CN110690324A - Crystalline silicon solar cell, preparation method thereof and photovoltaic module - Google Patents
Crystalline silicon solar cell, preparation method thereof and photovoltaic module Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
- H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic System
- H01L31/182—Special manufacturing methods for polycrystalline Si, e.g. Si ribbon, poly Si ingots, thin films of polycrystalline Si
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- H01L31/02—Details
- H01L31/0216—Coatings
- H01L31/02161—Coatings for devices characterised by at least one potential jump barrier or surface barrier
- H01L31/02167—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells
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- H01L31/186—Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
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- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/546—Polycrystalline silicon PV cells
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Abstract
The invention provides a crystalline silicon solar cell, a preparation method thereof and a photovoltaic module. The preparation method of the crystalline silicon solar cell comprises the following steps: forming a first intrinsic polysilicon layer on the crystalline silicon substrate; forming a polysilicon layer having a doping element on the first intrinsic polysilicon layer; forming a second intrinsic polysilicon layer on the polysilicon layer having the doping element; and heating the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer with the doping elements and the second intrinsic polycrystalline silicon layer to enable the doping elements in the polycrystalline silicon layer with the doping elements to enter the first intrinsic polycrystalline silicon layer and the second intrinsic polycrystalline silicon layer, so that the crystalline silicon solar cell is obtained. The preparation method of the crystalline silicon solar cell can improve the preparation speed of the crystalline silicon solar cell and is easy to realize the quality control of the crystalline silicon solar cell.
Description
Technical Field
The invention relates to a crystalline silicon solar cell, a preparation method thereof and a photovoltaic module.
Background
Polycrystalline Silicon (Poly-Si) films prepared by chemical vapor deposition are useful in the fabrication of crystalline Silicon-based photovoltaic devices, such as crystalline Silicon solar cells and the like. In the preparation method of the crystalline silicon solar cell, the chemical vapor deposition method mainly comprises the following steps: low Pressure Chemical Vapor Deposition (LPCVD), Atmospheric Pressure Chemical Vapor Deposition (APCVD), and Plasma Enhanced Chemical Vapor Deposition (PECVD). For example, in the case of chemical vapor deposition, silane can be used as a reaction gas to deposit an intrinsic polysilicon film under certain temperature and pressure conditions, and silane and phosphine gases can be used as reaction gases to obtain an in-situ doped polysilicon film. In the method for preparing the crystalline silicon solar cell, the in-situ doped polycrystalline silicon thin film is generally prepared on the crystalline silicon by introducing a doping substance during the deposition of the polycrystalline silicon thin film, however, this method can cause the deposition rate of the polycrystalline silicon thin film to be reduced, thereby reducing the preparation rate of the crystalline silicon solar cell, and is not beneficial to adjusting the passivation effect of the crystalline silicon substrate, thereby being difficult to realize the Quality Control (Quality Control) of the crystalline silicon solar cell.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a method for manufacturing a crystalline silicon solar cell, which can improve the manufacturing rate of the crystalline silicon solar cell and easily realize the quality control of the crystalline silicon solar cell.
In order to solve the technical problems, the invention adopts the following technical scheme:
the first aspect of the invention provides a method for preparing a crystalline silicon solar cell, which comprises the following steps:
forming a first intrinsic polysilicon layer on the crystalline silicon substrate;
forming a polysilicon layer having a doping element on the first intrinsic polysilicon layer;
forming a second intrinsic polysilicon layer on the polysilicon layer having the doping element; and
and heating the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer with the doping elements and the second intrinsic polycrystalline silicon layer to enable the doping elements in the polycrystalline silicon layer with the doping elements to enter the first intrinsic polycrystalline silicon layer and the second intrinsic polycrystalline silicon layer, thereby obtaining the crystalline silicon solar cell.
A second aspect of the present invention provides a crystalline silicon solar cell, which is prepared by the above-described preparation method of the first aspect of the present invention, and by controlling heating conditions, the concentration of a doping element in a polycrystalline silicon thin film in the finally prepared crystalline silicon solar cell is uniformly distributed throughout the thickness of the thin film.
A third aspect of the present invention provides a crystalline silicon solar cell including a crystalline silicon substrate and a polycrystalline silicon thin film having a doping element, wherein, in a thickness direction of the polycrystalline silicon thin film, a concentration of the doping element in a middle portion of the polycrystalline silicon thin film is greater than a concentration of the doping element in an edge portion of the polycrystalline silicon thin film.
A fourth aspect of the present invention provides a photovoltaic module comprising:
a plurality of the above-described crystalline silicon solar cells of the second aspect of the invention or the third aspect of the invention, and
a housing surrounding the crystalline silicon solar cell.
The preparation method of the crystalline silicon solar cell can improve the preparation speed of the crystalline silicon solar cell and is easy to realize the quality control of the crystalline silicon solar cell.
Drawings
Fig. 1 is a flowchart of a method of manufacturing a crystalline silicon solar cell of an embodiment of the present invention;
fig. 2 is a schematic structural view of a solar cell after step 3 of the method for manufacturing a crystalline silicon solar cell according to an embodiment of the present invention;
fig. 3 is a schematic structural view of a crystalline silicon solar cell of an embodiment of the present invention;
fig. 4 is a schematic view of a distribution of doping elements in a polycrystalline silicon thin film of the crystalline silicon solar cell shown in fig. 3;
fig. 5 is another distribution diagram of doping elements in a polycrystalline silicon thin film of the crystalline silicon solar cell shown in fig. 3;
fig. 6 is a graph showing concentration profiles of phosphorus in the polysilicon thin film in samples S1 and S2 of examples 1 and 2, in which,
the polycrystalline silicon thin film in sample S1 was a polycrystalline silicon thin film prepared from a first intrinsic polycrystalline silicon layer of 50nm, a polycrystalline silicon layer of 100nm having a phosphorus element as a doping element, and a second intrinsic polycrystalline silicon layer of 50 nm;
the polycrystalline silicon thin film in sample S2 was a polycrystalline silicon thin film prepared from a first intrinsic polycrystalline silicon layer of 100nm, a polycrystalline silicon layer of 100nm having a phosphorus element as a doping element, and a second intrinsic polycrystalline silicon layer of 100 nm.
Reference numerals:
a crystalline silicon substrate 10;
a silicon oxide layer 20;
a first intrinsic polycrystalline silicon layer 30;
a polysilicon layer 40 having a doping element;
a second intrinsic polycrystalline silicon layer 50;
an aluminum oxide film 60;
a silicon nitride film 70;
a conductive electrode 80;
a polysilicon film 100;
doping with element 1000.
Detailed Description
The details will be described below.
First, a method for manufacturing a crystalline silicon solar cell according to an embodiment of the first aspect of the present invention will be described in detail with reference to fig. 1. As shown in fig. 1, fig. 1 is a flowchart of a method for manufacturing a crystalline silicon solar cell according to an embodiment of the present invention. As can be seen from fig. 1, the preparation method of the crystalline silicon solar cell comprises the following steps:
and 4, heating the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer with the doping elements and the second intrinsic polycrystalline silicon layer to enable the doping elements in the polycrystalline silicon layer with the doping elements to enter the first intrinsic polycrystalline silicon layer and the second intrinsic polycrystalline silicon layer, so that the crystalline silicon solar cell is obtained.
In the above-described fabrication method, step 1 and step 3 are steps of forming an intrinsic polycrystalline silicon layer, and step 2 is a step of forming a polycrystalline silicon layer having a doping element, because the rate of forming the intrinsic polycrystalline silicon layer (for example, deposition by chemical vapor deposition using silane as a reaction gas) is greater than that of forming the polycrystalline silicon layer having a doping element (for example, in-situ deposition by chemical vapor deposition using silane and phosphane as reaction gases), the present invention has a faster fabrication rate in the case of forming the same thickness of the polycrystalline silicon layer having a doping element.
It should be noted that, in general, although the above-mentioned preparation method of the present invention further includes step 4, i.e., the heating step, since the heating step can be performed at a high temperature, the time consumption thereof is much smaller than that for forming the above-mentioned three polysilicon layers, and therefore, if considered together, the above-mentioned preparation method of the present invention has a higher preparation rate, or at least can be said to have a possibility of preparing a crystalline silicon solar cell at a higher preparation rate.
For example, the reaction gas of the first and second intrinsic polysilicon layers is silane, the deposition rate is 5nm/min (nm/min), the reaction gas of the polysilicon layer having phosphorus as a doping element is silane and phosphane, the deposition rate is 1nm/min (the deposition rate is the same as that of the in-situ doped polysilicon layer in the prior art), therefore, when the 150nm polysilicon film having a doping element needs to be deposited, 150min is required in the conventional method for obtaining the 150nm polysilicon film, while in the above preparation method of the present invention, the deposition of 50nm polysilicon layer having phosphorus as a doping element needs 50min, the deposition of 50nm polysilicon layer having phosphorus as a doping element needs 20min, if the heating temperature in step 4 is 850 ℃. (the deposition time is 50 min), the deposition time is 20min, and if the heating temperature in step 4 is 850 ℃. (the deposition time is 50 nm), The heating time is 20min, the required time for obtaining the polysilicon film with the thickness of 150nm is 90min which is far shorter than 150min in the prior art method, so that the preparation method can improve the deposition rate and shorten the process time.
In terms of quality control of crystalline silicon solar cells, in the related art manufacturing method, for example, reaction gases for forming a polycrystalline silicon layer having a phosphorus element as a doping element are silane and phosphane, and chemical vapor deposition is performed at a certain volume ratio, thereby obtaining a polycrystalline silicon layer having phosphorus doping. Compared with the preparation method of the invention, the silane and the phosphane need to be detected and controlled for a longer time in chemical vapor deposition, so the quality control difficulty is increased. In the preparation method of the invention, the control time for silane and phosphine is short, and the heating step of the step 4 is easy to control, so that the control of the polycrystalline silicon film on the surface of the crystalline silicon substrate can be realized. In addition, in the case where the thickness of the final polycrystalline silicon thin film (formed by heating the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer having the doping element, and the second intrinsic polycrystalline silicon layer) is determined, the thicknesses of the three layers of the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer having the doping element, and the second intrinsic polycrystalline silicon layer for forming the polycrystalline silicon thin film may have a certain degree of freedom, and thus, a larger design space may be provided for the manufacturing process of the crystalline silicon solar cell, and quality control may be easily achieved. For example, when the doping element is phosphorus, the thicknesses of the first and second intrinsic polysilicon layers affect the distribution of the phosphorus, so that the distribution of the phosphorus can be easily adjusted by selecting the thicknesses of the first and second intrinsic polysilicon layers with appropriate thicknesses, and the performance of the crystalline silicon solar cell with the polysilicon thin film can be improved. In addition, the concentration of phosphorus in the final polycrystalline silicon thin film can also be adjusted by adjusting the thickness of the polycrystalline silicon layer having phosphorus as a doping element and the concentration of phosphorus therein.
The respective steps will be described in detail below.
In the field of crystalline silicon solar cells, crystalline silicon includes P-type crystalline silicon and N-type crystalline silicon. In general, P-type crystalline silicon refers to crystalline silicon doped with an appropriate amount of 3-valent elements such as aluminum, indium, boron, and the like; the N-type crystalline silicon is formed by doping a proper amount of 5-valent elements such as phosphorus, arsenic and the like into crystalline silicon.
The crystalline silicon includes single crystal silicon and polycrystalline silicon. Polycrystalline silicon also includes ingot single crystals. In the present invention, the surface of the crystalline silicon substrate may contain other substances or other layers as long as the crystalline silicon substrate is not affected to fabricate the solar cell. For example, a crystalline silicon substrate has an oxide layer such as a silicon oxide layer on the surface thereof, which is obtained by thermally oxidizing the surface of the crystalline silicon substrate. In some embodiments, the crystalline silicon substrate is crystalline silicon without an oxide layer on the surface or crystalline silicon with an oxidized surface. For example, a surface of the sheet-like crystalline silicon has silicon oxide obtained by thermal oxidation. Whether or not the crystalline silicon substrate is subjected to surface oxidation, the crystalline silicon substrate can be used for the preparation method, the solar cell and the photovoltaic module. When the surface of the crystalline silicon substrate has an oxide layer, since the diffusion speed of the doping element such as phosphorus in the polysilicon in step 4 is fast, the presence of the oxide layer can block the doping element such as phosphorus from entering the crystalline silicon substrate or at least significantly reduce the entry of the doping element into the crystalline silicon substrate, thereby promoting passivation.
The theoretical intrinsic polycrystalline silicon layer means a polycrystalline silicon layer having the same number of free electrons and holes. In practice, the silicon element content of the polysilicon layer is only required to be larger than a certain value, for example, the polysilicon layer with the silicon element content of more than 99.999999%. In the present invention, the intrinsic polycrystalline silicon layer may contain an appropriate amount of impurity elements including a valence-3 element and a valence-5 element. That is, elements other than the 4-valent element are not intentionally introduced during the formation of the intrinsic polycrystalline silicon layer. That is, any polysilicon that has not been subjected to doping treatment and can be used as a base in the art may be regarded as intrinsic polysilicon.
The method of forming the first intrinsic polycrystalline silicon layer is not particularly limited, and may include: chemical vapor deposition, and the like. The chemical vapor deposition method can be a low pressure chemical vapor deposition method, a plasma enhanced chemical vapor deposition method, an atmospheric pressure chemical vapor deposition method, or the like. The specific process conditions of the chemical vapor deposition method are not particularly limited in the present invention. For example, the pressure in the reaction chamber of the chemical vapor deposition method may be 0.1 to 0.5Torr, or normal pressure, and the temperature range is 100 to 700 ℃, preferably 500 to 700 ℃. In the chemical vapor deposition method, silane may be used as a reaction gas.
There is no particular limitation on the thickness of the first intrinsic polycrystalline silicon layer. For example, the particle size may be in the range of 2 to 2000nm, such as 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1500nm, etc.
And 2, forming a polysilicon layer with a doping element on the first intrinsic polysilicon layer.
The doping element can be a valence 3 element such as aluminum, indium, boron, etc., or a valence 5 element such as phosphorus, arsenic, etc. In the formed polysilicon layer with the doping element, the content of the doping element can be adjusted according to the thickness of the finally formed polysilicon thin film.
The method of forming the polysilicon layer having the doping element is not particularly limited. For example, when doping a phosphorus element, a polysilicon layer having a doping element may be formed by a chemical vapor deposition method using silane and phosphane as reaction gases, and the two reaction gases may be introduced into a reaction chamber at a certain volume flow ratio. In connection with chemistryVapor deposition method, the form and process conditions of the chemical vapor deposition method described in step 1 may be selected and used by those skilled in the art. In one embodiment, the polysilicon layer with the doping element may be formed using in-situ doping. For example, when in-situ doping is carried out and phosphorus is taken as a doping element, the reaction gas is silane and phosphane, the volume flow ratio of the silane to the phosphane gas is 1 (0.02-0.6), and the doping concentration range of the phosphorus is 1E 19-2E 22atoms/cm3(atoms/cubic centimeter), i.e. 1X 1019～2×1022atoms/cm3。
There is no particular limitation on the thickness of the polysilicon layer having the doping element. For example, the particle size may be in the range of 2 to 2000nm, such as 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1500nm, etc.
And 3, forming a second intrinsic polycrystalline silicon layer on the polycrystalline silicon layer with the doping elements.
It should be noted that step 3 may differ from step 1 in terms of specific process conditions and second intrinsic polysilicon layer, etc., including formation method, temperature, gas flow rate, etc., and the thickness of the second intrinsic polysilicon layer may be the same as or different from that of the first intrinsic polysilicon layer. Step 1 and step 3 should be considered as separate steps.
And 4, heating the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer with the doping elements and the second intrinsic polycrystalline silicon layer to enable the doping elements in the polycrystalline silicon layer with the doping elements to enter the first intrinsic polycrystalline silicon layer and the second intrinsic polycrystalline silicon layer, so that the crystalline silicon solar cell is obtained.
In step 4, different polysilicon thin films may be formed according to different heating conditions. If the heating temperature is sufficiently high and the heating time is sufficiently long, the doping element in the polysilicon layer with the doping element will achieve complete diffusion, i.e., the concentration of the doping element in each portion of the polysilicon thin film is substantially uniform, i.e., there is no concentration gradient or concentration difference of the doping element. If the heating temperature and the heating time cannot achieve the above-described condition of complete diffusion, there is a concentration gradient or a concentration difference of the doping element in the polycrystalline silicon thin film because the doping element diffuses from the polycrystalline silicon layer having the doping element in the middle to the first intrinsic polycrystalline silicon layer and the second intrinsic polycrystalline silicon layer at both sides, and if complete diffusion is not achieved, there is a concentration gradient or a concentration difference of the doping element in the final polycrystalline silicon thin film. A typical concentration profile is such that the concentration of the doping element in the middle portion of the polycrystalline silicon thin film is greater than the concentration of the doping element in the edge portion of the polycrystalline silicon thin film in the thickness direction of the polycrystalline silicon thin film. To achieve a better passivation, the case of complete diffusion is generally chosen. Since the phosphorus element as the doping element can be rapidly diffused during heating, the above-mentioned complete diffusion is easily achieved.
The heating condition in the above step 4 is not particularly limited as long as the doping element in the polysilicon layer having the doping element can be made to enter the first and second intrinsic polysilicon layers. It is considered that, under a heating condition, generally under a high temperature condition, a doping element such as phosphorus atoms is activated to enter each lattice structure of the polysilicon layer with the doping element and diffused from the polysilicon layer with the doping element to the lattice structures of the first intrinsic polysilicon layer and the second intrinsic polysilicon layer on both sides, so that the doping element such as phosphorus atoms is redistributed in the polysilicon thin film, and further a passivation effect of the polysilicon thin film on the crystalline silicon substrate is obtained. For example, in one embodiment, the heating temperature is in the range of 600-900 ℃ and the annealing time is in the range of 15-60 min to achieve the above diffusion.
The heating step of step 4 may also be referred to as an annealing step.
With regard to the manufacturing method of the crystalline silicon solar cell, the processes of cleaning, texturing, doping to form a PN junction, etching the surface and the edge, preparing an antireflection film, printing and sintering the electrode, and the like of a crystalline silicon substrate are often involved. For these preparation processes, reference may be made to "principles of crystalline silicon solar cell manufacturing processes" (genu, zheng shidong, editions of chinese industrial and telecommunications publishing group, electronic industry press, version 1 of 3 months in 2017) and "solar cell foundation and applications" (jumeifang, editions of shaoxing, science press, 3 months in 2014, version 2).
As shown in fig. 2, fig. 2 is a schematic structural view of the solar cell after step 3 of the method for manufacturing a crystalline silicon solar cell according to the embodiment of the present invention. Wherein the cell structure comprises in sequence a sheet-like crystalline silicon substrate 10, a silicon oxide layer 20 (the silicon oxide layer 20 may be obtained by thermal oxidation), a first intrinsic polycrystalline silicon layer 30, a polycrystalline silicon layer 40 with doping elements, and a second intrinsic polycrystalline silicon layer 50. The cell structure shown in fig. 2 is heated (annealed), so that the doping elements in the polysilicon layer 40 having the doping elements can be introduced into the first and second intrinsic polysilicon layers 30 and 50, and the first intrinsic polysilicon layer 30, the polysilicon layer 40 having the doping elements, and the second intrinsic polysilicon layer 50 form an integrated polysilicon thin film. For simplicity, in the following drawings, the integrated polysilicon thin film formed by the first intrinsic polysilicon layer 30, the polysilicon layer 40 having the doping element, and the second intrinsic polysilicon layer 50 will also be denoted by reference numeral 100.
Next, a crystalline silicon solar cell of an embodiment of the present invention is described. As shown in fig. 3, fig. 3 is a schematic structural diagram of a crystalline silicon solar cell according to an embodiment of the present invention. The crystalline silicon solar cell includes: a crystalline silicon substrate 10, an alumina thin film 60 formed on one principal surface (upper surface as shown in fig. 3) of the crystalline silicon substrate 10, a silicon nitride thin film 70 formed on the alumina thin film 60, and a conductive electrode 80 located on the principal surface side (upper side), a silicon oxide layer 20 formed on the other principal surface (lower surface as shown in fig. 3) of the crystalline silicon substrate 10, a polysilicon thin film 100 formed on the silicon oxide layer 20, a silicon nitride thin film 70 formed on the polysilicon thin film, and a conductive electrode 80 located on the principal surface side (lower side). As shown in fig. 3, the conductive electrode 80 on one main surface (upper surface shown in fig. 3) of the crystalline silicon substrate 10 is in contact with the silicon substrate, and the conductive electrode 80 on the other main surface (lower surface shown in fig. 3) is in contact with the polysilicon thin film 100. When the conductive electrode 80 on the other main surface (the lower surface shown in fig. 3) is in contact with the polycrystalline silicon film 100, the passivation effect of the surface of the crystalline silicon substrate 10 can be improved, the contact resistance between the conductive electrode 80 and the crystalline silicon substrate 10 can be reduced, and the working performance and the conversion efficiency of the cell can be improved.
In the invention, the crystalline silicon solar cell can be a P-type cell or an N-type cell, for example, when the crystalline silicon solar cell is an N-type cell, a Back Surface Field (BSF) formed by depositing a layer of polycrystalline silicon film of the invention on the back surface of the N-type cell can improve the passivation effect of the silicon substrate surface, reduce the contact resistance between metal and the silicon substrate, and improve the working performance and the conversion efficiency of the cell.
As shown in fig. 4, fig. 4 is a schematic diagram of a distribution of doping elements in a polysilicon thin film of the crystalline silicon solar cell shown in fig. 3. In the polysilicon thin film 100 shown in fig. 4, the doping elements 1000 are uniformly distributed in the polysilicon thin film. That is, as described above, in step 4 of the method for manufacturing a crystalline silicon solar cell of the present invention, the heating temperature is sufficiently high and the heating time is sufficiently long, and the complete diffusion of the doping element 1000 will be achieved, that is, the concentration of the doping element 1000 in each part of the polycrystalline silicon thin film 100 is substantially uniform, that is, there is no concentration gradient or concentration difference of the doping element 1000. For example, if the heating temperature in step 4 is about 900 ℃ and the heating time is about 30min, uniform distribution of phosphorus as a doping element can be obtained.
As shown in fig. 5, fig. 5 is another distribution diagram of doping elements in the polycrystalline silicon thin film of the crystalline silicon solar cell shown in fig. 3. In the polysilicon thin film 100 shown in fig. 5, the concentration of the doping element 1000 in the middle of the polysilicon thin film 100 is greater than the concentration of the doping element 1000 in the edge of the polysilicon thin film 100 in the thickness direction X of the doping element 1000. As shown in fig. 5, the edge portion refers to a portion on both upper and lower sides, and the middle portion refers to a portion located in the middle of the portion on both upper and lower sides. That is, as described above, in step 4 of the method for manufacturing a crystalline silicon solar cell of the present invention, if the heating temperature and the heating time cannot reach the above-described conditions of complete diffusion, there is a concentration gradient or a concentration difference of the doping element 1000 in the polycrystalline silicon thin film 100 because the doping element 1000 diffuses from the middle polycrystalline silicon layer having the doping element to the first intrinsic polycrystalline silicon layer and the second intrinsic polycrystalline silicon layer on both sides, and if complete diffusion is not achieved, there is a concentration gradient or a concentration difference of the doping element in the final polycrystalline silicon thin film 100. A typical concentration gradient distribution is such that the concentration of the doping element 1000 decreases from the middle portion of the polysilicon thin film 100 to the edge portion of the polysilicon thin film 100 in the thickness direction X of the polysilicon thin film 100. In one embodiment, the concentration of the dopant element 1000 tends to decrease gradually from the middle of the polysilicon thin film 100 to the edge of the polysilicon thin film 100 in the thickness direction X of the polysilicon thin film 100.
In addition, the doping elements in the polycrystalline silicon thin film of the crystalline silicon solar cell have the following optional distribution modes. For example:
optionally, in the thickness direction of the polycrystalline silicon thin film, the concentration of the doping element of the part of the polycrystalline silicon thin film close to the crystal silicon substrate is less than the concentration of the doping element of the part of the polycrystalline silicon thin film far away from the crystal silicon substrate;
optionally, in the thickness direction of the polycrystalline silicon thin film, the concentration of the doping element tends to increase from a position of the polycrystalline silicon thin film close to the crystal silicon substrate to a position of the polycrystalline silicon thin film far away from the crystal silicon substrate;
optionally, in the thickness direction of the polycrystalline silicon thin film, the concentration of the doping element of the part of the polycrystalline silicon thin film close to the crystal silicon substrate is greater than the concentration of the doping element of the part of the polycrystalline silicon thin film far away from the crystal silicon substrate;
optionally, in the thickness direction of the polysilicon thin film, the concentration of the doping element tends to decrease from a portion of the polysilicon thin film close to the crystalline silicon substrate to a portion of the polysilicon thin film far from the crystalline silicon substrate.
The different distribution modes of the doping elements can be obtained by adjusting the thicknesses of the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer with the doping elements and the third intrinsic polycrystalline silicon layer. For example, by making the thickness of the first intrinsic polycrystalline silicon layer smaller than that of the second intrinsic polycrystalline silicon layer (for example, the thicknesses of the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer having the doping element, and the third intrinsic polycrystalline silicon layer are 20nm, 100nm, and 80nm, respectively), and then selecting appropriate heating conditions (i.e., not to a degree of complete diffusion, for example, the doping element of the polycrystalline silicon layer having the doping element has been completely uniformly distributed in the first intrinsic polycrystalline silicon layer but has not been completely uniformly distributed in the second intrinsic polycrystalline silicon layer upon heating), it is possible to obtain: the distribution mode of the concentration of the doping element at the part of the polycrystalline silicon thin film close to the crystal silicon substrate is larger than the concentration of the doping element at the part of the polycrystalline silicon thin film far away from the crystal silicon substrate in the thickness direction of the polycrystalline silicon thin film. In the thickness direction of the polycrystalline silicon film, the concentration of the doping element at the part of the polycrystalline silicon film close to the crystal silicon substrate is greater than that at the part of the polycrystalline silicon film far away from the crystal silicon substrate, so that the surface of the crystalline silicon substrate can be passivated by less doping elements. In the polycrystalline silicon thin film, in the thickness direction of the polycrystalline silicon thin film, the concentration of the doping element at the part of the polycrystalline silicon thin film close to the crystal silicon substrate is basically the same, and the concentration of the doping element at the part of the polycrystalline silicon thin film far away from the crystal silicon substrate has a concentration gradient; further, in one embodiment, at the site having the concentration difference, a decreasing concentration gradient is exhibited in a direction toward away from the crystalline silicon substrate.
In general, the thickness direction X is a direction perpendicular to the main surface of the crystalline silicon substrate.
The present invention also provides a photovoltaic module comprising: the solar cell comprises a plurality of the crystalline silicon solar cells and a shell surrounding the crystalline silicon solar cells. A photovoltaic module, also known as a solar module, is a solar cell assembly with external packaging and internal connections that can provide a direct current output alone. The external packaging means that a plurality of crystalline silicon solar cells are packaged through an adhesive film and a shell. Internal connection refers to the series and/or parallel electrical connection of a plurality of crystalline silicon solar cells. Regarding the structure, the working principle, the preparation method, the testing method, etc. of the photovoltaic module, reference may also be made to "manufacturing process principle of crystalline silicon solar cell" (edited by cheng geggy, zheng shidong, etc., electronic industry publishing agency of engineering and telecommunications publishing group in china, version 1 of 3 months in 2017) and "foundation and application of solar cell" (edited by jumeifang, shaoxing delicacy, etc., version 2 of 3 months in 2014).
The method for manufacturing a crystalline silicon solar cell of the present invention is further described below by way of specific examples.
Example 1
1) Selecting an N-type monocrystalline silicon wafer, wherein the bulk resistivity of the N-type monocrystalline silicon wafer is 2.0 omega cm;
2) using 25% tetramethyl ammonium hydroxide as an alkali solution to corrode the silicon wafer, and removing a surface damage layer to treat the surface of the silicon wafer;
3) cleaning the silicon wafer with 5% hydrofluoric acid solution, introducing oxygen into a furnace tube to grow a silicon oxide layer on the surface of the silicon wafer, wherein the oxidation temperature is 600 ℃, and the oxidation time is 30min to obtain the silicon wafer with the silicon oxide layer thickness of 1.7 nm;
4) and depositing a polycrystalline silicon film on the surface of the silicon wafer with the silicon oxide layer. Depositing a polysilicon film in an LPCVD system, depositing a first intrinsic polysilicon layer on the surface of a silicon oxide layer, depositing a polysilicon layer with phosphorus as a doping element on the surface of the first intrinsic polysilicon layer in situ, and further depositing a second intrinsic polysilicon layer on the surface of the polysilicon layer with phosphorus as the doping element, wherein the thickness of the first intrinsic polysilicon layer is 50nm, the thickness of the polysilicon layer with phosphorus as the doping element is 100nm, and the thickness of the second intrinsic polysilicon layer is 50 nm;
5) and (4) heating. Heating in a furnace tube to activate phosphorus element, wherein the heating temperature is 900 ℃, and the heating time is 30min, so as to obtain a sample S1;
6) sample S1 was washed with a 5% hydrofluoric acid solution, and a silicon nitride film having a thickness of 80nm and a refractive index of 2.08 was deposited on both the main surfaces of the front and back surfaces.
Example 2
Sample S2 was prepared in the same manner as in example 1, except that the thickness of the first intrinsic polycrystalline silicon layer was 100nm, the thickness of the polycrystalline silicon layer having phosphorus as a doping element was 100nm, and the thickness of the second intrinsic polycrystalline silicon layer was 100 nm.
Example 3
(1) Performance testing
The results of the performance tests such as minority carrier lifetime test on the samples S1 and S2 are shown in the following Table 1:
TABLE 1
As can be seen from Table 1, samples S1 and S2 both had better passivation effects. The minority carrier lifetimes of samples S1 and S2 both reach the millisecond range, and the pseudo-open circuit voltage can be optimized to 735 mv and 727 mv.
(2) Doping element concentration profile test
In addition, the concentration distribution of the dopant element (phosphorus element) in the polysilicon thin films in the above-described sample S1 and sample S2 obtained from example 1 and example 2, respectively, was measured by the ECV test method in which etching was performed with ammonium fluoride, and the result is shown in fig. 6. As can be seen from FIG. 6, the concentration of the doping element (phosphorus element) was substantially uniform throughout the thickness range (0 to 160nm, 0 to 240nm) for the polysilicon films of samples S1 and S2.
It should be noted that, taking sample S1 as an example, although the concentration of the doping element (phosphorus element) in the polysilicon thin film of sample S1 is substantially consistent in the range of 0nm to 160nm, it can be characterized that the concentration of the doping element (phosphorus element) is substantially consistent throughout the thickness of the polysilicon thin film of sample S1. One reason for this is that, in the process of preparing the sample S1, the deposited polysilicon is granular, and the thickness of the polysilicon film formed by the deposited polysilicon is reduced by subsequent high-temperature treatment (heating), and the polysilicon film is easily oxidized due to a large amount of grain boundary structures contained in the polysilicon film, and in the subsequent process, the sample S1 is washed with a 5% hydrofluoric acid solution, which can corrode and remove the oxide layer, and consume a part of the polysilicon, resulting in the final polysilicon film having a thickness of less than 200 nm. Sample S2 is similar to that of sample S1.
Example 4
1) Surface texturing: selecting N-type monocrystalline silicon as a silicon wafer for a crystalline silicon substrate, wherein the bulk resistivity of the silicon wafer is 2.0 omega cm, and texturing the surface of the silicon wafer to make the reflectivity of the front surface (a light receiving surface to be a crystalline silicon solar cell) of the silicon wafer 12%;
2) preparing a PN junction: using a boron diffusion method in a furnace tube, using BBr in the boron diffusion method3As a boron source, the square resistance of the emitter of the obtained silicon wafer is 80 omega/□;
3) leveling the back surface of the silicon wafer: etching the back surface (to be a back surface of a crystal solar cell) in a mixed solution of nitric acid, sulfuric acid and hydrofluoric acid (the volume ratio of the nitric acid to the sulfuric acid to the hydrofluoric acid is 2:1:2, wherein the mass fraction of the nitric acid is 67%, the concentration of the sulfuric acid is 48%, and the mass fraction of the hydrofluoric acid is 40%), reducing the specific surface area of the back surface of the silicon wafer, and removing a borosilicate glass layer (BSG) formed in the step on the front surface with a 5% hydrofluoric acid solution;
4) growing a tunneling oxide layer on the back surface: growing a tunneling oxide layer on a silicon wafer in an oxidation furnace tube, namely oxidizing the silicon wafer at high temperature to obtain a silicon oxide layer, wherein the growth temperature is 600 ℃, the growth time is 40min, and the thickness of the obtained silicon oxide layer is 1.8 nm;
5) and (3) depositing a polysilicon film on the back surface: depositing a silicon film in an LPCVD system, firstly depositing a first intrinsic polycrystalline silicon layer 30 with the thickness of 50nm, then depositing a polycrystalline silicon layer taking a phosphorus element with the thickness of 100nm as a doping element, and finally depositing a second intrinsic polycrystalline silicon layer with the thickness of 40 nm;
6) high temperature annealing (i.e. heating to diffuse phosphorus): activating the phosphorus-doped element in the silicon film by using a high-temperature furnace tube, wherein the activation temperature is 900 ℃, and the activation time is 30 min;
7) depositing alumina on the front surface: cleaning the silicon wafer by using a 5% hydrofluoric acid solution, and depositing an alumina film (passivation effect) on the front surface, wherein the thickness of the alumina film is 5 nm;
8) silicon nitride deposition on both the front and back surfaces (anti-reflection and passivation effect): depositing a silicon nitride film by using a PECVD system, wherein the thickness of the silicon nitride film is 80nm, and the refractive index of the silicon nitride film is 2.08;
9) printing a conductive electrode: printing silver paste as conductive electrodes on both the front surface and the back surface;
10) and (3) rapid sintering: and (3) rapidly sintering after drying, wherein the peak value of the sintering temperature is 800 ℃, and the sintering time is about 3 minutes. And the sintered front surface silver paste passes through the silicon nitride and aluminum oxide thin film to be contacted with the boron-doped silicon area, so that the conduction and the collection of front surface current carriers are completed, and the back surface silver paste passes through the silicon nitride to be contacted with the phosphorus-doped polycrystalline silicon thin film so that the back surface conduction is completed, so that the N-type solar cell is formed.
The detection proves that the N-type solar cell has a good passivation effect, reduces the contact resistance between metal and a silicon wafer, and improves the working performance and the conversion efficiency of the cell.
The foregoing is directed to embodiments of the present invention, and it is understood by those skilled in the art that various changes, modifications and improvements may be made without departing from the spirit and scope of the invention.
Claims (10)
1. The preparation method of the crystalline silicon solar cell comprises the following steps:
forming a first intrinsic polysilicon layer on the crystalline silicon substrate;
forming a polysilicon layer having a doping element on the first intrinsic polysilicon layer;
forming a second intrinsic polysilicon layer on the polysilicon layer having the doping element; and
and heating the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer with the doping elements and the second intrinsic polycrystalline silicon layer to enable the doping elements in the polycrystalline silicon layer with the doping elements to enter the first intrinsic polycrystalline silicon layer and the second intrinsic polycrystalline silicon layer, thereby obtaining the crystalline silicon solar cell.
2. The production method according to claim 1, wherein the first intrinsic polycrystalline silicon layer, the polycrystalline silicon layer having a doping element, and the second intrinsic polycrystalline silicon layer are formed by a chemical vapor deposition method; preferably, the chemical vapor deposition method is any one of a low pressure chemical vapor deposition method, a plasma enhanced chemical vapor deposition method, and an atmospheric pressure chemical vapor deposition method; preferably, in the chemical vapor deposition method, the pressure range is between 0.1 and 0.5Torr, and the temperature range is between 500 and 700 ℃; preferably, the reaction gas for forming the first and second intrinsic polycrystalline silicon layers is silane.
3. The method of claim 1 or 2, wherein the first and second intrinsic polysilicon layers have a thickness in a range of 2 to 2000 nm.
4. The method according to claim 1 or 2, wherein the doping element in the polysilicon layer with the doping element is a phosphorus element, and optionally, the reaction gases for forming the polysilicon layer with the doping element are silane and phosphane.
5. The preparation method according to claim 4, wherein the volume flow ratio of the silane to the phosphane is 1 (0.02-0.6); preferably, the concentration of phosphorus in the polysilicon layer with the doping element is in the range of 1E 19-2E 22atoms/cm3To (c) to (d); preferably, the thickness of the polycrystalline silicon layer with the doping element ranges from 4nm to 2000 nm.
6. The method according to any one of claims 1 to 5, wherein the heating temperature is in the range of 600 to 900 ℃ and the heating time is in the range of 15 to 60 min.
7. A crystalline silicon solar cell, characterized in that, prepared by the method of claim 1, and by controlling the heating conditions, the concentration of the doping element in the polycrystalline silicon thin film in the finally prepared crystalline silicon solar cell is uniformly distributed throughout the film thickness; preferably, the heating conditions are: the heating temperature is 600-900 ℃ and the heating time is 15-60 min.
8. The crystalline silicon solar cell comprises a crystalline silicon substrate and a polycrystalline silicon film with doping elements, and is characterized in that in the thickness direction of the polycrystalline silicon film, the concentration of the doping elements at the middle part of the polycrystalline silicon film is greater than that at the edge part of the polycrystalline silicon film;
optionally, in the thickness direction of the polycrystalline silicon thin film, the concentration of the doping element tends to decrease from the middle part of the polycrystalline silicon thin film to the edge part of the polycrystalline silicon thin film;
optionally, in the thickness direction of the polycrystalline silicon thin film, the concentration of the doping element of the part of the polycrystalline silicon thin film close to the crystal silicon substrate is less than the concentration of the doping element of the part of the polycrystalline silicon thin film far away from the crystal silicon substrate;
optionally, in the thickness direction of the polycrystalline silicon thin film, the concentration of the doping element tends to increase from a position of the polycrystalline silicon thin film close to the crystal silicon substrate to a position of the polycrystalline silicon thin film far away from the crystal silicon substrate;
optionally, in the thickness direction of the polycrystalline silicon thin film, the concentration of the doping element of the part of the polycrystalline silicon thin film close to the crystal silicon substrate is greater than the concentration of the doping element of the part of the polycrystalline silicon thin film far away from the crystal silicon substrate;
optionally, in the thickness direction of the polysilicon thin film, the concentration of the doping element tends to decrease from a portion of the polysilicon thin film close to the crystalline silicon substrate to a portion of the polysilicon thin film far from the crystalline silicon substrate.
9. The crystalline silicon solar cell according to claim 7 or 8, characterized in that the surface of the crystalline silicon matrix has silicon oxide.
10. A photovoltaic module comprising:
a plurality of crystalline silicon solar cells as defined in claim 7 or 8, and
a housing surrounding the crystalline silicon solar cell.
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