layer solution, where the concentration of cerium oxalate was 0.01 mg / mL.

[0088] Step 3): The same as in Example 1.

[0089] Step 4): The same as in Example 1.

[0090] Step 5): The same as in Example 1.

[0091] Step 6): The same as in Example 1.

[0092] Step 7): The same as in Example 1.

[0093] Step 8): The same as in Example 1.

[0094] The device prepared in Comparative Example 4 was irradiated with simulated sunlight at an intensity of 100 mW / cm 2 under the light intensity of AM 1.5G. The measured best power conversion efficiency was 6.73%.

[0095] Comparative Example 5

[0096] Step 1): The same as in Example 1.

[0097] Step 2): Cerium oxalate, methylammonium iodide, formamidinium iodide, stannous iodide, stannous fluoride and tin powder were mixed according to the molar ratio of 0.1 mg: 0.25 mol: 0.75 mol: 1.0 mol: 0.1 mol: 0.01 mol, and dissolved in a solvent of N,N-dimethylformamide and dimethyl sulfoxide with a volume ratio of 4:1. Then, it was stirred at 25-30 °C for 5 h to prepare a lead-free perovskite thin film light-absorbing layer solution, where the concentration of cerium oxalate was 0.1 mg / mL.

[0098] Step 3): The same as in Example 1.

[0099] Step 4): The same as in Example 1.

[0100] Step 5): The same as in Example 1.

[0101] Step 6): The same as in Example 1.

[0102] Step 7): The same as in Example 1.

[0103] Step 8): The same as in Example 1.

[0104] The device prepared in Comparative Example 5 was irradiated with simulated sunlight at an intensity of 100 mW / cm 2 under AM 1.5G, and the best photoelectric conversion efficiency measured was 5.57%.

[0105] Figure 1 The UV absorption spectra of the cells prepared in Example 1 and Comparative Example 1 are shown. From Figure 1 it can be seen that in the visible light region, the absorbance of the lead-free perovskite film in Example 1 is better than that in Comparative Example 1, indicating that cerium oxalate used as an additive can enhance the crystallinity of the lead-free perovskite film. At the same time, in the near-infrared region, Example 1 and Comparative Example have the same absorption curve, indicating that cerium oxalate used as an additive does not change the composition of the lead-free perovskite material. That is, cerium oxalate used as an additive can improve the crystallinity of the lead-free perovskite film without changing the composition of the lead-free perovskite material.

[0106] Figure 2 The X-ray diffraction patterns of the cells prepared in Example 1 and Comparative Example 1 are shown. From Figure 2 it can be seen that the characteristic peak intensity of the lead-free perovskite in Example 1 is significantly higher than that in Comparative Example 1, indicating that cerium oxalate used as an additive significantly improves the crystallinity of the lead-free perovskite and inhibits the film defects caused by the fast crystallization rate.

[0107] Figure 3 The current density-voltage test curves of the cells prepared in Example 1 and Comparative Example 1 are shown. From Figure 3 it can be seen that the optoelectronic performance of the lead-free perovskite solar cell in Example 1 is significantly better than that in Comparative Example 1, mainly manifested as an increase in the current density.

[0108] In addition, in terms of stability, after the devices with cerium oxalate added (Examples 1-3) were placed in air with a humidity of 20% for 300 hours, they still maintained a photoelectric conversion efficiency of over 85%. However, for the batteries prepared without adding cerium oxalate (Comparative Example 1) or by adding other metal oxalates (Comparative Example 3), they could only maintain 40% and 65.7% of the initial efficiency respectively. It can be seen that in the light-absorbing layer of the lead-free perovskite thin film of the present invention, cerium oxalate is introduced as an additive. By utilizing the coordination effect of the carboxyl group and cerium ions, the crystallization and growth process of perovskite is delayed, which has a dual effect of inhibiting oxidation and non-radiative recombination of lead-free perovskite, effectively improving the stability of the battery.

[0109] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can, without departing from the technical idea of the present invention, make various changes and modifications. The technical scope of the present invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A lead-free perovskite precursor solution, characterized in that: The lead-free perovskite precursor solution contains cerium oxalate.

2. The lead-free perovskite precursor solution according to claim 1, characterized in that The concentration of the cerium oxalate in the lead-free perovskite precursor solution is 0.03-0.08 mg / mL.

3. The lead-free perovskite precursor solution according to claim 1, characterized in that: The lead-free perovskite precursor solution includes cerium oxalate, methylamine iodine, formamidine iodine, stannous iodide, stannous fluoride and tin powder; the ratio of cerium oxalate, methylamine iodine, formamidine iodine, stannous iodide, stannous fluoride and tin powder is 0.03-0.08 mg: 0.25 mol: 0.75 mol: 1.00 mol: 0.1 mol: 0.01 mol.

4. The lead-free perovskite precursor solution according to claim 1, characterized in that The solvent of the lead-free perovskite precursor solution is one or both of N,N-dimethylformamide and dimethyl sulfoxide.

5. A lead-free perovskite light-absorbing layer, characterized in that: The lead-free perovskite light-absorbing layer is prepared from the lead-free perovskite precursor solution according to any one of claims 1 to 4, and the specific steps are: coating the lead-free perovskite precursor solution on a substrate under a protective atmosphere, adding an anti-solvent, and then annealing the substrate.

6. The lead-free perovskite light absorbing layer according to claim 5, characterized in that: The coating is performed by spin coating, and the spin coating is set to first rotate at a speed of 1000 rpm for 8 to 10 seconds, and then rotate at a speed of 3000 to 6000 rpm for 35 to 50 seconds; The anti-solvent is added dropwise during the 10th to 20th second of spin coating; The annealing is carried out in two steps, wherein the temperature of the first step annealing is 30-50° C. and the annealing time is 5-10 min, and the temperature of the second step annealing is 70-90° C. and the annealing time is 5-10 min.

7. The lead-free perovskite light absorbing layer according to claim 5, characterized in that: The thickness of the lead-free perovskite thin film light-absorbing layer is 200-400 nm.

8. A lead-free perovskite solar cell, characterized in that: The lead-free perovskite solar cell comprises the lead-free perovskite light-absorbing layer according to any one of claims 6 to 7.

9. The lead-free perovskite solar cell according to claim 8, characterized in that: The lead-free perovskite solar cell comprises, from bottom to top, at least one layer of a transparent conductive substrate, a hole transport layer, a lead-free perovskite light absorbing layer, an electron transport layer, a hole blocking layer, and an electrode layer.

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