KR20120014131A - Metal pastes and use thereof in the production of silicon solar cells - Google Patents

Abstract

(A) at least one electrically conductive metal powder selected from the group consisting of copper and nickel, (b) softening point temperature in the range of 571 to 636 ° C., 53 to 57% by weight of PbO, 25 to 29 A metal paste comprising at least one leaded glass frit containing wt% SiO ₂ , 2 to 6 wt% Al ₂ O ₃ and 6 to 9 wt% B ₂ O ₃ , and (c) an organic vehicle. will be.

Description

Its use in the manufacture of metal pastes and silicon solar cells {METAL PASTES AND USE THEREOF IN THE PRODUCTION OF SILICON SOLAR CELLS}

The present invention relates to its use in the manufacture of metal pastes and silicon solar cells.

Conventional solar cell structures having a p-type base typically have a cathode on the front or sun side of the cell and an anode on the back. It is well known that radiation of suitable wavelength falling to the p-n junction of a semiconductor body acts as an external energy source for generating hole-electron pairs in the body. Due to the potential difference present in the p-n junction, holes and electrons move in opposite directions across the junction, resulting in a current flow that can deliver power to external circuitry. Most solar cells are in the form of silicon wafers that are metallized, i.e., have metal contacts that are electrically conductive.

Most of the power generating solar cells in use today are silicon solar cells. In particular, the electrode is produced from a metal paste by using a method such as screen printing.

Typically, fabrication of silicon solar cells starts with a silicon wafer type p-type silicon substrate in which an n-type diffusion layer of reverse conductivity type is formed thereon by thermal diffusion such as phosphorus (P). Phosphorus oxychloride (POCl ₃ ) is commonly used as the gaseous phosphorus diffusion source, other liquid sources are phosphoric acid and the like. Without any particular modification, a diffusion layer is formed over the surface of the silicon substrate. a pn junction is formed where the concentration of the p-type dopant is equal to the concentration of the n-type dopant; Conventional cells with pn junctions near the solar side have junction depths of 0.05 to 0.5 μm.

After formation of this diffusion layer, excess surface glass is removed from the remaining surfaces by etching with an acid such as hydrofluoric acid.

Next, on the n-type diffusion layer, TiO _x , SiO _x , TiO _x / SiO _x , or especially SiN _{x in} a thickness of 0.05 to 0.1 μm by a process such as plasma CVD (chemical vapor deposition). Or an ARC (antireflective coating) layer (antireflective coating layer) of Si ₃ N ₄ is formed.

Conventional solar cell structures having a p-type base typically have a cathode grid electrode on the front or solar side of the cell and an anode electrode on the back. Typically, the grid electrode is applied by screen printing and drying the front side silver paste (front electrode forming silver paste) on the ARC layer on the front side of the cell. Typically, the front grid electrode is screen printed in a so-called H pattern comprising (i) thin parallel finger lines (collector lines) and (ii) two busbars that intersect the finger lines at right angles. . In addition, backside silver or silver / aluminum paste and aluminum paste are screen printed (or printed by some other application method) on the backside of the substrate and subsequently dried. Typically, the backside silver or silver / aluminum paste is first screen printed onto the backside of the silicon wafer as two parallel busbars or rectangular bodies (tabs) prepared to solder the interconnect string (pre-soldered copper ribbon). The aluminum paste is then printed in the bare area with a slight overlap on the backside silver or silver / aluminum. In some cases, silver or silver / aluminum paste is printed after the aluminum paste is printed. Subsequently, firing is typically performed in a belt furnace for a period of 1 to 5 minutes, with the wafer reaching a peak temperature in the range of 700 to 900 ° C. The front grid electrode and back electrode may be fired sequentially or cofiring.

Aluminum paste is generally screen printed and dried on the backside of the silicon wafer. The wafer is baked at a temperature above the melting point of aluminum to form an aluminum-silicon melt, which subsequently forms an epitaxially grown silicon layer doped with aluminum during the cooling step. This layer is commonly referred to as a back surface field (BSF) layer. The aluminum paste is converted from the dry state to the aluminum back electrode by firing. The backside silver or silver / aluminum paste is fired simultaneously to become a silver or silver / aluminum backside electrode. During firing, the boundary between the back side aluminum and the back side silver or silver / aluminum indicates an alloy state and is likewise electrically connected. Aluminum electrodes occupy most of the area of the back electrode, due in part to the need for the formation of the p + layer. The silver or silver / aluminum back electrode is formed over a portion of the back side (often as a busbar 2-6 mm wide) as an electrode for interconnecting solar cells by pre-soldered copper ribbon or the like. In addition, the front side silver paste printed as the front side grid electrode is sintered during firing and penetrates through the ARC layer, thereby allowing electrical contact with the n-type layer. This type of process is commonly referred to as "firing through."

WO 92/22928 discloses a method in which the front grid electrode is printed in two steps, in which the printing of the finger line and the printing of the busbar are separated. Finger lines are printed from the silver paste, which can be fired through the ARC coating, but this is not the case for the silver paste used to print busbars. Silver pastes used to print busbars do not have through firing capability. After firing, a grid electrode consisting of a throughfired finger line and a so-called non-contact busbar (floating busbar, ie a busbar not penetrating the ARC layer) is obtained. An advantage of grid electrodes fired only through finger lines is the reduction of recombination of holes and electrons at the metal / semiconductor interface. The reduction in recombination leads to an increase in open circuit voltage and thus an increase in the electrical yield of silicon solar electricity with this type of front grid electrode.

With improved solder leaching resistance and good adhesion to the ARC layer on the front surface of the silicon solar cell, the busbars have insufficient or even no penetrating plastic capacity and do not contact or only insufficiently contact the silicon substrate. There is a desire for the provision of thick film conductive compositions that allow manufacture. Good adhesion means the durability or extended service life of silicon solar cells.

The present invention relates to a thick film conductive composition, wherein the composition comprises (a) at least one electrically conductive metal powder selected from the group consisting of copper and nickel, (b) a softening point temperature (glass transition temperature, 10 K / min Heating rate, as measured by differential thermal analysis (DTA), ranges from 571 to 636 ° C. and ranges from 53 to 57 wt% (wt .-%) of PbO, from 25 to 29 wt% of SiO ₂ , from 2 to 6 wt% At least one leaded glass frit containing Al ₂ O ₃ and 6 to 9 weight percent B ₂ O ₃ , and (c) an organic vehicle.

The thick film conductive composition of the present invention has the form of a metal paste that can be applied by printing, in particular screen printing. In the following detailed description and in the claims, the thick film conductive composition will also be referred to as a "metal paste."

The metal paste of the present invention comprises at least one electrically conductive metal powder selected from the group consisting of silver, copper and nickel. Silver powder is preferred. The metal or silver powder may be uncoated or at least partially coated with a surfactant. The surfactant may be selected from, but is not limited to, stearic acid, palmitic acid, lauric acid, oleic acid, capric acid, myristic acid and linoleic acid and salts thereof, such as ammonium, sodium and potassium salts.

The average particle size of the electrically conductive metal powder or in particular the silver powder is, for example, in the range from 0.5 to 5 μm. The total content of the electrically conductive metal powder or in particular the silver powder in the metal paste of the invention is for example 50 to 92% by weight or in one embodiment 65 to 84% by weight.

In the description and claims, the term “average particle size” is used. This means the average particle diameter (d50) measured by laser scattering. All references made in the description and claims of the present invention with respect to average particle size relate to the average particle size of the relevant materials present in the metal paste.

In general, the metal paste of the present invention comprises only at least one electrically conductive metal powder selected from the group consisting of silver, copper and nickel. However, it is possible to replace a small proportion of electrically conductive metals selected from the group consisting of silver, copper and nickel with one or more other particulate metals. The proportion of such other particulate metal (s) is, for example, from 0 to 10% by weight, based on the total of the particulate metal contained in the conductive metal paste.

The metal paste of the present invention comprises at least one leaded glass frit as an inorganic binder. The at least one leaded glass frit has a softening point temperature in the range of 571 to 636 ° C., 53 to 57 wt% PbO, 25 to 29 wt% SiO ₂ , 2 to 6 wt% Al ₂ O ₃ and 6 to 9 weight % Of B ₂ O ₃ . The weight percentages of PbO, SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ may or may not be 100% by weight in total. If the weight percentage is not 100% by weight in total, the insufficient weight percentage is in particular one or more other oxides, for example alkali metal oxides such as Na ₂ O, alkaline earth metal oxides such as MgO and metals such as TiO ₂ and ZnO Donated by an oxide.

In one embodiment, the metal paste of the present invention comprises at least one lead free glass frit in addition to at least one leaded glass frit. In that embodiment, the metal paste of the present invention comprises (a) at least one electrically conductive metal powder selected from the group consisting of copper and nickel, (b) a softening point temperature in the range of 571 to 636 ° C., 53 to 57 At least one leaded glass frit containing, by weight, PbO, 25-29 weight percent SiO ₂ , 2-6 weight percent Al ₂ O ₃ and 6-9 weight percent B ₂ O ₃ , (c) softening point temperature Is in the range of 550 to 611 ° C. and contains 11 to 33% by weight of SiO ₂ , greater than 0 to 7% by weight, in particular 5 to 6% by weight of Al ₂ O ₃ and 2 to 10% by weight of B ₂ O ₃ At least one lead-free glass frit, and (d) an organic vehicle. In the case of lead-free glass frits, the weight percentages of SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ are not 100% by weight in total, and the lacking weight percentages are in particular one or more other oxides such as Na ₂ O Alkali metal oxides, alkaline earth metal oxides such as MgO and metal oxides such as Bi ₂ O ₃ , TiO ₂ and ZnO.

In one embodiment, the at least one lead-free glass frit contains 40 to 73% by weight, in particular 48 to 73% by weight of Bi ₂ O ₃ . In that embodiment, the metal paste of the present invention comprises (a) at least one electrically conductive metal powder selected from the group consisting of copper and nickel, (b) a softening point temperature in the range of 571 to 636 ° C., 53 to 57 At least one leaded glass frit containing, by weight, PbO, 25-29 weight percent SiO ₂ , 2-6 weight percent Al ₂ O ₃ and 6-9 weight percent B ₂ O ₃ , (c) softening point temperature Is in the range from 550 to 611 ° C., 40 to 73% by weight of Bi ₂ O ₃ , 11 to 33% by weight of SiO ₂ , greater than 0 to 7% by weight, in particular 5 to 6% by weight of Al ₂ O ₃ and 2 to At least one lead-free glass frit containing 10% by weight of B ₂ O ₃ , and (d) an organic vehicle. In the case of lead-free glass frits containing _{Bi 2 O 3, Bi 2 O} 3, SiO 2, the weight percentage of Al ₂ O ₃ and B ₂ O ₃ may be or may not be the entire 100% by weight. If the weight percentage is not 100% by weight in total, the insufficient weight percentage is in particular one or more other oxides, for example alkali metal oxides such as Na ₂ O, alkaline earth metal oxides such as MgO and metals such as TiO ₂ and ZnO Donated by an oxide.

Where the metal paste of the invention comprises at least one leaded glass frit as well as at least one lead free glass frit, the ratio between these two glass frit types ranges from all values, in other words greater than zero to infinity.

The average particle size of the glass frit (s) is for example in the range of 0.5-4 μm. The total glass frit content (at least one leaded glass frit plus optionally at least one lead-free glass frit) in the metal paste of the present invention is, for example, 0.25-8% by weight or in one embodiment 0.8-3.5% by weight.

The production of glass frits is well known and consists of melting together the components of the glass, for example in the form of oxides of the components, and pouring the molten composition into water to form the frit. As is known in the art, heating can be carried out to the peak temperature for a time when the melt becomes completely liquid and homogeneous.

In order to reduce the particle size of the frit and to obtain a frit of substantially uniform size, the glass can be milled in a ball mill with water or a low viscosity, low boiling inert organic liquid. The glass may then be precipitated in water or the organic liquid to separate the fines, and the supernatant liquid comprising the fines may be removed. Other classification methods may also be used.

The metal paste of the present invention comprises an organic vehicle. A wide variety of inert viscous materials can be used as the organic vehicle. The organic vehicle may be one in which the particulate component (electrically conductive metal powder, glass frit) is dispersible with an appropriate degree of stability. Properties of the organic vehicle, in particular rheological properties, are suitable for stable dispersion of insoluble solids, applications, in particular viscosity and thixotropy suitable for screen printing, adequate wettability of the ARC layer on the front side of silicon wafers and paste solids, good It may be such that it provides the metal paste with good application properties including drying rate, and good firing properties. The organic vehicle used in the metal paste of the present invention may be a non-aqueous inert liquid. The organic vehicle can be an organic solvent or an organic solvent mixture; In one embodiment, the organic vehicle may be a solution in which the organic polymer (s) is contained in the organic solvent (s). The use of any of a variety of organic vehicles, which may or may not include thickeners, stabilizers and / or other conventional additives, may be done. In one embodiment, the polymer used as a component of the organic vehicle may be ethyl cellulose. Other examples of polymers that can be used alone or in combination include poly (meth) acrylates of ethylhydroxyethyl cellulose, wood rosin, phenol resins and lower alcohols. Examples of suitable organic solvents include alpha- or beta-terpinol or other solvents thereof, such as kerosene, dibutylphthalate, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, hexylene glycol and high boiling alcohols, etc. Terpenes and ester alcohols such as mixtures. In addition, volatile organic solvents may be included in the organic vehicle to promote rapid curing after application of the metal paste. Various combinations of these and other solvents can be formulated to achieve the desired viscosity and volatility requirements.

The ratio of the organic vehicle to the inorganic component (electrically conductive metal powder + glass frit + other inorganic additives optionally present) in the metal paste of the present invention depends on the method of applying the metal paste and the type of organic vehicle used. Can change. Usually, the metal paste of the present invention will contain 58 to 95% by weight of inorganic components and 5 to 42% by weight of organic vehicle.

The metal paste of the present invention is a viscous composition, which can be prepared by mechanically mixing the electrically conductive metal powder (s) and glass frit (s) with an organic vehicle. In one embodiment, a manufacturing method called power mixing, which is a dispersion technique equivalent to conventional roll milling, may be used, and roll milling or other mixing techniques may also be used.

The metal pastes of the invention can be used as such or diluted, for example by the addition of additional organic solvent (s); Thus, the weight percentage of all other components of the metal paste can be reduced.

The metal paste of the present invention can be used for the production of front grid electrodes of silicon solar cells or for the production of silicon solar cells, respectively. Accordingly, the present invention also relates to such a manufacturing method and to a front grid electrode and a silicon solar cell produced by said manufacturing method.

The method for producing a front grid electrode comprises the steps of (1) providing a silicon wafer with an ARC layer on the front surface, and (2) printing, in particular screen printing and drying the metal paste of the invention on an ARC layer on the front surface of the silicon wafer. Forming at least two parallel busbars, (3) printing, in particular screen-printing and drying a metal paste having a through firing capability on the ARC layer to form a thin parallel finger line crossing the busbars at right angles, and (4 ) And firing the printed and dried metal paste. As a result of this method, a front grid electrode consisting of through-fired finger lines and non-contact busbars is obtained.

However, the method of manufacturing such a front grid electrode is also in the reverse order, namely (1) providing a silicon wafer with an ARC layer on the front surface, and (2) a metal paste having a through firing capability on the ARC on the front surface of the silicon wafer. Forming parallel finger lines which are printed on the layer, in particular screen printed and dried, (3) two metal pastes of the invention printed, in particular screen printed and dried, on the ARC layer at right angles to cross the finger lines Forming the parallel busbars as described above, and (4) firing the printed and dried metal paste. As a result of this method, a front grid electrode consisting of through-fired finger lines and non-contact busbars is obtained.

In step (1) of the processes disclosed in the previous two paragraphs, a silicon wafer is provided with an ARC layer on the front surface. Silicon wafers are conventional monocrystalline or polycrystalline silicon wafers commonly used in the manufacture of silicon solar cells, ie they typically have p-type regions, n-type regions and pn junctions. The silicon wafer has an ARC layer of TiO _x , SiO _x , TiO _x / SiO _x , or, in particular SiN _x or Si ₃ N ₄ , on its front surface. Such silicon wafers are well known to those skilled in the art; For simplicity, see the "Background" section. The silicon wafer may already be provided with conventional backside metallization, ie backside aluminum paste and backside silver or backside silver / aluminum paste, as described above in the "Background" section. Application of the backside metal paste may be performed before or after the frontside grid electrode is completed. The backside paste may be calcined separately or co-fired or even co-fired with the front metal paste printed on the ARC layer in steps (2) and (3).

In the description and claims, the term “metal paste with through firing capability” is used. This means a conventional metal paste that is in electrical contact with the surface of the silicon substrate by firing through the ARC layer, as opposed to the metal paste of the invention which does not. Such metal pastes include silver pastes with in particular through firing capability; These are known to those skilled in the art and they are described in various patent documents, one example of which is US Patent Application Publication 2006/0231801 A1.

After application of the metal paste in steps (2) and (3), the metal paste is dried, for example for a period of 1 to 100 minutes, at which time the silicon wafer reaches a peak temperature in the range of 100 to 300 ° C. For example, drying can be carried out using belts, rotary or stationary dryers, in particular IR (infrared) belt dryers.

The firing step (4) following step (2) and step (3) is a simultaneous firing step. However, although not preferred, it is also possible to carry out an additional firing step between step (2) and step (3). In any case, as a result of the manufacturing method comprising the steps (1) to (4), a grid electrode consisting of through-fired finger lines and non-contact busbars is produced on the ARC layer on the front surface of the silicon wafer. Parallel through fired finger lines have a distance between them, for example 2 to 5 mm, a layer thickness for example 3 to 30 μm and a width for example 50 to 150 μm. The fired but non-contact busbars have a layer thickness of, for example, 20 to 50 μm and a width of, for example, 1 to 3 mm.

The firing of step (4) can be carried out, for example, for a period of 1 to 5 minutes, in which the silicon wafer reaches a peak temperature in the range of 700 to 900 ° C. For example, firing can be carried out using single or multi-zone belt firing furnaces, in particular multi-zone IR belt firing furnaces. Firing takes place in an inert gas atmosphere or in the presence of oxygen, for example in the presence of air. During firing, organic materials, including non-volatile organic materials and organic parts not evaporated during the drying step, may be removed, ie burned and / or carbonized, in particular burned, and the glass frit is sintered with the electrically conductive metal powder . The metal paste used to print the thin parallel finger lines is etched and fired through the ARC layer so that the finger lines are in electrical contact with the silicon substrate, but this is not the case for the metal paste of the invention used to print busbars. . The busbars still remain as "contactless" busbars after firing, ie the ARC layer remains at least essentially between the busbar and the silicon substrate.

The grid electrode or silicon solar cell produced by the above methods using the metal paste of the present invention exhibits the advantageous electrical properties associated with non-contact busbars or only inadequate contact with silicon substrates, unlike through-fired busbars. . Busbars made by the process of the present invention are distinguished by good solder leaching resistance and good adhesion to the front side of the silicon solar cell or more precisely to the ARC layer on the front side.

Example

Embodiments mentioned herein relate to a metal paste fired on a conventional solar cell having a silicon nitride ARC layer on a front n-type emitter and a p-type silicon base.

The discussion below describes how to form solar cells using the compositions of the present invention and how the solar cells are tested for their technical properties.

(1) manufacture of solar cells

The solar cell was formed as follows:

(i) a 30 μm thick aluminum electrode on the back surface (screen printed with PV381, an Al composition available from EI Du Pont de Nemours and Company) and two 5 mm Busbars of width (screen-printed with PV505, an Ag composition available from E. DuPont Di Nemoir & Company, superimposed with aluminum film for 1 mm at both edges to ensure electrical continuity) Si substrate with an area of 243 cm 2, a 200 μm thick polycrystalline silicon wafer of p-type (boron) bulk silicon, with an n-type diffused POCl ₃ emitter, an acid textured surface, on an emitter of the wafer applied by CVD On the front side of the SiN _x ARC layer, the front side silver paste (PV142, available from E. DuPont D. Nemoa & Company) was thin parallel with 100 μm width and 20 μm thickness with a distance of 2.2 mm. It was a huge line screen printing and dried. The front busbar silver paste was then screen printed as two 2 mm wide and 25 μm thick thick parallel busbars that crossed the finger line at right angles. All metal pastes were dried before co-firing.

The front busbar silver paste of this example contained 81 wt% silver powder (average particle size 2 μm), 19 wt% organic vehicle (organic polymer resin and organic solvent) + glass frit (average particle size 0.8 μm). . Table 1 provides the composition data of the glass frit type used.

(ii) The printed wafers were then killed with a zone temperature set at 500 ° C. in zone 1, 525 ° C. in zone 2, 550 ° C. in zone 3, 600 ° C. in zone 4, 925 ° C. in zone 5 and 890 ° C. in the last zone. It was fired at a belt speed of 3000 mm / min in a patch furnace, so the wafer reached a peak temperature of 800 ° C. After firing, the metallized wafer becomes a functional photovoltaic device.

The electrical performance and fired adhesion between the front busbar and the SiN _x ARC layer were measured. Moreover, the through firing capacity was measured.

(2) test procedure

efficiency

For the purpose of measuring the light conversion efficiency, a solar cell formed according to the method described above was placed in a commercial I-V tester (supplied by h.a.l.m. elektronik GmbH). A lamp in the I-V tester simulated sunlight of known intensity (approximately 1000 W / m 2) and illuminated the emitters of the cell. The metal wiring on the cell was then contacted with an electrical probe. To calculate the I-V response curve, the photocurrent generated by the solar cell (Voc, open circuit voltage; Isc, short circuit current) was measured over various resistors.

Penetrating plastic ability

The front busbar silver paste was screen printed and fired with the H pattern described above including finger lines and busbars (the PV142 front silver paste for finger line printing was not used!). Next, the efficiency of the battery was measured. In the case of a front side busbar paste having no through firing capacity or only insufficient through firing capacity, the electrical efficiency of the solar cell is in the range of 0 to 4% (= no or only limited through firing).

Adhesion test

For the adhesion test, both the ribbon and the front busbars were wetted with liquid flux and soldered using a manual soldering iron moving at a constant speed along the entire length of the wafer. The soldering iron tip was adjusted to a specific temperature of 325 ° C. There was no predrying or preheating of the flux prior to soldering.

The flux and solder ribbons used in this test were Kester® 952S and 62Sn-36Pb-2Ag (a metal alloy consisting of 62 wt% tin, 36 wt% lead and 2 wt% silver), respectively. .

Adhesion was measured by pulling the solder ribbon at multiple points along the busbar at a speed of 100 mm / s and a pull angle of 90 ° using a Mecmesin adhesion tester. The force to remove the busbars was measured in grams.

Examples A to D mentioned in Table 2 show the electrical properties of the front side busbar silver paste as a function of the proportion and composition of the glass frit contained in the paste. The data in Table 2 indicate that the electrical performance of solar cells prepared using the front side busbar silver pastes according to Examples A to D was significantly higher than that of solar cells prepared with the front side busbar silver paste according to Comparative Example E. Confirm the improvement. The open circuit voltage Voc is increased, the adhesion is higher and the resistivity is lower.

Claims (15)

(a) is at least one electrically conductive metal powder selected from the group consisting of copper and nickel, (b) a softening point temperature in the range of 571 to 636 ° C., 53 to 57% by weight of PbO, 25 to 29% by weight A metal paste comprising SiO ₂ , 2 to 6 wt% Al ₂ O ₃ and 6 to 9 wt% B ₂ O ₃ , and (c) an organic vehicle. The softening point temperature of claim 1 is in the range of 550 to 611 ° C. and contains 11 to 33 wt.% SiO ₂ , greater than 0 to 7 wt.% Al ₂ O ₃ and 2 to 10 wt.% B ₂ O ₃ . A metal paste comprising at least one lead-free glass frit. The metal paste of claim 2, wherein the lead-free glass frit contains 40 to 73 weight percent Bi ₂ O ₃ . The metal paste according to any one of claims 1 to 3, wherein the total content of the electrically conductive metal powder is 50 to 92% by weight. 5. The metal paste of claim 1, wherein the at least one electrically conductive metal powder is a silver powder. 6. The metal paste of claim 1, wherein the total glass frit content is 0.25 to 8 wt%. 7. The metal paste of claim 2, wherein the ratio between the at least one leaded glass frit and the at least one lead free glass frit is in the range of greater than zero to infinity. 8. The metal paste of claim 1, wherein the metal paste contains from 58 to 95 wt% of the inorganic component and from 5 to 42 wt% of the organic vehicle. (1) providing a silicon wafer with an ARC layer on the front surface,
(2) printing and drying the metal paste of any one of claims 1 to 8 on an ARC layer on the front surface of the silicon wafer to form two or more parallel busbars,
(3) printing and drying a metal paste having fire through capability on the ARC layer to form a thin parallel finger line crossing the busbar at right angles, and
(4) A method for producing a front grid electrode comprising firing a printed and dried metal paste. (1) providing a silicon wafer with an ARC layer on the front surface,
(2) forming a parallel finger line for printing and drying a metal paste having a through-fire capability on the ARC layer on the front side of the silicon wafer,
(3) printing and drying the metal paste of any one of claims 1 to 8 on the ARC layer to form two or more parallel busbars crossing the finger lines at right angles, and
(4) A method for producing a front grid electrode comprising firing a printed and dried metal paste. The method of claim 9 or 10, wherein the ARC layer is selected from the group consisting of TiO _x , SiO _x , TiO _x / SiO _x , SiN _x or Si ₃ N ₄ ARC layers. The process according to claim 9, wherein a further firing step is carried out between step (2) and step (3). The method according to any one of claims 9 to 12, wherein the printing in steps (2) and (3) is screen printing. 14. A front grid electrode made according to the method of any one of claims 9 to 13. A silicon solar cell comprising a silicon wafer having an ARC layer on the front surface and a front grid electrode of claim 14.