阅读说明：本技术 晶体硅太阳能电池扩散层及其制备方法 (Crystalline silicon solar cell diffusion layer and preparation method thereof ) 是由 冯雪 蒋晔 陈颖 付浩然 张柏诚 刘兰兰 王志建 邰艳龙 彭祖军 于 2018-09-10 设计创作，主要内容包括：本发明涉及一种晶体硅太阳能电池扩散层及其制备方法,所述制备方法包括：⑴提供硅片以及扩散源；⑵将所述扩散源置于所述硅片表面上而形成预制层,所述预制层的厚度小于等于2μm；⑶对带有所述预制层的硅片进行退火处理,使所述预制层中的扩散元素扩散进入所述硅片中,形成扩散层。本发明的制备方法不受硅片厚度的限制,可实现扩散层的可控制备,不仅工艺简单、成本低,还可以保证硅片的完整性和工艺稳定性,可重复性好,得到的晶体硅太阳能电池扩散层的方阻为20Ω/□～110Ω/□,具有很好的实际应用价值。(The invention relates to a crystalline silicon solar cell diffusion layer and a preparation method thereof, wherein the preparation method comprises the steps of providing a silicon wafer and a diffusion source by ⑴, placing the diffusion source on the surface of the silicon wafer to form a prefabricated layer, wherein the thickness of the prefabricated layer is less than or equal to 2 mu m, annealing the silicon wafer with the prefabricated layer by ⑶, and diffusing diffusion elements in the prefabricated layer into the silicon wafer to form the diffusion layer.)

1. A preparation method of a crystalline silicon solar cell diffusion layer is characterized by comprising the following steps:

⑴ providing a silicon wafer and a diffusion source;

⑵ placing the diffusion source on the surface of the silicon wafer to form a prefabricated layer, the thickness of the prefabricated layer is less than or equal to 2 μm;

⑶ annealing the silicon wafer with the prefabricated layer to diffuse the diffusion elements in the prefabricated layer into the silicon wafer to form a diffusion layer.

2. The method for preparing the crystalline silicon solar cell diffusion layer as claimed in claim 1, wherein in the step (2), the diffusion source is placed on one surface of the silicon wafer by a printing method to form a prefabricated layer.

3. The method for preparing the crystalline silicon solar cell diffusion layer according to claim 2, wherein the printing method comprises one of ink direct writing and ink jet printing.

4. The method for preparing the crystalline silicon solar cell diffusion layer according to claim 1, wherein the thickness of the silicon wafer is 5 μm to 100 μm.

5. The method for preparing the crystalline silicon solar cell diffusion layer according to claim 1, wherein the diffusion source comprises a diffusion element comprising a B element or a P element;

when a P-type silicon wafer is adopted, the diffusion element is a P element;

when an n-type silicon wafer is adopted, the diffusion element is an element B.

6. The method for preparing the crystalline silicon solar cell diffusion layer as claimed in claim 1, wherein a plurality of the pre-fabricated layers are formed on the silicon wafer at intervals.

7. The method for preparing the crystalline silicon solar cell diffusion layer according to claim 1, wherein the annealing treatment temperature is 600-1000 ℃ and the time is 20-120 minutes.

8. The method for preparing the crystalline silicon solar cell diffusion layer as claimed in claim 1, wherein a protective gas is introduced during the annealing treatment, wherein the protective gas comprises at least one of nitrogen and argon.

9. The method for preparing the crystalline silicon solar cell diffusion layer according to claim 8, wherein the protective gas further comprises oxygen, and the introduction amount of the oxygen is less than or equal to 50%.

10. The crystalline silicon solar cell diffusion layer obtained by the preparation method of any one of claims 1 to 9, wherein the sheet resistance of the diffusion layer is 20 Ω/□ -110 Ω/□.

Technical Field

The invention relates to the field of solar cells, in particular to a crystalline silicon solar cell diffusion layer and a preparation method thereof.

Background

The process for manufacturing the crystalline silicon solar cell in a large-scale mode comprises diffusion, and a PN junction obtained after a diffusion layer is formed by diffusion is the heart of the crystalline silicon solar cell and directly influences the electrical property of the crystalline silicon solar cell.

Currently, the crystalline silicon solar cell generally adopts (100) p-type silicon as a base material, and is vertically inserted into a quartz boat back to use liquid phosphorus oxychloride (POCl)₃) As a diffusion source, a phosphorus source is carried into a reaction system by protective gas, and then a diffusion layer is formed in the silicon wafer through thermal diffusion treatment. Wherein, the thermal diffusion treatment is to decompose the phosphorus source at about 1000 ℃ and deposit the phosphorus source on the surface of the silicon wafer, and then carry out knot pushing for a period of time at 800-900 ℃ to form a diffusion layer.

However, with the decreasing thickness of silicon wafers, the ultra-thin silicon wafers cannot be inserted into the quartz boat back-to-back vertically, which causes a great compatibility problem in the above process. In addition, in the thermal diffusion treatment, diffusion layers are formed on both sides and edges of the silicon wafer, and the diffusion layers at the edges can conduct the upper and lower surfaces, so that the battery cannot work normally. In order to ensure the performance of the solar cell, the silicon wafer is generally floated on an acid solution in industrial production to remove the diffusion layer on the back surface and the edge. However, the existing post-cleaning equipment mainly adopts a roller assembly line to remove the diffusion layer on the back and the edge, and the minimum thickness of the silicon wafer is generally required to be 140-160 μm. If the process is adopted to directly etch the ultrathin silicon wafer, the corrosive solution at the bottom of the silicon wafer bypasses the edge of the silicon wafer and reaches the front side of the silicon wafer, so that the diffusion layer on the front side is damaged. Meanwhile, the ultrathin silicon wafer has certain flexibility, so that the ultrathin silicon wafer can be bent to a certain degree between the rollers, and the stability of the etching process is greatly reduced. Therefore, in the prior art, a method for directly growing a diffusion layer exists, but the method has higher equipment cost; the preparation of the diffusion layer can be realized by a method of spin coating the diffusion source or a method of diffusion after coating the diffusion source in a photoetching technology area, but the controllability of the diffusion layer is not high, the diffusion can only be realized in the whole area, and the photoetching technology cost of the diffusion layer is higher and the production efficiency is lower.

Disclosure of Invention

Therefore, the preparation method of the crystalline silicon solar cell diffusion layer is not limited by the thickness of a silicon wafer, controllable preparation of the diffusion layer can be realized, the integrity of the silicon wafer can be ensured, and the sheet resistance of the prepared diffusion layer is controllable.

A preparation method of a crystalline silicon solar cell diffusion layer comprises the following steps:

⑴ providing a silicon wafer and a diffusion source;

⑵ placing the diffusion source on the surface of the silicon wafer to form a prefabricated layer, the thickness of the prefabricated layer is less than or equal to 2 μm;

⑶ annealing the silicon wafer with the prefabricated layer to diffuse the diffusion elements in the prefabricated layer into the silicon wafer to form a diffusion layer.

In one embodiment, in step (2), the diffusion source is placed on a surface of the silicon wafer by a printing method to form a prefabricated layer.

In one embodiment, the printing method includes one of ink direct write, ink jet printing.

In one embodiment, the thickness of the silicon wafer is 5-100 μm.

In one embodiment, the diffusion source comprises a diffusion element comprising a B element or a P element;

when a P-type silicon wafer is adopted, the diffusion element is a P element;

when an n-type silicon wafer is adopted, the diffusion element is an element B.

In one embodiment, a plurality of the prefabricated layers are formed on the silicon wafer at intervals.

In one embodiment, the temperature of the annealing treatment is 600-1000 ℃ and the time is 20-120 minutes.

In one embodiment, a protective gas is introduced during the annealing process, and the protective gas comprises at least one of nitrogen and argon.

In one embodiment, the protective gas further comprises oxygen, and the introduction amount of the oxygen is less than or equal to 50%.

The preparation method of the invention has the following beneficial effects:

the invention realizes the uniform and controllable preparation of the prefabricated layer on the silicon wafer by the printing method without the limitation of the thickness of the silicon wafer. Particularly, when the silicon wafer is an ultrathin silicon wafer, a printing probe of the printing method is not in contact with the silicon wafer, the method for preparing the prefabricated layer in a non-pressure non-contact mode cannot damage the ultrathin silicon wafer, the integrity of the ultrathin silicon wafer is protected, and the reliability of the solar cell diffusion process of the ultrathin silicon wafer is improved.

In the annealing treatment process, the prefabricated layer is kept in the printing area and does not deviate, the diffusion elements diffuse into the silicon wafer after the solvent of the prefabricated layer is volatilized, the solid diffusion is realized, the diffusion layer cannot be formed on the other surface and the side surface of the silicon wafer, and the subsequent complicated cleaning process of the diffusion layer is not needed. And after annealing, no residual prefabricated layer is formed on the silicon wafer, compared with a preparation method for retaining the residual prefabricated layer, the whole preparation process is shortened, the whole preparation efficiency is improved, the process is simple, the cost is low, the integrity and the process stability of the silicon wafer can be ensured, the repeatability is good, and the method has good practical application value.

The sheet resistance of the crystalline silicon solar cell diffusion layer obtained by the preparation method is 20 omega/□ -110 omega/□.

The diffusion layer has good uniformity and proper sheet resistance range, can form a good pn junction with a silicon wafer, realizes the separation of photon-generated carriers under the illumination condition, can form good ohmic contact with a subsequently prepared electrode, realizes the transmission of the carriers, and is suitable for being applied to high-sensitivity devices, thin film batteries in the aviation field and the like.

Drawings

FIG. 1 is a flow chart of a preparation process of a crystalline silicon solar cell diffusion layer.

In the figure: 1. a silicon wafer; 2. prefabricating a layer; 3. a diffusion layer.

Detailed Description

The crystalline silicon solar cell diffusion layer and the preparation method thereof provided by the invention will be further explained below.

As shown in fig. 1, the method for preparing the crystalline silicon solar cell diffusion layer provided by the invention comprises the following steps:

⑴ providing silicon wafer 1 and a diffusion source;

⑵ placing the diffusion source on the surface of the silicon wafer 1 to form a prefabricated layer 2, wherein the thickness of the prefabricated layer 2 is less than or equal to 2 μm;

⑶ annealing the silicon wafer 1 with the prefabricated layer 2 to diffuse the diffusion elements in the prefabricated layer 2 into the silicon wafer 1 to form a diffusion layer 3.

In the step (1), the thickness of the silicon wafer 1 is not limited, and the preparation method is suitable for mainstream silicon wafers and ultrathin silicon wafers with the thickness of about 160-180 μm at present. Considering that the silicon wafer with the thickness of 5-100 microns has flexibility, the printing method belongs to a non-pressure non-contact additive manufacturing method, and cannot damage the silicon wafer, so that the silicon wafer 1 is preferably an ultrathin silicon wafer with the thickness of 5-100 microns, the controllable preparation of a diffusion layer on the ultrathin silicon wafer can be realized, the cost is low, and the efficiency is high.

The diffusion source is composed of organic carrier and various functionsPrepared by mixing powder phases, e.g. phosphorus doped (POCl)₃、P₂O₅) Or boron doping (BBr)₃、BCl₃、B₂H₆Boron powder), or boron-aluminum doped slurry obtained by doping a certain proportion of boron element in aluminum slurry, or a mixture containing phosphorus and silicon and using ethanol/ester as a solvent.

In the diffusion source, the diffusion element includes a B element or a P element. Preferably, when a P-type silicon wafer is used, the diffusion element is a P element to form n⁺A/p-type crystalline silicon solar cell; when an n-type silicon wafer is used, the diffusion element is B element to form p⁺An/n-type crystalline silicon solar cell. The two types of crystalline silicon solar cells have equivalent performances, but n⁺The irradiation resistance of the p-type crystalline silicon solar cell is superior to that of p⁺The/n type crystalline silicon solar cell is more suitable for space application.

In the step (2), the diffusion source is placed on one surface of the silicon wafer 1 by a printing method to form a prefabricated layer 2. Compared with pressure contact type coating methods such as a spin coating method, a screen printing method, an ink jet printing method, a slit coating method, a spraying method, a relief printing method, a gravure printing method and the like, a printing probe of the printing method is not in contact with a silicon wafer, the silicon wafer 1 is not damaged, a uniform prefabricated layer 2 can be formed on the silicon wafer 1, and the printing method is particularly suitable for ultrathin flexible silicon wafers and has an obvious effect.

Specifically, the printing method is not limited, and may preferably be one of direct ink writing and inkjet printing which are easy to handle.

If many small cells are made on the same silicon wafer 1, then the division is performed. The pitch of the preform layer 2 can be controlled to form a plurality of preform layers 2 at intervals on the silicon wafer 1.

It will be appreciated that the pre-form layer 2 may be formed in a single pass by modification of the printing apparatus. On the basis of the existing printing equipment, the prefabricated layer 2 can be formed by back and forth printing through the printing probe. Under the condition of the same printing speed, the cross-sectional volume of single printing is the same, and at the moment, the distance between the printing probe and the silicon wafer 1 needs to be adjusted to control the aspect ratio (the ratio of the height to the width) of the single printing, so as to control the thickness of the prefabricated layer 2. Considering that if the aspect ratio is too large during single printing, the diffusion source is easy to spread unevenly and is not beneficial to fully entering the silicon wafer 1 by diffusion elements during diffusion; if the aspect ratio is too small, surface holes are easy to appear in the printing process, so that the diffusion of the diffusion elements in the silicon wafer 1 is not uniform. Therefore, the aspect ratio during single printing is preferably 2:1 to 1:10, the thickness of the formed prefabricated layer 2 can be controlled, and the uniformity of the formed prefabricated layer 2 is relatively guaranteed.

In the step (3), the diffusion elements in the prefabricated layer 2 are diffused into the silicon wafer 1 through annealing treatment, and a diffusion layer 3 is formed in the silicon wafer 1. The diffusion process belongs to solid state diffusion, and a diffusion layer is not formed on other surfaces of the silicon wafer 1, so that the controllable preparation of the diffusion layer 3 can be realized.

Specifically, in the annealing process, with the rise of temperature, the organic carriers in the prefabricated layer 2 begin to volatilize, then the functional powder begins to melt and keeps good contact with the surface of the silicon wafer 1, and when the silicon wafer is melted for a period of time and reaches a thermal equilibrium state, the diffusion element boron or phosphorus begins to diffuse into the silicon wafer 1. After the annealing treatment is completed, the temperature starts to decrease, and the diffusion elements in the silicon wafer 1 start to precipitate due to saturation, and partially move in the direction of the original preform layer 2, thereby forming a concentration gradient. When the temperature drops below the active temperature of the diffusing element, the diffusion layer 3 reaches a steady state.

In particular, the gradient concentration of the diffusion layer ideally exhibits a steep drop, but in practice it is generally not completely steep, and only a relatively steep drop effect can be exhibited. The thickness of the prefabricated layer 2 is less than or equal to 2 microns, no prefabricated layer 2 is left after annealing, at the moment, if all diffusion elements in the prefabricated layer 2 are diffused into the silicon wafer 1 to form the diffusion layer 3, the diffusion distance of the diffusion elements is increased due to improper temperature or heat preservation time control, and further, on the premise that the total amount of the elements is limited, the concentration distribution of the diffusion layer 3 in the silicon wafer 1 is uniform, so that the relatively steep drop trend is gentle. Therefore, the corresponding relation between the annealing time, temperature and thickness needs to be strictly controlled, otherwise, the concentration gradient of the annealed diffusion layer is damaged, and the performance of the subsequent battery is influenced. Preferably, the temperature of the annealing treatment is 600-1000 ℃, and the time is 20-120 minutes, so as to obtain the diffusion layer 3 with proper sheet resistance.

Preferably, a protective gas is introduced during the annealing treatment, and the protective gas comprises at least one of nitrogen and argon.

Preferably, when the diffusion source is phosphorus doped (POCl)₃、P₂O₅) Or boron doping (BBr)₃、BCl₃、B₂H₆Boron powder), oxygen can be introduced into the protective gas, and a thin silicon oxide layer is formed on the surface of the silicon wafer by a thermal oxidation method, so that the solid solubility of the prefabricated layer 2 in the silicon oxide layer is higher, and the diffusion element can be conveniently diffused into the silicon wafer 1 to form the diffusion layer 3 with higher concentration. And the silicon oxide layer can be removed by etching solution such as HF solution after the diffusion is finished. Of course, when the oxygen concentration is too high, it is difficult to control the thickness and the quality of the silicon oxide layer, and therefore, the amount of the introduced oxygen is 50% or less, and more preferably 5% to 50%.

The invention realizes the uniform and controllable preparation of the prefabricated layer on the silicon wafer by the printing method without the limitation of the thickness of the silicon wafer. Particularly, when the silicon wafer is an ultrathin silicon wafer, a printing probe of the printing method is not in contact with the silicon wafer, the method for preparing the prefabricated layer in a non-pressure non-contact mode cannot damage the ultrathin silicon wafer, the integrity of the ultrathin silicon wafer is protected, and the reliability of the solar cell diffusion process of the ultrathin silicon wafer is improved.

In the annealing treatment process, the prefabricated layer is kept in the printing area and does not deviate, the diffusion elements diffuse into the silicon wafer after the solvent of the prefabricated layer is volatilized, the solid diffusion is realized, the diffusion layer cannot be formed on the other surface and the side surface of the silicon wafer, and the subsequent complicated cleaning process of the diffusion layer is not needed. And after annealing, no residual prefabricated layer is formed on the silicon wafer, compared with a preparation method for retaining the residual prefabricated layer, the whole preparation process is shortened, the whole preparation efficiency is improved, the process is simple, the cost is low, the integrity and the process stability of the silicon wafer can be ensured, the repeatability is good, and the method has good practical application value.

The invention also provides a crystalline silicon solar cell diffusion layer obtained by the preparation method, and the sheet resistance of the diffusion layer is 20 omega/□ -110 omega/□.

Specifically, when the prefabricated layers are arranged on the surface of the silicon wafer at intervals, the obtained diffusion layers are mutually spaced.

Preferably, when the silicon wafer is an ultra-thin silicon wafer of 5 μm to 100 μm, the diffusion layer is formed. The flexible crystalline silicon solar cell can be prepared on the basis of the ultrathin silicon wafer, and further, the flexible solar cell module can be prepared on the basis of the flexible crystalline silicon solar cell.

The diffusion layer has good uniformity and proper sheet resistance range, can form a good pn junction with a silicon wafer, realizes the separation of photon-generated carriers under the illumination condition, can form good ohmic contact with a subsequently prepared electrode, realizes the transmission of the carriers, and is suitable for being applied to high-sensitivity devices, thin film batteries in the aviation field and the like.

Hereinafter, the crystalline silicon solar cell diffusion layer and the method for preparing the same will be further described by the following specific examples.