Nanometer silicon material densification film forming method, diffusion type heterojunction and preparation method and application of diffusion type heterojunction

Abstract

The invention provides a method for densifying a nanometer silicon material into a film, a diffusion type heterojunction and a preparation method and application of the diffusion type heterojunction. According to the method, a silicon source, especially liquid silane, is used as a densifying agent and is mixed with the nanometer silicon material to form slurry, the slurry is used for forming a precursor film layer, and film layer densification can be achieved after heating treatment; by means of the method, a densified film layer is formed on a silicon substrate with the opposite doping type through a doped nanometer silicon material, especially a doped silicon nanowire, and diffusion treatment is carried out with the densified film layer as a doping source, so that the diffusion type heterojunction can be obtained. The densification film formation method and the preparation method for forming the diffused heterojunction by using the densification film formation method are simple and convenient, are beneficial to large-scale application in production of photovoltaic products, and can effectively improve the productivity of related photovoltaic cells.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor material preparation, and relates to a method for forming a nano-silicon material densification film, a diffusion-type heterojunction, and a preparation method and application thereof. Background Art

[0002] When the silicon material reaches the nanoscale, a series of physical effects will appear, such as quantum size effect, macroscopic quantum tunneling effect, Coulomb blockade effect, small size effect and volume effect, etc. Nano silicon materials, such as silicon nanowires, which are one-dimensional nano materials, have all the physical effects of nano materials and are the primary representatives of semiconductor nano materials. They have their own special properties in the semiconductor field and physical properties different from bulk silicon materials, such as field emission, visible photoluminescence and thermal conductivity, etc. They have a good application market in sensors, field effect transistors, photocatalysis and batteries.

[0003] Doping silicon nanowires is to dope trivalent elements such as boron, aluminum, gallium or indium into the silicon lattice during the preparation of silicon nanowires to generate holes with positive charge, i.e. P-type silicon nanowires; or dope pentavalent elements such as phosphorus or arsenic into the silicon lattice to generate surplus electrons with negative charge, i.e. N-type silicon nanowires. Doping can improve the conductivity of silicon nanowires. In the application of photovoltaic cells, it can be used to make P / N junctions as the emitter of the battery to convert photoelectrons into majority carriers, i.e. current; or to make high-low concentration junctions to reduce contact resistance and increase the minority carrier lifetime, thereby improving the photoelectric conversion efficiency of photovoltaic cells.

[0004] For example, CN106876592A discloses a multi-colored solar cell and a preparation method thereof, wherein an ordered mask is first made on the surface of a silicon substrate using a nano-ball template method, an electron beam exposure method, or a nano-imprinting technique, and then an ordered nanowire array is etched thereon using a wet process or a reactive ion etching process, and then the surface of the silicon substrate on which the ordered silicon nanowire array is placed is doped with boron elements using a diffusion process, and then a dielectric layer is made on the obtained silicon substrate on which the ordered silicon nanowire array with a PN junction formed on the surface is made using a chemical vapor deposition method, an electron beam evaporation method, an atomic layer deposition technique, or a spin coating method, and then an electrode is made thereon to obtain the target product.

[0005] At present, the mainstream method for preparing the P / N junction of photovoltaic cells is to perform thermal diffusion (such as the above-mentioned CN106876592A) or ion implantation on P-type or N-type cell silicon wafers (such as CN103811582A and CN103400741A, etc.). The high-temperature diffusion method can only dope the entire surface of the silicon substrate, while regional selective doping must use masking, etching and other processes, the steps are cumbersome and the process is time-consuming. Ion implantation can be used for local doping, but it causes serious damage to the battery, affecting the conversion efficiency, and requires annealing and repair processes. And due to the limitation of physical diffusion; moreover, the N-type doping sources commonly used in the above process, such as BBr3 / BCl3 and P-type doping sources POCl3, will introduce impurity elements O, Cl or Br, etc., which increases the difficulty of the subsequent cleaning process and affects the battery performance.

[0006] Therefore, research on new methods of using doped nano-silicon materials to manufacture diffused heterojunctions is of great significance to meeting the development and application needs of heterojunction batteries. Summary of the invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for densification film formation of nano-silicon materials, a diffuse heterojunction, and a preparation method and application thereof. The present invention uses a silicon source, especially liquid silane, as a densifier, mixes it with a nano-silicon material to form a slurry, and uses the slurry to form a precursor film layer. After a heating treatment, the film layer can be densified; the method is used to form a densified film layer on a silicon substrate with an opposite doping type, and the densified film layer is used as a doping source for diffusion treatment to obtain a diffuse heterojunction; the densification film forming method and the preparation method of using the same to form a diffuse heterojunction are simple and convenient, which is conducive to large-scale application in the production of photovoltaic products and can effectively improve the production capacity of related photovoltaic cells.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for forming a nano-silicon material into a densified film, the method comprising:

[0010] A slurry containing both nano-silicon material and silicon source is prepared to form a precursor film layer from the slurry, and a heat treatment is performed to densify the precursor film layer to obtain a densified film layer of nano-silicon material.

[0011] The present invention uses a silicon source, especially liquid silane, as a densifier to densify a nano-silicon material, especially a film layer formed by doped silicon nanowires. Specifically, liquid silane and nano-silicon material are formed into a slurry. When the slurry is used to obtain a precursor film layer, silane already exists in the composite film layer. Therefore, through subsequent heat treatment, the silane can be decomposed into silicon atoms (amorphous silicon), which are filled between the nano-silicon materials and combined with them, so that the composite film is densified.

[0012] If the nano-silicon material has been doped beforehand, such as using P-type or N-type doped silicon nanowires, during the heat treatment process, the doping elements will be evenly distributed in the densified film layer through thermal diffusion, so that the entire densified film layer presents the corresponding doping type and is electrically active;

[0013] It should be emphasized that, because silicon nanowires have a large aspect ratio, their stacking is not dense, and silicon nanowires have large gaps, so the method is very suitable for the densification of silicon nanowire film layers. However, it is not limited to silicon nanowires or doped silicon nanowires, but is also applicable to the densification of nano-silicon material film layers with other morphologies.

[0014] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0015] As a preferred technical solution of the present invention, the nano-silicon material includes silicon nanowires, preferably doped silicon nanowires; the doped silicon nanowires include P-type doped silicon nanowires or N-type doped silicon nanowires.

[0016] Preferably, the mass fraction of the doping element in the doped silicon nanowires is 3% to 10%, for example, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.7%, 6%, 6.3%, 6.5%, 6.8%, 7%, 7.3%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.7%, 9%, 9.3%, 9.5%, 9.8% or 10%, etc., but are not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0017] Preferably, the diameter of the silicon nanowire is 150-250nm, for example 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, 230nm, 240nm or 250nm, and the length is 5-20μm, for example 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0018] As a preferred technical solution of the present invention, the method for preparing the slurry includes: using liquid silane as a silicon source, mixing and grinding the liquid silane with nano-silicon material to obtain the slurry.

[0019] Preferably, the liquid silane is an organosilicon compound that does not contain oxygen.

[0020] Preferably, the molecular structure of the liquid silane includes a combination of any one or at least two of a linear silane and a cyclic silane or a branched silane, and typical but non-limiting examples of the combination include a combination of a linear silane and a cyclic silane, a combination of a linear silane and a branched silane, or a combination of a linear silane, a cyclic silane and a branched silane.

[0021] Preferably, the linear silane includes trisilane and / or n-butylsilane, the cyclic silane includes polycarbosilane (PCS), and the branched silane includes polymethylsilane (PMS).

[0022] Preferably, the mass ratio of the nano-silicon material to the liquid silane is 1:(1-4), for example 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1 or 4:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0023] Preferably, the method for preparing the slurry further comprises: firstly stirring and wetting the liquid silane and the nano-silicon material, then adding an additive, and mixing and grinding.

[0024] Preferably, the additive comprises a low molecular weight organic thickener, more preferably sandalwood.

[0025] Preferably, based on the total mass of the liquid silane, the nano-silicon material and the additive as 100%, the mass of the nano-silicon material is 2% to 10%, for example, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt% or 10wt%, etc., and the mass of the liquid silane is 5 to 20wt%, for example, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% %, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, etc., the mass of the additive is 70-93wt%, for example, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt%, 91wt%, 92wt% or 93wt%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0026] As a preferred technical solution of the present invention, the mixed grinding includes ball milling.

[0027] Preferably, the ball-to-material ratio of the ball mill is 1:(2-3), for example 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9 or 1:3, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0028] Preferably, the grinding balls used in the ball milling include zirconium oxide balls and / or corundum balls.

[0029] Preferably, the rotation speed of the ball mill is 1000-3000rpm, for example 1000rpm, 1200rpm, 1400rpm, 1600rpm, 1800rpm, 2000rpm, 2200rpm, 2400rpm, 2600rpm, 2800rpm or 3000rpm, and the time is 10-60min, for example 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min or 60min, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0030] Preferably, the fineness of the slurry is less than 1 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or 0.9 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0031] Preferably, the viscosity of the slurry is 10000-18000cps, for example, 10000cps, 10500cps, 11000cps, 11500cps, 12000cps, 12500cps, 13000cps, 13500cps, 14000cps, 14500cps, 15000cps, 15500cps, 16000cps, 16500cps, 17000cps, 17500cps or 18000cps, and more preferably 12000cps, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0032] As a preferred technical solution of the present invention, the method of forming the precursor film layer with the slurry includes spraying and / or screen printing.

[0033] It should be noted that the requirements for the slurry (such as viscosity and fineness) vary depending on the film-forming method. The slurry prepared in the present invention is a non-Newtonian fluid, which requires the dispersion medium system to have a higher viscosity and thixotropic properties to form a finer pattern by screen printing, spraying, etc. When the slurry viscosity needs to be increased, silicon nanowires with larger diameters can be selected to reduce the amount of thickener required for their aggregation, making it easier to control the slurry viscosity.

[0034] Preferably, the thickness of the precursor film layer is ≥ the fineness of the slurry.

[0035] Preferably, the thickness of the precursor film layer is 1 to 3 μm, for example, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm or 3 μm, and more preferably 1.2 to 1.5 μm, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0036] Preferably, the heat treatment is performed on the precursor film layer after it is dried.

[0037] Preferably, the drying method includes drying in a vacuum oven at 260-300°C, for example, 260°C, 270°C, 280°C, 290°C or 300°C, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0038] When the slurry contains small molecule additives, such as sandalwood, the drying temperature needs to be controlled above 200°C to effectively decompose and volatilize the additives to avoid residual oxygen-containing organic phase in the film layer.

[0039] Preferably, the heat treatment is performed under the protection of an inert atmosphere.

[0040] Preferably, the inert atmosphere comprises argon.

[0041] Preferably, the temperature of the heat treatment is 450-600°C, for example 400°C, 460°C, 470°C, 480°C, 490°C, 500°C, 520°C, 540°C, 560°C, 580°C or 600°C, and more preferably 500-550°C, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0042] During the heat treatment process, when the nano-silicon material uses a nano-silicon material with a doping type, such as doped silicon nanowires, the doping elements of the nano-silicon material will be activated during the high-temperature densification of the film layer, and will be evenly distributed in the densified film layer, so that the entire densified film layer will present a uniform corresponding doping type.

[0043] As a preferred technical solution of the present invention, the method comprises:

[0044] The doped silicon nanowires are used as nano-silicon materials and are stirred and wetted with liquid oligomeric silane with a molecular weight of ≤1000, and sandalwood is added as an additive. The mass fraction of the doped element in the doped silicon nanowires is 3% to 10%, the diameter is 150 to 250nm, and the length is 5 to 20μm; the liquid oligomeric silane includes trisilane and / or n-butylsilane; the mass of the nano-silicon material is controlled to be 2 to 10wt% of the total mass, the mass of the liquid silane is 5 to 20wt% of the total mass, and the rest is sandalwood, and corundum balls with a diameter of 1mm and a diameter of 0.2mm are added. Grinding beads, controlling the ball-to-material ratio to be 1:(2-3), mixing and grinding at 1000-3000 rpm for 10-60 min to obtain a slurry with a fineness of less than 1 μm and a viscosity of 10000-18000 cps; using spraying and / or screen printing to form a precursor film layer from the slurry, placing the obtained precursor film layer in a vacuum oven at 260-300° C. for drying, and then placing it in a sintering furnace, and under the protection of an inert atmosphere, heat-treating it at 450-600° C. for 30-60 min to densify the precursor film layer to obtain a densified film layer of nano-silicon material.

[0045] In a second aspect, the present invention provides a method for preparing a diffused heterojunction, the preparation method comprising:

[0046] Prepare a silicon substrate with a first doping type; prepare a nano-silicon material with a second doping type; the first doping type is opposite to the second doping type;

[0047] The method for densification film formation of nano-silicon materials described in the first aspect is used to form a densified film layer of the nano-silicon material on the silicon substrate, and diffusion treatment is performed to diffuse the doping elements in the doped silicon nanowires into the silicon substrate to obtain a diffused heterojunction.

[0048] The present invention forms a dense film layer on a silicon substrate of opposite doping type by using a densification film forming method of nano silicon material, thereby constructing a heterojunction structure, and further through a diffusion process, the doping elements in the densified film layer diffuse into the silicon substrate, and a diffusion junction can be obtained. That is, after the slurry forms a precursor film layer, first during the heat treatment process, the doping elements diffuse in the new amorphous silicon layer on the surface, so that the amorphous silicon layer has the corresponding doping type, and then during the diffusion treatment process, it continues to diffuse into the original silicon substrate. Therefore, in order to make the slurry have a sufficient concentration of doping elements, the mass fraction of the doping elements in the doped silicon nano material or the amount of the doped silicon nano material in the slurry can be adjusted as needed. The type of PN junction formed depends on the temperature of the diffusion treatment. If the diffusion treatment temperature is appropriate (>900°C), the doping elements of the densified layer will diffuse into the silicon substrate, and a diffusion type PN junction is formed at this time. If the temperature of the diffusion treatment process is too low (<750°C), the doping elements will not diffuse into the silicon substrate, and a mutation type PN junction is formed at this time.

[0049] It should be noted that when the nano-silicon material is P-type doped and the silicon substrate is N-type doped, the constructed heterojunction structure type is a pin junction; when the nano-silicon material is N-type doped and the silicon substrate is P-type doped, the constructed heterojunction structure type is a nip junction.

[0050] Compared with the traditional process of introducing a doping source (such as BBr3 / BCl3 commonly used for boron source; or POCl3 commonly used for phosphorus source) to perform boron diffusion or phosphorus diffusion on the silicon substrate when manufacturing heterojunctions in photovoltaic devices, the preparation method of the present invention can avoid the introduction of impurity elements such as O, Cl, and Br brought by the boron source or phosphorus source, and effectively solve the problem of difficult cleaning in subsequent processes; and at the same time, compared with the process temperature of boron diffusion >1000°C and phosphorus diffusion at 900-1050°C in the traditional process, the present invention can achieve film densification at a lower temperature while activating the film layer by the doping elements to obtain the target type of doping state, which benefits from the reduction in the temperature required for the diffusion of the doping elements in amorphous silicon. Therefore, the scheme of the present invention can significantly reduce energy consumption.

[0051] As a preferred technical solution of the present invention, the temperature of the diffusion treatment is 900-1000°C, for example, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C or 1000°C, and the time is 40-60min, for example, 40min, 42min, 44min, 46min, 48min, 50min, 52min, 54min, 56min, 58min or 60min, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0052] Preferably, after the diffusion treatment, the mass fraction of the doping elements from the nano-silicon material in the silicon substrate is 1% to 10%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0053] Preferably, the nano-silicon material having the second doping type is a doped silicon nanowire.

[0054] The present invention finds that when the nano-silicon material is selected as doped silicon nanowires, the effects of the formed diffused heterojunction and further diffusion treatment are better.

[0055] Preferably, the silicon substrate is pre-treated to remove the cutting damage layer and is cleaned.

[0056] Preferably, the pretreatment method comprises soaking in a washing solution, wherein the washing solution comprises a 1 mol / L NaOH aqueous solution.

[0057] Preferably, the obtained diffused heterojunction is first cleaned and then subjected to the diffusion treatment.

[0058] Preferably, the cleaning comprises first performing BOE cleaning and then performing water cleaning.

[0059] In a third aspect, the present invention provides a diffused heterojunction obtained using the preparation method described in the second aspect.

[0060] In a fourth aspect, the present invention provides a photovoltaic device comprising the diffused heterojunction described in the third aspect.

[0061] As a preferred technical solution of the present invention, compared with the prior art solution, the present invention has at least the following

[0062] Beneficial effects:

[0063] The present invention uses a silicon source, especially liquid silane, as a densifier, mixes it with a nano-silicon material to form a slurry, uses the slurry to form a precursor film layer, and after heating treatment, the film layer can be densified; using the method, doped nano-silicon materials, especially doped silicon nanowires, form a densified film layer on a silicon substrate with opposite doping types, and uses the densified film layer as a doping source for diffusion treatment to obtain a diffuse heterojunction; the densification film forming method and the preparation method of using the same to form a diffuse heterojunction are simple and convenient, and avoid the traditional process of manufacturing heterojunctions. The problem of impurity elements such as O, Cl, Br, etc. introduced by introducing boron or phosphorus doping sources can effectively solve the problem of difficult cleaning in subsequent processes; and compared with the traditional process using a boron source or a phosphorus source for diffusion, the present invention can form an amorphous silicon dense film layer as a doping source at a lower temperature, and effectively reduce the energy required for the diffusion of doping elements in the film layer and the silicon substrate, thereby significantly reducing energy consumption. The densification film forming method and the preparation method of the diffused heterojunction provided by the present invention are both conducive to large-scale application in the production of photovoltaic products, and can effectively improve the production capacity of related photovoltaic cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 is a concentration distribution curve of doping elements from nano-silicon materials in the heterojunction structure obtained in Example 1;

[0065] Figure 2 Schematic diagram of the heterojunction structure obtained in Example 1. DETAILED DESCRIPTION

[0066] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0067] Example 1

[0068] This embodiment provides a method for preparing a diffused heterojunction, the method comprising:

[0069] Under the protection of inert gas, 2g of P-type silicon nanowires with a boron content of 2wt% were added to a ball mill containing 5g of liquid silane, wherein the diameter of the silicon nanowires was 150-250nm and the length was 5-20μm, and the liquid silane was trisilane and polymethylsilane in a volume ratio of 1:1; after stirring to wet the mixture, 93g of sandalwood was added, and then 10g of Al2O3 ball milling beads with a diameter of 1mm and 30g of Al2O3 ball milling beads with a diameter of 0.2mm were added, and the mixture was ball milled at a speed of 2000rpm for 20min. The slurry fineness was measured by a scraper fineness meter and was less than 1μm. The viscosity was 12000cps, and 100g of slurry was obtained;

[0070] Take an N-type silicon wafer as a silicon substrate, place it in a 1M NaOH solution to remove the cutting damage layer, clean it with BOE and rinse it with deionized water, place it on the printing table of a screen printer, take 20g of slurry and place it in the screen of the screen printer, print it on the N-type silicon wafer according to the preset pattern, move it to a heating plate at 280°C and dry it for 8 minutes to form a precursor film layer with a thickness of 1.5μm;

[0071] The silicon wafer loaded with the dried precursor film layer is placed at 600°C for constant temperature heat treatment for 30 minutes to densify the obtained film layer and activate the doped element boron to form an electrically active P-type densified film layer. It is then cleaned with BOE and rinsed with deionized water. It is then placed in a diffusion furnace for diffusion treatment at a constant temperature of 950°C for 50 minutes to diffuse the boron atoms into the N-type silicon wafer to obtain a diffused heterojunction of a pin structure.

[0072] Example 2

[0073] This embodiment provides a method for preparing a diffused heterojunction, the method comprising:

[0074] Under the protection of inert gas, 10g of P-type silicon nanowires with a boron content of 5wt% are added to a ball mill containing 10g of liquid silane, wherein the diameter of the silicon nanowires is 150-250nm and the length is 5-20μm, and the liquid silane is n-butylsilane and polycarbosilane in a volume ratio of 1:1; after stirring to wet it, 80g of sandalwood is added, and then 10g of Al2O3 ball milling beads with a diameter of 1mm and 30g of Al2O3 ball milling beads with a diameter of 0.2mm are added, and the ball milling is carried out at a speed of 3000rpm for 10min. The slurry fineness is measured by a scraper fineness meter and is less than 1μm. The viscosity is 18000cps, and 100g of slurry is obtained;

[0075] Take an N-type silicon wafer as a silicon substrate, place it in a 1M NaOH solution to remove the cutting damage layer, clean it with BOE and rinse it with deionized water, place it on the printing table of a screen printer, take 20g of slurry and place it in the screen of the screen printer, print it on the N-type silicon wafer according to the preset pattern, move it to a heating plate at 260°C and dry it for 10 minutes to form a precursor film layer with a thickness of 2.8μm;

[0076] The silicon wafer loaded with the dried precursor film layer is placed at 450°C for constant temperature heat treatment for 60 minutes to densify the obtained film layer and activate the doped element boron to form an electrically active P-type densified film layer. It is then cleaned with BOE and rinsed with deionized water, and then placed in a diffusion furnace for diffusion treatment at a constant temperature of 900°C for 60 minutes to diffuse the boron atoms into the N-type silicon wafer to obtain a diffused heterojunction of a pin structure.

[0077] Example 3

[0078] This embodiment provides a method for preparing a diffused heterojunction, the method comprising:

[0079] Under the protection of inert gas, 5 g of P-type silicon nanowires with a boron content of 8 wt% were added to a ball mill containing 20 g of liquid silane, wherein the diameter of the silicon nanowires was 150-250 nm and the length was 5-20 μm, and the liquid silane was trisilane, polycarbosilane and polymethylsilane in a volume ratio of 2:1:1; after stirring to wet the mixture, 75 g of sandalwood was added, and then 10 g of Al2O3 ball milling beads with a diameter of 1 mm and 30 g of Al2O3 ball milling beads with a diameter of 0.2 mm were added, and the mixture was ball milled at a speed of 1000 rpm for 60 min. The slurry fineness was measured by a scraper fineness meter and was less than 1 μm. The viscosity was 10000 cps, and 100 g of slurry was obtained;

[0080] Take an N-type silicon wafer as a silicon substrate, place it in a 1M NaOH solution to remove the cutting damage layer, clean it with BOE and rinse it with deionized water, and then place it on the printing table of a screen printer. Take 20g of slurry and place it in the screen of the screen printer. Print it on the N-type silicon wafer according to the preset pattern, move it to a heating plate at 300°C and dry it for 6 minutes to form a precursor film layer with a thickness of 1.2μm.

[0081] The silicon wafer loaded with the dried precursor film layer is placed at 600°C for constant temperature heat treatment for 30 minutes to densify the obtained film layer and activate the doped element boron to form an electrically active P-type densified film layer. It is then cleaned with BOE and rinsed with deionized water, and then placed in a diffusion furnace for diffusion treatment at a constant temperature of 1000°C for 40 minutes to diffuse the boron atoms into the N-type silicon wafer to obtain a diffused heterojunction of a pin structure.

[0082] Example 4

[0083] This embodiment provides a method for preparing a diffused heterojunction, the method comprising:

[0084] Under the protection of inert gas, 4g of N-type silicon nanowires with a boron content of 4wt% were added to a ball mill containing 8g of liquid silane, wherein the diameter of the silicon nanowires was 150-250nm and the length was 5-20μm, and the liquid silane was trisilane and polymethylsilane in a volume ratio of 1:1; after stirring to wet the mixture, 88g of sandalwood was added, and then 10g of Al2O3 ball milling beads with a diameter of 1mm and 30g of Al2O3 ball milling beads with a diameter of 0.2mm were added, and the mixture was ball milled at a speed of 1000rpm for 60min. The slurry fineness was measured by a scraper fineness meter and was less than 1μm. The viscosity was 14000cps, and 100g of slurry was obtained;

[0085] Take a P-type silicon wafer as a silicon substrate, place it in a 1M NaOH solution to remove the cutting damage layer, clean it with BOE and rinse it with deionized water, and then place it on the printing table of a screen printer. Take 20g of slurry and place it in the screen of the screen printer. Print it on the P-type silicon wafer according to the preset pattern, move it to a heating plate at 280°C and dry it for 8 minutes to form a precursor film layer with a thickness of 2.4μm.

[0086] The silicon wafer loaded with the dried precursor film layer is placed at 530°C for constant temperature heat treatment for 30 minutes to densify the obtained film layer and activate the doped element boron to form an electrically active N-type densified film layer. It is then cleaned with BOE and rinsed with deionized water. It is then placed in a diffusion furnace for diffusion treatment at a constant temperature of 950°C for 50 minutes to diffuse the boron atoms into the P-type silicon wafer to obtain a diffused heterojunction, which is a nip structure.

[0087] Example 5

[0088] This embodiment provides a method for preparing a heterojunction, wherein the preparation method uses P-type doped silicon particles instead of P-type doped silicon nanowires, wherein the P-type doped silicon particles are spherical particles with a particle size D50 of 80 nm. Apart from this, other conditions are exactly the same as those in Example 1.

[0089] Example 6

[0090] This embodiment provides a method for preparing a heterojunction, wherein the preparation method uses N-type doped silicon particles instead of N-type doped silicon nanowires, wherein the N-type doped silicon particles are spherical particles with a particle size D50 of 80 nm. Apart from this, other conditions are exactly the same as those of Example 4.

[0091] Example 7

[0092] This embodiment provides a method for preparing a diffusion-type heterojunction. In the preparation method, the temperature of the diffusion treatment is adjusted from 950° C. to 850° C. Apart from this, other conditions are exactly the same as those in Embodiment 1.

[0093] Example 8

[0094] This embodiment provides a method for preparing a diffusion-type heterojunction. In the preparation method, the temperature of the diffusion treatment is adjusted from 950° C. to 850° C. Apart from this, other conditions are exactly the same as those of Embodiment 4.

[0095] Comparative Example 1

[0096] This comparative example provides a method for preparing a heterojunction, which uses the process in the prior art, uses a boron source BCl3, diffuses boron into an N-type silicon substrate, forms a P-type doping layer, and obtains a heterojunction structure.

[0097] Comparative Example 2

[0098] This comparative example provides a method for preparing a heterojunction, which uses the process in the prior art, uses a phosphorus source POCl3, diffuses phosphorus into a P-type silicon substrate, forms an N-type doping layer, and obtains a heterojunction structure.

[0099] Comparative Example 3

[0100] This comparative example provides a method for preparing a heterojunction structure. In the preparation method, liquid silane is not used when preparing the slurry, that is, the amount of liquid silane is adjusted from 6 g to 0 g, and the amount of sandalwood is adjusted from 91 g to 97 g, the total amount of P-type silicon nanowires and sandalwood is kept at 100 g, and the P-type silicon nanowires account for 3 wt% of the total mass. Apart from this, other conditions are exactly the same as those in Example 1.

[0101] The heterojunction structures obtained in the examples and comparative examples were tested:

[0102] (1) Using secondary ion mass spectrometry (SIMS) to measure the concentration distribution curve of doping elements in nano-silicon materials:

[0103] Figure 1 This is the distribution curve of doping element concentration in the heterojunction structure obtained in Example 1. It can be seen from the figure that the surface concentration of boron is as high as 6*10 20 atm / cc, and the diffusion depth is about 5μm. This shows that P-type silicon nanowire slurry is a very convenient boron source. Patterns of different shapes can be printed by screen printing, and boron diffusion is carried out in the slurry coverage area. The surface boron concentration and diffusion depth can be adjusted according to the requirements of battery design by selecting the boron concentration of P-type silicon nanowires and the diffusion temperature and time.

[0104] Figure 2 Schematic diagram of the heterojunction structure obtained in Example 1. The structure on the left side of the arrow represents the precursor film layer formed on the silicon substrate. N-Si represents the N-type silicon substrate, and the surface of the substrate contains P-SiNW and Si X H n The film layer, P-SiNW represents the P-type doped silicon nanowire component, Si X H n Represents silane component; "HT" on the arrow represents heat treatment and diffusion treatment. The structural diagram on the right side of the arrow represents the formed densified film layer, wherein a-Si represents the amorphous silicon component. At this time, the boron element in the densified film layer is activated to make the entire densified film layer P-type doped. At the same time, the boron element in the densified film layer diffuses into the silicon substrate, so that the densified film layer and the silicon layer constitute a diffused heterojunction structure.

[0105] (2) The sheet resistance of the heterojunction structure and the thickness of the diffused heterojunction were measured using a four-probe thin-layer sheet resistance instrument. The results are listed in Table 1.

[0106] (3) Fabricating the obtained heterojunction structure into a heterojunction battery: In the preparation methods provided in the embodiments and comparative examples, the silicon wafer used is cleaned and textured, and then a heterojunction structure is prepared thereon. Then, a TCO conductive film is deposited on both sides of the silicon wafer by a PVD method, and a grid line silver electrode is screen-printed on the TCO conductive film. After the electrodes are sintered, a battery is obtained, and the battery is tested to obtain an open circuit voltage (V oc ), short circuit current (J sc ) and photoelectric conversion efficiency (η) values ​​are recorded in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] It can be seen from Table 1 that:

[0111] In Examples 5-6, Si particles are used to form films. After the quality of the film material decreases, the density is poor, and the open circuit voltage and current both decrease significantly; in Examples 7-8, the diffusion temperature is too low, and the doping elements cannot diffuse evenly on the surface of amorphous silicon, the square resistance and current density decrease significantly, and the efficiency is extremely low; it should be noted that when the diffusion temperature is further increased (lower than the melting point of crystalline silicon but more than 1000°C), there is no obvious effect on the formation and properties of the diffusion-type heterojunction, and only the problem of increased energy consumption is involved; Comparative Examples 1-2 are processes using BCl3 and POCl3 as B and P sources. Compared with the two, in addition to simplifying the process, the performance and efficiency of the resulting battery can be comparable to the performance of the existing PN junction manufacturing process; In Comparative Example 3, no liquid silane is added, resulting in a film layer formed by doped silicon nanowires on the surface of the silicon substrate containing a large number of gaps and holes, and the diffusion efficiency is extremely low and the photoelectric efficiency of the resulting battery is extremely low.

[0112] The present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0113] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0114] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0115] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for forming a nano-silicon material into a densified film, characterized in that: The method comprises: A slurry containing both nano-silicon material and silicon source is prepared to form a precursor film layer from the slurry, and a heat treatment is performed to densify the precursor film layer to obtain a densified film layer of nano-silicon material.

2. The method according to claim 1, characterized in that The nano-silicon material includes silicon nanowires, preferably doped silicon nanowires; Preferably, the mass fraction of the doping element in the doped silicon nanowire is 3% to 10%; Preferably, the silicon nanowire has a diameter of 150-250 nm and a length of 5-20 μm.

3. The method according to claim 1 or 2, characterized in that: The method for preparing the slurry comprises: using liquid silane as a silicon source, mixing and grinding the liquid silane with a nano-silicon material to obtain a slurry; Preferably, the liquid silane is an oxygen-free liquid organosilicon compound; Preferably, the molecular structure of the liquid silane includes any one or a combination of at least two of linear silane and cyclic silane or branched silane; Preferably, the linear silane includes trisilane and / or n-butylsilane, the cyclic silane includes polycarbosilane, and the branched silane includes polymethylsilane; Preferably, the mass ratio of the nano-silicon material to the liquid silane is 1:(1-4); Preferably, the method for preparing the slurry further comprises: firstly stirring and wetting the liquid silane and the nano-silicon material, then adding an additive, and mixing and grinding; Preferably, the additive includes a low molecular weight organic thickener, more preferably sandalwood; Preferably, taking the total mass of liquid silane, nano-silicon material and additive as 100%, the mass of the nano-silicon material is 2% to 10%, the mass of the liquid silane is 5 to 20wt%, and the mass of the additive is 70 to 93wt%.

4. The method according to claim 3, characterized in that The mixed grinding includes ball milling; Preferably, the ball-to-material ratio of the ball mill is 1:(2-3); Preferably, the grinding balls used in the ball milling include zirconium oxide balls and / or corundum balls; Preferably, the ball milling speed is 1000-3000 rpm, and the time is 10-60 min; Preferably, the fineness of the slurry is less than 1 μm; Preferably, the viscosity of the slurry is 10000-18000 cps, more preferably 12000 cps.

5. The method according to any one of claims 1 to 4, characterized in that: The method of forming the precursor film layer by the slurry includes spraying and / or screen printing; Preferably, the thickness of the precursor film layer is ≥ the fineness of the slurry; Preferably, the thickness of the precursor film layer is 1 to 3 μm, more preferably 1.2 to 1.5 μm; Preferably, the heat treatment is performed after the precursor film layer is dried; Preferably, the drying method comprises drying in a vacuum oven at 260-300°C; Preferably, the heat treatment is carried out under the protection of an inert atmosphere; Preferably, the inert atmosphere comprises argon; Preferably, the heat treatment temperature is 450-600°C, more preferably 500-550°C.

6. The method according to any one of claims 1 to 5, characterized in that: The method comprises: The doped silicon nanowires are used as nano-silicon materials and are stirred and wetted with liquid silane with a molecular weight of ≤1000, and sandalwood is added as an additive. The mass fraction of the doped element in the doped silicon nanowires is 3% to 10%, the diameter is 150 to 250nm, and the length is 5 to 20μm. The molecular structure of the liquid silane includes any one of linear silane and cyclic silane or branched silane or a combination of at least two of them. The mass of the nano-silicon material is controlled to be 2 to 10wt% of the total mass, the mass of the liquid silane is controlled to be 5 to 20wt% of the total mass, and the rest is sandalwood. The nano-silicon material with a diameter of 1mm and the liquid silane with a diameter of 0.2m are added. m corundum ball milling beads, controlling the ball-to-material ratio to be 1:(2-3), mixing and grinding at 1000-3000 rpm for 10-60 minutes to obtain a slurry with a fineness of less than 1 μm and a viscosity of 10000-18000 cps; using spraying and / or screen printing to form a precursor film layer with a thickness of 1-3 μm, placing the obtained precursor film layer in a vacuum oven at 260-300° C. for drying, and then placing it in a sintering furnace, and under the protection of an inert atmosphere, heat-treating it at 450-600° C. for 30-60 minutes to densify the precursor film layer, thereby obtaining a densified film layer of nano-silicon material.

7. A method for preparing a diffused heterojunction, characterized in that: The preparation method comprises: Prepare a silicon substrate with a first doping type; prepare a nano-silicon material with a second doping type; the first doping type is opposite to the second doping type; The method for forming a densified film of nano-silicon material according to any one of claims 1 to 6 is used to form a densified film layer of the nano-silicon material on the silicon substrate, and then a diffusion treatment is performed to obtain a diffused heterojunction.

8. The preparation method according to claim 7, characterized in that: The diffusion treatment is performed at a temperature of 900 to 1000°C and for a time of 40 to 60 minutes; Preferably, after the diffusion treatment, the mass fraction of the doping element from the nano-silicon material in the silicon substrate is 1% to 10%; Preferably, the nano-silicon material having the second doping type is a doped silicon nanowire; Preferably, the silicon substrate is pre-treated to remove the cutting damage layer and is cleaned; Preferably, the pretreatment method comprises soaking in a washing solution, wherein the washing solution comprises a 1 mol / L NaOH aqueous solution; Preferably, the obtained diffused heterojunction is first cleaned and then subjected to the diffusion treatment; Preferably, the cleaning comprises first performing BOE cleaning and then performing water cleaning.

9. A diffused heterojunction, characterized in that: Obtained using the preparation method described in claim 7 or 8.

10. A photovoltaic device, characterized in that: A diffused heterojunction according to claim 9 is included.

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