Method for preparing lead-free tin-based perovskite thin films and solar cells without anti-solvent by using ionic salts

Abstract

The present invention relates to a method for preparing lead-free tin-based perovskite thin films and solar cells thereof without an anti-solvent by using an ionic salt. Taking hydrazine acetate (HAAc) ionic salt as a crystallization controller and using a mixed solution of one or both of DMF or DMAc as a solvent, at room temperature, a flat, dense, uniform and highly crystalline tin-based perovskite thin film can be obtained after one-step anti-solvent spin coating and heat treatment. Compared with the traditional anti-solvent dripping process, the preparation process disclosed in the present invention has the characteristics of simplicity, rapidity, high efficiency and easy operation. Based on the thin film, the prepared tin-based perovskite solar cell device has a high photoelectric conversion efficiency and good device stability.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic materials and devices, and relates to a method for preparing lead-free tin-based perovskite thin films and solar cells without an antisolvent by using ionic salts. Background Art

[0002] In recent years, the increasingly prominent problem of climate change has accelerated the world economy's in-depth development towards low carbonization. Renewable energy represented by "photovoltaics" has gradually become the main force of a new round of energy revolution. Developing efficient, stable, green and economic new photovoltaic technologies is of great strategic significance for building a sustainable modern energy system. With the increasing maturity of traditional silicon-based photovoltaic technologies, the large-scale commercial application of photovoltaic technologies faces challenges such as complex processes and serious pollution. Perovskite photovoltaic technology has emerged as the times require. Due to its simple process, low cost, flexible preparation and excellent optoelectronic performance, it has quickly become a research hotspot and frontier in this field.

[0003] So far, efficient perovskite photovoltaic technology still mainly uses Pb-based perovskite materials, and the photoelectric conversion efficiency has been broken through to 25.5% in a short time. However, the problems of the natural environment and public health caused by the toxicity of heavy metal lead in the preparation process of Pb-based perovskite photovoltaic materials and devices restrict their further development. At the same time, according to the Shockley-Queisser limit theory, due to the relatively wide bandgap (1.55 eV) of Pb-based perovskite, the theoretical value of the photoelectric conversion limit efficiency is less than 31%. To effectively control environmental pollution from the source and break through the limitation of the theoretical limit efficiency, non-lead perovskite materials represented by 2+ Sn 2+ Ge 3+ Sb 3+ Bi 3+ have been developed. Especially for Sn-based perovskite, since Snaith first synthesized Sn-based perovskite in 2014, its photoelectric conversion efficiency has been increased to 14.8%, and it is considered to be the most promising environmentally friendly perovskite photovoltaic material.

[0004] However, due to the too fast crystallization rate of Sn-based perovskite thin films and the easy oxidation of Sn 2+ to Sn 4+ , the film-forming quality is poor and the density of defect states is high. Its optoelectronic performance is still far lower than that of current Pb-based perovskite. Especially the use of the antisolvent method increases the complexity and process cost of the film-forming process, and pollutes the environment to a certain extent. Based on this, it is very necessary to develop a simple method for preparing Sn-based perovskite thin films while ensuring their excellent optoelectronic performance. Summary of the Invention

[0005] Technical Problems to be Solved

[0006] To avoid the deficiencies of the prior art, the present invention proposes a method for preparing lead-free tin-based perovskite thin films and solar cells without an antisolvent through an ionic salt, aiming to solve the drawbacks of the existing tin-based perovskite thin films that must use an antisolvent and the problem of difficulty in preparing high-quality thin films at room temperature.

[0007] Technical solution

[0008] A method for preparing lead-free tin-based perovskite thin films and solar cells without an antisolvent through an ionic salt, characterized in that the steps are as follows:

[0009] Step 1: Dissolve formamidinium iodide, stannous iodide, and stannous fluoride in a solvent prepared from an ionic salt and an organic solvent, and stir until completely dissolved to prepare a lead-free tin-based perovskite precursor solution;

[0010] The molar ratio of formamidinium iodide, stannous iodide, and stannous fluoride is 1:1:0.1;

[0011] Step 2: Spin-coat and deposit a hole transport material on the cleaned and treated ITO transparent conductive glass;

[0012] Step 3: Deposit the lead-free tin-based perovskite precursor solution prepared in Step 1 on the ITO transparent conductive glass with a deposited hole transport layer to form a tin-based perovskite thin film, and then obtain a flat and dense active layer after annealing treatment;

[0013] Step 4: Spin-coat and deposit an electron transport layer on the tin-based perovskite thin film;

[0014] Step 5: Then, vacuum thermally evaporate an interface modification layer and a metal electrode on the electron transport layer to obtain a solar cell.

[0015] The ionic liquid salt in Step 1 is hydrazine acetate.

[0016] The organic solvent is one or a mixture of two of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

[0017] The concentration of the lead-free tin-based perovskite precursor solution is 0.6 - 0.7 mmol / mL.

[0018] The hole transport layer deposited on the transparent conductive ITO electrode in Step 2 is PEDOT:PSS.

[0019] The steps of Step 2 are: after spin-coating PEDOT:PSS, anneal at 150 °C for 20 min.

[0020] In Step 3, a one-step antisolvent-free spin-coating method is used to deposit the tin-based perovskite thin film, and the spin-coating temperature is room temperature.

[0021] In step 4, the spin-coated and deposited electron transport layer is ICBA, and ICBA is dissolved in a chlorobenzene solution at a concentration of 6-8 mg / mL.

[0022] In step 5, the interfacial modification layer is BCP, and the metal electrode is Ag.

[0023] The steps of step 5 are as follows: BCP is thermally evaporated on the electron transport layer with a thickness of 6 nm; the thickness of the metal Ag electrode is 120 nm.

[0024] A further technical solution of the present invention is that the special solvent in step (1) is prepared by dissolving 100 mg of HAAc in 1 mL of DMF with a concentration of 100 mg / mL. This method is more conducive to the one-step film formation of tin-based perovskite.

[0025] A further technical solution of the present invention is that the spin-coating speed of the perovskite film in step (4) is 5000 revolutions per minute for 60 s. This spin-coating speed is conducive to the formation of a perovskite film with better properties.

[0026] A further technical solution of the present invention is that in step (5), ICBA is dissolved in a chlorobenzene solution at a concentration of 6-8 mg / mL. The electron transport layer prepared at this concentration has a moderate thickness and is conducive to carrier transport.

[0027] A further technical solution of the present invention is that the spin-coating method of ICBA in step (5) is in two steps. The first step is to spin-coat at 1000 revolutions per minute for 50 s, and the second step is to spin-coat at 3000 revolutions per minute for 5 s to obtain the electron transport layer without heat treatment.

[0028] Beneficial effects

[0029] A method for preparing a lead-free tin-based perovskite film and a solar cell thereof by realizing an anti-solvent-free preparation through an ionic salt according to the present invention uses hydrazine acetate (HAAc) ionic salt as a crystallization control agent and a mixed solution of one or two of DMF or DMAc as a solvent. At room temperature, a flat, dense, uniform, and highly crystalline tin-based perovskite film can be obtained after one-step anti-solvent-free spin-coating and heat treatment. Compared with the traditional anti-solvent dripping process, the preparation process disclosed by the present invention has the characteristics of simplicity, rapidity, high efficiency, and easy operation. Based on the film prepared, the tin-based perovskite solar cell device has a high photoelectric conversion efficiency and good device stability.

[0030] The beneficial effects of the present invention:

[0031] (1) Invented a special solvent, realized the one-step spin-coating method for preparing tin-based perovskite film without anti-solvent, and obtained a flat and dense tin-based perovskite film;

[0032] (2) Compared with the traditional anti-solvent method, the present invention simplifies the preparation process flow of the tin-based perovskite thin film and reduces the environmental pollution caused by the use of anti-solvent;

[0033] (3) After the process parameters are optimized, under the condition of no other additives, the photoelectric conversion efficiency of the prepared tin-based perovskite solar cell device is > 6%. Description of the Drawings

[0034] Figure 1 It is the SEM image of the tin-based perovskite thin film prepared by the present invention in a nitrogen atmosphere, where a is the thin film prepared by the special solvent, and b is the thin film prepared by the DMF solvent;

[0035] Figure 2 It is the XRD image of the tin-based perovskite thin film prepared by the present invention in a nitrogen atmosphere, where the solid line curve is the thin film prepared by the HAAc / DMF special solvent, and the dotted line curve is the thin film prepared by the DMF solvent;

[0036] Figure 3 It is the structural diagram of the tin-based perovskite solar cell device prepared by the present invention;

[0037] Figure 4 It is the J-V curve diagram of the tin-based perovskite solar cells prepared by the present invention under different solvents; Detailed Embodiments

[0038] The present invention will be further described below in combination with the embodiments and the drawings:

[0039] Example 1

[0040] Under the special solvent (HAAc / DMF mixture), the preparation method of the FASnI 3 perovskite thin film and its solar cell:

[0041] Step 1) The etched ITO conductive glass is ultrasonically treated in ethanol, ultrapure water plus cleaning agent, ultrapure water, and ethanol for 30 minutes each. After drying with nitrogen, it is placed in an oven for baking to obtain a clean ITO substrate.

[0042] Step 2) Weigh 100 mg of HAAc and dissolve it in 1 mL of DMF, with a concentration of 100 mg / mL. Stir at 60 °C for 4 hours until evenly mixed to prepare a special solvent.

[0043] Step 3) Weigh 60.2 mg of formamidinium iodide, 130.4 mg of stannous iodide, and 5.5 mg of stannous fluoride and dissolve them in 0.5 mL of the special solvent (193.4 μL of HAAc / DMF mixture and 306.6 μL of DMF solvent), and stir at room temperature for 2 hours until completely dissolved to prepare a perovskite precursor solution with a concentration of 0.7 mmol / mL.

[0044] Step 4) Treat the cleaned ITO substrate in step 1) with ultraviolet ozone for 15 min.

[0045] Step 5) Take 40 μL of the hole transport material PEDOT:PSS and drop it onto the ITO conductive glass treated in step 4) with a pipette. After spinning at a speed of 5000 revolutions per minute for 50 seconds, anneal the ITO coated with PEDOT:PSS at 150 °C for 20 min.

[0046] Step 6) Place the ITO conductive substrate coated with the hole transport layer after annealing in step 5) on a spin coater and blow the surface clean with a rubber bulb.

[0047] Step 7) Take 55 μL of the perovskite precursor solution prepared in step 3) and drop it onto the ITO substrate with a hole transport layer spun in step 6). Spin-coat to form a film, and then anneal to obtain a perovskite film. The spinning speed of the perovskite precursor solution is 5000 revolutions per minute for 60 seconds, and anneal at 100 °C for 5 min in a nitrogen atmosphere. Figure 1 (a) is the SEM image of the perovskite film under this addition method. The film grains are dense, flat, continuous and of uniform size, indicating that the film quality is good. Figure 2 The solid line HAAc / DMF curve is the XRD pattern of the perovskite film under this addition method, indicating that the film has good crystallinity.

[0048] Step 8) Weigh 6 mg of ICBA, completely dissolve it in 1 ml of chlorobenzene solvent, and prepare a 6 mg / mL ICBA spin-coating solution.

[0049] Step 9) Spin-coat the ICBA spin-coating solution in step 8) onto the perovskite film in step 7). Spin-coating of ICBA is carried out in two steps. The first step is to spin at 1000 revolutions per minute for 50 seconds, and the second step is to spin at 3000 revolutions per minute for 5 seconds to obtain an electron transport layer.

[0050] Step 10) Use vacuum thermal evaporation technology to evaporate 6 nm of BCP and 120 nm of metal electrode Ag on the electron transport layer in step 9) to obtain a perovskite solar cell.

[0051] Step 11) Under standard test conditions (AM 1.5G illumination), Figure 4 For the optoelectronic performance of the solar cell device prepared in this example, the photoelectric conversion efficiency is 6.27%, the open-circuit voltage is 0.61 V, and the short-circuit current is 16.59 mA / cm 2 , and the fill factor is 61.94%.

[0052] Example 2

[0053] Under a special solvent (HAAc / DMAc mixture), FASnI 3 Preparation method of perovskite thin film and its solar cell:

[0054] Step 1) The etched ITO conductive glass is ultrasonically treated in ethanol, ultrapure water plus cleaning agent, ultrapure water, and ethanol for 30 minutes each. After drying with nitrogen, it is placed in an oven for baking to obtain a clean ITO substrate.

[0055] Step 2) Weigh 100 mg of HAAc and dissolve it in 1 mL of DMAc to a concentration of 100 mg / mL. Stir at 60 °C for 4 hours until evenly mixed to prepare a special solvent.

[0056] Step 3) Weigh 60.2 mg of formamidinium iodide, 130.4 mg of stannous iodide, and 5.5 mg of stannous fluoride and dissolve them in 0.5 mL of the special solvent (193.4 μL of HAAc / DMAc mixture and 306.6 μL of DMAc solvent), and stir at room temperature for 2 hours until completely dissolved to prepare a perovskite precursor solution with a concentration of 0.7 mmol / mL.

[0057] Step 4) The cleaned ITO substrate in Step 1) is treated with ultraviolet ozone for 15 minutes.

[0058] Step 5) Take 40 μL of the hole transport material PEDOT:PSS and pipette it onto the ITO conductive glass treated in Step 4). After spinning at a speed of 5000 revolutions per minute for 50 seconds, the ITO coated with PEDOT:PSS is annealed at 150 °C for 20 minutes.

[0059] Step 6) Place the ITO conductive substrate coated with the hole transport layer after annealing in Step 5) on a spin coater and blow the surface clean with an ear bulb.

[0060] Step 7) Take 55 μL of the perovskite precursor solution prepared in Step 3) and drop it onto the ITO substrate with the hole transport layer spun in Step 6). Spin-coat to form a film, and then anneal to obtain a perovskite thin film. The spin-coating speed of the perovskite precursor solution is 5000 revolutions per minute for 60 seconds, and it is annealed at 100 °C for 5 minutes in a nitrogen atmosphere.

[0061] Step 8) Weigh 6 mg of ICBA and completely dissolve it in 1 ml of chlorobenzene solvent to prepare a 6 mg / mL ICBA spin-coating solution.

[0062] Step 9) Spin-coat the ICBA spin-coating solution in Step 8) onto the perovskite thin film in Step 7). Spin-coating of ICBA is carried out in two steps. The first step is to spin-coat at 1000 revolutions per minute for 50 seconds, and the second step is to spin-coat at 3000 revolutions per minute for 5 seconds to obtain an electron transport layer.

[0063] Step 10) Using vacuum thermal evaporation technology, deposit 6 nm of BCP and 120 nm of metal electrode Ag on the electron transport layer in Step 9) to obtain a perovskite solar cell.

[0064] Step 11) Under standard test conditions (AM 1.5G illumination), Figure 4 For the optoelectronic performance of the solar cell device prepared in this example, the photoelectric conversion efficiency is 3.72%, the open-circuit voltage is 0.55 V, and the short-circuit current is 11.26 mA / cm 2 , and the fill factor is 59.29%.

[0065] Example 3

[0066] In a special solvent (HAAc / (DMF + DMAc) mixture), FASnI 3 Preparation method of perovskite thin film and its solar cell:

[0067] Step 1) Ultrasonically clean the etched ITO conductive glass in ethanol, ultrapure water with cleaning agent, ultrapure water, and ethanol for 30 minutes each. After drying with nitrogen, place it in an oven for baking to obtain a clean ITO substrate.

[0068] Step 2) Weigh 100 mg of HAAc and dissolve it in a mixed solvent of DMF and DMAc (DMF:DMAc = 4:1) with a concentration of 100 mg / mL. Stir at 60 °C for 4 hours until evenly mixed to prepare a special solvent.

[0069] Step 3) Weigh 60.2 mg of formamidinium iodide, 130.4 mg of stannous iodide, and 5.5 mg of stannous fluoride and dissolve them in 0.5 mL of the special solvent (193.4 μL of HAAc / DMF + DMAc mixture and 306.6 μL of the DMF and DMAc mixed solvent, DMF:DMAc = 4:1), and stir at room temperature for 2 hours until completely dissolved to prepare a perovskite precursor solution with a concentration of 0.7 mmol / mL.

[0070] Step 4) Treat the cleaned ITO substrate in Step 1) with ultraviolet ozone for 15 minutes.

[0071] Step 5) Take 40 μL of the hole transport material PEDOT:PSS and drop it onto the ITO conductive glass treated in Step 4) with a pipette. After spinning at 5000 revolutions per minute for 50 seconds, anneal the ITO coated with PEDOT:PSS at 150 °C for 20 minutes.

[0072] Step 6) Place the annealed ITO conductive substrate coated with the hole transport layer in Step 5) on a spin coater and blow the surface clean with an ear bulb.

[0073] Step 7) Take 55 μL of the perovskite precursor solution prepared in Step 3) and drop it onto the ITO substrate with a hole transport layer spun in Step 5), spin-coat to form a film, and then anneal to obtain a perovskite thin film. The rotation speed of spin-coating the perovskite precursor solution is 5000 revolutions per minute for 60 seconds, and anneal at 100 °C for 5 min in a nitrogen atmosphere.

[0074] Step 8) Weigh 6 mg of ICBA, completely dissolve it in 1 ml of chlorobenzene solvent, and prepare a 6 mg / mL ICBA spin-coating solution.

[0075] Step 9) Spin-coat the ICBA spin-coating solution in Step 8) onto the perovskite thin film in Step 7). Two-step method is used for spin-coating ICBA. The first step is to spin-coat at 1000 revolutions per minute for 50 seconds, and the second step is to spin-coat at 3000 revolutions per minute for 5 seconds to obtain an electron transport layer.

[0076] Step 10) Use vacuum thermal evaporation technology to evaporate 6 nm of BCP and 120 nm of metal electrode Ag on the electron transport layer in Step 8) to obtain a perovskite solar cell.

[0077] Step 11) Under standard test conditions (AM 1.5G illumination), Figure 4 The photoelectric conversion efficiency of the solar cell device prepared in this example is 5.17%, the open-circuit voltage is 0.58 V, the short-circuit current is 17.23 mA / cm 2 , and the fill factor is 54.41%.

[0078] Comparative Example 1

[0079] Under traditional solvents (pure DMF solvent), FASnI 3 Preparation method of perovskite thin film and its solar cell:

[0080] Step 1) Ultrasonic clean the etched ITO conductive glass in ethanol, ultrapure water with cleaning agent, ultrapure water, and ethanol for 30 min each. After drying with nitrogen, put it into an oven for baking to obtain a clean ITO substrate.

[0081] Step 2) Weigh formamidinium iodide, 130.4 mg of stannous iodide, and 5.5 mg of stannous fluoride, dissolve them in 0.5 mL of DMF solvent, and stir at room temperature for 2 hours until completely dissolved to prepare a perovskite precursor solution with a concentration of 0.7 mmol / mL.

[0082] Step 3) Treat the cleaned ITO substrate in Step 1) with ultraviolet ozone for 15 min.

[0083] Step 4) Take 40 μL of the hole transporting material PEDOT:PSS and drop it onto the ITO conductive glass processed in Step 3) with a pipette. After spinning at a speed of 5000 revolutions per minute for 50 seconds, anneal the ITO coated with PEDOT:PSS at 150 °C for 20 min.

[0084] Step 5) Place the ITO conductive substrate coated with the hole transport layer completed in Step 4) on a spin coater and blow the surface clean with a rubber bulb.

[0085] Step 6) Take 55 μL of the perovskite precursor solution prepared in Step 2) and drop it onto the ITO substrate with the hole transport layer spun in Step 5), spin-coat to form a film, and then anneal to obtain a perovskite film. The spin-coating speed of the perovskite precursor solution is 5000 revolutions per minute for 60 seconds, and anneal at 100 °C for 5 min in a nitrogen atmosphere. Figure 1 (b) is the SEM image of the perovskite film under this addition method. The film only forms isolated perovskite crystals with uneven size distribution, showing poor film-forming quality. Figure 2 The dotted DMF curve is the XRD pattern of the perovskite film under this addition method, indicating poor crystallinity of the film.

[0086] Step 7) Weigh 6 mg of ICBA, completely dissolve it in 1 ml of chlorobenzene solvent, and prepare a 6 mg / mL ICBA spin-coating solution.

[0087] Step 8) Spin-coat the ICBA spin-coating solution in Step 7) onto the perovskite film in Step 6). The spin-coating of ICBA adopts a two-step method. The first step is to spin-coat at 1000 revolutions per minute for 50 seconds, and the second step is to spin-coat at 3000 revolutions per minute for 5 seconds to obtain an electron transport layer.

[0088] Step 9) Use vacuum thermal evaporation technology to evaporate 6 nm of BCP and 120 nm of metal electrode Ag on the electron transport layer in Step 8) to obtain a perovskite solar cell.

[0089] Step 10) Under standard test conditions (AM 1.5G illumination), the device is short-circuited, indicating extremely poor film-forming quality of the tin-based perovskite film under this method.

[0090] Table 1

[0091] Solvent type <![CDATA[J SC / mA·cm -2 > <![CDATA[V OC / V]]> FF / % PCE / % HAAc / DMF 16.59 0.61 61.94 6.27 HAAc / DMAc 11.26 0.55 59.29 3.72 HAAc / (DMF:DMAc = 4:1) 17.23 0.58 54.41 5.17

[0092] The present invention is not limited to the specific technical solutions described in the above embodiments. Any technical solutions formed by equivalent modifications or replacements are within the scope of protection required by the present invention.

Claims

1. A method for preparing lead-free tin-based perovskite thin films and their solar cells without an antisolvent by using ionic salts, characterized in that the steps are as follows: Step 1: Dissolve formamidinium iodide, stannous iodide, and stannous fluoride in a solvent prepared from an ionic salt and an organic solvent, and stir until completely dissolved to prepare a lead-free tin-based perovskite precursor solution; the molar ratio of formamidinium iodide, stannous iodide, and stannous fluoride is 1:1:0.1; Step 2: Spin-coat and deposit a hole transport material on the cleaned and treated ITO transparent conductive glass; Step 3: Deposit the lead-free tin-based perovskite precursor solution prepared in Step 1 on the ITO transparent conductive glass with a deposited hole transport layer to form a tin-based perovskite thin film, and then obtain a flat and dense active layer after annealing treatment; Step 4: Spin-coat and deposit an electron transport layer on the tin-based perovskite thin film; Step 5: Subsequently, vacuum thermally evaporate an interface modification layer and a metal electrode on the electron transport layer to obtain a solar cell; the ionic salt in Step 1 is hydrazine acetate; the organic solvent is one or a mixture of two of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc); the concentration of the lead-free tin-based perovskite precursor solution is 0.6 - 0.7 mmol / mL; the hole transport layer deposited on the ITO transparent conductive glass in Step 2 is PEDOT:PSS; the steps of Step 2 are: after spin-coating PEDOT:PSS, anneal at 150 °C for 20 min; Step 3 uses a one-step antisolvent spin-coating method to deposit the tin-based perovskite thin film, and the spin-coating temperature is room temperature; the spin-coated electron transport layer in Step 4 is ICBA, and ICBA is dissolved in a chlorobenzene solution at a concentration of 6 - 8 mg / mL; the interface modification layer in Step 5 is BCP, and the metal electrode is Ag; the steps of Step 5 are: thermally evaporate BCP on the electron transport layer with a thickness of 6 nm; the thickness of the metal Ag electrode is 120 nm.

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