EP3284111A1

EP3284111A1 - Screen-printable boron doping paste with simultaneous inhibition of phosphorus diffusion in co-diffusion processes

Info

Publication number: EP3284111A1
Application number: EP16713735.5A
Authority: EP
Inventors: Oliver Doll; Ingo Koehler; Sebastian Barth
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2015-04-15
Filing date: 2016-03-24
Publication date: 2018-02-21
Also published as: TW201710410A; CN107484432A; US20180122640A1; KR20170139580A; WO2016165812A1

Abstract

The present invention relates to a novel printable boron doping paste in the form of a hybrid gel on the basis of inorganic oxide precursors, preferably precursors of silicon dioxide, aluminum oxide and boron oxide, in the presence of organic polymer particles, the pastes according to the invention being usable in a simplified process for the production of solar cells, and the hybrid gel according to the invention functioning as a doping medium as well as a diffusion barrier.

Description

Screen-printable boron doping paste with simultaneous inhibition of phosphorus diffusion in co-diffusion processes

The present invention relates to a novel printable Bordotierpaste in the form of a hybrid gel based on precursors of inorganic oxides, preferably of silica, alumina, and boron oxide, in the presence of organic polymer particles, wherein the

pastes according to the invention in a simplified process for

Production of solar cells can be used, wherein the hybrid gel according to the invention act both as a doping medium and as a diffusion barrier.

PRIOR ART The production of simple or currently the largest in the market

Represented in the market share comprises the main production steps outlined below:

1. saw damage etching and texture

A silicon wafer (monocrystalline, multicrystalline or quasi-monocrystalline, p- or n-type base doping) is freed of adherent saw damage by means of an etching process and "simultaneously", usually in the same etching bath, texturized under texturing is in this case the creation of a preferred Surface (texture) as a result of the etching step or simply to understand the targeted, but not particularly oriented roughening of the wafer surface

Surface of the wafer now as a diffuse reflector and thus reduces the directional, wavelength and the angle of impact dependent reflection, which ultimately leads to an increase in the absorbed portion of the incident light on the surface and thus the

Conversion efficiency of the solar cell increased.

In the case of monocrystalline wafers, the aforementioned etching solutions for treating the silicon wafers typically consist of dilute potassium hydroxide solution to which isopropyl alcohol has been added as solvent. It can instead, other alcohols of higher vapor pressure or higher boiling point than isopropyl alcohol may be added, provided that the desired etching result can be achieved. Typically, the desired etch result is a morphology that is randomly-etched, or rather etched out of the original surface.

Pyramids is characterized by square base. The density, the height and thus the base area of the pyramids can be influenced by a suitable choice of the above-mentioned constituents of the etching solution, the etching temperature and the residence time of the wafers in the etching basin.

Typically, the texturing of the monocrystalline wafer in

Temperature range of 70 - <90 ° C performed, with Ätzabträge of up to 10 pm per wafer side can be achieved.

In the case of multicrystalline silicon wafers, the etching solution may consist of potassium hydroxide solution with an average concentration (10-15%). However, this etching technique is hardly used in industrial practice. More often becomes one

Etching solution consisting of nitric acid, hydrofluoric acid and water used. This etching solution can be modified by various additives such as sulfuric acid, phosphoric acid, acetic acid, N-methylpyrrolidone and also surfactants, which u. a.

Wetting properties of the etching solution and their etch rate can be specifically influenced. These acid etch mixtures produce a morphology of interstitially arranged etch pits on the surface. The etching is typically carried out at temperatures in the range between 4 ° C to <10 ° C and the Ätzabtrag here is usually 4 pm to 6 pm.

Immediately following texturing, the silicon wafers are thoroughly cleaned with water and treated with dilute hydrofluoric acid to prepare the chemical oxide layer layer resulting therefrom, as well as adsorbed and adsorbed therefrom, to prepare the following

To remove high temperature treatment. 2. Diffusion and doping The wafers etched and cleaned in the previous step (in this case p-type base doping) are heated at higher temperatures,

typically between 750 ° C and <1000 ° C, treated with steam consisting of phosphorus oxide. The wafers are exposed in a tube furnace in a controlled atmosphere quartz glass tube consisting of dried nitrogen, dried oxygen and phosphoryl chloride. The wafers are introduced at temperatures between 600 and 700 ° C in the quartz glass tube. The gas mixture is transported through the quartz glass tube. During transport of the gas mixture through the highly heated tube, the phosphoryl chloride decomposes to a vapor consisting of phosphorus oxide (eg P 2 O 5) and chlorine gas. The vapor of phosphorus oxide u. a. on the wafer surfaces down (occupancy). At the same time, the silicon surface is at these

Temperatures oxidized to form a thin oxide layer. In this layer, the precipitated phosphorus oxide is embedded, whereby a mixed oxide of silicon dioxide and phosphorus oxide on the

Wafer surface emerges. This mixed oxide is called phosphosilicate glass (PSG). Depending on the concentration of phosphorus oxide contained, this PSG glass has different softening points and different diffusion constants with regard to the phosphorus oxide. The mixed oxide serves as the silicon wafer

Diffusion source, wherein in the course of diffusion, the phosphorus oxide diffuses in the direction of the interface between PSG glass and silicon wafer and there by reaction with the silicon on the wafer surface

(silicothermal) is reduced to phosphorus. The resulting

Phosphorus has a solubility in silicon which is orders of magnitude greater than in the glass matrix from which it is formed, and thus dissolves preferentially in silicon due to the very high segregation coefficient. After dissolution, the phosphorus in silicon diffuses along the concentration gradient into the volume of silicon. Concentration gradients of the order of 105 between typical surface concentrations of 1021 atoms / cm ² and base doping in the range of 1016 are formed in this diffusion process

Atoms / cm ² . The typical depth of diffusion is from 250 to 500 nm and depends on the selected diffusion temperature (for example 880 ° C.) and the total exposure duration (heating & occupancy phase & drive-in phase & Cooling) of the wafers in the highly heated atmosphere.

During the coating phase, a PSG layer is formed, which typically has a layer thickness of 40 to 60 nm. in the

Following the wetting of the wafers with the PSG glass, during which diffusion into the volume of the silicon already takes place, the drive-in phase follows. This can be decoupled from the occupancy phase, but is conveniently coupled in terms of time usually directly to the occupancy and therefore usually takes place at the same temperature. The composition of the

Gas mixture adjusted so that the further supply of

Phosphorylchlorids is prevented. During the onset, the surface of the silicon is further oxidized by the oxygen contained in the gas mixture, whereby between the actual doping source, the phosphoric oxide strongly enriched PSG glass and the

Silicon wafer is a phosphorus depleted silicon dioxide layer is generated, which also contains phosphorus oxide. The growth of this layer is much faster relative to the mass flow of the dopant from the source (PSG glass) because the oxide growth is accelerated by the high surface doping of the wafer itself

(Acceleration by one or two orders of magnitude). As a result, in some way, a depletion or separation of the doping source is achieved, whose penetration is influenced by diffusing phosphorus oxide from the flow of material, which depends on the temperature and thus the

Diffusion coefficient is dependent. In this way, the doping of the silicon can be controlled within certain limits. A typical one

Diffusion duration consisting of occupancy and Eintrreibphase is for example 25 minutes. Following this treatment, the tube furnace is automatically cooled and the wafers can be removed from the process tube at temperatures between 600 ° C to 700 ° C.

In the case of a boron doping of the wafers in the form of an n-type base doping, another method is used, which will not be explained separately here. The doping is in these cases, for example, with

Boron trichloride or boron tribromide. Depending on the choice of

Composition of the gas atmosphere used for doping, the formation of a so-called boron skin can be detected on the wafers. This boron skin is dependent on various influencing factors:

relevant to the doping atmosphere, the temperature, the doping time, the source concentration and the coupled (or linear combined) aforementioned parameters.

In such diffusion processes, it goes without saying that there are no regions of preferred diffusion in the wafers used

Doping may (except those caused by inhomogeneous gas flows and resulting inhomogeneous gas packages), unless the substrates were previously subjected to an appropriate pre-treatment (for example, their structuring with diffusion-inhibiting and / or -unterbindenden layers and materials).

For the sake of completeness, it should be pointed out here that there are still other diffusion and doping technologies which have established themselves to varying degrees in the production of crystalline solar cells based on silicon. So be mentioned

The ion implantation,

• the doping, mediated by the gas phase deposition of

Mixed oxides, such as those of PSG and BSG (borosilicate) glass, by APCVD, PECVD, MOCVD and LPCVD methods,

• (co) sputtering of mixed oxides and / or ceramic materials and hard materials (eg boron nitride), the gas phase deposition of both of the latter, - the purely thermal gas phase deposition

starting from solid dopant sources (eg boron oxide and boron nitride) as well as

• the liquid phase deposition of doping liquids (inks) and pastes.

The latter are often used in so-called in-line doping in which the corresponding pastes and inks are applied to the side of the wafer to be doped by suitable methods. After or even during the application, those in the for doping Removed solvents contained by means of temperature and / or vacuum treatment. As a result, the actual dopant remains on the wafer surface. As liquid

Doping sources, for example, dilute solutions of phosphoric or boric acid, as well as sol-gel-based systems or solutions of polymeric Borazilverbindungen can be used. Appropriate

Doping pastes are characterized almost exclusively by the use of additional thickening polymers, and contain dopants in a suitable form. The evaporation of the solvents from the abovementioned doping media is usually followed by treatment at high temperature, during which the undesired and interfering additives which cause the formulation are either "burned" and / or pyrolyzed

Solvents and burnout may or may not occur simultaneously. Subsequently, the coated substrates pass

usually a continuous furnace at temperatures between 800 ° C and 1000 ° C, which can be slightly increased in comparison to the gas phase diffusion in the tube furnace to reduce the cycle time, the temperatures. The gas atmosphere prevailing in the continuous furnace may be different according to the requirements of the doping and of dry nitrogen, dry air, a mixture of dry oxygen and dry nitrogen and / or, depending on the design of the furnace to be passed, zones of one and the other of the above mentioned

Gas atmospheres exist. Other gas mixtures are conceivable, but currently have little industrial significance. One

Characteristic of the inline diffusion is that the assignment and the driving in of the dopant can in principle be decoupled from each other. 3. Dopant source removal and optional edge isolation

The wafers present after the doping are coated on both sides with more or less glass on both sides of the surface. More or less in this case refers to modifications that can be applied in the context of the doping process: double-sided diffusion vs. quasi one-sided diffusion mediated by back-to-back arrangement of two Wafers in a parking space of the used process boats. The latter variant allows a predominantly one-sided doping, but does not completely prevent the diffusion on the back. In both cases, it is currently state of the art to remove the glasses present after doping by etching in dilute hydrofluoric acid from the surfaces. For this purpose, the wafers are on the one hand transhipped in batches in wet process boats and with their help in a solution of dilute hydrofluoric acid, typically 2% to 5%, immersed and left in this until either the surface is completely removed from the glasses, or Process cycle has expired, which is a sum parameter of the necessary Ätzdauer and the machine

Represents process automation. The complete removal of the glasses, for example, based on the complete dewetting of the

Silicon wafer surface can be detected by the dilute aqueous hydrofluoric acid solution. The complete removal of a PSG glass under these process conditions, for example, with 2%

Hydrofluoric acid solution reached within 210 seconds at room temperature. The etching of corresponding BSG glasses is slower and requires longer process times and possibly also higher concentrations of the hydrofluoric acid used. After the etching, the wafers are rinsed with water.

On the other hand, the etching of the glasses on the wafer surfaces can also take place in a horizontally operating method, in which the wafers are introduced in a constant flow into an etching system, in which the wafers pass through the corresponding process tanks horizontally (in-line installation). In this case, the wafers are conveyed on rollers and rollers either through the process tanks and the etching solutions contained therein or the etching media are transported onto the wafer surfaces by means of roller application. The typical residence time of the wafers in the case of etching the PSG glass is about 90 seconds, and the hydrofluoric acid used is somewhat more concentrated than in the case of the

batch processes to compensate for the shorter residence time due to an increased etch rate. The concentration of hydrofluoric acid is typically 5%. Optionally, in addition, the pool temperature may be slightly elevated compared to the room temperature (> 25 ° C <50 ° C). In the method outlined last, it has become established to carry out the so-called edge isolation sequentially simultaneously, which results in a slightly modified process flow: Edge insulation - glass etching. The edge insulation is a process engineering necessity, which results from the system-inherent characteristics of the double-sided diffusion, even with intentional unilateral back-to-back diffusion. On the

(later) rear side of the solar cell is a large-scale parasitic p-n transition, which, although process-related, partially, but not completely removed in the course of the subsequent processing. As a result, the front and back sides of the solar cell are replaced by a parasitic and residual p-n junction (tunnel junction).

be shorted, which reduces the conversion efficiency of the subsequent solar cell. To remove this transition, the wafers are guided on one side via an etching solution consisting of nitric acid and hydrofluoric acid. The etching solution may contain as minor constituents, for example, sulfuric acid or phosphoric acid. Alternatively, the etching solution is transported via rollers mediated on the back of the wafer. The etching removal typically achieved with these methods amounts to about 1 μm silicon at temperatures between 4 ° C. to 8 ° C. (including the glass layer present on the surface to be treated). In this method, the glass layer still present on the opposite side of the wafer serves as a mask, which exerts some protection against etching attacks on this side. This glass layer is subsequently using the already

described glass etching removed.

In addition, the edge isolation can also be done with the help of

Plasma etching processes are performed. This plasma etching is then usually carried out before the glass etching. For this purpose, several wafers are stacked on each other and the outer edges become the plasma

exposed. The plasma is filled with fluorinated gases, for example

Tetrafluoromethane, fed. The plasma decay of these gases

occurring reactive species etch the edges of the wafer. in the

Following the plasma etching, glass etching is then generally carried out.

4. Coating the front with an antireflection coating Following the etching of the glass and the optional

Edge insulation, the coating of the front side of the subsequent solar cells takes place with an anti-reflection coating, which usually consists of amorphous and hydrogen-rich silicon nitride. Alternative antireflection coatings are conceivable. Possible coatings may include titanium dioxide, magnesium fluoride, tin dioxide and / or

corresponding stack layers of silicon dioxide and silicon nitride exist. But there are also different compounds

Antireflection coatings technically possible. The coating of the wafer surface with the silicon nitride mentioned above is fulfilled in

Essentially two functions: On the one hand, the layer generates an electric field due to the numerous incorporated positive charges, that charge carriers in the silicon can keep away from the surface and the recombination speed of these charge carriers at the

On the other hand, depending on its optical parameters, such as refractive index and layer thickness, this layer generates a reflection-reducing property which contributes to the fact that more light can be coupled into the later solar cell. Both effects can increase the conversion efficiency of the solar cell. typical

Properties of the layers currently used are: a layer thickness of ~ 80 nm using only the above-mentioned silicon nitride, which has a refractive index of about 2.05. Antireflection reduction is most evident in

Wavelength range of the light of 600 nm. The directed and non-directional reflection shows a value of about 1% to 3% of the originally incident light (vertical incidence to the

Surface normal of the silicon wafer). The above-mentioned silicon nitride films are currently deposited on the surface generally by direct PECVD method. For this purpose, a gas atmosphere of argon is ignited a plasma, in which silane and ammonia are introduced. The silane and the ammonia are converted in the plasma by ionic and radical reactions to silicon nitride and thereby deposited on the wafer surface. The properties of the layers can z. B. on the individual gas flows the reactants are adjusted and controlled. The deposition of the above-mentioned silicon nitride layers can also be carried out using hydrogen as the carrier gas and / or the reactants alone. typical

Separation temperatures are in the range between 300 ° C to 400 ° C. Alternative deposition methods may be, for example, LPCVD and / or sputtering.

5. Generation of the front electrode grid After depositing the antireflection coating is on with

Silicon nitride coated wafer surface defines the front electrode. In industrial practice, the electrode has been established using the screen printing method using metallic

To produce sinter pastes. This is just one of many

different ways to produce the desired metal contacts.

In screen printing metallization is usually a strong with

Silver particles enriched paste (silver content <= 80%) used. The sum of the residual constituents results from the rheological aids necessary for formulating the paste, such as, for example, solvents, binders and thickeners. Furthermore, the silver paste contains a special Glasfrit mixture, mostly oxides and mixed oxides based on silica, borosilicate glass and lead oxide and / or bismuth oxide. The glass frit fulfills essentially two functions: on the one hand it serves as a bonding agent between the wafer surface and the mass of the silver particles to be sintered, on the other hand it is responsible for the penetration of the silicon nitride covering layer to the direct ohmic

To allow contact with the underlying silicon. The

Penetration of the silicon nitride takes place via an etching process

subsequent diffusion of dissolved silver in the glass frit matrix present in the silicon surface, whereby the ohmic contact formation is achieved. In practice, the silver paste is deposited by screen printing on the wafer surface and then dried at temperatures of about 200 ° C to 300 ° C for a few minutes. For the sake of completeness, it should be mentioned that even double-printing processes are industrial

Find an application that will allow you to be on during the first one Pressure step generated electrode grid to print a congruent second. Thus, the strength of the silver metallization is increased, which can positively influence the conductivity in the electrode grid.

During this drying, the solvents contained in the paste are expelled from the paste. Subsequently, the printed wafer passes through a continuous furnace. Such an oven generally has several heating zones, which can be independently controlled and tempered. When passivating the continuous furnace, the wafers are heated to temperatures up to about 950 ° C. However, the single wafer is typically exposed to this peak temperature for only a few seconds. During the remaining run-up phase, the wafer has temperatures of 600 ° C to 800 ° C. At these temperatures, contained in the silver paste organic impurities, such as binders, burned out and the etching of the

Silicon nitride layer is initiated. During the short time interval of the prevailing peak temperatures, contact formation occurs

Silicon instead. Subsequently, the wafers are allowed to cool.

The process of contact formation outlined so briefly is usually carried out simultaneously with the two remaining contact formations (see Figures 6 and 7), which is why in this case one also speaks of a co-firing process.

The front electrode grid itself consists of thin fingers (typical number> = 68) which have a width of typically 80 pm to 140 pm, as well as collecting buses with widths in the range of 1.2 mm to 2.2 mm (depending on their number, typically two to three). The typical height of the printed silver elements is usually between 10 pm and 25 pm. The aspect ratio is rarely greater than 0.3.

6. Generation of back-bus buses

The rear bus buses are also usually applied and defined by screen printing. For this purpose, one of the similar silver paste used for front metallization is used. This paste is similar in composition but contains an alloy Silver and aluminum, wherein the proportion of aluminum is typically 2%. In addition, this paste contains a lower glass frit content. The bus busses, usually two pieces, are screen printed with a typical width of 4mm on the back of the wafer

be printed and compacted and sintered as already described under point 5.

7. Generation of the back electrode The back electrode is connected to the pressure of the back electrode

Shared buses defined. The electrode material is made of aluminum, which is why an aluminum-containing paste is printed by screen printing on the remaining free surface of the wafer backside with an edge distance <1mm to define the electrode. The paste is <80% aluminum. The remaining components are those already mentioned under point 5 (such as solvents, binders, etc.). The aluminum paste is bonded to the wafer during co-firing by heating during heating

Aluminum particles begin to melt and silicon dissolves from the wafer in the molten aluminum. The melt mixture acts as a dopant source and delivers aluminum to the silicon

(Solubility limit: 0.016 atomic%), whereby the silicon is p + doped as a result of this drive-in. As the wafer cools, it will precipitate on the wafer surface u. a. a eutectic mixture of aluminum and silicon, which solidifies at 577 ° C and has a composition with a mole fraction of 0.12 Si.

As a result of the driving of the aluminum into the silicon, a highly doped p-type layer is formed on the backside of the wafer, which acts as a kind of mirror on parts of the free charge carriers in the silicon ("electric mirror"). These charge carriers can not overcome this potential wall and thus become very efficient from the backward one

Keep remote wafer surface, which thus manifests itself in an overall reduced recombination of charge carriers on this surface. This potential wall is generally referred to as the back surface field or back surface field. The sequence of process steps described in items 5, 6 and 7 may or may not be the same as outlined herein. The person skilled in the art will appreciate that the sequence of the described process steps can, in principle, be carried out in any imaginable combinatorics.

8. Optional edge isolation

If the edge isolation of the wafer has not already been carried out as described under point 3, this is typically carried out after co-firing with the aid of laser beam methods. For this purpose, a laser beam is directed to the front of the solar cell and the front p-n junction is severed by means of the energy coupled in by this beam. Here, trenches are generated with a depth of up to 15 pm as a result of the action of the laser. This silicon is over a

Ablation mechanism removed from the treated area or thrown out of the laser ditch. Typically, this laser trench is 30 μητι to 60 pm wide and about 200 pm away from the edge of the solar cell. After their production, the solar cells are characterized and

according to their individual achievements in individual

Performance categories classified.

The person skilled in the art knows solar cell architectures with both n-type and p-type base materials. These solar cell types include u. a.

• PERC solar cells

• PERL solar cells

• PERT solar cells

· As a result, MWT-PERT and WT-PERL solar cells

• Bifacial solar cells

• backside contact cells

Backside Contact Cells with Interdigitating Contacts (IBC Cells) The choice of alternative doping technologies, as an alternative to the gas phase doping already described above, can generally also be used for the Do not resolve the problem of creating locally differently doped regions on the silicon substrate. As alternative technologies here the deposition of doped glasses, or of amorphous mixed oxides, by means of PECVD and APCVD method mentioned. From these glasses, a thermally induced doping of the silicon located under these glasses can be easily achieved. To create locally differently doped areas, these glasses must, however, by means of

Mask processes are etched to prepare the corresponding structures out of these. Alternatively, structured

Diffusion barriers are deposited before depositing the glasses on the Siliziumwafem, so as to the doped areas to

define. However, a disadvantage of this method is that in each case only one polarity (n or p) can be achieved in the doping of the substrates.

Figure 1: shows a simplified cross section through an IBC solar cell (not scaled, without surface texture, without anti-reflection and

Passivation layers, without back metallization). The

alternating pn junctions may have different arrangements, such as directly adjacent to one another, or with gaps with intrinsic regions).

In the following we will focus on a possible excerpt from the manufacturing process of a so-called IBC solar cell (Figure 1). This section and sub-process sketched out in this regard does not claim to be exhaustive, neither to exclusivity. There are effortless deviations and

Modifications of the process chain presented imagine as well

realizable. It starts with a CZ wafer having, for example, a one-sided alkaline polished or saw damage etched surface. This wafer is fully coated on one side, which is not polished, and thus the later front, by means of a CVD oxide of suitable thickness, such as 200 nm or more. After the one-sided coating with the CVD oxide, the wafer of a B diffusion in a conventional tube furnace, by means of, for example Bortribromide precursor subjected. Subsequent to boron diffusion, the wafer must be locally patterned on the now diffused back surface to provide the areas for later contacts to the base and for fabrication of the phosphorus diffused in this case

Back field and ultimately create. These

Structuring can be achieved, for example, with the aid of a laser, which locally ablates the doped glass present on the back. The use of laser radiation in the manufacture of highly efficient solar cells is controversial due to the damage to the bulk of the silicon wafer. For the sake of simplicity let us assume that it is possible and that there are no other fundamental problems. Then, following the laser treatment, the undisputably damaged silicon present at least on the surface must be removed with the aid of an alkaline damage set. Conveniently, at the same time, the boron emitter present at this point is also dissolved and removed (insofar as one also assumes in this case that, as is commonly known, boron highly doped silicon does not constitute an etch stop for KOH-based etching solutions) - insofar as one does

can legitimately assume that the remaining

Borosilicate glass (BSG) at the closed places is a sufficient protection of the silicon over the KOH solution (etch rate of SiO2 in 30% KOH at 80 ° C is about 3 nm / min, one assumes in BSG from a "disturbed oxide", then this could possibly be a bit higher in KOH.) In the silicon, a plateau or a kind of trench is etched in. Alternatively, one could create the base contacts with the later local back field in such a way that an etching mask is applied to the back, for example by means of Screening, and then aftertreated the open areas by means of two consecutive or even one etching step: one-sided removal of the glass by etching in hydrofluoric acid and subsequent etching in KOH solution, or etching of both materials in one step, followed by either the etching mask and the doped glass or just the doped glass, both on each side on the back remove Hopefully, a CVD oxide layer would be deposited on the back of the wafer, opening and structuring it locally, at the locations where the boron emitter was previously removed. The wafers would then become one Be subjected to phosphorus diffusion. Depending on how the

Seeking process parameters of this diffusion in detail, the structurings described above would be required even in a simple embodiment, and for example in such a case, if the execution of the phosphorus diffusion the Bordotierprofil already obtained in the simultaneous presence of the glass BSG no longer, or just in controllable Way would influence. Subsequently, the wafers on the front side would be unilaterally freed from the protective oxide and subjected to weak phosphorus diffusion. Of the

For the sake of simplicity, it was assumed at this point that the PSG glass present on the rear side can remain on the wafer surface and thus no further disturbances or

Would cause interference. After the weak diffusion on the front, the wafers are etched with hydrofluoric acid and all oxides and glasses are removed. In sum, the process outlined above is characterized by the following steps and their total number

(simplified for structuring by means of a laser process, in the case of using atzresists the printing and stripping of the lacquer would have to be added):

1. Fronseitige ganzflächige oxide mask

2. Boron diffusion

3. Back structuring and etching

4. Back full-area oxide mask

5. Back structuring

6. Phosphorus diffusion

7. Removal of front oxide mask

8. Phosphorus diffusion

9. Removal of all glasses

In total, there are nine process steps to achieve a structured doping of the wafer. In contrast, there would be, depending on the method of counting, eight process steps for producing a complete standard aluminum BSF solar cell. In the production of IBC cells, other possibilities may be used, the expenditure for achieving the structured doping is in any case very high and is in each of these cases costly, sometimes as costly as the production of a single standard aluminum BSF Soalrzelle. The further broadening of this cell technology will in any case be dependent on the reduction of the process costs, which means that they will be used by the

Establishment of simplifying, yet high cell efficiencies permitting, process alternatives will benefit significantly.

Task The technologies commonly used in the industrial production of solar cells for doping, namely by the

gas-phase-mediated diffusion with reactive precursors, such as

Phosphoryl chloride and / or boron tribromide, do not allow to selectively generate local dopants and / or locally different dopants on silicon wafers. The creation of such structures is possible by using known doping technologies only by consuming and costly structuring of the substrates. In the

Structuring different masking processes must be coordinated, what the industrial mass production such

Substrates made very complex. For this reason, concepts for the production of solar cells, which require such a structuring, have not been able to prevail. It is therefore an object of the present invention to provide an inexpensive, easy to carry out method and a usable in this method medium, whereby these problems and the normally required masking steps are obsolete and thus eliminated. In addition, the locally applicable doping source is characterized in that it is preferably established by means of known and in the art of solar cell production

Printing technologies can be applied to the wafer surfaces. Moreover, the peculiarity of the method according to the invention results from the fact that the printable doping media used have a diffusion-inhibiting effect on the industrially conventionally used gas phase dopant phosphoryl chloride, as well as similar (which, to put it correctly, can be dopants due to their combustion in the gas phase to

Phosphorus pentoxide be implemented), and thus in the simplest Simultaneously, but also arbitrarily sequential diffusion and doping with two dopants for either simultaneous or sequential doping opposite polarities in silicon allow. Brief description of the invention

The present invention relates to printable boron dopants and / or gels based on precursors, such as silicon dioxide.

Alumina, and boron oxides, which by means of suitable printing processes on silicon surfaces for the purpose of local and / or full-area, one-sided diffusion and doping in the production of solar cells, preferably of highly efficient structured doped solar cells,

imprinted, dried and then by means of a suitable high-temperature process for delivering the Boroxidprecursors contained in the dried paste to that under the boron paste

Substrate for targeted doping of the substrate itself be brought.

These are printable boron dopants based on precursors of the following oxide materials: a) Silicon dioxide: one to fourfold symmetric and asymmetric

substituted carboxy, alkoxy and alkoxyalkylsilanes, explicitly

Alkylalkoxysilanes containing in which the central silicon atom may have a degree of substitution of at least one hydrogen atom bonded directly to the silicon atom, such as triethoxysilane, and further wherein a

Degree of substitution refers to the number of possible existing carboxy and / or alkoxy groups, which have both single and different saturated, unsaturated branched, unbranched aliphatic, alicyclic and aromatic radicals in each case at alkyl and / or alkoxy and / or carboxy groups, which in turn at any position of the alkyl, alkoxide or carboxy radical by heteroatoms selected from the group O, N, S, Cl and Br

may be functionalized, as well as mixtures of the aforementioned precursors; individual compounds which are mentioned in the above

Claims are: tetraethyl orthosilicate and the like, Triethoxysilane, ethoxytrimethylsilane, dimethyldimethoxysilane,

Dimethyldiethoxysilane, triethoxyvinylsilane, bis [triethoxysilyl] ethane and bis [diethoxymethylsilyl] ethane b) Aluminum oxide: symmetrically and asymmetrically substituted

Aluminum alcoholates (alkoxides), such as aluminum triethanolate,

Aluminum trisopropylate, aluminum tri-sec-butylate, aluminum tributylate, aluminum triamylate and aluminum tri-iso-pentoxide, aluminum tris (-β-diketones) such as aluminum acetylacetonate or aluminum tris (1,3-cyclohexanedionates), aluminum tris (β-keto ester ), Aluminum monoacetylacetonate monoalcoholate, aluminum tris- (hydroxyquinolates), aluminum soaps such as mono- and dibasic aluminum stearate and aluminum tristearate, aluminum carboxylates such as basic aluminum acetate, aluminum triacetate, basic

Aluminum formate, aluminum tri-formate and aluminum trioctoate, aluminum hydroxide, aluminum metahydroxide and aluminum trichloride and the like, and mixtures thereof c) boron oxide: diboroxide, simple boric acid alkyl esters, such as triethyl borate, trisopropyl borate, boric acid esters of functionalized 1,2-glycols, such as, for example, ethylene glycol, functionalized 1, 2, 3 -Triols, such as glycerol, functionalized 1,3-glycols, such as, 1,3-propanediol, boric acid esters with boric acid esters containing the aforementioned structural motifs as structural subunits, such as 2,3-dihydroxysuccinic acid and the like

Enantiomers, boric acid esters, from ethanolamine, diethanolamine, triethanolamine, propanolamine, dipropanolamine and tripropanolamine, mixed anhydrides of boric acid and carboxylic acids such as tetraacetoxy diborate, boric acid, metaboric acid, and mixtures of precursors mentioned above

under aqueous or anhydrous conditions using the sol-gel technique either simultaneously or sequentially to partial or complete intra- and / or interspecific condensation, and due to the set condensation conditions, such as precursor concentrations, water content, catalyst content, reaction temperature and time, the addition of condensation controlling agents, such as For example, various of the above-mentioned complex and chelating agents, various solvents and their individual volume fractions, as well as the targeted elimination of volatile reaction auxiliaries and unfavorable by-products, the degree of gelation of the resulting doping inks and Dotiertintengele specifically controlled and influenced in the desired manner, so storage stable, very good printable and pressure stable formulations are obtained.

In particular, it is the printable Bordotierpasten according to the invention, which at least one classic polymeric

containing thickening substance, these rheology influencing substances are selected from the group

Polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyvinylimidazole, polyvinylbutyral, methylcelluloses, ethylcelluloses, hydroxyethylcelluloses, hydroxypropylcelluloses, microcrystalline celluloses, sodium starch

Glycolates, xanthan and gellan gum, gelatin, agar, alginic acid and alginates, guar gum, pectin, carubin, polacrylic acids, polyacrylates, associatively thickening polyurethanes, and mixtures thereof, although polyvinylpyrrolidone, polyvinyl acetate, polyvinyl butyral and

Ethyl cellulose, and mixtures thereof are particularly preferred.

These printable boron dopants are prepared using polymeric thickening substances, which associatively and structurally interact with parts of the hybrid sol via, for example, coordinative and chelating mechanisms and thus lead to a significantly more pronounced structural viscosity than by the use of polymer thickening compounds alone.

In particular, printable Bordotierpasten are the subject of

present invention, which are prepared using

Aluminum hydroxides and aluminas, colloidal or fumed silica, tin dioxide, boron nitride, silicon carbide,

Silicon nitride, aluminum titanate, titanium dioxide, titanium carbide, titanium nitride,

Titanium carbonitride as a rheology-modifying, as well as the layer thickness of the dried paste positively influencing, particulate

Formulation aids. These borosilicate pastes can be prepared by means of the following printing processes such as spin coating or dip coating, drop casting, curtain or Schlitzdusen coating, screen or flexo printing, gravure, ink jet or aerosol jet printing, offset printing, Micro Contact -To Print,

electrohydrodynamic dispensing, roll or spray coating, ultrasonic spray coating, Pipe Jet printing, laser transfer printing, pad printing, flatbed screen printing and rotary screen printing, but more preferably process by means of the flatbed screen and deposited on the surfaces to be processed.

Printable Bordotierpasten, according to the claims 1 to 6, as doping media for processing of silicon wafers for photovoltaic, microelectronic, micromechanical and micro-optical applications. The printable boron dopants provided here are particularly well suited for the production of PERC, PERL, PERT, IBC solar cells and others, whereby the solar cells have more

Architectural features such as MWT, EWT, Selective Emitter, Selective Front Surface Field, Selective Back Surface Field, and Bifaciality.

In particular, the new printable ones described here are

Bordotierpasten suitable both as boron-containing doping medium

Silicon act as well as a diffusion barrier or as

diffusion-inhibiting layer against the diffusion of

Phosphorus by these media themselves and the latter completely block or inhibit to a sufficient extent, so that the printed media under this predominantly p-type doping, ie are boron-containing.

Be particularly advantageous that has proved by the

According to the invention printable Bordotierpasten by suitable

Temperature treatment, a doping of the printed substrate and simultaneously and / or sequentially doping of the unprinted

Silicon wafer surfaces with dopants of opposite polarity is induced by conventional gas phase diffusion, wherein the printed Bordotierpasten opposite the Dotanden the

opposite polarity act as a diffusion barrier.

According to the invention, a process for producing solar cells using the printable boron dopants described here is characterized in that

a) silicon wafers with Bordotierpasten locally on one or both sides or on one side over the entire surface are printed, the paste dried, compacted and the silicon wafers are then exposed to a subsequent gas phase diffusion with, for example, phosphoryl chloride, whereby p-type dopants in the printed areas and n-type dopants in to be preserved in the areas that

are exposed exclusively to gas phase diffusion,

or

b) Bordotierpaste printed on a large area on the silicon wafer

is compacted and from the dried and / or compacted paste by means of laser irradiation, the local doping of the underlying substrate material is initiated, followed by a

High-temperature diffusion and doping for the production of

two-stage p-type doping levels is induced in the silicon,

or

c) the silicon wafer is locally printed on one side with Bordotierpasten,

wherein the structured landfill may optionally have alternating lines, the printed structures are dried and compacted and the silicon wafer subsequently on the same

Wafer side is coated over the entire surface with the aid of PVD and / or CVD deposited phospordotierend acting dopant sources, wherein the printed structures of Bordotierpasten be encapsulated, and the overlapping forest structure by suitable

High temperature treatment for structured doping of the

Silicon wafer is brought, wherein the printed boron paste against the overlying phosphorus-containing dopant source and the dopant contained therein acts as a diffusion barrier, or

d) the silicon wafer is locally printed on one side with Bordotierpasten, the structured landfill optionally alternating Lines can have the printed structures dried and compacted and the silicon wafer subsequently on the same

Wafer side is coated over the entire surface using phosphor doping doping or doping pastes, wherein the printed structures of Bordotierpasten are encapsulated, and the

overlapping forest by appropriate

High temperature treatment for structured doping of the

the silicon wafer is locally printed on one side with Bordotierpasten, the structured landfill may optionally have alternating lines, the printed structures dried and compacted and the silicon wafer subsequently on the same

Wafer side is printed negatively structured to the previous printing using a phosphor paste, and the whole structure by suitable Hochtemperäturbehandlung in the presence of a conventional phosphorus-based gas phase diffusion source, such as phosphoryl chloride, for structured unilateral and full-face doping of the silicon wafer is brought, the printed boron paste over the other at the same time present phosphorus-containing diffusion sources acts as a diffusion barrier

or

the silicon wafer is locally printed on one side with boron dopants, wherein the structured landfill may optionally have alternating lines, the printed structures are dried and compacted, and the silicon wafer is subsequently negatively structured on the same wafer side compared to the previous print using a phosphor paste, then the opposite side of the same wafer is printed with a further Phosphordotierpaste, the order of the

Pressure steps of the application of phosphorus doping pastes must not necessarily be made in the said series, and the whole structure by suitable high temperature treatment for structured one-sided and full-surface opposite

Doping the silicon wafer is brought, with the printed boron paste against the other simultaneously present

phosphorus-containing diffusion sources acts as a diffusion barrier.

Detailed description of the invention

Surprisingly, it has been found that boron-containing doping inks prepared based on the sol-gel process can be formulated with the aid of conventional thickeners in such a way that very readily printable formulations can be obtained therefrom. As suitable printing methods, at least the following may be considered: spin coating or dip coating, drop casting, curtain or slot die coating, screen or flexo printing, gravure, ink jet or aerosol jet printing, offset printing, micro Contact printing, electrohydrodynamic dispensing, roll or spray coating, ultrasonic spray coating, pipe jet printing, laser transfer printing, pad printing, flatbed screen printing and rotary screen printing. The boron-containing dopant inks further formulated are preferred, but not

exclusively by means of the screen printing process on silicon surfaces. The boron-containing doping inks are in this case prepared by the sol-gel process and consist at least of Oxidprecursoren the following oxides: alumina, silica and boron oxide. The

Mixing ratios of the mentioned oxide precursors can be present in arbitrarily chosen proportions. The following are typical, but not limited to the examples given

Precursors of the oxides for the preparation of boron-containing doping inks according to the invention, also referred to below as hybrid brines, presented: alumina: symmetrically and asymmetrically substituted

Aluminum alcoholates (alkoxides), such as aluminum triethanolate,

Aluminum trisopropylate, aluminum tri-sec-butylate, aluminum tributylate, aluminum triamylate and aluminum tri-iso-pentoxide, aluminum tris (-β-diketones) such as aluminum acetylacetonate or aluminum tris (1,3-cyclohexanedionates), aluminum tris (β-keto ester ), Aluminum monoacetylacetonate monoalcoholate, aluminum tris- (hydroxyquinolates), Aluminum soaps, such as mono- and dibasic aluminum stearate and

Aluminum tristearate, aluminum carboxylates such as basic aluminum acetate, aluminum triacetate, basic aluminum formate, aluminum tri-formate and aluminum trioctoate, aluminum hydroxide, aluminum metahydroxide and

Aluminum trichloride and the like, and mixtures thereof.

Silicon dioxide: one to fourfold symmetric and asymmetric

substituted carboxy, alkoxy and alkoxyalkylsilanes, explicitly

Alkylalkoxysilanes containing, in which the central silicon atom may have a degree of substitution of at least one hydrogen atom bonded directly to the silicon atom, such as

Triethoxysilane, and further wherein a degree of substitution refers to the number of possible carboxy and / or alkoxy groups present, which in the case of alkyl and / or alkoxy and / or carboxy groups, single or different saturated, unsaturated branched, unbranched aliphatic, alicyclic and aromatic radicals which in turn may be functionalized at any position of the alkyl, alkoxide or carboxy radical by heteroatoms selected from the group O, N, S, Cl and Br, as well as mixtures of the aforementioned precursors. Separate

Compounds which satisfy the abovementioned claims are:

Tetraethylorthosilicate and the like, triethoxysilane, ethoxytrimethylsilane, dimethyldimethoxysilane, dimethyldiethoxysilane, triethoxyvinylsilane,

Bis [triethoxysilyl] ethane and bis [diethoxymethylsilyl] ethane. Boron oxide: diboroxide, simple boric acid alkyl esters, such as triethyl borate,

Trisopropyl borate, boric acid esters of functionalized 1, 2-glycols, such as ethylene glycol, functionalized 1, 2, 3-triols, such as

for example, glycerol, functionalized 1, 3-glycols, such as, for example,

1, 3-propanediol, boric acid esters with boric acid esters containing the aforementioned structural motifs as structural subunits, such as

2, 3-dihydroxysuccinic acid and its Enantionmere, boric acid esters, from ethanolamine, diethanolamine, triethanolamine, propanolamine, dipropanolamine and tripropanolamine, mixed anhydrides of boric acid and

Carboxylic acids, such as tetraacetoxy diborate, boric acid,

Metaboric acid, and mixtures of previously mentioned precursors. Furthermore, the possible combinations are not necessarily limited to the abovementioned compositional possibilities: as additional components, other substances may be present in the hybrid brine which can impart advantageous properties to the brines. They may be: oxides, basic oxides, hydroxides, alkoxides, carboxylates, β-diketonates, β-ketoesters, silicates and the like of cerium, tin, zinc, titanium, zirconium, hafnium, zinc, germanium, gallium, niobium, yttrium in the sol-gel synthesis can be used directly or pre-condensed application. The

Hybrid sols are sterically stabilized by the use of complexing and chelating substances which can also control the condensation behavior of the oxide precursors, in particular that of aluminum, as well as other metal cations. Such substances are, for example, acetylacetone, 1,3-cyclohexanedione, isomeric compounds of dihydroxybenzoic acids, acetaldoxime, as well as those disclosed in patent applications WO 2012/1 9686 A, WO2012119685 A1, WO2012119684 A, EP12703458.5 and EP12704232.3 are disclosed and included. The content of these publications is therefore included in the disclosure of the present application. The hybrid sols can be prepared using anhydrous as well as hydrous sol-gel synthesis. In addition, further auxiliaries can be used in the formulation of the hybrid sols according to the invention for screen-printable pastes. Such adjuvants may be:

Surfactants, tensio-active compounds for influencing the wetting and drying behavior,

Defoamer and deaerator for influencing the drying behavior, Strong carboxylic acids for initiating the condensation reaction of

Oxidic precursors, as suitable carbonyls may at least serve: formic acid, acetic acid, oxalic acid, trifluoroacetic acid, mono-, di- and trichloroacetic acid, glyoxylic acid, tartaric acid, maleic acid, malonic acid, pyruvic acid, malic acid, 2-oxoglutaric acid

high and low boiling nonpolar as well as polar protic and aprotic solvents for influencing the particle size distribution, the degree of pre-condensation, condensation, wetting and

Drying and printing behavior, which may be: glycols, glycol ethers, glycol ether carboxylates, polyols, terpineol, Texanol, Butyl benzoate, benzyl benzoate, dibenzyl ether, butyl benzyl phthalate and

Others, as their mixture previously mentioned,

particulate additives for influencing the theological

Properties,

particulate additives (eg, aluminum hydroxides and

Aluminas, colloidally precipitated or fumed silica, tin dioxide, boron nitride, silicon carbide, silicon nitride, aluminum titanate, titanium dioxide, titanium carbide, titanium nitride, titanium carbonitride) for influencing the dry film thicknesses resulting after drying and their morphology,

particulate additives (eg, aluminum hydroxides and

Aluminas, colloidally precipitated or fumed silica, tin dioxide, boron nitride, silicon carbide, silicon nitride, aluminum titanate, titanium dioxide, titanium carbide, titanium nitride, titanium carbonitride) for influencing the scratch resistance of the dried films,

Capping agents selected from the group acetoxytrialkylsilanes,

Alkoxytrialkylsilanes, Halogentrialkylsilane and their derivatives to

Influence on Condensation Rates and Storage Stability Waxes and waxy compounds, such as beeswax,

Synchrowachs, lanolin, carnauba wax, jojoba, Japan wax and the like, fatty acids and fatty alcohols, fatty glycols, esters of fatty acids and fatty alcohols, triglycerides, fatty aldehydes, fatty ketones and fatty ß-diketones and mixtures thereof, wherein the aforementioned substance classes each branched and unbranched carbon chains containing chain lengths greater than or equal to twelve carbon atoms

Polymer thickening rheology-modifying additives such as polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyvinylimidazole, polyvinyl butyral, methylcelluloses, ethylcelluloses, hydroxyethylcelluloses, hydroxypropylcelluloses, microcrystalline celluloses, sodium starch glycolates, xanthan and gellan gums, gelatin, agar, Alginic acid and alginates, guar gum, pectin, carubin, polacrylic acids, polyacrylates, associatively thickening polyurethanes, and mixtures thereof A synthetic method is based on the dissolution of oxide precursors of the alumina in a solvent or a solvent mixture, preferably selected from the group of high-boiling glycol ethers or preferably high-boiling glycol ethers and alcohols, which

then with a suitable acid, preferably a carboxylic acid, and in this case particularly preferably with formic acid or acetic acid, and by the addition of suitable complexing and chelating agents, such as

for example, suitable β-diketones, such as acetylacetone or, for example, 1, 3-cyclohexanedione, α- and β-ketocarboxylic acids and their esters, such as pyruvic acid and its esters acetoacetic acid and ethyl acetoacetate, isomeric dihydroxybenzoic acids, such as

for example, 3, 5-dihydroxybenzoic acid, and / or oximes, such as

For example, acetaldoxime, and other such cited compounds, as well as any mixtures of the aforementioned complex, chelating and condensation degree controlling agents, is completed. The solution of the alumina precursor is then at room temperature with a mixture consisting of the o. G. Solvent or

Mixed solvent, and water added dropwise and then heated at 80 ° C for up to 24 h under reflux. The gelation of the

Aluminum oxide precursors can be determined by the molar ratio of

Alumina precursors to water, the acid used as well as the amounts of substance and the nature of the complexing agents used are specifically controlled. The respectively necessary synthesis conditions are also dependent on the aforementioned molar ratios. The volatile and desired parasitic substances occurring during the reaction

By-products are then removed by vacuum distillation from the finished and possibly already diluted further reaction mixture. The vacuum distillation is achieved by gradually reducing the final pressure to 30 mbar at a constant temperature of 70 ° C. The

Hybrid gels are either after or already before the distillative

Treatment by targeted addition of suitable and the rheology and

Printability of the paste-promoting solvent, such as high-boiling glycols, glycol ethers, Glycolethercarboxylate and further solvents such as terpineol, Texanol, butyl benzoate, benzyl benzoate,

Dibenzyl ether, butyl benzyl phthalate, and solvent mixtures

adjusted in terms of their desired properties and optionally diluted. Parallel to the dilution and adjustment of the

Paste properties are added to a mixture consisting of condensed oxide precursors of silica and boron oxide. For this purpose, precursors of boron oxide in a solvent such as dibenzyl ether, butyl benzyl phthalate, benzyl benzoate, butyl benzoate, THF or comparable, are presented, with a suitable carboxylic anhydride such as acetic anhydride, formyl acetate or propionic anhydride or comparable, added and dissolved under reflux or reacted until a clear solution is obtained. In this solution, suitable precursors of the silicon dioxide, if necessary. In the used

Reaction solvent pre-dissolved, added dropwise. The

Reaction mixture is then heated for up to 24 h or

Reflux. After mixing all the components, the

Paste rheology paste rheology continue to be adjusted and rounded according to specific requirements in accordance with and with the auxiliaries and additives also previously described in detail, wherein the inventive use of said polymeric thickener plays a special role. The thickeners are stirred into the mixture with vigorous stirring, the stirring time being dependent on the particular thickener used. Optionally, the stirring of the thickener may be completed with a vacuum treatment step during which air bubbles entrained in the high-viscosity mass are removed. Depending on the thickener used, the resulting paste may need to be re-swollen for a period of up to three days.

An alternative method of synthesis is based on the preparation of a condensed sol of oxide precursors of silica and boron oxide. For this purpose, precursors of the boron oxide in a solvent, such as, for example, dibenzyl ether, butyl benzyl phthalate,

Benzyl benzoate, butyl benzoate, THF or similar, initially charged, with a suitable carboxylic anhydride, such as acetic anhydride, formyl acetate or propionic anhydride or comparable, added and dissolved under refluxing or reacted until a clear solution is present. Suitable precursors of the silicon dioxide, if appropriate pre-dissolved in the reaction solvent used, are added dropwise to this solution added. The reaction mixture is then heated or refluxed for up to 24 hours. Thereafter, the sol is treated with suitable solvents such as, for example, glycols, glycol ethers, glycol ether carboxylates and also solvents such as terpineol, texanol, butyl benzoate, benzyl benzoate, dibenzyl ether, butyl benzyl phthalate, or their solvent mixtures in which suitable complexing and chelating agents, for example suitable β- Diketones, such as acetylacetone or, for example, 1, 3-cyclohexanedione, α- and β-ketocarboxylic acids and their esters, such as pyruvic acid and its esters acetoacetic acid and ethyl acetoacetate, isomeric

Dihydroxybenzoic acids, such as, for example, 3, 5-dihydroxybenzoic acid, and / or oximes, such as acetaldoxime, and other such cited compounds, as well as any mixtures of the aforementioned complex, chelating and the degree of condensation controlling agents are already pre-dissolved in the presence of water, mixed and stirred, if necessary. At the same time increases the temperature of the reaction mixture. The duration of mixing of the two solutions can be between 0.5 minutes and five hours. The total mixture is tempered with the aid of an oil bath whose temperature is usually set to 155 ° C. After a suitable known duration of mixing of two partial solutions completed total solution, this is then a suitable alumina precursor, which in turn was pre-dissolved in one of the above solvent or solvent mixtures, the

The reaction mixture is added dropwise or allowed to flow so that the addition will be completed in a time window of five minutes from the beginning of the addition. The thus completed reaction mixture is then heated to reflux for one to four hours. The warm gelled mixture can now be further modified with respect to its rheological properties by the use of additional auxiliaries already mentioned above, especially and especially preferably by the use of the polymeric thickeners to be used according to the invention. The thickeners are stirred with intensive stirring into the mixture, the stirring time of each to

Application depending thickener is dependent. Optionally, that can

Stirring in the thickener with a vacuum treatment step

be completed while in the highly viscous mass stirred-in air bubbles are removed. Depending on the thickener used, the resulting paste may need to be re-swollen for a period of up to three days. Surprisingly, it was found that the at the

Paste formulation used can interact associatively with the components contained in the hybrid sols advantageous. This interaction is based on coordination or

Chelate complexing between the polymers incorporated into the formulation and the components contained in the hybrid sol, in this case preferably those of aluminum.

In the following examples, the preferred embodiments of the present invention are shown.

As stated above, the present description enables a person skilled in the art to comprehensively apply the invention. Without further explanation, it is therefore assumed that a person skilled in the art can make the most of the above description.

Any ambiguity goes without saying, the quoted

Publications and patent literature. Accordingly, these documents are considered part of the disclosure of the present application

Description.

For a better understanding and clarification of the invention, examples are given below which are within the scope of the present invention. These examples are also used for

Illustration of possible variants. Due to the general validity of the described principle of the invention, however, the examples are not suitable for reducing the scope of protection of the present application only to these.

Furthermore, it is obvious to the person skilled in the art that both in the given examples and in the remainder of the description, the amounts of components contained in the compositions in the Sum only up to 100% by weight, based on the total composition, and can not exceed it, even if higher values could result from the stated percentage ranges. Unless otherwise stated, therefore,% data are in terms of weight, mol or vol.%.

The temperatures given in the examples and the description as well as in the claims are always in ° C.

EXAMPLES Example 1 8 g of boron oxide were placed in a glass flask and 80 g

Acetic anhydride and 160 g of tetrahydrofuran are suspended. The mixture was made to reflux and treated with 24.2 g of ethylene glycol monobutyl ether (EGB). Then, 24.2 g of diethoxydimethylsian and 31 g of dimethyldimethoxysilane were added to the refluxing mixture, and it was heated to boiling for 30 minutes. A solution consisting of 480 g of EGB and 250 g of Texanol in which 2.5 g of water, 2 g of 1, 3-cyclohexadione and 4.2 g of acetaldoxime were dissolved was added to the solution containing the siloxanes and for 20 minutes

let it mix. During the same period the

Reaction temperature increased from 80 ° C to 120 ° C. After .

By mixing, 50 g of aluminum tri-sec-butylate dissolved in 400 g of dibenzyl ether was allowed to flow into the reaction mixture within five minutes, and the completed mixture was allowed to react for an additional 55 minutes. Thereafter, the reaction mixture was freed from volatile solvents and reaction products by vacuum distillation at 70 ° C until reaching a final pressure of 30 mbar. By stirring in ethyl cellulose, various pasty mixtures were prepared from the boron-containing doping ink.

Table 1: Boron-containing doping inks using

Ethyl cellulose subsequently thickened mixtures. Mixtures from 2.9% to 3.4% by mass were good for screen printing.

Paste mixtures with a mass fraction> 5% of ethyl cellulose were no longer printable.

Example 2:

A paste according to Example 1, characterized by a

A mass fraction of 4.3% of ethyl cellulose, using a screen with 350 mesh and a thread diameter of 16 pm, an emulsion thickness of 8 pm to 12 μητι, and further using a doctor speed of 200 mm / s and a squeegee pressure of 1 bar printed on a silicon wafer surface and then drying in a continuous furnace using the following

Heating zone temperatures, 350/350/375/375/375/400/400 ° C.

Paste mixtures with a mass fraction greater than 5%, as well as those with less than 2.5% by mass, can not be processed by the screen printing process.

FIG. 2 shows one with the aid of a boron-containing invention

Doping paste and according to the composition and preparation of Example 1 printed silicon wafer after drying in a continuous furnace. The different colors (interference colors) correspond to differences in locally existing glass film thicknesses. The optimization of the printing process leads to a more homogeneous color appearance of the printed wafer.

Example 3:

In a glass flask, 4 g of boron oxide were introduced and in 40 g

Suspended acetic anhydride and 80 g of tetrahydrofuran. The mixture was brought to reflux and treated with 11.25 g of ethylene glycol monobutyl ether (EGB). Subsequently, 12.1 g of diethoxydimethylsilane and 15.1 g of dimethyldimethoxysilane was added to the refluxing mixture and this was boiled for 30 minutes. 32.5 g of the solution containing the siloxanes was mixed with 69.8 g of a solution consisting of 240 g of EGB and 125 g of Texanol, and the temperature was from 80 ° C to 120 ° C within 20 minutes with stirring the Reaction mixture increased. In the reaction mixture were dissolved 1.75 g of 1,3-cyclohexanedione, 0.75 g of acetaldoxime and 0.5 g of water.

Subsequently, 10 g of aluminum tri-sec-butoxide was dissolved in 40 g

Add dibenzyl ether to the reaction mixture within five minutes. After the addition, the mixture was allowed to react for an additional 55 minutes. The reaction mixture was then to liberation of volatile solvents and reaction products of a

Subjected to vacuum distillation at 70 ° C until reaching a final pressure of 30 mbar. A mass loss of 31, 74 g was determined. By stirring ethylcellulose, various pasty mixtures were prepared from the boron-containing doping ink: 5.1 g

Ethyl cellulose stirred into 106.1 g of the doping ink. The paste was allowed to rest overnight after stirring. Example 4:

The paste according to the invention according to Example 3 was printed with the aid of a 400 mesh and 8 μιτι thread diameter having sieve on an alkali-etched n-type CZ wafer. The remaining

Print parameters were the same as those already described in Example 2 (as was the layout used). The printed wafer was spray-coated with a phosphorus-containing doping ink, and then the wafer was co-diffused at 935 ° C for 30 minutes, followed by oxidation in dry artificial air for 5 minutes, followed by another 15 minute driving step subjected. The boron doped region was investigated by secondary ion mass spectrometry (SIMS). The main doping of the wafer corresponded to p-type doping with boron. FIG. 3: shows SIMS doping profiles of an alkali-etched n-type CZ wafer, printed with a doping paste according to the invention according to Example 3. The doped structure has exclusively an intensive boron doping. The phosphorus doping corresponds to the background doping of the n-type wafer.

Example 5:

Inventive pastes according to Example 1 were examined for their dynamic viscosity by means of a cone-plate rheometer. The pastes had non-Newtonian flow properties.

Round-trip curve. Table 2: Dynamic viscosity of pastes of the invention according to Example 1.

In a separate approach, 150 g of ethylene glycol monobutyl ether, 75.9 texanol and 121.9 g of dibenzyl ether were mixed. The viscosity of the solvent mixture was 3.47 mPa * s. In each 100 g of the

Solvent were stirred once 3.5 g of Ethocel and stirred in the second case, 4.5 g of Ethocel. Furthermore, the dynamic viscosity of the boron-containing doping ink was determined according to Example 1. All

investigated media showed Newtonian flow properties.

Table 3: Dynamic viscosity of pastes according to the invention according to Example 1.

From comparison of Tables 2 and 3 it is clear that the addition of the thickener to the solvent mixture in which the hybrid brines are dissolved causes the viscosity of the mixture to increase. Without one

Interaction with the active components of the hybrid sol, an increase in viscosity to -600 mPas would be expected. In contrast, a corresponding pasting with the same mass fraction of ethyl cellulose shows a dynamic viscosity of 26.1 Pa ^* s, ie the

rounded up 45 times the expected value. It is therefore to be expected that the thickeners used in these examples will associate with portions of the hybrid sol, thereby significantly increasing the solubilization occurring in the solution over that occurring in the pure solvent mixture. This structure formation can by means of complex and

Chiat complexation of the polymer with the aluminum cores contained in the hybrid sol.

Claims

P A T E N T A N S P R E C H E

Printable boron doping pastes and / or gels based on precursors, such as silicon dioxide, aluminum oxide, and boron oxide containing at least one polymer as thickener selected from polyvinylpyrrolidone, polyvinylalcohol, polyvinylacetate, polyvinylimidazole, polyvinylbutyral, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, microcrystalline Cellulose, sodium starch glycolate, xanthan and gellan gum, gelatin, agar, alginic acid, alginates, guar gum, pectin, carubin, polacrylic acid, polyacrylate, associatively thickening polyurethane or mixtures thereof, for local and / or full-area, one-sided diffusion and doping can be used in manufacturing processes of solar cells.

Printable Bordotierpasten according to claim 1, comprising at least one polymer as a thickener selected from the group

Polyvinylpyrrolidone, polyvinyl acetate, polyvinyl butyral and ethyl cellulose or mixtures thereof.

Printable borne doping pastes according to claim 1 or 2, containing at least one polymer as thickener, which associatively and structurally interacts with components of the hybrid sol and produces a significantly more pronounced intrinsic viscosity than comparable pastes containing only polymer thickening compounds.

Printable Bordotierpasten according to one or more of

Claims 1 to 3, comprising at least one polymer as a thickener, which interacts with coordinating and / or chelating mechanisms with components of the hybrid sol

Printable Bordotierpasten according to one or more of

Claims to 3, containing additives selected from the group of aluminum hydroxides and aluminum oxides, colloidally precipitated or fumed silica, tin dioxide, boron nitride, silicon carbide, silicon nitride, aluminum titanate, titanium dioxide, titanium carbide, titanium nitride and Titanium carbonitride for adjusting the paste rheology, as well as the

Layer thickness of the dried paste positively influencing, particulate formulation auxiliaries.

Printable Bordotierpasten according to one or more of

Claims 1 to 5, characterized in that it

Compositions based on precursors of silica, alumina and boron oxide are.

Printable Bordotierpasten according to one or more of

Claims 1 to 5, characterized in that it

Compositions based on mixtures of precursors of silica, alumina and boron oxide are.

Printable Bordotierpasten according to one or more of

Claims 1 to 7, characterized in that they are based on precursors of silicon dioxide, selected from the group of mono- to tetra-symmetrically or asymmetrically substituted

Carboxy, alkoxy and alkoxyalkylsilanes, in particular

Alkylalkoxysilanes in which at least one hydrogen atom is bonded to the central silicon atom,

Carboxy, alkoxy and alkoxyalkylsilanes, in particular

alkylalkoxysilanes

which have individual or different saturated, unsaturated branched, unbranched aliphatic, alicyclic and aromatic radicals, which in turn may be functionalized at any position of the alkyl, alkoxide or carboxy radical by heteroatoms selected from the group O, N, S, Cl and Br, such as

Mixtures of these precursors have been obtained.

Printable Bordotierpasten according to one or more of

Claims 1 to 7, characterized in that they are based on precursors of the silicon dioxide selected from the group

Tetraethyl orthosilicate and the like, triethoxysilane,

Ethoxytrimethylsilane, dimethyldimethoxysilane, dimethyldiethoxysilane, triethoxyvinylsilane, bis [triethoxysilyl] ethane and To [diethoxymethylsilyl] ethane, and mixtures thereof are obtained.

10. Printable Bordotierpasten according to one or more of

Claims 1 to 7, characterized in that they are based on

Precursors of the alumina, selected from the group of symmetrically and asymmetrically substituted aluminum alcoholates (alkoxides), aluminum tris (-ß-diketone), aluminum tris (-ß-ketoester), aluminum soaps, aluminum carboxylates, and mixtures thereof can be obtained.

11. Printable Bordotierpasten according to one or more of

Claims 1 to 7, characterized in that they are based on precursors of the alumina, selected from the group

Aluminum triethanolate, aluminum trisopropylate, aluminum tri-sec-butylate, aluminum tributylate, aluminum triamylate and aluminum tri-isopentanolate, aluminum acetylacetonate or aluminum tris (1,3-cyclohexanedionates), aluminum monoacetylacetonate monoalcoholate, aluminum tris (hydroxyquinolates), mono- and dibasic

Aluminum stearate and aluminum tristearate, aluminum acetate,

Aluminum triacetate, basic aluminum format, aluminum triformate and aluminum trioctoate, aluminum hydroxide, aluminum metahydroxide and aluminum trichloride, and mixtures thereof. 12. Printable Bordotierpasten according to one or more of

Claims 1 to 7, characterized in that they are based on precursors of boron oxide selected from the group of

Borsäurealkylester, boric acid esters of functionalized 1, 2-glycols, boric acid esters of alkanolamines, mixed anhydrides of boric acid and carboxylic acids, and mixtures thereof are obtained.

13. Printable Bordotierpasten according to one or more of

Claims 1 to 7, characterized in that they are based on precursors of boron oxide selected from the group boron oxide,

Diboroxide, triethyl borate, trisopropyl borate, boric acid glycol ester,

Borsäureethylenglykolester, Borsäureglycerinester, boric acid esters of 2, 3-dihydroxysuccinic acid, tetraacetoxydiborate, and boric acid esters of the alkanolamines ethanolamine, diethanolamine, triethanolamine,

Propanolamine, dipropanolamine and tripropanolamine have been obtained.

14. Printable Bordotierpasten according to one or more of

Claims 1 to 7, obtainable by precursors of claims 8 to 13 under aqueous or anhydrous conditions using the sol-gel technique either simultaneously or sequentially brought to partial or complete intra- and / or interspecific condensation, which storage stable, very good printable and pressure-stable formulations are formed.

15. Printable Bordotierpasten according to claim 14, obtainable by

Removing volatile reaction aids and by-products during the condensation reaction.

16. Printable Bordotierpasten according to claim 14 or 15, obtainable by adjusting the precursor concentrations of the water and

Catalyst content, and the reaction temperature and time.

17. Printable Bordotierpasten according to one or more of claims 14 to 16, by specific addition of condensation-controlling agents, in the form of complex and / or chelating agents, various solvents in fixed amounts based on the

Total volume, whereby the degree of gelation of the resulting

Hybrid sols and gels are controlled in a targeted manner.

18. Use of the printable boron doping pastes and / or gels based on precursors, of the silicon dioxide, aluminum oxide, and boron oxide according to one or more of claims 1 to 17 in one

Process for the production of solar cells, wherein these by means of

suitable printing process on silicon surfaces for the purpose of local and / or full-area, one-sided diffusion and doping in the production of solar cells, preferably of highly efficient

structured doped solar cells, printed and dried and then by means of a suitable high-temperature process to deliver the contained in the dried paste

Boroxidprecursors be placed on the substrate located under the boron paste for targeted doping of the substrate itself.

19. Use of the printable boring pastes according to one or

in any of claims 1 to 17 in a process for the production of solar cells, wherein these by means of a printing process selected from the group of spin coating or dip coating, drop casting, curtain or slot die coating, screen or flexographic printing, engraving, Ink jet or aerosol jet printing, offset printing, micro contact printing, electrohydrodynamic dispensing, roll or spray coating, ultrasonic spray coating, pipe jet printing, laser transfer printing, pad printing, flatbed bar printing and rotary screen printing, processed and deposited.

20. Use of printable boring pastes according to one or

several of claims 1 to 17 as doping media for processing silicon wafers for photovoltaic, microelectronic,

micromechanical and micro-optical applications.

21. Use of printable boring pastes according to one or

of any of claims 1 to 17 for the production of PERC, PERL, PERT, IBC solar cells and comparable solar cells, wherein the solar cells further architectural features such as MWT, EWT, Selective

Emitter, Selective Front Surface Field, Selective Back Surface Field and Bifacialität exhibit.

22. Use of the printable boring pastes according to one or

more of claims 1 to 17, which acts as a boron-containing doping medium to silicon, wherein the medium at the same time as

Diffusion barrier or as a diffusion-inhibiting layer against unwanted ingress of phosphorus by this medium acts and the latter completely blocked or inhibited sufficiently, so that the printed media under this

predominant doping p-type, ie boron-containing, is.

23. Use according to claim 22, characterized in that by suitable temperature treatment, a doping of the

printed substrate and simultaneously and / or sequentially doping of the unprinted silicon wafer surfaces with dopants of the opposite polarity by means of conventional

Gas phase diffusion is induced, the printed

Bordotierpasten opposite the dopants of the opposite polarity act as a diffusion barrier. 24. A method for doping of silicon wafers, characterized in that Bordotierpasten, characterized in that

a) silicon wafer with printable Bordotierpasten according to the

Claims 1 to 17 are printed locally on one or both sides or on one side over the entire surface, the printed paste

dried, compacted and then the silicon wafer of a subsequent gas phase diffusion with, for example

Be exposed to phosphoryl chloride, causing p-type

Dopings in the printed areas and n-type dopants are obtained in the areas that are exposed exclusively to the gas phase diffusion,

or

b) on the silicon wafer printed on a large surface Bordotierpaste according to claims 1 to 17 is compressed and from the dried and / or compacted paste by means of laser irradiation, the local doping of the underlying

Substrate material is initiated, followed by a high-temperature treatment, whereby a diffusion and doping for the production of two-stage p-type doping levels is induced in the silicon,

or

c) the silicon wafer is locally printed on one side with Bordotierpasten according to claims 1 to 17, wherein the structured landfill may optionally have alternating lines, the printed structures are dried and compacted, and the silicon wafer subsequently on the same wafer side over the entire surface with the help of PVD and / or CVD-deposited phosphorous dopant sources is coated, wherein the printed structures of the Bordotierpasten be encapsulated, and the Überlppende whole structure is brought by suitable high temperature treatment for structured doping of the silicon wafer, wherein the printed boron paste against the overlying phosphorus containing

Dopant source and the dopant contained therein acts as a diffusion barrier

or

d) the silicon wafer is locally printed on one side with Bordotierpasten according to claims 1 to 17, wherein the structured

Deposit may optionally have alternating lines, the printed structures are dried and compacted, and the silicon wafer subsequently on the same wafer side over the entire surface with the help of phosphorus doping

acting doping inks or doping pastes are encapsulated, wherein the printed structures of the Bordotierpasten are encapsulated, and the overlapping structure is brought by suitable high temperature treatment for structured doping of the silicon wafer, and wherein the printed

Boron paste against the overlying phosphorus-containing dopant source and the dopant contained therein acts as a diffusion barrier

or

e) the silicon wafer is locally printed on one side with Bordotierpasten according to claims 1 to 17, wherein the structured

Deposit may optionally have alternating lines, the printed structures are dried and compacted, and the silicon wafer is subsequently printed on the same wafer side negatively structured compared to the previous printing using a phosphor paste, and the whole structure by suitable high temperature treatment in the presence of a conventional phosphorus-based

Gasephasendiffusionsquelle, such as phosphoryl chloride, for the structured one-sided and full-surface facing doping of the silicon wafer is brought, wherein the printed boron paste against the other simultaneously present phosphorus-containing diffusion sources as

Diffusion barrier acts

or

the silicon wafer is locally printed on one side with Bordotierpasten according to claims 1 to 17, wherein the structured

Deposit may optionally have alternating lines, the printed structures are dried and compacted, and the silicon wafer is subsequently printed negatively structured on the same wafer side to the previous printing using a phosphor paste, then the opposite side of the same wafer is printed with a further phosphorus dopant paste the order of the printing steps of the application of the phosphorus doping pastes need not necessarily take place in the said series, and the entire structure is brought to the structured unilateral and full-surface opposing doping of the silicon wafer by suitable high-temperature treatment, wherein the

printed boron paste against the other simultaneously present phosphorus-containing diffusion sources as

Diffusion barrier acts.