阅读说明：本技术 用于制造pert太阳能电池的方法 (Method for producing a PERT solar cell ) 是由 弗洛里恩·巴克霍尔兹 皮尔明·普赖斯 克里斯托弗·皮特 于 2018-05-15 设计创作，主要内容包括：提供了一种用于制造PERT太阳能电池(10)的方法,其具有以下步骤：制备n掺杂或p掺杂的硅基板(1)；实施第一掺杂工艺,利用所述第一掺杂工艺对所述n掺杂或p掺杂的硅基板(1)的至少一侧进行掺杂,或者将至少一个掺杂层施加到所述n掺杂或p掺杂的硅基板(1)的一侧,以生成第一掺杂侧；至少在所述PERT太阳能电池(10)的所述第一掺杂侧上沉积至少一种钝化表面或掩盖表面的物质；实施第二掺杂工艺,利用所述第二掺杂工艺至少掺杂所述n掺杂或p掺杂的硅基板的与所述第一掺杂侧相对的另一侧,或者在其上施加掺杂层,其中,在实施这些步骤之后,对所述PERT太阳能电池(10)的边缘(11,12)进行湿法化学蚀刻,其中,在湿法化学蚀刻时,所述PERT太阳能电池(10)的与所述第一掺杂侧相对的另一侧由水帽(4)保护,并且其中,在将所述钝化表面或掩盖表面的物质(5)至少沉积在所述PERT太阳能电池(10)的所述第一掺杂侧上之后并且在所述边缘的湿法化学蚀刻之前,使沉积在所述PERT太阳能电池(10)的所述第一掺杂侧上的所述钝化表面或掩盖表面的物质(5)通过高温处理来烧结。(A method for manufacturing a PERT solar cell (10) is provided, having the steps of: preparing an n-doped or p-doped silicon substrate (1); performing a first doping process with which at least one side of the n-doped or p-doped silicon substrate (1) is doped or at least one doped layer is applied to one side of the n-doped or p-doped silicon substrate (1) to create a first doped side; depositing at least one surface-passivating or surface-masking substance at least on the first doped side of the PERT solar cell (10); performing a second doping process with which at least the other side of the n-doped or p-doped silicon substrate opposite to the first doped side is doped or onto which a doped layer is applied, wherein, after carrying out these steps, the edges (11, 12) of the PERT solar cell (10) are wet-chemically etched, wherein the other side of the PERT solar cell (10) opposite to the first doped side is protected by a water cap (4) upon wet chemical etching, and wherein, sintering the passivating or surface masking substance (5) deposited on the first doped side of the PERT solar cell (10) by a high temperature process after depositing the passivating or surface masking substance (5) at least on the first doped side of the PERT solar cell (10) and before wet chemical etching of the edges.)

1. A method for manufacturing a PERT solar cell (10) having the steps of:

-preparing an n-doped or p-doped silicon substrate (1);

-performing a first doping process with which at least one side, preferably the back side (14), of the n-doped or p-doped silicon substrate (1) is doped, or applying at least one doped layer to one side, preferably the back side (14), of the n-doped or p-doped silicon substrate (1) to create a first doped side;

-depositing at least one surface-passivating or surface-masking substance (5) at least on the first doped side of the PERT solar cell (10);

-performing a second doping process with which at least the other side of the n-doped or p-doped silicon substrate (1) opposite to the first doping side, preferably the front side (13), is doped or onto which a doped layer is applied,

it is characterized in that the preparation method is characterized in that,

after carrying out these steps, the edges (11, 12) of the PERT solar cell (10) are wet-chemically etched, wherein the other side of the PERT solar cell (10) opposite to the first doping side, preferably the front side (13), is protected by a water cap (4) during the wet-chemical etching,

the surface-passivating or surface-masking substance (5) is sinterable, and

after depositing the passivating or masking surface substance (5) at least on the first doped side, preferably on the back side (14), of the PERT solar cell (10) and before the wet chemical etching of the edges (11, 12), sintering the passivating or masking surface substance (5) deposited on the first doped side, preferably on the back side (14), of the PERT solar cell (10) by a high-temperature treatment, so that the substance (5) is not attacked or is not attacked to a too great extent by an etching liquid (30) used for the wet chemical etching of the edges (11, 12) than the edges (11, 12) of the PERT solar cell (10), even when these edges (11, 12) parasitically have a passivating or masking surface substance (5) deposited when depositing it at least on the first doped side of the PERT solar cell (10) The same applies to the substance (5) of the face.

2. The method of claim 1, wherein a high temperature treatment is performed while the diffusion step is performed in the second doping process.

3. The method of claim 1, wherein a high temperature treatment is performed while performing a necessary annealing process in the second doping process.

4. The method of claim 1, 2 or 3, wherein the PERT solar cell (10) is exposed to a temperature of at least 500 ℃ for a period of at least 1 second at high temperature treatment.

5. Method according to any of the preceding claims, characterized in that the etching liquid (30) is HF, HNO₃And H₂SO₄Or comprising the components HF, HNO₃And H₂SO₄At least one of (1).

6. The method according to claim 5, characterized in that the volume content of HF in the etching liquid (30) is between 5% and 40%.

7. Method according to any of the preceding claims, characterized in that an additional process step is performed between the deposition of the passivating or surface masking substance (5) on at least the first doping side of the PERT solar cell (10) and the sintering of the passivating or surface masking substance (5) by a high temperature treatment, in which additional process step part of the passivating or surface masking substance (5) is removed.

8. Method according to one of the preceding claims, characterized in that an oxide layer is applied on the first to-be-treated side of the PERT solar cell (10), in particular on the rear side (14), before the doped layer for generating the first doped side is applied.

Technical Field

The present invention relates to a method for manufacturing a PERT solar cell.

Background

A PERT (passivated emitter and rear fully diffused) solar cell is a well-known solar cell. They have an overall highly doped region (p +/n +) on both the front and back sides. These solar cells are typically fabricated by diffusing dopants such as phosphorus, boron, arsenic or antimony from suitable sources at high temperatures. However, the dopants can also be introduced by implantation and epitaxial growth of single crystals or deposition of amorphous or polycrystalline highly doped silicon layers by CVD processes. So-called PERPoly (Passivated Emitter rear polysilicon contact) solar cells, as well as solar cells with POLO or TopCON contacts, in which a highly doped silicon or silicon carbide or other semiconductor layer is separated from a substrate by a thin interfacial layer, typically made of silicon oxide or aluminum oxide, are all explicitly referred to herein as PERT cell types.

Here, the base material of the PERT cell may be n-doped and p-doped silicon or another semiconductor material, and both the n + doped and p + doped regions may be located on the front side, that is, on the main light incidence side.

However, a problem with this type of solar cell is that during the manufacturing process, opposite highly doped (p +/n +) regions are present adjacent to each other at the edges of the solar cell, which regions lead to a low shunt resistance and a low breakdown voltage of the solar cell. As a result, under reverse loading (reverse bias) which occurs when a single solar cell is shaded in the solar module, the entire current of the respective string will flow through the relevant solar cell in the blocking direction of the diode, thereby resulting in a larger local energy density and thus in heat generation, also referred to as hot spot formation. This heat build-up can lead to damage to the solar cells and the entire solar module.

For example, if a so-called critical value of the reverse current of about 1 ampere is exceeded when a voltage of-12 volts is applied, a strong heat formation may occur, so that temperatures of >100 ℃ may occur in operation, which may lead to damage of the module components, in particular of the encapsulation material (for example EVA or POE) used in the module and of the backside film.

Thus, many manufacturers of PERT cells have laser edge insulation as the last process step in the manufacture of such solar cells. Here, on the emitter side of the solar cell, i.e. on the side of doping opposite the wafer, trenches of a few μm depth are produced in the solar cell by means of laser light; the silicon located there is removed by the laser. The laser trench is created a few hundred μm from the edge. The solar cell emitter, which is typically located at the front side of the solar cell, typically has a depth of less than 1-2 μm, so that the laser trench separates the solar cell emitter from the opposite doped side. A high breakdown voltage of the solar cell can be achieved by the separation, so the solar cell does not allow significant current flow in the cut-off direction even under reverse bias conditions, wherein no significant current flow is present in this specification when the reverse current is less than 1 ampere when a negative voltage of-12 volts is applied. In this way the shunt resistance can be increased to values >100 ohm.

However, this approach has two serious drawbacks: firstly, the effective area of the solar cell is reduced, since the charge carriers generated in the edge region outside the trench cannot contribute or only contributes very little to the current of the solar cell. Secondly, the laser leaves significant damage on the surface of the solar cell, the laser region no longer being passivated, but rather a very high recombination site, which leads to an increase in the off-saturation current and thus to a reduction in the fill factor. These two effects together result in an absolute efficiency loss of 0.2% for the PERT solar cell with laser edge insulation compared to the untreated same type of solar cell.

An alternative but less commonly used edge isolation method is to separate the front and back sides of the solar cell from each other by a plasma etching step after creating the highly doped regions. The doped silicon layer present there is etched away at the edge of the solar cell by means of a plasma and thus a separation of the front side and the back side is achieved. Moreover, plasma etching also has significant drawbacks, as it is an expensive processing step, making it necessary to stack wafers in this step, increasing scrap due to mechanical damage and breakage.

Wet chemical etching methods for edge insulation have been used in solar cell technology, wherein in particular the substrate surface of the substrate can be protected by a water cap, as is known, for example, from DE102009050845a 1. However, these methods have so far only been used for so-called Al-BSF, MWT and PERC solar cells, since they require that one of the doped surfaces of the solar cell, usually the back side, is etched away by an etching solution. The possibility of using this method, in particular in a PERT solar cell, has not been found.

Disclosure of Invention

It is therefore an object of the present invention to provide a method for manufacturing a PERT solar cell, which method achieves wet chemical edge insulation. This object is achieved by a method for producing a PERT solar cell having the features of claim 1. Advantageous developments of the method are the subject matter of the dependent claims.

The method according to the invention for producing a PERT solar cell, as known for producing solar cells of this type, has the following steps:

-preparing an n-doped or p-doped silicon substrate;

-performing a first doping process with which at least a first side (hereinafter first doped side), preferably at least a rear side, of the PERT solar cell is doped to create a first doped side, or applying at least one doped layer to create a first doped side.

Here, the at least one applied doped layer can also be a component of a stack of passivation and conductive layers. In particular, in this first doping step, the corresponding side of the PERT solar cell is preferably highly doped, wherein in the context of the present description "highly doped" means at least 10¹⁹Doping atoms/cm³Doping of (3).

-depositing at least one substance passivating or masking a surface at least on the first doped side of the PERT solar cell; and

-performing a second doping process with which at least the other side, preferably the front side, of the n-doped or p-doped silicon substrate, opposite to the first doped side, is doped. The doping process also preferably results in a high doping in the sense of "high doping" defined above.

These steps are carried out in the given order, but not necessarily immediately one after the other. In this case, it should be noted that by using the expressions "performing the first doping process" and "at least one substance passivating or masking a surface", in particular also for a PERT solar cell with a passivation and masking stack, for example POLO or PERPOLY or TOPCON may be used in such solar cells with a passivated contact.

It is essential to the invention that, after carrying out these steps, the edge of the PERT solar cell is wet-chemically etched, wherein, during the wet-chemical etching, the other side of the PERT solar cell opposite to the first doped side, or the first doped side of the p-doped or n-doped silicon substrate from which the solar cell is produced during the execution of the method, i.e. preferably the subsequent front side of the PERT solar cell, is protected by a water cap.

The wet chemical etching of the edge is achieved in particular in that the passivating or surface-masking substance is sinterable and that after the deposition of the passivating or surface-masking substance at least on the first doped side of the PERT solar cell or on the first doped side of the p-doped or n-doped silicon substrate from which the solar cell is produced when the method is carried out and before the wet chemical etching of the edge, the substance deposited on the first doped side of the PERT solar cell (10) or on the first doped side of the p-doped or n-doped silicon substrate from which the solar cell is produced when the method is carried out is sintered by a high-temperature treatment in such a way that it is not attacked by the etching liquid used for the wet chemical etching of the edge or is attacked to a lesser extent than that of the edge of the PERT solar cell Even when these edges parasitically have a passivating or surface masking substance deposited when depositing a passivating or surface masking substance at least on the first doped side of the PERT solar cell.

In this way, edge insulation can be achieved without damaging the wafer, which also allows implementation at significantly higher throughput than laser systems or plasma etching apparatuses and only produces very low chemical consumption due to the small etching volume.

It should be noted that in some places in the present disclosure, for the sake of higher clarity and simplicity of expression, the term "PERT" solar cell is also used in part for intermediate products (cell precursors) from which such cells are derived when performing the method.

One preferred material for such sinterable substance is, for example, silicon nitride, and another material which can advantageously be used is silicon carbide.

The method can be carried out particularly economically when a diffusion step is carried out in the second doping process and therefore a high-temperature treatment is carried out in temporal parallel to this otherwise necessary step.

Another economic way of high temperature treatment is to perform high temperature treatment while performing the necessary annealing process in the second doping process.

High temperature processes have proven particularly effective in which the PERT solar cell (i.e. the just manufactured subsequent PERT solar cell) is subjected to a temperature of at least 500 ℃, preferably above 700 ℃, for a period of at least one second in the high temperature process. A brief "light-off" at these high temperatures is sufficient.

This can be achieved in particular by the process steps which are usually provided in the first place, for example the surface texture of the n-doped silicon substrate and/or the boron or phosphorus glass etching, being adaptable with respect to the process duration and/or the concentration of the chemicals used. In this way, it is possible to prevent, when necessary, i.e. in particular when the desired layer thickness of the surface-passivating or surface-masking substance is so high that the parasitic coating of the edge will also become an etch stop layer by means of the heat treatment, that the parasitic coating will also sinter at the edge by means of the high-temperature treatment and then no longer be able to be wet-chemically etched.

It has also proven to be advantageous to apply a preferably designed thin oxide layer on the rear side of the PERT solar cell before applying the doped layer.

Drawings

The invention is explained in more detail below with reference to the drawings. In the drawings:

fig. 1 shows a schematic diagram of a wet chemical edge etching step in the manufacture of a PERT solar cell.

Detailed Description

In the schematic illustration of fig. 1, a solar cell 10 (or rather its precursor) can be seen, which solar cell 10 is moved by means of a transport roller 20 in the direction indicated by an arrow through a chamber having HF, HNO₃And H₂SO₄The mixture of (a) to cause wet chemical etching of the edges 11, 12 of the PERT solar cell 10.

In this example, the PERT solar cell 10 has: an n-doped silicon substrate 1, a p + -doped emitter 2 constituting on a front side 13 of the silicon substrate 1, and an n + -doped back side field 3 constituting on a back side 14 of the silicon substrate 1. The front side 13 of the silicon substrate 1 may be optionally configured. The rear side 14 of the silicon substrate 1 may optionally be polished or structured.

In the wet-chemical etching process shown, the front side 13 is protected by a water cap 4, while the back side 14 is protected by a sintered layer of a surface-passivating or surface-masking substance 5, in particular, for example, a silicon nitride layer or a stack of silicon oxide and silicon nitride layers. In this way, parasitic deposition residues 6 of substances 5 passivating or masking the surface, in particular, for example, parasitic silicon nitride deposits on the edges 11, 12, do not or no longer deposit there at the point in time of the high-temperature treatment which causes sintering in a concentration sufficient to constitute a closed etch barrier, and the edge regions 7, 8 of the silicon substrate 1 where the differently doped regions touch one another are etched away and thus wet-chemical edge insulation is achieved.

As is immediately clear to the person skilled in the art, the embodiments described herein are not limited to n-doped substrates and given dopants, in particular dopants of the emitter and which are used to generate the back surface field, but can be transferred directly to highly doped regions of different doping.

Description of reference numerals:

1 n-doped silicon substrate

2 p + -doped emitter

3 n + -doped back surface field

4 water cap

5 substances for passivating or masking surfaces

6 substances for parasitically passivating or covering surfaces

7, 8 edge regions in contact with differently doped regions

10 PERT solar cell (or its precursor structure)

11, 12 edges

13 front side of the substrate

14 rear side of the substrate

20 conveying roller

30 etching solution