Alpha-Fe2O3 crystal as well as preparation method and application thereof

Abstract

The invention discloses an alpha-Fe2O3 crystal as well as a preparation method and application thereof. The preparation method comprises the following steps: weighing an iron oxide raw material and a composite fluxing agent according to a molar ratio of (6-30): (94-70), mixing and grinding for 3-5 hours to obtain a mixed material; putting the mixed material into a crucible in a vacuum glove box, and sealing; placing the crucible in a crystal growth furnace with a vertical temperature gradient, heating to 1200-1300 DEG C at different rates, preserving heat for 12-16 hours, then cooling to 1150-1100 DEG C, then cooling to 800-880 DEG C, preserving heat for 8-10 hours, finally cooling to room temperature, and stripping the crucible to obtain an original crystal ingot; and finally, mechanically stripping the original crystal ingot, grinding and polishing to remove the fluxing agent, and cleaning to obtain the alpha-Fe2O3 crystal. According to the method, the alpha-Fe2O3 crystal is grown by adopting a fluxing agent gradient solidification method, so that the melting point of the crystal can be effectively reduced, the crystal growth difficulty is reduced, the crystallization range is wider and faster, and the yield is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystal growth and specifically relates to an α-Fe 2 O 3 Crystal and its preparation method and application. Background Art

[0002] With the rapid development of modern industry and urbanization, energy crisis and environmental pollution are becoming increasingly serious. As a clean and safe new energy source, the development and utilization of solar energy has received widespread attention. At present, silicon-based solar cells dominate the field of solar cells, but their production cost is high, energy consumption is high, and there are environmental pollution problems. Therefore, it is of great significance to develop new solar cells with low production cost and low energy consumption. Iron oxide (α-Fe 2 O 3 ) As an n-type semiconductor material with low price, abundant reserves, less environmental pollution, excellent stability and corrosion resistance, it has strong light absorption ability in the visible light region, can absorb about 50% of solar energy, and has a high photoelectric conversion efficiency.

[0003] Iron oxide materials have great potential in the field of solar cells, but current research is mainly focused on polycrystalline thin film technology. However, the preparation process of polycrystalline thin films is complex, costly, and difficult to prepare large-area films. In the prior art, iron oxide single crystals are grown by vapor phase method, hydrothermal method, flux method, etc. However, due to the high melting point of iron oxide crystals, the container material for crystal growth is easily corroded, and the grown single crystals are difficult to peel off and prone to cracking. Summary of the invention

[0004] In order to solve the shortcomings of the prior art, the present invention aims to provide an α-Fe 2 O 3 Crystal and its preparation method and application. The present invention adopts flux gradient solidification method to grow α-Fe 2 O 3 Crystals can effectively lower the melting point of crystals, reduce the difficulty of crystal growth, make the crystallization range larger and faster, and can improve the yield rate, solving the problems of easy cracking and difficult growth of crystals in existing methods.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] In one aspect, the present invention provides an α-Fe 2 O 3 The crystal growth method comprises the following steps:

[0007] (1) Mixing and pretreatment: weigh the iron oxide raw material and the composite flux according to a molar ratio of (6-30):(94-70), mix and grind for 3-5 hours to obtain a mixed material;

[0008] (2) Loading and packaging: loading the mixed material into a crucible in a vacuum glove box and sealing the crucible;

[0009] (3) Crystal growth: placing a crucible in a crystal growth furnace with a vertical temperature gradient, raising the temperature to 1200° C. to 1300° C. at a rate of 100 to 150° C. / h, keeping the temperature for 12 to 16 hours, then reducing the temperature to 1150 to 1100° C. at a rate of 5° C. / min to 10° C. / min, then reducing the temperature to 800 to 880° C. at a rate of 6 to 10° C. / h and keeping the temperature for 8 to 10 hours, finally cooling naturally to room temperature, and peeling off the crucible to obtain the original crystal ingot;

[0010] (4) Ingot processing: Mechanically peeling and polishing the original ingot to remove the flux, and cleaning to obtain the α-Fe 2 O 3 Crystal.

[0011] Before step (1), the method further comprises:

[0012] The iron oxide raw material and the composite flux are dried at a temperature of 150° C. for 10 hours.

[0013] In step (1), the composite flux is PbO, B in a molar ratio of (4-6): (1-3): (1-3): 1 2 O 3 ,BaO,Y 2 O 3 mixture.

[0014] In step (1), the iron oxide raw materials, PbO, B 2 O 3 , BaO and Y 2 O 3 The purity is ≥99.99%;

[0015] In step (1), the grinding process is carried out in a corundum mortar.

[0016] Before step (2), the method further comprises:

[0017] The crucible is pretreated, specifically comprising: cleaning the crucible with deionized water and an organic solvent by ultrasonic heating in sequence, and then performing an annealing treatment.

[0018] The crucible is annealed at a temperature of 150°C for 5 hours.

[0019] The organic solvent is acetone or anhydrous ethanol;

[0020] The ultrasonic heating cleaning time is 1 hour.

[0021] In step (2), the crucible is a platinum crucible with a thickness of 0.2 to 1.0 mm.

[0022] In step (3), the crucible is sealed by mechanical folding;

[0023] In step (4), the cleaning step specifically includes: soaking in deionized water at a temperature of 80° C. to 100° C. for 5 hours, and then cleaning with anhydrous ethanol.

[0024] In another aspect, the present invention provides an α-Fe 2 O 3 Crystal, which consists of the above-mentioned α-Fe 2 O 3 The crystal growth method is obtained.

[0025] In a third aspect, the present invention further provides the above-mentioned α-Fe 2 O 3 Crystal growth method for preparing α-Fe 2 O 3 Crystal, or the above α-Fe 2 O 3 Application of crystals in the preparation of optoelectronic device materials.

[0026] The positive and progressive effects of the present invention are:

[0027] 1. The present invention adopts PbO+B 2 O 3 +BaO+Y 2 O 3 The composite flux system significantly reduces the melting point of the raw materials, allowing them to be completely melted within the range of 1200-1300°C, while effectively inhibiting the volatilization of the PbO composite flux. 2 O 3 The addition of plays a key role in regulating the melt characteristics and broadens the component range of crystal precipitation. In addition, the present application also achieves efficient separation of crystals and flux by mechanical stripping, grinding and polishing, and high-temperature boiling to treat the crystal ingot, significantly improving the growth efficiency and quality of the crystal.

[0028] 2. The crucible of the present invention is made of Pt material, which has a high melting point and excellent corrosion resistance. The specific thickness design effectively reduces the adhesion problem between the crucible and the melt. This optimization not only ensures the safety of the crystal growth process, but also reduces the difficulty of crystal peeling, thereby ensuring the integrity of the grown crystal and a high yield rate.

[0029] 3. The crystal growth of the present invention adopts a gradient temperature solidification method, and realizes crystal growth under normal pressure by controlling the temperature gradient at multiple stages with different rates. This method expands the crystallization range of the crystal, significantly reduces the crystal growth temperature and melt viscosity, inhibits the volatilization of components, and promotes the mass and heat transfer during the crystal growth process. At the same time, this method effectively reduces component segregation, improves crystallization quality, and promotes the growth and growth of crystals. In addition, the specific temperature gradient design reduces stress cracking inside the crystal, reduces the difficulty of growth, and further improves the yield. Through this innovative method, the existing α-Fe 2 O 3 The limitations of crystal preparation technology have been overcome, and flake α-Fe with obvious hexagonal characteristics has been successfully prepared. 2 O 3 Crystal. The crystal has a smooth surface, regular morphology, and a clear structural exposure surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 α-Fe grown in Example 1 of the present invention 2 O 3 Crystal diagram;

[0031] Figure 2 α-Fe grown in Example 1 of the present invention 2 O 3 Crystal powder XRD pattern;

[0032] Figure 3 α-Fe grown in Example 1 of the present invention 2 O 3 The volt-ampere characteristic curve of the crystal;

[0033] Figure 4 This is the XRD diagram of the ingot powder grown in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0034] The present invention is described in detail below in conjunction with the embodiments, and the technical scheme of the present invention is clearly and completely described to facilitate the understanding of the present invention by those skilled in the art. The described embodiments are only 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 ordinary technicians in the field without creative work are within the scope of protection of the present invention. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0035] In the following examples, the iron oxide raw materials, PbO, B 2 O 3 , BaO and Y2 O 3 The purity is ≥99.99%.

[0036]

Performance test

[0037] The product prepared in the embodiment was tested for its application performance, and the test method is as follows:

[0038] 1. X-ray diffraction pattern: The test was conducted using an X-ray diffractometer model D / MAX-2000 produced by Rigaku Corporation of Japan.

[0039] 2. Volt-ampere characteristic curve: The test was conducted using a solar energy detection system produced by Shenzhen Purui Materials Technology Co., Ltd.

[0040] Example 1

[0041] A growth α-Fe 2 O 3 A crystal method comprising the steps of:

[0042] (1) Ingredients and pretreatment: The iron oxide raw material and the composite flux (PbO, B in a molar ratio of 5:2:2:1) were mixed. 2 O 3 ,BaO,Y 2 O 3 ) After drying at 150° C. for 10 h, the components were accurately weighed according to a molar ratio of 25:75, and the weighed components were ground in a corundum mortar for 4 h to obtain a fully mixed material.

[0043] (2) Crucible pretreatment: A platinum crucible with a thickness of 0.5 mm was cleaned with deionized water and anhydrous ethanol by ultrasonic heating for 1 h to remove surface impurities, and then annealed at 150 °C in a muffle furnace for 5 h.

[0044] (3) Loading and packaging: The fully ground and mixed materials of step (1) are loaded into the platinum crucible treated in step (2) in a vacuum glove box and sealed by mechanical folding.

[0045] (4) Crystal growth: Place the packaged crucible in a crystal growth furnace with a vertical temperature gradient, raise the temperature to 1240°C at 120°C / h and keep it for 14 hours to ensure that the raw materials are fully melted. Then reduce the temperature to 1130°C at 8°C / min and then to 850°C at 8°C / h, and keep it for 9 hours to prevent crystal stress cracking. Then cool naturally to room temperature, peel off the crucible and take out the original crystal ingot.

[0046] (5) Ingot processing: Mechanical stripping and polishing were used to remove excess flux, and the surface contamination was removed by soaking in 90°C deionized water for 5 h. The α-Fe 2O 3 Crystal.

[0047] Figure 1 The α-Fe grown in this example 2 O 3 From the crystal diagram, it can be clearly seen that the obtained crystal has a clear and regular exposed surface.

[0048] Figure 2 The XRD pattern of the crystal powder in this example proves that the obtained crystal is α-Fe 2 O 3 Crystal.

[0049] Figure 3 This is the volt-ampere characteristic curve of the crystal test in this embodiment. The battery structure is at 100m W / cm 2 Under simulated sunlight, the open circuit photovoltage is 1.1V and the short circuit current density is 24.91m A / cm 2 , the filling factor is 59.98, and the photoelectric conversion efficiency is 16.5%. This also shows that the grown crystals have a highly ordered and complete crystal structure compared to the thin film, with regular internal atomic arrangement and fewer defects and lattice distortions. This structure is conducive to the directional transmission of photogenerated carriers in the crystal, reducing the scattering and trapping of carriers during transmission, so that the photogenerated carriers can be more efficiently transported to the electrode to form a photocurrent. In addition, the surface states of the single crystal are relatively few, which also reduces the possibility of surface recombination, allowing the photogenerated carriers to participate in the formation of photocurrent more effectively.

[0050] Example 2

[0051] A growth α-Fe 2 O 3 A crystal method comprising the steps of:

[0052] (1) Ingredients and pretreatment: The iron oxide raw material and the composite flux (PbO, B in a molar ratio of 4:1:3:1) were mixed. 2 O 3 ,BaO,Y 2 O 3 ) After drying at 150° C. for 10 h, the components were accurately weighed according to a molar ratio of 15:85, and the weighed components were ground in a corundum mortar for 3 h to obtain a fully mixed material.

[0053] (2) Crucible pretreatment: A platinum crucible with a thickness of 0.2 mm was cleaned with deionized water and anhydrous ethanol by ultrasonic heating for 1 h to remove surface impurities, and then annealed at 150 °C in a muffle furnace for 5 h.

[0054] (3) Loading and packaging: The fully ground and mixed materials of step (1) are placed in a vacuum glove box into the platinum crucible treated in step (2), and sealed by mechanical folding.

[0055] (4) Crystal growth: Place the packaged crucible in a crystal growth furnace with a vertical temperature gradient, raise the temperature to 1200°C at 100°C / h and keep it for 12 hours to ensure that the raw materials are fully melted. Then reduce the temperature to 1150°C at 5°C / min and then to 880°C at 6°C / h, and keep it for 8 hours to prevent crystal stress cracking. Finally, cool naturally to room temperature, peel off the crucible and take out the original crystal ingot.

[0056] (5) Ingot treatment: The flux was removed by mechanical stripping and polishing, and then the surface contamination was removed by soaking in deionized water at 80°C for 5 h. The crystal was taken out and repeatedly washed with anhydrous ethanol to obtain α-Fe 2 O 3 The solar cell structure thus prepared was placed under standard illumination of 100 m W / cm 2 The photoelectric conversion efficiency was 14.3%.

[0057] Example 3

[0058] A growth α-Fe 2 O 3 A crystal method comprising the steps of:

[0059] (1) Ingredients and pretreatment: The iron oxide raw material and the composite flux (PbO, B in a molar ratio of 6:3:1:1) were mixed. 2 O 3 ,BaO,Y 2 O 3 ) After drying at 150° C. for 10 h, the components were accurately weighed according to a molar ratio of 30:70, and the weighed components were ground in a corundum mortar for 5 h to obtain a fully mixed material.

[0060] (2) Crucible pretreatment: A platinum crucible with a thickness of 1.0 mm was cleaned with deionized water and anhydrous ethanol by ultrasonic heating for 1 h to remove surface impurities, and then annealed at 150 °C in a muffle furnace for 5 h.

[0061] (3) Loading and packaging: The fully ground and mixed materials of step (1) are placed in a vacuum glove box into the platinum crucible treated in step (2), and sealed by mechanical folding.

[0062] (4) Crystal growth: Place the packaged crucible in a crystal growth furnace with a vertical temperature gradient, raise the temperature to 1300°C at 150°C / h and keep it for 16 hours to ensure that the raw materials are fully melted. Then reduce the temperature to 1100°C at 10°C / min and then to 800°C at 10°C / h, and keep it for 10 hours to prevent crystal stress cracking. Then cool naturally to room temperature, peel off the crucible and take out the original crystal ingot.

[0063] (5) Ingot processing: Remove excess flux by mechanical stripping and polishing, soak in 100°C deionized water for 5 h, take out the crystal and repeatedly wash it with anhydrous ethanol to obtain α-Fe 2 O 3 The solar cell structure thus prepared was placed under standard illumination of 100 m W / cm 2 The photoelectric conversion efficiency was 11.3%.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that the composite flux is PbO+BaO+Y in a molar ratio of 7:2:1. 2 O 3 The other process steps were carried out according to Example 1. After the growth was completed and then cooled naturally to room temperature, the crucible was peeled off and the original crystal ingot was taken out. It was found that the grown crystal had obvious hexagonal characteristics of α-Fe 2 O 3 The crystals are very small in size and difficult to separate from the flux. There are also cracks on the surface of the crystals, which break directly when mechanical stripping is used.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that the Y 2 O 3 Replace with Bi 2 O 3 The other process steps were carried out according to Example 1. After the growth was completed and then cooled naturally to room temperature, the crucible was peeled off and the original ingot was taken out. It was found that the grown ingot did not produce α-Fe with obvious hexagonal characteristics. 2 O 3 The crystal, the whole surface of the ingot is reddish brown. The main product is lead-containing compounds, such as Figure 4 .

[0068] Comparative Example 3

[0069] The difference from Example 1 is that in step (4), the crystal growth temperature is: the temperature is raised to 1100°C at 120°C / h and kept at this temperature for 14h to melt the raw materials. Then the temperature is lowered to 900°C at 5°C / h, and then naturally cooled to room temperature. The original crystal ingot is taken out of the crucible, and it is found that the whole crystal ingot is reddish brown. Analysis shows that the raw materials are not fully melted, and the morphology at the time of charging is retained, and no crystallization phenomenon is formed.

[0070] Comparative Example 4

[0071] The difference from Example 1 is that the crucible used is a quartz crucible. After the growth is completed, it is found that the crucible has been largely integrated with the crystal ingot and cannot be separated. From the appearance, it can be seen that there are holes distributed on the outside of the crucible and traces of corrosion and blackening can be clearly observed. Ultimately, the growth fails and no crystals are produced.

[0072] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and equivalent changes made by using the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for growing α-Fe2O3 crystals, characterized in that: The following steps are involved: (1) Mixing and pretreatment: weigh the iron oxide raw material and the composite flux according to a molar ratio of (6-30):(94-70), mix and grind for 3-5 hours to obtain a mixed material; (2) Loading and packaging: loading the mixed material into a crucible in a vacuum glove box and sealing the crucible; (3) Crystal growth: placing a crucible in a crystal growth furnace with a vertical temperature gradient, raising the temperature to 1200° C. to 1300° C. at a rate of 100 to 150° C. / h, keeping the temperature for 12 to 16 hours, then reducing the temperature to 1150 to 1100° C. at a rate of 5° C. / min to 10° C. / min, then reducing the temperature to 800 to 880° C. at a rate of 6 to 10° C. / h and keeping the temperature for 8 to 10 hours, finally cooling naturally to room temperature, and peeling off the crucible to obtain the original crystal ingot; (4) Ingot processing: Mechanically peel and polish the original ingot to remove the flux, and clean it to obtain the α-Fe2O3 crystal.

2. The method for growing α-Fe2O3 crystals according to claim 1, characterized in that: In step (1), the composite flux is a mixture of PbO, B2O3, BaO, and Y2O3 in a molar ratio of (4-6):(1-3):(1-3):

1.

3. The method for growing α-Fe2O3 crystals according to claim 2, characterized in that: In step (1), the purity of the iron oxide raw material, PbO, B2O3, BaO and Y2O3 is ≥99.99%; And / or, in step (1), the grinding process is carried out in a corundum mortar.

4. The method for growing α-Fe2O3 crystals according to claim 1, characterized in that: Before step (2), the method further comprises: The crucible is pretreated, specifically comprising: cleaning the crucible with deionized water and an organic solvent by ultrasonic heating in sequence, and then performing an annealing treatment.

5. The method for growing α-Fe2O3 crystals according to claim 4, characterized in that: The crucible is annealed at a temperature of 150° C. for 5 hours; And / or, the organic solvent is acetone or anhydrous ethanol; And / or, the ultrasonic heating cleaning time is 1 hour.

6. The method for growing α-Fe2O3 crystals according to claim 1, characterized in that: Before step (1), the method further comprises: The iron oxide raw material and the composite flux are dried at a temperature of 150° C. for 10 hours.

7. The method for growing α-Fe2O3 crystals according to claim 1, characterized in that: In step (2), the crucible is a platinum crucible with a thickness of 0.2 to 1.0 mm.

8. The method for growing α-Fe2O3 crystals according to claim 1, characterized in that: In step (3), the crucible is sealed by mechanical folding; And / or, in step (4), the cleaning step specifically includes: soaking in deionized water at a temperature of 80° C. to 100° C. for 5 hours, and then cleaning with anhydrous ethanol.

9. An α-Fe2O3 crystal, characterized in that: It is obtained by the growth method of α-Fe2O3 crystals as described in claims 1 to 8.

10. An α-Fe2O3 crystal prepared by the α-Fe2O3 crystal growth method as claimed in claims 1 to 8, or use of the α-Fe2O3 crystal as claimed in claim 9 in preparing optoelectronic device materials.

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