Nanometer silicon material densification film forming method, mutant heterojunction, preparation method and application thereof

Abstract

The invention provides a nanometer silicon material densification film formation method, a mutant heterojunction and a preparation method and application thereof, the nanometer silicon material is prepared into dispersion liquid ink, and a film formed by the dispersion liquid ink is densified by gaseous silane to obtain a densified film layer of the nanometer silicon material; according to the method, a densified film layer is formed on a silicon substrate with an opposite doping type by using a doped nano silicon material, especially a doped silicon nanowire, so that a mutant heterojunction can be obtained; the densification film formation method and the preparation method for forming the mutant heterojunction by using the densification film formation method are simple and convenient, are beneficial to large-scale application in the production of photovoltaic products, and can effectively improve the performance and 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 densification and film formation of nano silicon materials, a mutant 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 and affects the conversion efficiency, and requires annealing and repair processes. And due to the limitation of physical diffusion, the P / N junction prepared by the above method is usually a gradient junction with a wide depletion zone. With the development of the photovoltaic industry, the photoelectric conversion efficiency of photovoltaic cells has experienced a change from ordinary P-type cells, P-type-PERC cells, to N-type-TopCon cells, and the mass production photoelectric conversion efficiency has increased from 21%, 22.9%, to 24.8% accordingly. The next generation of high-efficiency cells will be N-type-heterojunctions, and their photoelectric conversion efficiency is expected to be as high as 26%. The core of the N-type heterojunction battery is to construct a mutant heterojunction, which is different from the gradient P / N junction. The mutant heterojunction has a narrower depletion region and a larger built-in potential difference V. bi and higher voltage output, thereby showing higher photoelectric conversion efficiency.

[0006] Therefore, it is still necessary to develop a new technical solution to utilize the characteristics of doped nano-silicon materials such as doped silicon nanowires and to construct an effective mutant heterojunction to meet the development and application needs of high-efficiency N-type 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 and film formation of nano-silicon materials, a mutant heterojunction, and a preparation method and application thereof. The present invention prepares the nano-silicon material into a dispersion ink, and densifies the formed film using gaseous silane to obtain a densified film layer of the nano-silicon material; using the method, a densified film layer is formed on a silicon substrate with the opposite doping type by doping nano-silicon materials, especially doped silicon nanowires, to obtain a mutant heterojunction; the densification film formation method and the preparation method using the densification film formation method to form a mutant heterojunction are simple and convenient, which is conducive to large-scale application in the production of photovoltaic products, and can effectively improve the performance and 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] The nano-silicon material and the solvent are prepared into a dispersion ink, the dispersion ink is made to form a precursor film layer, a silicon source is introduced for heat treatment, the precursor film layer is densified, and a nano-silicon material densified film layer is obtained.

[0011] The present invention utilizes a silicon source as a densifier to densify a film layer formed by nano-silicon materials, especially doped silicon nanowires; specifically, a dispersion ink containing nano-silicon materials is prepared for film formation, and after obtaining a precursor film layer, a silicon source, preferably gaseous silane, is used to first deposit the film layer, and then a heat treatment is performed, so that the deposited material can be thermally decomposed into amorphous silicon that fills between the nano-silicon materials, thereby forming a continuous composite film layer, making the film layer densified.

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

[0013] It should be noted that the requirements for dispersion ink vary according to the different film-forming methods, and those skilled in the art should make adaptive adjustments based on the actual situation. Specifically, dispersion ink is a Newtonian fluid with relatively low viscosity, and is a suspension formed by nano-silicon materials dispersed in a solvent. Dispersion ink used for spin coating generally requires that the medium dispersion system (solvent) has a small surface tension, the medium is easily volatile, and it is easy to spread on the substrate to form a uniform film; dispersion ink for inkjet printing requires a large surface tension, easy to form stable liquid beads, so as to support the formation of fine printing patterns of smaller size, and the medium has low volatility to prevent nozzle clogging and affect production.

[0014] It should be emphasized that, due to the large aspect ratio of silicon nanowires, their stacking is not dense, resulting in large gaps between the silicon nanowires. Therefore, the densification film forming method provided by the present invention is very suitable for the densification of silicon nanowire film layers, but 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.

[0015] 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.

[0016] 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.

[0017] Preferably, the mass fraction of the doping element in the doped silicon nanowires is 1% to 5%, for example, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.7%, 4%, 4.3%, 4.5%, 4.8% or 5%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0018] Preferably, the diameter of the silicon nanowire is 50 to 150 nm, for example, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm or 150 nm, and the length is 5 to 20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0019] As a preferred technical solution of the present invention, the method for preparing the dispersion ink comprises: placing the nano-silicon material in a solvent for ultrasonic dispersion, and taking the upper stable suspension as the dispersion ink.

[0020] Preferably, the ultrasonic dispersion time is 30 to 60 min, for example, 30 min, 34 min, 38 min, 42 min, 46 min, 50 min, 54 min, 58 min or 60 min, and the power is 100 to 300 W, for example, 100 W, 120 W, 140 W, 160 W, 180 W, 200 W, 220 W, 240 W, 260 W, 280 W or 300 W, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0021] Preferably, the solvent comprises isopropanol.

[0022] Preferably, based on the mass of the dispersion ink as 100%, the nano-silicon material accounts for 0.5% to 5%, for example, 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8% or 5%, and the solvent accounts for 95% to 99.5%. %, for example, 95%, 95.2%, 95.5%, 95.7%, 96%, 96.2%, 96.5%, 96.7%, 97%, 97.2%, 97.5%, 97.7%, 98%, 98.2%, 98.5%, 98.7%, 99%, 99.2% or 99.5%, etc., but are not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0023] Preferably, the viscosity of the dispersion ink is 20 to 150 cps, for example, 20 cps, 30 cps, 40 cps, 50 cps, 60 cps, 70 cps, 80 cps, 90 cps, 100 cps, 110 cps, 120 cps, 130 cps, 140 cps or 150 cps, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0024] As a preferred technical solution of the present invention, the method for forming the precursor film layer includes any one of spin coating, dip coating or inkjet printing or a combination of at least two of them. Typical but non-limiting examples of the combination include a combination of spin coating and dip coating, a combination of spin coating and inkjet printing, or a combination of inkjet printing and dip coating.

[0025] Preferably, the thickness of the precursor film layer is 20 to 300 nm, for example, 20 nm, 50 nm, 70 nm, 90 nm, 110 nm, 130 nm, 150 nm, 170 nm, 190 nm, 210 nm, 230 nm, 250 nm, 280 nm or 300 nm, and is further preferably 200 to 280 nm, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0026] Preferably, the heat treatment is performed on the precursor film layer after it is dried.

[0027] Preferably, the drying method includes drying in a vacuum oven at 60-80°C, for example, 60°C, 64°C, 68°C, 72°C, 74°C, 76°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the silicon source includes gaseous silane, and the gaseous silane contains only silicon and hydrogen elements.

[0029] Preferably, monosilane (SiH4) and disilane (H6Si2) are included.

[0030] Preferably, the heat treatment is performed under the protection of an inert atmosphere.

[0031] Preferably, the inert atmosphere comprises argon.

[0032] Preferably, the gaseous silane is introduced with the inert atmosphere as a carrier gas.

[0033] Preferably, the flow ratio of the gaseous silane to the inert atmosphere is 1:(20-100), for example 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95 or 1:100, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0034] Preferably, the heat treatment comprises first performing a low temperature deposition treatment and then performing a high temperature densification treatment.

[0035] Preferably, the temperature of the low-temperature deposition treatment is 300-500°C, for example, 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, 420°C, 440°C, 460°C, 480°C or 500°C, and is further preferably 400-450°C, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0036] Preferably, the temperature of the high-temperature densification treatment is 550-750°C, for example, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C or 750°C, etc., and more preferably 650-750°C, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0037] Preferably, the silicon source is continuously introduced during the low-temperature deposition process, and the introduction of the silicon source is stopped during the high-temperature densification process.

[0038] The low temperature deposition process of the present invention uses a silicon source, especially gaseous silane, to perform low pressure chemical vapor deposition. When the nano silicon material uses a nano silicon material with a doping type, such as doped silicon nanowires, during the high temperature densification process, the doping elements of the nano silicon material will be activated and evenly distributed in the densified film layer, so that the entire densified film layer presents a uniform corresponding doping type.

[0039] As a preferred technical solution of the present invention, the method comprises:

[0040] Doped silicon nanowires are placed as nano-silicon materials in a solvent of isopropanol, wherein the diameter of the doped silicon nanowires is 50-150 nm, the length is 5-20 μm, the mass fraction of the doping element is 1%-5%, and the mass of the nano-silicon material is controlled to be 0.5%-5%; then ultrasonic dispersion is performed at a power of 100-300 W for 30-60 min, and the upper layer of the stable suspension is taken as the dispersion ink, and the viscosity of the obtained dispersion ink is 20-150 cps; any one of spin coating, dip coating or inkjet printing is used. The method comprises the following steps: forming a precursor film layer with a thickness of 20 to 300 nm by using a dispersion ink in a manner of one or a combination of at least two of the above; placing the obtained precursor film layer in a vacuum oven at 60 to 80° C. to dry it, and then placing it in a sintering furnace, introducing a mixed gas of gaseous silane and argon at a flow ratio of 1:(20 to 100), performing a low-temperature deposition treatment on the dried precursor film layer at 300 to 500° C., and then stopping the introduction of gaseous silane; raising the furnace temperature to 550 to 750° C., performing a high-temperature densification treatment, and obtaining a nano-silicon material densified film layer.

[0041] In a second aspect, the present invention provides a method for preparing a mutant heterojunction, the preparation method comprising:

[0042] 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;

[0043] The method for forming a densified film of nano-silicon material described in the first aspect is used to form a densified film layer of the nano-silicon material on the silicon substrate to obtain a mutant heterojunction.

[0044] 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, which belongs to a mutation junction. In the process of densification, after the precursor film layer is decomposed on the silicon substrate to form an amorphous silicon film layer, due to the low temperature (<750°C) of the high-temperature densification treatment, the doping element (referring to the doping element in the nano silicon material with the second doping type) diffuses only in the newly generated amorphous silicon film layer, and does not diffuse into the original crystalline silicon substrate; in the present invention, the lower the viscosity of the ink, the lower its solid content, and the greater the thickness loss of the formed film layer after spin coating and drying. Considering that the impurities of the mutation heterojunction do not need to diffuse into the silicon wafer, the coating thickness of the precursor film layer should be controlled to be relatively thin, so as to facilitate the diffusion of the doping element inside the amorphous film layer, and at the same time, prevent local enrichment caused by too high a doping element content.

[0045] 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.

[0046] 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.

[0047] Preferably, the nano-silicon material having the second doping type is a doped silicon nanowire.

[0048] Preferably, the silicon substrate is pre-treated to remove the cutting damage layer and is cleaned.

[0049] Preferably, the pretreatment method comprises soaking in a washing solution, wherein the washing solution comprises a 1 mol / L NaOH aqueous solution.

[0050] Preferably, the cleaning comprises first performing BOE cleaning and then performing water cleaning.

[0051] In a third aspect, the present invention provides a mutant heterojunction obtained using the preparation method described in the second aspect.

[0052] In a fourth aspect, the present invention provides a photovoltaic device comprising the mutant heterojunction described in the third aspect.

[0053] As a preferred technical solution of the present invention, compared with the prior art solution, the present invention has at least the following

[0054] Beneficial effects:

[0055] The present invention prepares nano-silicon materials into a dispersion ink to form a precursor film layer, uses a silicon source, especially gaseous silane, as a densifier, and heat treats the precursor film layer to achieve densification of the film layer; using this densification film-forming method, doped nano-silicon materials, especially doped silicon nanowires, are formed on a silicon substrate with opposite doping types to form a densified film layer, thereby obtaining a mutant heterojunction; the present invention uses doped silicon nanowires as a film-forming network, and forms an amorphous silicon film material (precursor film layer) by epitaxy after decomposing a silicon source, wherein the film material has a high degree of homogenization, and the diffusion of doping elements in the amorphous silicon layer is more uniform; the densification film-forming method of the present invention and the formation of the densification film using the same The preparation method of the mutant heterojunction is simple and convenient, and avoids the problem of introducing impurity elements such as O, Cl, Br, etc. due to the introduction of boron or phosphorus doping sources when manufacturing heterojunctions in traditional processes, and effectively solves the problem of difficult cleaning in subsequent processes. At the same time, compared with the traditional process using a boron source or a phosphorus source for diffusion, the present invention can achieve film densification at a lower temperature, so that the film layer is activated by the doping element to obtain a target type of doping state, effectively reducing the energy required for the doping element to diffuse in the film layer and the silicon substrate, thereby significantly reducing energy consumption, which is conducive to large-scale application in the production of photovoltaic products and can effectively improve the open circuit voltage, stability and production capacity of photovoltaic cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a concentration distribution curve of doping elements from nano-silicon materials in the heterojunction structure obtained in Example 1;

[0057] Figure 2 is a concentration distribution curve of doping elements from nano-silicon materials in the heterojunction structure obtained in Example 5;

[0058] Figure 3 Schematic diagram of the heterojunction structure obtained in Example 1. DETAILED DESCRIPTION

[0059] 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.

[0060] Example 1

[0061] This embodiment provides a method for preparing a mutant heterojunction, the preparation method comprising:

[0062] Weighing 0.9 g of P-type doped silicon nanowires with a boron content of 2 wt%, wherein the diameter of the doped silicon nanowires is 50 to 150 nm and the length is 5 to 20 μm, placing the doped silicon nanowires as nano-silicon materials in a solvent of isopropanol, controlling the mass of the nano-silicon materials to account for 0.9 wt % of the total mass, performing ultrasonic dispersion at a power of 200 W for 50 min, taking the upper layer of the stable suspension as a dispersion ink, and the viscosity of the dispersion ink is 35 cps;

[0063] Take an N-type silicon wafer as the 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 in a spin coater, take 1 mL of the dispersion ink and place it in the center of the N-type silicon wafer, spin coat it at 1500 rpm for 0.5 min to form a precursor film layer with a thickness of 200 nm, then move it to a heating plate, heat it to 80°C, and dry it for 2 min;

[0064] The silicon substrate carrying the dried precursor film layer is placed in a sintering furnace. After the furnace temperature rises to 400°C, a mixed gas of SiH4 and argon is introduced at a flow ratio of 1:60 to perform a low-temperature deposition treatment on the film layer for 30 minutes, and then the introduction of SiH4 is stopped, while the introduction of argon is maintained;

[0065] The furnace temperature is increased to 650°C, and a high-temperature densification treatment is performed for 50 minutes to densify the film layer and activate the doped element boron to form an electrically active P-type densified film layer, thereby obtaining a mutant heterojunction of the pin structure type.

[0066] Example 2

[0067] This embodiment provides a method for preparing a mutant heterojunction, the preparation method comprising:

[0068] Weighing 0.9 g of P-type doped silicon nanowires with a boron content of 1 wt%, wherein the diameter of the doped silicon nanowires is 50 to 150 nm and the length is 5 to 20 μm, placing the doped silicon nanowires as nano-silicon materials in a solvent of isopropanol, controlling the mass of the nano-silicon materials to account for 5 wt % of the total mass, performing ultrasonic dispersion at a power of 300 W for 30 min, taking the upper layer of the stable suspension as a dispersion ink, and the viscosity of the dispersion ink is 145 cps;

[0069] Take an N-type silicon wafer as the 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 in a spin coater, take 1 mL of the dispersion ink and place it in the center of the N-type silicon wafer, spin coat it at 3000 rpm for 1 min to form a precursor film layer with a thickness of 150 nm, then move it to a heating plate, heat it to 70°C, and dry it for 3 min;

[0070] The silicon substrate carrying the dried precursor film layer is placed in a sintering furnace. After the furnace temperature rises to 300°C, a mixed gas of SiH4 and argon is introduced at a flow ratio of 1:100 to perform a low-temperature deposition treatment on the film layer for 40 minutes, and then the introduction of SiH4 is stopped, while the introduction of argon is maintained;

[0071] The furnace temperature is increased to 550° C., and a high-temperature densification treatment is performed for 60 minutes to densify the film layer and activate the doped element boron to form an electrically active P-type densified film layer, thereby obtaining a mutant heterojunction of the pin structure type.

[0072] Example 3

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

[0074] Weighing 0.9 g of P-type doped silicon nanowires with a boron content of 5 wt%, wherein the diameter of the doped silicon nanowires is 50 to 150 nm and the length is 5 to 20 μm, placing the doped silicon nanowires as nano-silicon materials in a solvent of isopropanol, controlling the mass of the nano-silicon materials to account for 0.5 wt % of the total mass, performing ultrasonic dispersion at a power of 100 W for 60 min, taking the upper layer of the stable suspension as a dispersion ink, and the viscosity of the dispersion ink is 20 cps;

[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 in a spin coater, take 1 mL of the dispersion ink and place it in the center of the N-type silicon wafer, spin coat it at 800 rpm for 0.5 min to form a precursor film layer with a thickness of 260 nm, then move it to a heating plate, heat it to 65 ° C, and dry it for 5 min;

[0076] The silicon substrate carrying the dried precursor film layer is placed in a sintering furnace. After the furnace temperature rises to 500°C, a mixed gas of SiH4 and argon is introduced at a flow ratio of 1:20 to perform a low-temperature deposition treatment on the film layer for 20 minutes, and then the introduction of SiH4 is stopped, while the introduction of argon is maintained;

[0077] The furnace temperature is increased to 750°C, and a high-temperature densification treatment is performed for 30 minutes to densify the film layer and activate the doped element boron to form an electrically active P-type densified film layer, thereby obtaining a mutant heterojunction of the pin structure type.

[0078] Example 4

[0079] This embodiment provides a method for preparing a mutant heterojunction, the preparation method comprising:

[0080] Weighing 0.5 g of N-type doped silicon nanowires with a phosphorus content of 3 wt%, wherein the diameter of the doped silicon nanowires is 50 to 150 nm and the length is 5 to 20 μm, placing the doped silicon nanowires as nano-silicon materials in a solvent of isopropanol, controlling the mass of the nano-silicon materials to account for 3 wt % of the total mass, performing ultrasonic dispersion for 40 min at a power of 200 W, taking the upper stable suspension as a dispersion ink material, and the viscosity of the dispersion ink is 35 cps;

[0081] 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, place it in a spin coater, take 0.6mL of the dispersion ink and place it in the center of the P-type silicon wafer, spin coat it at 2000rpm for 0.5min to form a precursor film layer with a thickness of 220nm, then move it to a heating plate, heat it to 85℃, and dry it for 2min;

[0082] The silicon substrate carrying the dried precursor film layer is placed in a sintering furnace. After the furnace temperature rises to 450°C, a mixed gas of SiH4 and argon is introduced at a flow ratio of 1:60 to perform a low-temperature deposition treatment on the film layer for 40 minutes, and then the introduction of SiH4 is stopped, while the introduction of argon is maintained;

[0083] The furnace temperature is increased to 700°C, and a high-temperature densification treatment is performed for 40 minutes to densify the obtained film layer and activate the doped element phosphorus to form an electrically active N-type densified film layer, thereby obtaining a mutant heterojunction of the nip structure type.

[0084] Example 5

[0085] 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.

[0086] Example 6

[0087] 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.

[0088] Example 7

[0089] This embodiment provides a method for preparing a mutant heterojunction. In the preparation method, the temperature of the high-temperature densification treatment is adjusted from 650° C. to 800° C. Apart from this, other conditions are exactly the same as those in Example 1.

[0090] Example 8

[0091] This embodiment provides a method for preparing a mutant heterojunction. In the preparation method, the temperature of the high-temperature densification treatment is adjusted from 650° C. to 500° C. Apart from this, other conditions are exactly the same as those in Example 1.

[0092] Comparative Example 1

[0093] This comparative example provides a method for preparing a heterojunction structure, which does not use silane, that is, the preparation method does not deposit the silicon wafer with the formed precursor film layer, but directly places it at 650°C and performs constant temperature heating treatment for 50 minutes to obtain a heterojunction structure; except for this, other conditions are exactly the same as those in Example 1.

[0094] Comparative Example 2

[0095] This comparative example provides a method for preparing a heterojunction structure, wherein the preparation method does not use silane, that is, the preparation method does not deposit the silicon wafer with the formed precursor film layer, but directly places it at 650° C. and performs constant temperature heating treatment for 50 minutes to obtain a heterojunction structure. Apart from this, other conditions are exactly the same as those in Example 4.

[0096] The heterojunction structures obtained in the examples and comparative examples were tested:

[0097] (1) Use secondary ion mass spectrometry (SIMS) to measure the concentration distribution curve of doping elements from nano-silicon materials in silicon substrates:

[0098] Figure 1 The concentration distribution curve of doping elements in the heterojunction structure obtained in Example 1 is shown in the figure. It can be seen that the boron concentration is approximately rectangular and the concentration is slightly higher than 2*10 20 atm / cc, and this concentration value is maintained throughout the entire thickness of the P layer (P-type silicon nanowire film layer). When the depth enters the interface between the P layer and the silicon wafer, the boron concentration curve slowly decreases, and it seems that the boron in the P layer diffuses into the silicon wafer, but this is an illusion caused by the hysteresis effect of the SIMS measurement method. Because Example 1 is only heat treated at 650°C, boron will not diffuse, and diffusion treatment above 900°C must be performed for boron diffusion to occur. When the depth reaches the silicon wafer body, since the detection limit of the SIMS instrument is about 1*10 17 atm / cc, the concentration value is noise, showing large fluctuations.

[0099] Figure 2This is the distribution curve of doping element concentration in the heterojunction structure obtained in Example 5. It can be seen from the figure that when Si particles are used as raw material, the doping concentration of boron atoms decreases slowly with increasing depth. This is because the Si particles cannot serve as a supporting skeleton during the film formation process, resulting in local enrichment of crystalline Si during the film formation process and enrichment of the grown amorphous silicon in another area. As a result, in the subsequent doping element diffusion process, the doping elements are concentrated in the area where crystalline silicon is enriched, thereby increasing the diffusion depth.

[0100] Figure 3 The schematic diagram of the heterojunction structure obtained in Example 1. The structure on the left side of the arrow represents the structure of the P-SiNW and Si loaded on the surface of the silicon substrate after low-temperature deposition. X H n The film layer, N-Si represents the N-type silicon substrate, P-SiNW represents the P-type doped silicon nanowire component, Si X H n Represents silane component; "HT" on the arrow represents high-temperature densification treatment. The structural diagram on the right side of the arrow represents the formed densification film layer, and the mutant heterojunction structure formed by the densification film layer and the silicon substrate, wherein a-Si represents the amorphous silicon component. At this time, the boron element in the densification film layer is activated to make the entire densification film layer form P-type doping.

[0101] (2) The sheet resistance of the heterojunction structure and the thickness of the mutant heterojunction were measured using a four-probe thin-layer sheet resistance instrument. The results are listed in Table 1.

[0102] (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.

[0103] Table 1

[0104]

[0105] It can be seen from Table 1 that:

[0106] The battery performance obtained in Examples 1-4 is excellent after densification and formation of a mutant heterojunction; Examples 5-6 use Si particles to form films, and the density is poor after the film quality decreases, and the open circuit voltage and current both decrease significantly; the activation temperature of Example 7 is too high, the doping elements are activated to the surface of the doped silicon wafer, and the open circuit voltage is significantly reduced; the activation temperature of Example 8 is too low, 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; Comparative Example 1-2 does not add a gaseous silicon source, and its density is lower than that of Si particle film formation, and its square resistance, open circuit voltage and current density decrease more significantly.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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: The nano-silicon material and the solvent are prepared into a dispersion ink, the dispersion ink is made to form a precursor film layer, a silicon source is introduced for heat treatment, the precursor film layer is densified, and a nano-silicon material densified film layer is obtained.

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 1% to 5%; Preferably, the silicon nanowire has a diameter of 50 to 150 nm and a length of 5 to 20 μm.

3. The method according to claim 1 or 2, characterized in that: The method for preparing the dispersion ink comprises: placing the nano silicon material in a solvent for ultrasonic dispersion, and taking the upper stable suspension as the dispersion ink; Preferably, the ultrasonic dispersion time is 30 to 60 minutes and the power is 100 to 300 W; Preferably, the solvent comprises isopropanol; Preferably, based on the mass of the dispersion ink being 100%, the nano-silicon material accounts for 0.5% to 5%, and the solvent accounts for 95% to 99.5%; Preferably, the viscosity of the dispersion ink is 20-150 cps.

4. The method according to any one of claims 1 to 3, characterized in that: The method of forming the precursor film layer includes any one of spin coating, dip coating or inkjet printing or a combination of at least two thereof; Preferably, the thickness of the precursor film layer is 20 to 300 nm, more preferably 200 to 280 nm; Preferably, the precursor film layer is subjected to the heat treatment after being dried; Preferably, the drying method comprises drying in a vacuum oven at 60-80°C.

5. The method according to any one of claims 1 to 4, characterized in that: The silicon source includes gaseous silane, and the gaseous silane contains only silicon and hydrogen elements; Preferably, it includes monosilane and disilane; Preferably, the heat treatment is carried out under the protection of an inert atmosphere; Preferably, the inert atmosphere comprises argon; Preferably, the gaseous silane is introduced with the inert atmosphere as a carrier gas; Preferably, the flow ratio of the gaseous silane to the inert atmosphere is 1:(20-100); Preferably, the heat treatment comprises first performing a low temperature deposition treatment and then performing a high temperature densification treatment; Preferably, the temperature of the low temperature deposition treatment is 300-500° C., more preferably 400-450° C.; Preferably, the temperature of the high temperature densification treatment is 550-750°C, more preferably 650-750°C; Preferably, the silicon source is continuously introduced during the low-temperature deposition process, and the introduction of the silicon source is stopped during the high-temperature densification process.

6. The method according to any one of claims 1 to 5, characterized in that: The method comprises: Doped silicon nanowires are placed as nano-silicon materials in a solvent of isopropanol, wherein the diameter of the doped silicon nanowires is 50-150 nm, the length is 5-20 μm, the mass fraction of the doping element is 1%-5%, and the mass of the nano-silicon material is controlled to be 0.5%-5%; then ultrasonic dispersion is performed at a power of 100-300 W for 30-60 min, and the upper layer of the stable suspension is taken as the dispersion ink, and the viscosity of the obtained dispersion ink is 20-150 cps; any one of spin coating, dip coating or inkjet printing is used. The method comprises the following steps: the method comprises the steps of: forming a precursor film layer with a thickness of 20 to 300 nm by using a dispersion ink, drying the precursor film layer in a vacuum oven at 60 to 80° C., and then placing the precursor film layer in a sintering furnace, introducing a mixed gas of gaseous silane and argon at a flow ratio of 1:(20 to 100), performing a low-temperature deposition treatment on the dried precursor film layer at 300 to 500° C., and then stopping the introduction of gaseous silane; raising the furnace temperature to 550 to 750° C., performing a high-temperature densification treatment, and obtaining a densified film layer of a nano-silicon material.

7. A method for preparing a mutant 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 to obtain a mutant heterojunction.

8. The preparation method according to claim 7, characterized in that: 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 cleaning comprises first performing BOE cleaning and then performing water cleaning.

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

10. A photovoltaic device, characterized in that: Containing the mutant heterojunction according to claim 9.

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