DE102017114097A1 - A method of patterning a diamond wire sawn multicrystalline silicon wafer and method of making a solar cell - Google Patents

Abstract

According to various embodiments, a method (100) of patterning a diamond wire sawn multicrystalline silicon wafer (202) may include:
a first wet chemical etching of a surface (202a) of the diamond wire sawn multicrystalline silicon wafer (202) in a first acidic etch solution; then a second wet chemical etching of the surface (202a) of the diamond wire sawn multicrystalline silicon wafer (202) in a second acidic etch solution to create an etch pit structure on the surface (202a).

Description

The invention relates to a method for structuring a diamond-wire sawn, multicrystalline silicon wafer and to a method for producing a solar cell.

For a high efficiency of a solar cell, a high light output is essential. In order to achieve high luminous efficacy, special structures (i.e., rough textures) may be formed on at least one surface of a silicon wafer which may be used to make the solar cell. By generating such special structures on a surface of the solar cell can be achieved, for example, that incident light is reflected several times after hitting the surface of the solar cell. For industrial solar cells, for example, two textures play a role, namely randomly distributed pyramids and randomly distributed pits.

Surface Structures Based on Random Pyramid Layout (Green, High Efficiency Silicon Solar Cells, Aedermannsdorf: Trans Tech Publ., 1987; Wang, Wang, High-efficiency Solar Cells: Physics, Materials, and Devices.) Cham: Springer , 2014) can be produced for example for producing a monocrystalline solar cell by treating the monocrystalline silicon wafer in alkalis (potassium hydroxide, sodium hydroxide or tetramethylammonium hydroxide) with surface-active additives (i-propanol, surfactants) at temperatures (eg between 70 ° C. and 80 ° C.) ( such as in DE 10 2008 014 166 B3 or EP 2 605 289 A2 is described). However, these textures can only be applied to single crystal silicon material with the crystal direction ( 100 ) be generated.

On a multicrystalline silicon surface, conventionally used alkaline etching processes leave different surfaces depending on the crystal orientation, which is not suitable for use in the photovoltaic industry. Therefore, on a multicrystalline solar cell, ie on a multicrystalline silicon wafer, pit structures (so-called isotropic textures) can be generated by treating the multicrystalline silicon wafer in a nitric acid-containing hydrofluoric acid solution (also referred to as HF-HNO ₃ -containing etching solution). The nitric acid-containing hydrofluoric acid solution may in some cases contain further mineral acids or further oxidizing agents (eg US 2003/0119332 A1 ). Partly the surface-active substances are added to the nitric acid-containing hydrofluoric acid solution in order to increase the wetting of the silicon surface of the multicrystalline silicon wafer (eg US 2013/0130508 A1 ). The advantage lies in the direction-independent production of the etch pits, so that polycrystalline silicon wafers that are cheaper to produce can be used for solar cell production.

Silicon wafers can, for example, be sawn from a block (also referred to as ingot). Conventionally, essentially two types of methods are used, namely, the SiC slurry method and the diamond wire method. In the SiC slurry process, a thin steel wire is passed over the block along with a glycol-silicon carbide (SiC) slurry. In the diamond wire process, the wafers are separated by a wire filled with diamond crystals. The diamond wire process (also referred to as diamond wire saws) offers significant advantages over the SiC slurry process. On the one hand, the material loss is significantly lower, since the effective cut surface (or the cutting width) is significantly smaller. On the other hand, the roughness of the sawn surface of the silicon wafer produced in the diamond wire method is considerably lower than in the case of the SiC slurry method. In addition, the sub-surface material is less damaged (i.e., so-called sub-surface damage is avoided), which can significantly reduce the likelihood of breakage of the silicon wafer or finished solar cell.

The different sawing methods cause differently damaged surfaces. While uniform surface damage occurs in the SiC slurry process, surfaces produced in diamond wire processes alternate large smooth surfaces and sawing depths due to wire guidance during sawing. For example, the surface of the silicon wafer resulting from the diamond wire process can not be removed by conventional etching techniques, e.g. based on a HF-HNO3-containing solution, textured. This prevents the use of diamond wire saws for the production of multicrystalline wafers for the production of multicrystalline solar cells (Meinel, Koschwitz, Blocks, Acker, Comparison of diamond wire cut and silicon carbide slurry processed silicon wafer surfaces after acidic texturization, Mater. Sci. Semicond ., 2014).

In accordance with various embodiments, a method is described herein which enables a uniformly textured surface to be formed on a diamond wire sawn multicrystalline silicon wafer. This is done by wet chemical etching. For this purpose, in a first step, illustratively an etching pretreatment or pre-texturing, a rough (ie pre-texturized) surface is produced on the diamond-wire-sawn, multicrystalline silicon wafer. Clearly, the smooth diamond-wire-sawn surface of the multicrystalline silicon wafer is roughened, for example by means of a wet-chemical etching step in an acidic etching solution. In a subsequent second etching step is by means of a further acidic etching solution, for example a HF-HNO ₃ -containing etching solution, the desired final texture produced. Thus, for example, by means of the method described herein, a surface texture can be generated on a diamond-wire-sawn, multicrystalline silicon wafer, which can conventionally only be produced on a SiC slurry-sawn wafer. Further, by combining the two etching steps as described below, a surface texture improved over that conventionally produced on a SiC slurry-sawn wafer can be produced.

• • den Einsatz einer Laservorbehandlung (Blattmann, Trusheim, Progress on Silicon Wafer Texturing by Hybrid Laser-Etching-Process, Proc. 31nd EU PVSEC, Hamburg, 2015),
• • eine Vorbehandlung durch Zusatz von Metallen in ein isotropes Ätzbad zur Erzeugung von porösen Siliziumoberflächen (Kumagai, Texturization using metal catalyst wet chemical etching for multicrystalline diamond wire sawn wafer, Sol. Energy Mater. Sol. Cerls, 2015), oder
• • eine Vorbehandlung durch Sandstrahlprozesse (Wang, Lih, The Influence of Surface Quality on Diamond Wire Sawn Multi-Crystalline Silicon Wafer, Proc. 32nd EU PVSEC, München, 2016).

This also allows, for example, the use of the advantageous diamond wire sawing in the production of multicrystalline solar cells. Alternative methods of producing a rough surface on diamond wire sawn multicrystalline silicon wafer surface include, for example:

• The use of laser pretreatment (Blattmann, Trusheim, Progress on Silicon Wafer Texturing by Hybrid Laser Etching Process, Proc. 31nd EU PVSEC, Hamburg, 2015),
• A pre-treatment by addition of metals in an isotropic etching bath for the production of porous silicon surfaces (Kumagai, Texturization using metal catalyst wet chemical etching for multicrystalline diamond wire sawn wafers, Sol Energy Mater, Sol., Cerls, 2015), or
• • Pre-treatment by sand blasting processes (Wang, Lih, The Influence of Surface Quality on Diamond Wire Sawn Multi-Crystalline Silicon Wafer, Proc. 32nd EU PVSEC, Munich, 2016).

However, the use of these conventional industrial-scale methods significantly increases production costs, which, for example, can not make their use in the production of diamond-wire-sawn, multicrystalline wafers in solar cell production economically viable.

For example, according to various embodiments, it has been recognized that on a diamond wire sawn, multicrystalline silicon wafer, a uniformly rough (e.g., pre-texturized) surface can be formed by treating the surface with a mixture of hydrofluoric acid and a chlorine source (e.g., chlorine gas and / or hydrochloric acid). This pretreated (pre-texturized) surface of the diamond-wire-sawn, multicrystalline silicon wafer makes it possible, for example, to use an HF-HNO 3 mixture for generating a uniform, dense pit texture (also referred to as etch pit structure).

According to various embodiments, regardless of the crystal orientation of the crystallites, a substantially identical surface texture is generated on the surface of the diamond-wire-sawn, multicrystalline silicon wafer. Clearly, the same texture is produced on the entire treated surface of the diamond-wire sawn, multicrystalline silicon wafer.

According to various embodiments, it has been recognized that an etching pit structure can be produced on a diamond-wire-sawn, multicrystalline silicon wafer, which is advantageous for the production of a solar cell, by means of two etching steps which are carried out using two mutually different acid etching solutions. For example, the etch pit structure may be formed by the method described herein such that the reflectivity of the surface (at least in the visible region of the light) is substantially reduced (eg, more than 10%, more than 20%, or even more than 30%) with the reflectivity of a surface of an untreated, diamond-wire-sawn, multicrystalline silicon wafer).

According to various embodiments, only acidic etch solutions are used to texturize the surface of the diamond wire sawn multicrystalline silicon wafer. This may be advantageous, for example, since acid etching solutions are more stable to metal contaminants than basic etching solutions. In particular, wire sawing produces significant metal contamination on the sawn surface. For example, by means of the method described herein of texturing a surface of a diamond-wire-sawn, multicrystalline silicon wafer, the life of an etch line may be allowed to be economically efficient, e.g. longer than a week, so that these methods can be used on an industrial scale.

Embodiments of the invention are illustrated in the figures and are explained in more detail below.

• 1 ein schematisches Ablaufdiagramm eines Verfahrens zum Strukturieren eines diamantdrahtgesägten, multikristallinen Siliziumwafers, gemäß verschiedenen Ausführungsformen;
• 2A und 2B eine schematische Darstellung und eine Elektronenmikroskopie-Aufnahme eines diamantdrahtgesägten, multikristallinen Siliziumwafers nach einem ersten Schritt des Strukturierens, gemäß verschiedenen Ausführungsformen;
• 2C und 2D eine schematische Darstellung und eine Elektronenmikroskopie-Aufnahme eines diamantdrahtgesägten, multikristallinen Siliziumwafers nach einem zweiten Schritt des Strukturierens, gemäß verschiedenen Ausführungsformen;
• 3A und 3B jeweils ein Bild der Oberfläche eines diamantdrahtgesägten, multikristallinen Siliziumwafers während des Strukturierens, gemäß verschiedenen Ausführungsformen;
• 3C ein Bild der Oberfläche eines ohne diamantdrahtgesägten, multikristallinen Siliziumwafers, der ohne Vortexturierung in nur einem Schritt strukturiert wurde, als Vergleichsbeispiel;
• 3D ein Bild einer texturierten Oberfläche eines SiC-Slurry-gesägten multikristallinen Siliziumwafers, der ohne Vortexturierung in nur einem Schritt strukturiert wurde, als Vergleichsbeispiel;
• 4 ein schematisches Ablaufdiagramm eines Verfahrens zum Herstellen einer Solarzelle, gemäß verschiedenen Ausführungsformen; und
• 5 einen schematischen Aufbau einer Solarzelle basierend auf dem strukturierten, diamantdrahtgesägten, multikristallinen Siliziumwafer, gemäß verschiedenen Ausführungsformen.

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• 1 12 is a schematic flow diagram of a method of patterning a diamond wire sawn, multicrystalline silicon wafer, according to various embodiments;
• 2A and 2 B a schematic representation and an electron micrograph of a diamond wire sawn, multicrystalline silicon wafer after a first step structuring, according to various embodiments;
• 2C and 2D a schematic representation and an electron micrograph of a diamond wire sawn, multicrystalline silicon wafer after a second step of structuring, according to various embodiments;
• 3A and 3B an image of the surface of a diamond wire sawn, multicrystalline silicon wafer during patterning, according to various embodiments;
• 3C an image of the surface of a diamond wire sawed, multicrystalline silicon wafer, which was structured without pre-texturing in only one step, as a comparative example;
• 3D an image of a textured surface of a SiC slurry sawn multicrystalline silicon wafer, which was structured in one step without pre-texturing, as a comparative example;
• 4 a schematic flow diagram of a method for manufacturing a solar cell, according to various embodiments; and
• 5 12 shows a schematic structure of a solar cell based on the structured, diamond-wire-sawn, multicrystalline silicon wafer, according to various embodiments.

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It should be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. It should be understood that the features of the various exemplary embodiments described herein may be combined with each other unless specifically stated otherwise. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

In the figures, identical or similar elements are provided with identical reference numerals, as appropriate.

According to various embodiments, there is provided a method of patterning a diamond wire sawn multicrystalline silicon wafer and a patterned diamond wire sawn multicrystalline silicon wafer, wherein the surface of the diamond wire sawn multicrystalline silicon wafer is patterned such that light can be optimally absorbed by it. Thus, the patterned diamond wire sawn polycrystalline silicon wafer or the method of patterning the diamond wire sawn multicrystalline silicon wafer may be used in the photovoltaic industry, for example to provide a highly efficient and inexpensive solar cell.

According to various embodiments, the diamond wire sawn multicrystalline silicon wafer is subjected to at least two wet chemical etching steps, both of which are acidic, i. the at least two etch solutions used in the at least two wet chemical etch steps both have a PH of less than 7, e.g. less than 6, or less than 5.

According to various embodiments, no further etching step may be necessary between the two etching steps. In other words, the two etching steps can follow each other directly.

1 illustrates a schematic flow diagram of a method 100 for patterning a diamond-wire-sawn, multicrystalline silicon wafer. The method may include, for example: in 110 , a first wet-chemical etching of a surface of the diamond-wire-sawn, multicrystalline silicon wafer in a first acidic etching solution to produce a defect structure on the surface; and then, in 120 , a second wet-chemical etching of the surface of the diamond-wire-sawn multicrystalline silicon wafer in a second acidic etching solution to form an etch pit structure on the surface.

According to various embodiments, the first wet chemical etch, in step 110 of the procedure 100 , an anisotropic wet-chemical etching. Further, the second wet chemical etching, in step 120 of the procedure 100 , an isotropic wet-chemical etching. In this case, the anisotropic wet-chemical etching causes sufficient defects on the surface of the diamond-wire-sawn, multicrystalline silicon wafer, so that the desired texture, for example an etch pit structure with randomly distributed etching pits, can be produced during the isotropic wet-chemical etching.

At the first wet chemical etching, in step 110 of the procedure 100 For example, an etching solution (referred to herein as the first etching solution) comprising or consisting of hydrofluoric acid (HF, aq) and a chlorine source may be used. In this case, the chlorine source gaseous chlorine, which is introduced into the etching solution, and / or hydrochloric acid or consist thereof.

Illustratively, for example, a hydrofluoric acid / hydrochloric acid mixture can be used as the first etching solution. Similarly, gaseous chlorine may be introduced into the first etching solution and, in aqueous solution, to hydrochloric acid and disproportionated hypochlorous acid, form a hydrofluoric acid / hydrochloric acid mixture.

According to various embodiments, the first acid etching solution may further comprise an oxidizing agent. The oxidizing agent may for example comprise or be at least one of the following group of oxidizing agents: hydrogen peroxide (H ₂ O ₂ ); Chlorine (Cl ₂ , HOCL, etc.); Copper ions (Cu ²⁺ ). For example, gaseous chlorine may be introduced into the first etching solution and, when disproportionated in aqueous solution to hydrochloric acid and hypochlorous acid, form hypochlorous acid as an oxidizing agent. In this case, the gaseous chlorine may also be partially or physically dissolved in the etching solution.

In the second wet chemical etching, in step 120 of the procedure 100 For example, an etching solution (referred to herein as a second etching solution) comprising or consisting of hydrofluoric acid (HF _aq ) and nitric acid (HNO _{3, aq} ) may be used.

The two etching steps are carried out successively, e.g. in two different etching baths. For example, the surface of the diamond wire sawn multicrystalline silicon wafer may be rinsed between the first wet chemical etch and the second wet chemical etch, e.g. with deionized water or other suitable liquid.

The back side of the diamond-wire sawn, multicrystalline silicon wafer 202 That is, the surface facing away from the surface, for example, can be covered in the etching steps, if this is not to be etched. Alternatively, two-sided treatment of the diamond-wire sawn, multicrystalline silicon wafer is also possible 202 possible.

2A illustrates a diamond wire sawed, multicrystalline silicon wafer 202 after the first wet-chemical etching (ie after the step 110 of the procedure 100 ) in a schematic side or cross-sectional view. According to various embodiments, the diamond wire sawn multicrystalline silicon wafer 202 a first surface structure 204a on.

The diamond-wire-sawn, multicrystalline silicon wafer 202 has a surface 202a with a plurality of crystallites of different crystal orientation (also referred to as grains) on. According to various embodiments, the crystal orientations of the crystallites may be on the surface 202a essentially randomly distributed or have the typical distribution of the manufacturing process of the silicon block.

The surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 can be treated by means of the first etching solution such that on this surface 202a the first surface structure 204a is formed. The first surface structure 204a can as a defect structure 204a which forms the basis for the second etching step.

2 B illustrates a plan view of the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 after the first wet-chemical etching (ie after the step 110 of the procedure 100 ) on the basis of a photograph taken by means of a scanning electron microscope.

In 2 B is a grain boundary 204g between two adjacent grains of the diamond-wire-sawn, multicrystalline silicon wafer 202 recognizable. After the (eg anisotropic) etching in the first step 110 of the procedure 100 As described herein, the surface is 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 essentially attacked regardless of the crystal orientation of the grains, ie roughened or in other words vortexturiert. Illustratively, defects (eg etching damage) on the surface can occur 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 which are essentially random on the surface 202a are distributed. By means of conventional methods, for example, it is not possible to roughen or pre-texture smooth surfaces or smooth surface sections, such as those produced by diamond wire sawing.

2C illustrates the diamond wire sawed multicrystalline silicon wafer 202 after the first wet-chemical etching (ie after the step 110 of the procedure 100 ) and after the second wet chemical etching (ie after the step 120 of the procedure 100 ) in a schematic side or cross-sectional view. According to various embodiments, the diamond wire sawn multicrystalline silicon wafer 202 a second surface structure 204b (also referred to as etch pit structure), which depends on the first surface structure 204a is different. The second surface structure 204b has a greater roughness than the first surface structure 204a on. eg measured by means of an atomic force microscope or any other suitable measuring method).

The surface structure 204a of the diamond-wire sawn, multicrystalline silicon wafer 202 as a starting point can be treated by means of the second etching solution such that an etch pit structure 204b is formed with, for example, randomly distributed etching pits.

2D illustrates a plan view of the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 after the procedure 100 was performed on the basis of a picture taken using a scanning electron microscope.

The spatial distribution of the etching pits and their geometry can be evaluated optically, e.g. by scanning electron microscopy.

According to various embodiments, the first wet chemical etch and the second wet chemical etch may be performed such that the etch pits of the generated etch pit structure 204b concerning the location on the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 random (fluctuating around a mean) are distributed.

According to various embodiments, the first wet chemical etch and the second wet chemical etch may be performed such that the etch pits of the generated etch pit structure 204b with respect to whose width and / or depth are randomly distributed (fluctuating around an average value). The etch pits of the generated etch pit structure 204b For example, in the arithmetic mean, they may have a width (eg, a geometrically averaged diameter of the respective etch pit) in a range of about 1 μm to about 30 μm. Furthermore, the etch pits of the generated etch pit structure 204b in the arithmetic mean a depth (eg, each having a maximum depth of the respective etching pit) in a range of about 1 micron to about 30 microns.

Such as in 2D 1, the first wet chemical etching and the second wet chemical etching may be performed such that the number of etch pit structures produced by the etch pits of the generated etch pit structure 204b per square millimeter on the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 is greater than 100 , eg greater than 250 , or greater than 500 ,

Illustratively, the etch pit structure 204b be generated so that it has the desired optical properties. For example, the geometry of the etching pits, their spatial distribution and / or their number per unit area can be designed accordingly.

By means of the etching pit structure 204b , which has, for example, irregular or randomly distributed etch pits, as used for example in 2D For example, an undesirable anisotropy in the optical properties (eg, reflectivity) of the surface may be exemplified 202a diamond wire sawn multicrystalline silicon wafers 202 be avoided.

In 3A and 3B are the first surface structure 204a and the second surface structure 204b (ie the etch pit structure 204b) exemplified, starting from the in 2 B and 2D shown recording the respective upper edges of the wells are highlighted.

In 3C is another surface structure 304 as a comparative example, wherein a diamond wire sawn, multicrystalline silicon wafer 202 was textured only by means of an HF-HNO ₃ etching solution, ie vividly without the pre-texturing, as in the step 110 of the procedure 100 he follows.

In 3D is another surface structure 314 as a comparative example, wherein a SiC slurry sawed, multicrystalline silicon wafer was textured only by means of a HF-HNO ₃ etching solution, ie illustratively without the pre-texturing, as in step 110 of the procedure 100 he follows.

In the following, some etching solutions are described by way of example, by means of which the surface structure 204b can be produced.

• • Flusssäure (HF), z.B. mit einer Konzentration von 0,2 mol/L,
• • Salzsäure (HCl), z.B. mit einer Konzentration von 11,7 mol/L), und
• • Wasserstoffperoxid (H₂O₂), z.B. mit einer Konzentration von 0,2 mol/L.

According to a first example, the first etching solution in the first step 110 of the procedure 100 Have:

• Hydrofluoric acid (HF), eg with a concentration of 0.2 mol / L,
• Hydrochloric acid (HCl), eg with a concentration of 11.7 mol / L), and
• • Hydrogen peroxide (H ₂ O ₂ ), eg with a concentration of 0.2 mol / L.

In this case, the first etching solution during the first wet-chemical etching (in step 110 of the procedure 100 ) by means of stirring (eg with a rotational speed of 150 Revolutions per minute) in flow relative to the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 added.

• • Flusssäure (HF), z.B. mit einer Konzentration von 3,2 mol/L, und
• • Salpetersäure (HNO₃), z.B. mit einer Konzentration von 5,6 mol/L.

Furthermore, subsequently (in step 120 of the procedure 100 ) the etch pit structure 204b produced by the second etching solution, which comprises

• Hydrofluoric acid (HF), eg at a concentration of 3.2 mol / L, and
• • Nitric acid (HNO ₃ ), eg at a concentration of 5.6 mol / L.

• • Flusssäure (HF), z.B. mit einer Konzentration von 5,5 mol/L,
• • Salzsäure (HCl), z.B. mit einer Konzentration von 9,6 mol/L), und
• • Chlor (Cl₂), das in die erste Ätzlösung während des Ätzens eingeleitet wird.

According to a second example, the first etching solution in the first step 110 of the procedure 100 Have:

• Hydrofluoric acid (HF), eg with a concentration of 5.5 mol / L,
• Hydrochloric acid (HCl), eg with a concentration of 9.6 mol / L), and
• • Chlorine (Cl ₂ ), which is introduced into the first etching solution during the etching.

• • Flusssäure (HF), z.B. mit einer Konzentration von 3,2 mol/L, und
• • Salpetersäure (HNO₃), z.B. mit einer Konzentration von 5,6 mol/L.

Furthermore, subsequently (in step 120 of the procedure 100 ) the etch pit structure 204b produced by the second etching solution, which comprises

• Hydrofluoric acid (HF), eg at a concentration of 3.2 mol / L, and
• • Nitric acid (HNO ₃ ), eg at a concentration of 5.6 mol / L.

• • Flusssäure (HF), z.B. mit einer Konzentration von 1,4 mol/L,
• • Salzsäure (HCl), z.B. mit einer Konzentration von 9,6 mol/L), und
• • Chlor (Cl₂), das in die erste Ätzlösung während des Ätzens eingeleitet wird.

According to a third example, the first etching solution in the first step 110 of the procedure 100 Have:

• Hydrofluoric acid (HF), eg with a concentration of 1.4 mol / L,
• Hydrochloric acid (HCl), eg with a concentration of 9.6 mol / L), and
• • Chlorine (Cl ₂ ), which is introduced into the first etching solution during the etching.

In this case, the first etching solution during the first wet-chemical etching (in step 110 of the procedure 100 ) by means of stirring (eg with a rotational speed of 150 Revolutions per minute) in flow relative to the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 added.

• • Flusssäure (HF), z.B. mit einer Konzentration von 3,2 mol/L,
• • Salpetersäure (HNO₃), z.B. mit einer Konzentration von 5,6 mol/L, und
• • Hexafluorokieselsäure (H₂SiF₆), z.B. mit einer Konzentration von 0,8 mol/L.

Furthermore, subsequently (in step 120 of the procedure 100 ) the etch pit structure 204b produced by the second etching solution, which comprises

• Hydrofluoric acid (HF), eg with a concentration of 3.2 mol / L,
• • nitric acid (HNO ₃ ), eg at a concentration of 5.6 mol / L, and
• Hexafluorosilicic acid (H ₂ SiF ₆ ), eg with a concentration of 0.8 mol / L.

The first etching structures thus formed 204a each have randomly disposed first recesses or etching damage on the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 and the second etched structures thus formed 204b (herein as etch pit structures 204b each have randomly disposed second recesses or etching pits. In this case, the first depressions are smaller (for example, the first depressions are less deep and / or less ready or have a smaller diameter) than the second depressions.

The first etching solution in which the diamond-wire-sawn, multicrystalline silicon wafer 202 was at least according to some embodiments by means of stirring, for example, with a rotational speed of about 150 Revolutions per minute, in flow. However, other rotational speeds may be used, eg, less or more than about 150 Revolutions per minute.

For example, if chlorine was used as the oxidizing agent, the chlorine may be provided by bubbling chlorine gas into the aqueous first etching solution. In this case, for example, the first etching solution can also be caused to flow by means of a continuous supply of chlorine gas (Cl ₂ ), according to various embodiments.

Further, chlorine may be provided as an oxidizing agent by supplying chlorine gas or at least a chlorine-containing gas to the first etching solution. For example, the gas may be supplied at a volumetric flow rate (in liters per minute, L / min) in a range of about 0.1 L / min to about 10 L / min. By adjusting or controlling the volumetric flow of the gas (e.g., the chlorine gas), the rate of removal and / or surface morphology generated can be influenced.

For example, a hydrofluoric acid / hydrochloric acid mixture may be used as (e.g., first) etching solution. Similarly, gaseous chlorine may be introduced into a hydrofluoric acid etching solution and, disproportionated in aqueous solution to hydrochloric acid and hypochlorous acid, form a hydrofluoric acid / hydrochloric acid mixture. The gaseous chlorine can act as an oxidant at the same time.

Alternatively, at least one solid may or may not be added to the first etching solution, eg hypochlorite, chlorate, perchlorate or a chloride-containing salt (such as sodium chloride (NaCl), potassium chloride (KCl) and / or ammonium chloride (NH ₄ Cl)). The solid may dissolve in the solution, for example, and / or, for example, decompose and / or react in contact with the solution, thereby releasing chlorine or chloride and thus acting as a chlorine source. Depending on which surface morphology is to be generated, a suitable solid can be supplied, which releases a certain amount of chlorine or chloride. For example, low removal rates can be achieved by adding hypochlorite or perchlorate. Alternatively or in combination, multiple solids may be added.

• • Behandlungsdauer t = 1 min, t = 5 min oder t = 10 min, z.B. mit einer Behandlungsdauer in einem Bereich von ungefähr 1 min bis ungefähr 20 min, z.B. in einem Bereich von ungefähr 1 min bis ungefähr 10 min;
• • Behandlungstemperatur ϑ = 20 °C, ϑ = 25 °C oder ϑ = 30 °C, z.B. mit einer Behandlungstemperatur in einem Bereich von ungefähr 15 °C bis ungefähr 35 °C.

According to various embodiments, the first wet chemical etch of the diamond wire sawn, multicrystalline silicon wafer 202 using the following additional process parameters:

• Treatment duration t = 1 min, t = 5 min or t = 10 min, eg with a treatment duration in a range of about 1 min to about 20 min, eg in a range of about 1 min to about 10 min;
• Treatment temperature θ = 20 ° C, θ = 25 ° C or θ = 30 ° C, eg with a treatment temperature in a range from about 15 ° C to about 35 ° C.

• • Behandlungsdauer t = 1 min, t = 10 min oder t = 30 min, z.B. mit einer Behandlungsdauer in einem Bereich von ungefähr 1 min bis ungefähr 60 min, z.B. in einem Bereich von ungefähr 1 min bis ungefähr 30 min;
• • Behandlungstemperatur ϑ = 20 °C, ϑ = 25 °C oder ϑ = 30 °C, z.B. mit einer Behandlungstemperatur in einem Bereich von ungefähr 15 °C bis ungefähr 35 °C.

According to various embodiments, the second wet chemical etch of the diamond wire sawn, multicrystalline silicon wafer 202 using the following additional process parameters:

• Treatment duration t = 1 min, t = 10 min or t = 30 min, eg with a treatment duration in a range of about 1 min to about 60 min, eg in a range of about 1 min to about 30 min;
• Treatment temperature θ = 20 ° C, θ = 25 ° C or θ = 30 ° C, eg with a treatment temperature in a range from about 15 ° C to about 35 ° C.

According to various embodiments, the process parameters of both wet chemical etching step in the process 100 be selected such that a surface structure 204b on the diamond-wire-sawn, multicrystalline silicon wafer 202 is etched, which has a minimum reflectance or a maximum absorption of light.

According to various embodiments, the first etching solution may include a surfactant (component), e.g. from the group of surfactants, be added or be.

According to various embodiments, the second etching solution may include a surfactant (component), e.g. from the group of surfactants, be added or be.

The concentrations of the etching solutions described herein (expressed in moles per liter, mol / L) can be determined, for example, mathematically based on the mass of the mixture components. Further, the concentrations of, for example, fluoride, chloride, and sulfate ions, respectively, can be determined by ion exchange chromatography, e.g. using a Dionex ICS 2000.

The geometry or size and distribution of the etch pits of the surface structure 204b can be determined for example by means of a scanning electron microscope (SEM), cf. 2 B and 2D , eg by means of a Vega Tescan TS 5130 SB system.

The reflectance of a structurally etched diamond-wire sawn, multicrystalline silicon wafer 202 can be determined by means of a reflection measurement, for example by means of a Jasco UV / VIS spectrometer, being integrated via a spherical surface, and wherein the diamond-wire-sawn, multicrystalline silicon wafer 202 is arranged relative to the light source of the spectrometer, so that the light of the light source perpendicular to the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 incident. As a reference wavelength, for example 700 nm can be used. Alternatively, the reflectance can also be averaged over the wavelength range of visible light (eg from 400 nm to 700 nm).

The respective etching step 110 . 120 of the procedure 100 can be terminated, for example, that the diamond wire sawn, multicrystalline silicon wafer 202 is removed from the respective etching solution and rinsed with deionized Waser.

According to various embodiments, the treatment temperature may be less than 30 ° C during the first wet chemical etch and / or during the second wet chemical etch. Illustrative is in the method described herein 100 no heating of the respective etching solution during the etching necessary. For example, the method 100 be carried out at the respective prevailing room temperature.

According to various embodiments, in addition to the hydrofluoric acid and nitric acid, the second etching solution may also contain another acid, for example acetic acid (CH ₃ COOH), sulfuric acid (H ₂ SO ₄ ), hexafluorosilicic acid (H ₂ SiF ₆ ), etc.

At the in 2 B The picture shown became the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 treated by means of an etching solution of hydrofluoric acid (HF), hydrochloric acid (HCL) and an added oxidizing agent. At the in 2D The picture shown became the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 then textured by means of an etching solution of hydrofluoric acid (HF) and nitric acid (HNO ₃ ).

4 illustrates a schematic flow diagram of a method 400 for manufacturing a solar cell. The method may include, for example: in 410 , Structuring a surface 202a (eg on a front side) of a diamond-wire sawn, multicrystalline silicon wafer 202 by means of a two-stage etching process using two acidic etching solutions (eg by means of the process 100 ), in 420 , Forming at least one pn junction 508 in the diamond-wire-sawn, multicrystalline silicon wafer 202 ; in 430 , Forming a first metallization 504 for electrically contacting the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 ; and, in 440m, forming a second metallization 506 for electrically contacting one of the surfaces 202a opposite further surface 202r (eg on a back side) of the diamond-wire sawn, multicrystalline silicon wafer 202 ,

For example, according to various embodiments, the method may include: patterning a front side of a diamond-wire-sawn multicrystalline silicon wafer by a two-step etching process using two acidic etching solutions (eg, by the method 100 Forming at least one pn junction in the diamond wire sawn multicrystalline silicon wafer; Forming a front side metallization for electrically contacting the front side as a light incident side; and forming a backside metallization for electrically contacting a back side of the diamond wire sawn multicrystalline silicon wafer opposite the light incident side.

In 5 is a solar cell 502 shown in a schematic cross-sectional view, according to various embodiments. The solar cell 502 For example, a diamond-wire-sawn, multicrystalline silicon wafer 202 as described above, see for example 2C and 2D , In function as a solar cell, the diamond wire sawn, multicrystalline silicon wafer 202 be doped accordingly, so that in the diamond wire sawn, multicrystalline silicon wafer 202 at least one appropriately designed pn junction 508 is provided. For electrically contacting the diamond-wire sawn, multicrystalline silicon wafer 202 For example, a first metallization (eg, a front side metallization 504 ) and a second metallization (eg, a backside metallization 506 ) used. Each of the metallizations 504 . 506 For example, it may have one or more electrical contacts.

According to various embodiments, the solar cell 502 at least one light incident side 501e exhibit. The surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 on the light side 501e is, for example, treated as described above and has an etch pit structure 204b on.

The first metallization 504 For example, for electrically contacting the light incident side 501e the solar cell 502 be used. Furthermore, the second metallization 506 for electrically contacting one of the light incident side 501e opposite side 501r the solar cell 502 be used. The second metallization 506 may be, for example, a back-side metallization or have for electrically contacting the back 501r the solar cell 502 ,

According to various embodiments, the solar cell is 502 constructed in such a way that light 501 on the second surface structure 204b can impinge from the multitude of randomly distributed etching pits and thus can be efficiently converted into electrical energy.

It is understood that the design of the solar cell 502 can be done according to the known designs for multicrystalline solar cells. For doping the diamond-wire sawn, multicrystalline silicon wafer 202 and for applying the metallizations 504 . 506 For example, conventional methods of the photovoltaic industry may be used, for example, thermal diffusion or the like for doping the diamond-wire-sawn, multicrystalline silicon wafer 202 and soldering, screen printing and / or the like for applying the metallizations 504 . 506 ,

According to various embodiments, a diamond wire sawn, multicrystalline silicon wafer 202 as described herein and used to make a solar cell.

According to various embodiments, a hydrochloric acid mixture may be used as the etching solution. For this purpose, gaseous chlorine can be introduced into an aqueous solution and, disproportionated in this to hydrochloric acid and hypochlorous acid, form a hydrochloric acid mixture.

Exemplary embodiments which relate to the figures described above are listed below.

Example 1 is a method 100 for patterning a diamond-wire-sawn, multicrystalline silicon wafer 202 the method comprising: a first wet-chemical etching of a surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 in a first acidic etching solution (eg to create a defect structure 204a on the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 ); and then a second wet-chemical etching of the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 in a second acidic etching solution (eg to create an etch pit structure 204b on the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 ).

In Example 2, the method of Example 1 optionally includes that the first wet chemical etching is an anisotropic wet chemical etching.

In Example 3, the method of Example 1 or 2 optionally indicates that the second wet-chemical etching is an isotropic wet-chemical etching.

In Example 4, the method according to any one of Examples 1 to 3 optionally includes that the first acid etching solution has hydrofluoric acid (HF _aq ) and a chlorine source. The first acid etching solution may include, for example, hydrofluoric acid (HF _aq ) and hydrochloric acid (HCl _aq ).

In Example 5, the process according to Example 4 optionally comprises that the chlorine source comprises at least one of the following group of chlorine sources: gaseous chlorine (Cl ₂ ); and hydrochloric acid (HCl _aq ).

In Example 6, the method according to Example 4 or 5 optionally includes that the first acid etching solution further comprises an oxidizing agent.

In Example 7, the process according to Example 6 optionally comprises that the oxidizing agent comprises at least one of the following group of oxidizing agents: hydrogen peroxide (H ₂ O ₂ ); Chlorine (eg gaseous chlorine (Cl ₂ ) or hypochlorous acid (HOCl) or hypochlorite (ClO ^- )); Copper ions (Cu ²⁺ ).

In Example 8, the method according to any one of Examples 1 to 7 optionally further comprises: generating a flow of the first acidic etching solution relative to the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 during the first wet chemical etching.

In Example 9, the process according to Example 8 optionally has the flow by stirring the first acidic etching solution, circulating the first acidic etching solution and / or by introducing a gas (eg by introducing gaseous chlorine or a chlorine-containing gas) into the first acidic etching solution is produced.

In Example 10, the method according to any of Examples 1 to 9 optionally shows that the second acid etching solution has hydrofluoric acid (HF _aq ) and nitric acid (HNO _{3, aq} ).

In Example 11, the process according to any of Examples 1 to 10 optionally has the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 is rinsed between the first wet chemical etch and the second wet chemical etch. The rinsing can be done, for example, with deionized water.

In Example 12, the method according to any of Examples 1 to 11 optionally includes that the first wet chemical etching and the second wet chemical etching are performed such that the generated etch pit structure 204b has a plurality of etch pits.

In Example 13, the method according to Example 12 optionally has the etch pits with respect to the location on the surface of the diamond-wire-sawn, multicrystalline silicon wafer 202 are distributed randomly.

In Example 14, the method according to Example 12 or 13 optionally shows that the etch pits are randomly distributed with respect to their width and / or depth.

In Example 15, the method according to any one of Examples 12 to 14 optionally includes the etching pits on the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 (eg, in arithmetic mean) have a width in a range of about 1 μm to about 30 μm.

In Example 16, the method according to any one of Examples 12 to 15 optionally includes that the etch pits (e.g., in arithmetic mean) have a depth in a range of about 1 μm to about 30 μm.

In Example 17, the method according to any one of Examples 1 to 16 optionally includes that the first wet chemical etching and the second wet chemical etching are performed such that the generated etch pit structure 204b more than 100 Etch pits per square millimeter of the surface of the diamond-wire sawn, multicrystalline silicon wafer 202 having.

Example 18 is a method for manufacturing a solar cell 502 For example, the method comprises: patterning a surface 202a a diamond-wire sawn, multicrystalline silicon wafer 202 according to any of examples 1 to 17, forming at least one pn junction 508 in the diamond-wire-sawn, multicrystalline silicon wafer 202 ; Forming a first metallization 504 for electrically contacting the surface 202a of the diamond-wire sawn, multicrystalline silicon wafer 202 ; and forming a second metallization 506 for electrically contacting one of the surfaces 202a opposite further surface 202r of the diamond-wire sawn, multicrystalline silicon wafer 202 ,

According to Example 19, a diamond wire sawn, multicrystalline silicon wafer 202 , which has been treated according to any one of Examples 1 to 17, for producing a solar cell 502 be used.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008014166 B3 [0003]
• EP 2605289 A2 [0003]
• US 2003/0119332 A1 [0004]
• US 2013/0130508 A1 [0004]

Claims (10)

A method (100) of patterning a diamond wire sawn multicrystalline silicon wafer (202), the method comprising: A first wet-chemical etching of a surface (202a) of the diamond-wire-sawn multicrystalline silicon wafer (202) in a first acidic etching solution to create a defect pattern on the surface (202a); and subsequently A second wet-chemical etching of the surface (202a) in a second acidic etch solution to create an etch pit structure on the surface (202a). Method according to Claim 1 wherein the first wet chemical etching is an anisotropic wet chemical etching. Method according to Claim 1 or 2 wherein the second wet chemical etching is an isotropic wet chemical etching. Method according to one of Claims 1 to 3 wherein the first acid etching solution comprises hydrofluoric acid and hydrochloric acid. Method according to Claim 4 wherein the first acid etching solution further comprises an oxidizing agent. Method according to one of Claims 1 to 5 , further comprising: generating a flow of the first acidic etch solution relative to the surface (202a) of the diamond wire sawn multicrystalline silicon wafer (202) during the first wet chemical etch. Method according to one of Claims 1 to 6 wherein the second acid etching solution comprises hydrofluoric acid and nitric acid. Method according to one of Claims 1 to 7 wherein the first wet chemical etch and the second wet chemical etch are such that the generated etch pit structure has a plurality of etch pits, wherein the etch wells are preferably randomly distributed with respect to location on the surface of the diamond wire sawn multicrystalline silicon wafer (202). A method of manufacturing a solar cell, the method comprising: • patterning a surface (202a) of a diamond wire sawn, multicrystalline silicon wafer (202) according to any one of Claims 1 to 8th • forming at least one pn junction (508) in the diamond wire sawn multicrystalline silicon wafer (202); Forming a first metallization (504) for electrically contacting the surface (202) of the diamond wire sawn multicrystalline silicon wafer (202); and forming a second metallization (506) for electrically contacting another surface (202r) of the diamond wire sawn multicrystalline silicon wafer (202) opposite the surface (202a). Using a diamond wire sawed, multicrystalline silicon wafer (202), which according to one of Claims 1 to 8th is treated for producing a solar cell (502).

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