An oriented iron oxide thin film, a preparation method thereof, and an application thereof in a solar cell

Abstract

The present invention discloses an oriented iron oxide thin film, a preparation method thereof and an application thereof in a solar cell, belonging to the technical fields of thin film materials and solar cells. In this method, flaky iron oxide particles are added to a molten metal liquid. After the molten metal liquid cools and solidifies, the flaky iron oxide will be oriented and spread flat on the surface of the metal. The iron oxide particles that are not in direct contact on the metal surface are removed to obtain an oriented iron oxide thin film. This method is simple in operation, low in energy consumption, high in repeatability and suitable for large-scale production. Low-melting-point metals with different characteristics can be selected as the substrate, and the thickness of the oriented thin film can be regulated by controlling the thickness of the flaky iron oxide particles (there is no phenomenon of stacking of flaky particles), and the thin film is firmly combined with the substrate. Using the oriented iron oxide thin film as the light absorption layer of the solar cell shows strong light absorption ability, has a higher light voltage and photoelectric conversion efficiency compared with the randomly oriented iron oxide thin film, and has stable performance.

Description

Technical Field

[0001] The present invention belongs to the technical fields of thin film materials and solar cells, and particularly relates to an oriented iron oxide thin film, a preparation method thereof, and an application thereof in solar cells. Background Art

[0002] Currently, solar cells led by monocrystalline silicon and polycrystalline silicon have the most mature technologies. With relatively high photoelectric conversion efficiency (PCE), they have become the main solar cells for large-scale commercial applications in the market. However, they have high production costs, high energy consumption, and environmental pollution. Thin film solar cells of amorphous silicon and multi-component compounds, such as III-V compounds such as gallium arsenide, II-VI compounds such as cadmium telluride, and materials such as copper indium gallium selenide, although their costs have been greatly reduced compared with crystalline silicon solar cells, their disadvantages are also relatively prominent. For example, amorphous silicon thin film batteries are inferior to crystalline silicon batteries in terms of PCE and stability. Arsenic and cadmium in gallium arsenide and cadmium telluride thin film battery materials have strong toxicity and will cause certain harm to the natural environment and the health of organisms. Since 2009, organic-inorganic hybrid metal halide materials with perovskite structures have entered the field of vision of scientific researchers, and their PCE has rapidly increased from 3.8% to 25.8% in just ten years. Although perovskite solar cells have the advantages of low cost and high efficiency, due to the instability and easy decomposition of the light absorption layer (perovskite layer), it is currently difficult to industrialize. Therefore, it is of great significance to develop new solar cells with low production costs, low energy consumption, and environmental friendliness.

[0003] Iron oxide (α-Fe 2 O 3 ) is an n-type semiconductor with low price, less environmental pollution, excellent stability and corrosion resistance, and is a material with relatively high photoelectric conversion efficiency. It has a strong light absorption ability in the visible light region and can absorb about 30% of solar energy. Usually, iron oxide thin films are used as photoanodes and show good performance in the field of photoelectrocatalytic water splitting. Currently, the iron oxide thin films prepared by people are non-oriented, mainly using spherical iron oxide nanoparticles and prepared by methods such as spin coating. Oriented thin films usually use flaky particles and are obtained by casting the directionally arranged flaky particles, and are mainly applied in the fields of oriented electronic thin films or ceramics.

[0004] However, as a photoelectric thin film material, there is a phenomenon of a large number of stacked flaky particles during the directional arrangement by the casting method. The particle stacking will increase the impedance of the thin film and reduce the migration rate of photo-generated carriers, resulting in low photoelectric conversion efficiency. In addition, after the directional arrangement by the casting method, further heat treatment is required to firmly bond the flaky particles to the substrate. Summary of the Invention

[0005] To overcome the disadvantages of the above-mentioned prior art, the object of the present invention is to provide an oriented iron oxide thin film, a preparation method thereof and an application in a solar cell, which can solve the problems of increased film impedance caused by particle stacking and poor binding between particles and the substrate.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The first object of the present invention is to provide a preparation method of an oriented iron oxide thin film, comprising the following steps:

[0008] 1) Under the protection of an inert atmosphere, heat a low-melting-point metal to a molten state;

[0009] 2) Add iron oxide particles to the molten metal, stir and let stand. After the iron oxide particles float to the liquid surface of the molten metal, stop heating, naturally cool to room temperature and stop the atmosphere protection. The liquid metal cools and solidifies into a shape, and the iron oxide particles are fixed on the surface of the formed metal;

[0010] 3) Remove the iron oxide particles that are not in direct contact on the metal surface, and retain the iron oxide particles that are in direct contact with the metal to obtain the oriented iron oxide thin film.

[0011] Further, in step 1), the inert atmosphere is nitrogen, argon or other inert gases.

[0012] Further, in step 1), the low-melting-point metal is metal Bi, Sn, Zn, In or their alloys, etc., with a melting point below 450 °C.

[0013] Further, in step 1), the temperature for heating to the molten state is above the melting point.

[0014] Further, in step 2), the iron oxide is α-Fe 2 O 3 , an ion-doped α-Fe 2 O 3 or α-Fe co-doped with multiple ions 2 O 3 .

[0015] Even further, it is Sn 2+ doped α-Fe 2 O 3 , Cu 2+ doped α-Fe 2 O 3 or α-Fe doped with one or more other ions 2 O.

[0016] Further, in step 2), the iron oxide particles are flaky in morphology, with a thickness of 100 - 500 nm and a diameter of 5 - 20 μm.

[0017] Further, in step 2), the stirring time is 5 - 10 min.

[0018] Further, in step 2), the standing time is the time required from the start of timing after stopping stirring until all the iron oxide particles float to the molten metal surface.

[0019] Further, in step 2), the shape of the liquid metal after cooling and solidification is flat.

[0020] Further, in step 3), the method for removing the iron oxide particles that are not in direct contact with the metal surface can be blowing, rinsing with deionized water or other inert solvents, or rinsing under ultrasonic conditions.

[0021] The second object of the present invention is to provide an application of using the above - prepared oriented iron oxide thin film as a light - absorbing layer to prepare a solar cell. Specifically, during the preparation, the operations are as follows:

[0022] 1) Prepare an indium oxide transparent hole - transporting layer on the oriented iron oxide thin film by magnetron sputtering;

[0023] 2) Prepare a transparent indium tin oxide electrode on the hole - transporting layer by magnetron sputtering.

[0024] In the oriented thin - film materials prepared by the traditional casting method, there is a phenomenon of a large number of flaky particles stacking. The particle stacking will increase the impedance of the thin film and reduce the migration rate of photo - generated carriers, resulting in low photoelectric conversion efficiency. In addition, after the casting method for orientation arrangement, further heat treatment is required to firmly bond the flaky particles to the substrate, which has the disadvantage of high energy consumption. Therefore, compared with the prior art, the present invention has the following beneficial effects:

[0025] In the present invention, flaky iron oxide particles are added to the molten metal. After the molten metal cools and solidifies, the flaky iron oxide will be oriented and tiled on the surface of the metal. Then, the iron oxide particles that are not in direct contact with the metal surface are removed to obtain an oriented iron oxide thin film. The present invention utilizes the characteristics that inorganic metal oxides have a small density and are easy to float on the surface of molten metal (with a large density). By adding flaky iron oxide particles to the molten metal and cooling and solidifying, an oriented iron oxide thin film is formed on the metal surface. The flaky particles in this thin film have no stacking phenomenon, are firmly bonded to the metal substrate, and the thickness is controllable. This method is simple in operation, low in energy consumption, high in repeatability, and suitable for large - scale production. Different low - melting - point metals with different characteristics can be selected as the substrate, and the thickness of the oriented thin film can be adjusted by controlling the thickness of the flaky iron oxide particles (without the phenomenon of flaky particle stacking), and the thin film is firmly bonded to the substrate.

[0026] The flaky particles in the oriented iron oxide thin film prepared by the present invention have no stacking phenomenon, are firmly combined with the metal matrix, and have a controllable thickness. Using this oriented iron oxide thin film as the light absorption layer of a solar cell, it exhibits strong light absorption ability, has a higher photovoltage and photoelectric conversion efficiency compared with randomly oriented iron oxide thin films, and has stable performance and other characteristics. Description of the Drawings

[0027] Figure 1 It is the forward and reverse scan J-V curve diagram of the oriented iron oxide thin film solar cell prepared in Example 1;

[0028] Figure 2 It is the forward and reverse scan J-V curve diagram of the oriented iron oxide thin film solar cell prepared in Example 2;

[0029] Figure 3 It is the forward and reverse scan J-V curve diagram of the oriented iron oxide thin film solar cell prepared in Example 3;

[0030] Figure 4 It is the forward and reverse scan J-V curve diagram of the oriented iron oxide thin film solar cell prepared in Example 4. Detailed Description of the Invention

[0031] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0032] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above drawings are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0033] The present invention will be further described in detail below with reference to the accompanying drawings:

[0034] Example 1

[0035] A preparation method of an oriented iron oxide thin film, comprising the following steps:

[0036] Step 1) Under the protection of a nitrogen atmosphere, heat metallic tin to melting.

[0037] Step 2) Add sheet-shaped α-Fe 2 O 3 particles with a thickness of 100 nm and a diameter of 5 μm into the molten metallic tin, stir for 5 min, and let stand. After the iron oxide particles float to the liquid surface of the molten metal, stop heating, naturally cool to room temperature, and stop the atmosphere protection. The liquid metallic tin cools and solidifies into a plate shape, and the iron oxide particles are fixed on the surface of the metal.

[0038] Step 3) Adopt the method of blowing with wind to remove the iron oxide particles that are not in direct contact on the metal surface, and obtain the oriented iron oxide thin film.

[0039] Use the oriented iron oxide thin film prepared in this example to prepare a solar cell, and the operation is as follows:

[0040] Step 1: Use the magnetron sputtering method to prepare an indium oxide transparent hole transport layer on the oriented iron oxide thin film. Place the oriented iron oxide thin film in the sputtering chamber, use indium oxide ceramic as the target, the target distance is 65 mm, the rotation rate is 10 r / min, the background low vacuum is 5×10 -3 Pa, introduce high-purity argon gas, adjust the power to 45 W, and then start sputtering. The sputtering gas pressure for film coating is 0.5 - 1.1 Pa, the sputtering time is 5 min, and the substrate temperature is 150 °C.

[0041] Step 2: Use the magnetron sputtering method to prepare a transparent indium tin oxide electrode on the hole transport layer. Place the sample obtained in step 5) in the sputtering chamber, use indium tin oxide ceramic as the target, the target distance is 65 mm, the rotation rate is 10 r / min, the background low vacuum is 5×10 - 3 Pa, introduce high-purity argon gas, adjust the power to 45 W, the sputtering gas pressure for film coating is 0.5 - 1.1 Pa, the sputtering time is 5 min, and the substrate temperature is 150 °C.

[0042] The forward and reverse scan J-V curves of the prepared solar cell are as Figure 1 shown, and it can be seen from Figure 1 that the photoelectric conversion efficiency of this solar cell is 5.41%.

[0043] Example 2

[0044] A preparation method of an oriented iron oxide thin film, comprising the following steps:

[0045] Step 1) Under the protection of an argon atmosphere, heat metallic bismuth to melting.

[0046] Step 2) Add flaky Sn with a thickness of 100 nm and a diameter of 5 μm 2+ Doped α-Fe 2 O 3 particles into the molten metal bismuth, stir for 10 min, and let it stand. After the iron oxide particles float to the liquid surface of the molten metal, stop heating, naturally cool to room temperature, and stop the atmosphere protection. The liquid metal bismuth cools and solidifies into a plate shape, and the iron oxide particles are fixed on the surface of the metal.

[0047] Step 3) Use the water rinsing method to remove the iron oxide particles that are not in direct contact on the metal surface with deionized water to obtain the oriented iron oxide thin film.

[0048] Use the oriented iron oxide thin film prepared in this example to prepare a solar cell, and the operation is as follows:

[0049] Step 1: Adopt the magnetron sputtering method, put the oriented iron oxide thin film into the sputtering chamber, the target material is indium oxide ceramic, the target distance is 65 mm, the rotation rate is 10 r / min, the background low vacuum is 5×10 -3 Pa, introduce high-purity argon gas, adjust the power to 45 W, the sputtering gas pressure for coating is 0.5 - 1.1 Pa, the sputtering time is 10 min, and the substrate temperature is 100 °C. Prepare an indium oxide transparent hole transport layer on the oriented iron oxide thin film.

[0050] Step 2: Adopt the magnetron sputtering method to prepare a transparent indium tin oxide electrode on the hole transport layer. Put the sample obtained in step 5) into the sputtering chamber, the target material is indium tin oxide ceramic, the target distance is 65 mm, the rotation rate is 10 r / min, the background low vacuum is 5×10 - 3 Pa, introduce high-purity argon gas, adjust the power to 45 W, the sputtering gas pressure for coating is 0.5 - 1.1 Pa, the sputtering time is 10 min, and the substrate temperature is 150 °C.

[0051] The forward and reverse scan J-V curves of the prepared solar cell are as Figure 2 shown, and it can be seen from Figure 2 that the photoelectric conversion efficiency of this solar cell is 6.84%.

[0052] Example 3

[0053] A preparation method of an oriented iron oxide thin film, comprising the following steps:

[0054] Step 1) Under the protection of an argon atmosphere, heat metallic indium to melting.

[0055] Step 2) Add flaky Cu with a thickness of 300 nm and a diameter of 10 μm 2+ Doped α-Fe2 O 3 The particles are added to the molten metal bismuth and stirred for 10 min and then left standing. After the iron oxide particles float to the liquid surface of the molten metal, heating is stopped, and it is naturally cooled to room temperature and the atmosphere protection is stopped. The liquid metal bismuth is cooled and solidified into a plate shape, and the iron oxide particles are fixed on the surface of the metal.

[0056] Step 3) Under ultrasonic conditions, the water flushing method is adopted to remove the iron oxide particles that are not in direct contact on the metal surface, and the oriented iron oxide thin film is obtained.

[0057] Using the oriented iron oxide thin film prepared in this example to prepare a solar cell, the operations are as follows:

[0058] Step 1: By the magnetron sputtering method, the oriented iron oxide thin film is loaded into the sputtering chamber. The target material is indium oxide ceramic, the target distance is 65 mm, the rotation rate is 10 r / min, the background low vacuum is 5×10 -3 Pa, high-purity argon gas is introduced, the power is adjusted to 45 W, the sputtering gas pressure for film coating is 0.5 - 1.1 Pa, the sputtering time is 20 min, and the substrate temperature is 70 °C. An indium oxide transparent hole transport layer is prepared on the oriented iron oxide thin film.

[0059] Step 2: By the magnetron sputtering method, a transparent indium tin oxide electrode is prepared on the hole transport layer. The sample obtained in step 5) is loaded into the sputtering chamber. The target material is indium tin oxide ceramic, the target distance is 65 mm, the rotation rate is 10 r / min, the background low vacuum is 5×10 - 3 Pa, high-purity argon gas is introduced, the power is adjusted to 45 W, the sputtering gas pressure for film coating is 0.5 - 1.1 Pa, the sputtering time is 20 min, and the substrate temperature is 70 °C.

[0060] The forward and reverse sweep J-V curves of the prepared solar cell are as Figure 3 shown, and it can be seen from Figure 3 that the photoelectric conversion efficiency of this solar cell is 3.60%.

[0061] Example 4

[0062] A preparation method of an oriented iron oxide thin film, comprising the following steps:

[0063] Step 1) Under the protection of a nitrogen atmosphere, metallic zinc is heated to melting.

[0064] Step 2) Add sheet-shaped α-Fe with a thickness of 500 nm and a diameter of 20 μm 2 O 3Particles are added to molten metal bismuth and stirred for 10 min and then left standing. After the iron oxide particles float to the liquid surface of the molten metal, heating is stopped, and it is naturally cooled to room temperature and the atmosphere protection is stopped. The liquid metal bismuth cools and solidifies into a plate shape, and the iron oxide particles are fixed on the surface of the metal.

[0065] Using the oriented iron oxide thin film prepared in this example to fabricate a solar cell, the operations are as follows:

[0066] Step 1: By using the rinsing method with ethanol (inert solvent), the iron oxide particles that are not in direct contact on the metal surface are removed to obtain the oriented iron oxide thin film.

[0067] Step 2: By using the magnetron sputtering method, the oriented iron oxide thin film is placed into the sputtering chamber. The target material is indium oxide ceramic, the target distance is 65 mm, the rotation rate is 10 r / min, the background low vacuum is 5×10 -3 Pa, high-purity argon gas is introduced, the power is adjusted to 45 W, the sputtering gas pressure for film coating is 0.5 - 1.1 Pa, the sputtering time is 5 min, and the substrate temperature is 150 °C. A transparent indium oxide hole transport layer is prepared on the oriented iron oxide thin film.

[0068] Step 5) By using the magnetron sputtering method, a transparent indium tin oxide electrode is prepared on the hole transport layer. The sample obtained in step 5) is placed into the sputtering chamber. The target material is indium tin oxide ceramic, the target distance is 65 mm, the rotation rate is 10 r / min, the background low vacuum is 5×10 - 3 Pa, high-purity argon gas is introduced, the power is adjusted to 45 W, the sputtering gas pressure for film coating is 0.5 - 1.1 Pa, the sputtering time is 5 min, and the substrate temperature is 150 °C.

[0069] The forward and reverse scan J-V curves of the fabricated solar cell are as Figure 4 shown. It can be seen from Figure 4 this that the photoelectric conversion efficiency of this solar cell is 2.03%.

[0070] In summary, in the present invention, sheet-shaped iron oxide particles are added to the molten metal liquid. After the molten metal liquid cools and solidifies into a mold, the sheet-shaped iron oxide will be arranged in an oriented manner and spread flat on the surface of the metal. Then, the iron oxide particles that are not in direct contact on the metal surface are removed to obtain the oriented iron oxide thin film. This method has simple operations, low energy consumption, high repeatability, and is suitable for large-scale production. Low-melting-point metals with different characteristics can be selected as the substrate, and the thickness of the oriented thin film can be regulated by controlling the thickness of the sheet-shaped iron oxide particles (there is no phenomenon of stacking of sheet-shaped particles), and the thin film and the substrate are firmly combined. Using the oriented iron oxide thin film prepared by the present invention as the light absorption layer of the solar cell, it shows strong light absorption ability, has a higher light voltage and photoelectric conversion efficiency compared with the randomly oriented iron oxide thin film, and has stable performance.

[0071] The above content is only for explaining the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an oriented iron oxide thin film, characterized in that, it comprises the following steps; 1) Under the protection of an inert atmosphere, heat a low-melting-point metal to a molten state; 2) Add iron oxide particles to the molten metal obtained in step 1), stir and stand still until all the iron oxide particles float to the liquid surface of the molten metal, stop heating, cool to room temperature and stop the inert atmosphere protection. Wait for the liquefied metal to cool and solidify into a shape, and the iron oxide particles are fixed on the surface of the formed metal; 3) Remove the iron oxide particles that are not in direct contact on the metal surface, and retain the iron oxide particles in direct contact with the metal to obtain an oriented iron oxide thin film.

2. The method for preparing an oriented iron oxide thin film according to claim 1, characterized in that, the low-melting-point metal is a metal with a melting point below 450 °C.

3. The method for preparing an oriented iron oxide thin film according to claim 2, characterized in that, the metals with a melting point below 450 °C include metals Bi, Sn, Zn, In and their alloys.

4. The method for preparing an oriented iron oxide thin film according to claim 1, characterized in that, in step 1), the inert atmosphere is nitrogen or argon; the heating temperature is above the melting point of the low-melting-point metal.

5. The method for preparing an oriented iron oxide thin film according to claim 1, characterized in that, The iron oxide particles are α-Fe 2 O 3 or ion-doped α-Fe 2 O 3 ; the morphology of the iron oxide particles is flaky, with a thickness of 100 - 500 nm and a diameter of 5 - 20 μm.

6. The method for preparing an oriented iron oxide thin film according to claim 1, characterized in that, in step 2), the stirring time is 5-10 min.

7. The method for preparing an oriented iron oxide thin film according to claim 1, characterized in that, in step 3), remove the iron oxide particles that are not in direct contact on the metal surface by rinsing or blowing.

8. An oriented iron oxide thin film prepared by using the preparation method according to any one of claims 1-7, characterized in that, this oriented iron oxide thin film is formed by sheet-shaped iron oxide particles being oriented and tiled on the surface of a flat plate formed by the condensation of molten metal, and the sheet-shaped iron oxide particles are firmly combined with the flat plate.

9. The oriented iron oxide thin film according to claim 8, characterized in that, the thickness of this oriented iron oxide thin film is controllable.

10. The application of the oriented iron oxide thin film according to claim 8 or 9 in the preparation of a perovskite battery, characterized in that, during production: use magnetron sputtering to prepare an indium oxide transparent hole transport layer on the oriented iron oxide thin film, and then use magnetron sputtering to prepare a transparent indium tin oxide electrode on the hole transport layer.

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