阅读说明：本技术 一种类单晶硅铸锭用籽晶的回收利用方法 (Method for recycling seed crystals for monocrystalline silicon-like ingot casting ) 是由 陈伟 王万胜 李林东 王全志 周硕 陈志军 丁云飞 邢国强 于 2019-11-18 设计创作，主要内容包括：本发明提供了一种类单晶硅铸锭用籽晶的回收利用方法,其包括以下步骤：提供硅锭方棒,硅锭方棒包括位于底部的单晶硅籽晶层以及位于单晶硅籽晶层上侧的类单晶硅铸锭层；在硅锭方棒底端一侧距离硅锭方棒底面设定距离位置处截断硅锭方棒,并在截断硅锭方棒之前或之后对单晶硅籽晶层的底面一侧进行设定厚度单晶硅的切除；获取回收籽晶,回收籽晶包含有底面一侧切除设定厚度单晶硅的单晶硅籽晶层；本发明所提供的回收利用方法可以实现单晶硅籽晶的二次甚至多次利用,大大降低了铸造类单晶的籽晶制作成本；而且回收籽晶二次利用时还能避免引入上一次使用过程中因与坩埚底部接触所形成的污染,可确保类单晶硅二次铸造的品质。(The invention provides a method for recycling seed crystals for monocrystalline silicon-like ingots, which comprises the following steps: providing a silicon ingot square rod, wherein the silicon ingot square rod comprises a monocrystalline silicon seed crystal layer positioned at the bottom and a monocrystalline silicon-like ingot casting layer positioned on the upper side of the monocrystalline silicon seed crystal layer; cutting off the silicon ingot square rod at a position with a set distance from the bottom surface of the silicon ingot square rod on one side of the bottom end of the silicon ingot square rod, and cutting off the monocrystalline silicon with a set thickness on one side of the bottom surface of the monocrystalline silicon seed crystal layer before or after the silicon ingot square rod is cut off; obtaining a recovered seed crystal, wherein the recovered seed crystal comprises a monocrystalline silicon seed crystal layer with a set thickness of monocrystalline silicon cut off from one side of the bottom surface; the recycling method provided by the invention can realize secondary and even repeated utilization of the monocrystalline silicon seed crystal, thereby greatly reducing the manufacturing cost of the seed crystal of the casting type monocrystalline; and when the seed crystal is recycled for secondary use, the pollution caused by contact with the bottom of the crucible in the previous use process can be avoided, and the secondary casting quality of the monocrystalline silicon-like material can be ensured.)

1. A method for recycling seed crystals for monocrystalline silicon-like ingots is characterized by comprising the following steps:

providing a silicon ingot square rod, wherein the silicon ingot square rod comprises a monocrystalline silicon seed crystal layer positioned at the bottom and a monocrystalline silicon-like ingot casting layer positioned on the upper side of the monocrystalline silicon seed crystal layer;

cutting off the silicon ingot square rod at a position with a set distance from the bottom surface of the silicon ingot square rod on one side of the bottom end of the silicon ingot square rod, and cutting off the monocrystalline silicon with a set thickness on one side of the bottom surface of the monocrystalline silicon seed crystal layer before or after cutting off the silicon ingot square rod;

and obtaining a recovered seed crystal, wherein the recovered seed crystal comprises the monocrystalline silicon seed crystal layer with a set thickness of monocrystalline silicon cut off from one side of the bottom surface.

2. The recycling method according to claim 1, further comprising a step of performing a surface grinding process on a side surface of the square ingot rod before the cutting of the square ingot rod.

3. The recycling method according to claim 1 or 2, further comprising a step of subjecting the recovered seed crystal to an acid washing treatment.

4. The recycling method according to claim 3, wherein the solution used in the step of pickling is a mixed solution of nitric acid and hydrofluoric acid.

5. The recycling method according to claim 1 or 2, further comprising a step of detecting a minority carrier lifetime of the square ingot bar by using a minority carrier lifetime detecting device before the square ingot bar is cut off, wherein the minority carrier lifetime of a region where the cut-off position of the square ingot bar is located is within a set threshold.

6. The recycling method according to claim 5, wherein the set threshold is 2.5-3.5 μ s.

7. The recycling method according to claim 1 or 2, wherein the thickness of the recycled seed crystal is 25-40mm, and the thickness of the monocrystalline silicon in the recycled seed crystal is 5-15 mm.

8. The method according to claim 1 or 2, wherein the predetermined thickness of the cut-off portion of the single-crystal silicon on the bottom surface side of the seed crystal layer is 2 to 8 mm.

9. The recycling method according to claim 1 or 2, wherein the square ingot is produced by squaring a mono-like silicon ingot.

10. The recycling method according to claim 1 or 2, wherein the laying position and direction of the recovered seed crystals when the recovered seed crystals are used for re-casting the similar monocrystalline silicon ingot are the same as those of the seed crystals used for obtaining the similar monocrystalline silicon ingot of the recovered seed crystals.

Technical Field

The invention relates to the field of monocrystalline silicon-like ingots, in particular to a method for recycling seed crystals for monocrystalline silicon-like ingots.

Background

The solar energy has abundant resources and wide distribution, and is the renewable energy with the most development potential. With the increasingly prominent problems of global energy shortage, environmental pollution and the like, solar photovoltaic power generation has become a new industry which is generally concerned and intensively developed by countries in the world due to the characteristics of cleanness, safety, convenience, high efficiency and the like.

In the prior art, monocrystalline silicon used for preparing solar cells is generally prepared and obtained by utilizing a czochralski technology or a zone melting technology, but the preparation cost and the energy consumption of the monocrystalline silicon are high. The polycrystalline silicon is prepared by a casting technology, so that the manufacturing cost is low, but the photoelectric conversion efficiency of the prepared solar cell is relatively low. In order to combine the advantages of monocrystalline silicon preparation and polycrystalline silicon preparation, the industry provides a monocrystalline-like silicon between monocrystalline silicon and polycrystalline silicon, namely monocrystalline-like silicon with efficiency close to that of monocrystalline silicon is prepared by utilizing a polycrystalline silicon casting technology, wherein monocrystalline silicon is used as seed crystals and placed at the bottom of a crucible, silicon materials are arranged above the seed crystals, then heating and melting are carried out in a polycrystalline ingot casting mode, the seed crystals are ensured not to be completely melted, after the seed crystals reach the required height, a crystal growth stage is carried out, a proper temperature gradient is established by adjusting the temperature and the lifting rate of a heat insulation system, and molten silicon starts to grow on the unmelted seed crystals, so that the monocrystalline-like silicon is produced and prepared.

However, most of the seed crystals adopted in the process of casting the similar monocrystalline silicon in the prior art are used once, namely the seed crystals are used as common silicon materials to be recycled after one-time seeding and ingot casting is finished, and the single-use mode of the seed crystals related to the prior art greatly improves the casting cost of the similar monocrystalline silicon.

In view of the above, there is a need to provide an improved solution to the above problems.

Disclosure of Invention

The invention aims to solve at least one technical problem in the prior art, and provides a method for recycling seed crystals for monocrystalline silicon-like ingots to achieve the aim.

A method for recycling seed crystals for monocrystalline silicon-like ingots comprises the following steps:

providing a silicon ingot square rod, wherein the silicon ingot square rod comprises a monocrystalline silicon seed crystal layer positioned at the bottom and a monocrystalline silicon-like ingot casting layer positioned on the upper side of the monocrystalline silicon seed crystal layer;

cutting off the silicon ingot square rod at a position with a set distance from the bottom surface of the silicon ingot square rod on one side of the bottom end of the silicon ingot square rod, and cutting off the monocrystalline silicon with a set thickness on one side of the bottom surface of the monocrystalline silicon seed crystal layer before or after cutting off the silicon ingot square rod;

and obtaining a recovered seed crystal, wherein the recovered seed crystal comprises the monocrystalline silicon seed crystal layer with a set thickness of monocrystalline silicon cut off from one side of the bottom surface.

Further, before the cutting of the square ingot, a step of surface grinding of the side surface of the square ingot is further included.

Further, the method also comprises the step of carrying out acid washing treatment on the recovered seed crystal.

Further, the solution adopted in the step of acid cleaning treatment is a mixed solution of nitric acid and hydrofluoric acid.

Further, before the silicon ingot square rod is cut off, the method further comprises the step of detecting the minority carrier lifetime of the silicon ingot square rod by adopting minority carrier lifetime detection equipment, wherein the minority carrier lifetime of an area where the silicon ingot square rod is cut off is within a set threshold value.

Further, the set threshold is 2.5-3.5 μ s.

Further, the thickness of the recovered seed crystal is 25-40mm, and the thickness of monocrystalline silicon in the recovered seed crystal is 5-15 mm.

Further, the set thickness of the cut monocrystalline silicon on the bottom surface side of the monocrystalline silicon seed crystal layer is 2-8 mm.

Further, the silicon ingot square bar is prepared by cutting a mono-like silicon ingot.

Further, when the recovered seed crystal is adopted to carry out the similar monocrystalline silicon ingot casting again, the laying position and the direction of the recovered seed crystal are consistent with those of the seed crystal used for obtaining the similar monocrystalline silicon ingot casting of the recovered seed crystal.

The invention has the beneficial effects that: based on the method for recycling the seed crystal for the monocrystalline silicon-like ingot casting, provided by the invention, the secondary and even multiple utilization of the monocrystalline silicon seed crystal can be realized, and the manufacturing cost of the seed crystal for casting the monocrystalline silicon-like ingot is greatly reduced; and the recycled seed crystals recycled by the recycling method provided by the invention can be used for the second time, so that the pollution caused by the contact with the bottom of the crucible in the previous using process can be avoided, and the quality of the secondary casting of the monocrystalline silicon-like crystals can be ensured.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a first implementation flow chart of seed crystal recycling for monocrystalline silicon-like ingot casting according to the invention;

FIG. 2 is a flow chart of a second embodiment of seed crystal recycling for monocrystalline silicon-like ingot casting according to the invention;

FIG. 3 is a third flow chart for recycling seed crystals for monocrystalline silicon-like ingot production according to the present invention;

FIG. 4 is a flow chart showing a fourth embodiment of seed crystal recycling for single crystal silicon-like ingot casting according to the present invention;

FIG. 5 is a flow chart showing a fifth embodiment of seed crystal recycling for single-crystal silicon-like ingot casting according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, the method for recycling seed crystals for a monocrystalline silicon-like ingot provided by this embodiment includes the following steps:

a square ingot of silicon ingot 100 is provided, the square ingot of silicon ingot 100 comprising a monocrystalline silicon seed layer (not shown) at the bottom and a monocrystalline silicon-like ingot layer (not shown) on the top side of the monocrystalline silicon seed layer. In the specific implementation process, the silicon ingot square bar 100 is made by squaring a mono-like silicon ingot, the mono-like silicon ingot adopts monocrystalline silicon as seed crystals, and mono-like silicon grows and is formed on the upper side of the seed crystals, in the mono-like forming process, part of the seed crystals are not melted, the non-melted monocrystalline silicon forms a monocrystalline silicon seed crystal layer positioned at the bottom in the silicon ingot square bar 100, and a silicon layer grown and formed on the upper side of the monocrystalline silicon seed crystal layer forms a mono-like silicon ingot layer.

Further, the method further includes cutting the silicon ingot square bar 100 at a position spaced apart from the bottom surface of the silicon ingot square bar 100 by a predetermined distance on the bottom end side of the silicon ingot square bar 100 after providing the silicon ingot square bar 100. Referring to fig. 1, the distance between the position of the cut surface 101 and the bottom surface of the square ingot 100 is a predetermined distance. In this embodiment, the silicon ingot square bar 100 is generally cut along the cut surface 101 by a mechanism such as a diamond wire saw or a diamond band saw, and the upper portion 12 of the silicon ingot square bar 100 cut along the cut surface 101 can be further processed into a silicon single crystal-like wafer to be used as a substrate of a cell. In the process of forming the mono-like silicon wafer by using the upper portion 12, it is usually necessary to cut off the top end of the upper portion 12 by a certain thickness, and it is referred to the prior art and will not be further developed.

In this embodiment, the cutting of the silicon ingot square bar 100 further includes cutting off the silicon single crystal of a predetermined thickness from the bottom surface side of the silicon single crystal seed layer. Specifically, in the single crystal-like casting molding process, the bottom surface side of the silicon ingot square bar 100 is in direct contact with the crucible and is generally contaminated by the bottom surface of the crucible to some extent, and the contaminated portion can be removed by cutting off the single crystal silicon with a set thickness on the bottom surface side, so that the quality of the subsequent single crystal-like secondary casting is ensured. In this embodiment, the thickness of the single crystal silicon on the bottom side corresponds to the waste layer 11, the recovered seed crystal 10 can be obtained by cutting off the waste layer 11 along the cutting plane 102 at the lower part of the square ingot 100 cut off along the cutting plane 101, and the recovered seed crystal 10 includes a single crystal silicon seed layer with the thickness of the single crystal silicon on the bottom side cut off. The recovered seed crystal 10 can be used as the seed crystal for the next mono-like casting.

Based on the method for recycling the seed crystal for the monocrystalline silicon-like ingot casting, provided by the invention, the secondary and even repeated utilization of the monocrystalline silicon seed crystal can be realized, and the manufacturing cost of the seed crystal for casting the monocrystalline silicon-like ingot is greatly reduced.

In the specific implementation process, in order to ensure the quality of the secondary casting type single crystal of the recovered seed crystal 10, it is generally required to ensure that the recovered seed crystal 10 has sufficient cleanliness, and referring to fig. 1, the recovery and utilization method according to the embodiment further includes a step of performing an acid pickling treatment on the recovered seed crystal 10. In this embodiment, the solution used in the step of acid cleaning is a mixed solution of nitric acid and hydrofluoric acid.

In addition, before the silicon ingot square rod 100 is cut off, a step of detecting the minority carrier lifetime of the silicon ingot square rod 100 by using minority carrier lifetime detection equipment is further included, wherein the minority carrier lifetime of the region where the cutting position of the silicon ingot square rod 100 is located is within a set threshold, which is shown in fig. 1, that is, the minority carrier lifetime of the region where the cutting surface 101 is located is within the set threshold. Based on the single crystal-like casting molding process, the minority carrier lifetime of the bottom end part of the silicon ingot square rod 100 is shorter than that of the middle part, and the minority carrier lifetime of the bottom end part tends to gradually increase from bottom to top, and by limiting the cutting position of the silicon ingot square rod 100 to a region where the minority carrier lifetime is within a set threshold, the superior minority carrier lifetime of the upper part 12 obtained after the silicon ingot square rod 100 is cut can be ensured.

In the practical implementation, the minority carrier lifetime of the cut-off silicon ingot square bar 100 is approximately in the range of 1-5 μ s. In the present embodiment, the threshold is set to 2.5-3.5 μ s as a preferred embodiment of the present invention, that is, the minority carrier lifetime of the region where the truncated surface 101 is located is 2.5-3.5 μ s. For example, in the specific implementation, the position with minority carrier lifetime of 3 μ s is selected at the bottom end of the silicon ingot square bar 100 as the cutting plane 101 for cutting off the silicon ingot square bar 100.

In the embodiment, the thickness of the recovered seed crystal 10 is 25-40mm, and the thickness of the monocrystalline silicon in the recovered seed crystal 10 is 5-15 mm. The thickness of the cut monocrystalline silicon on the bottom surface side of the monocrystalline silicon seed crystal layer is set to be 2-8 mm.

In a specific implementation scenario, when monocrystalline silicon is used as seed crystal to perform first-time quasi-monocrystalline casting, the initial thickness of the related seed crystal is 25mm, in the quasi-monocrystalline casting process, the height of the remaining monocrystalline after the seed crystal is melted is 15mm, the 15mm monocrystalline constitutes the monocrystalline seed crystal layer of the silicon ingot square rod 100, in the process of obtaining the recovered seed crystal 10, a 5mm thick waste layer 11 needs to be cut off from one side of the bottom surface of the monocrystalline seed crystal layer, and then the recovered seed crystal 10 with the thickness of 10mm is obtained, and the recovered seed crystal 10 also has a quasi-monocrystalline with a certain thickness.

In this embodiment, as a preferable aspect of the present invention, when the single-crystal-like silicon ingot is again cast using the recovered seed crystal, the placement position and direction of the recovered seed crystal 10 are the same as the placement position and direction of the seed crystal when the single-crystal-like silicon ingot for obtaining the recovered seed crystal is to be placed. This ensures that the recovered seed crystal 10 has similar quality to the single-like crystal cast from the original seed crystal.

In addition, when the recovered seed crystal 10 is used for casting the mono-like silicon ingot, the mono-like silicon on the upper side of the recovered seed crystal 10 needs to be completely melted, namely the height of the reserved solid after the recovered seed crystal 10 is melted is not more than the thickness of the mono-like silicon in the recovered seed crystal 10. Particularly for the recovered seed crystal 10 with the thickness of 10mm, the height of the solid remained after the recovered seed crystal 10 is melted is not more than 10mm, so that the high-quality similar single crystal can be grown subsequently.

Referring to fig. 2, a second embodiment of the present invention is shown, which is different from the embodiment of fig. 1 in that the step of cutting the single crystal silicon to a predetermined thickness from the bottom surface side of the seed layer of the single crystal silicon is performed before the ingot square bar 100 is cut.

Referring to fig. 3, a third embodiment of the present invention is shown, which is different from the embodiment of fig. 1 in that in this embodiment, a step of performing a surface grinding process on a side surface of a square rod 100 of a silicon ingot before cutting off the square rod 100 of the silicon ingot is further included. In the specific implementation process, a pair of facing disks 200 arranged oppositely is adopted to simultaneously perform facing treatment on a pair of opposite side surfaces of the silicon ingot square rod 100. Based on the step of surface grinding treatment, the obtained side surface of the seed crystal 10 has better verticality and flatness, so that when the seed crystal is adopted for casting secondary monocrystalline silicon, dislocation of the monocrystalline silicon during initial crystal growth can be reduced, head dislocation of the monocrystalline silicon is reduced, and casting quality of the monocrystalline silicon is improved.

Referring to fig. 4, a fourth embodiment of the present invention is shown, which is a modification of the basis of the embodiment shown in fig. 2. Specifically, in this embodiment, before the step of cutting off the silicon single crystal with a predetermined thickness from the bottom surface side of the seed crystal layer, the step of polishing the side surface of the square ingot 100 is further included.

Referring to fig. 5, a fifth embodiment of the present invention is shown, which is another improvement of the basis of the embodiment shown in fig. 2. In this embodiment, the step of performing the surface grinding process on the side surface of the square rod 100 of silicon ingot is between the two steps of "cutting the single crystal silicon to a predetermined thickness on the bottom surface side of the seed crystal layer of the single crystal silicon" and "cutting the square rod 100 of silicon ingot".

It is easy to understand that the embodiments shown in fig. 4 and 5 both have the step of grinding the side surface of the square ingot 100, and the recovered seed crystal obtained by the embodiments also has the advantages of the recovered seed crystal obtained by the embodiments shown in fig. 3, and is not further developed herein.

It should be understood that although the present description refers to embodiments, not every embodiment contains only a single technical solution, and such description is for clarity only, and those skilled in the art should make the description as a whole, and the technical solutions in the embodiments can also be combined appropriately to form other embodiments understood by those skilled in the art.

The above-listed detailed description is only a specific description of a possible embodiment of the present invention, and they are not intended to limit the scope of the present invention, and equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the scope of the present invention.