HK1180295B - Thick-film pastes containing lead-tellurium-boron-oxides, and their use in the manufacture of semiconductor devices - Google Patents

Description

Thick film pastes containing lead-tellurium-boron-oxides and their use in the manufacture of semiconductor devices

Technical Field

The present invention provides a thick film paste for printing the front side of a solar cell device having one or more insulating layers. The thick film paste comprises a conductive metal or derivative thereof, and a lead-tellurium-boron-oxide dispersed in an organic medium.

Background

Conventional solar cell structures with p-type substrates have a negative electrode, typically on the front side (the illuminated side) of the cell, and a positive electrode on the back side. Radiation of an appropriate wavelength incident on the p-n junction of the semiconductor body acts as an external energy source generating charge carriers for electron-hole pairs. These electron-hole pair charge carriers migrate in the electric field generated by the p-n semiconductor junction and are collected by a conductive mesh or metal contact applied to the semiconductor surface. The generated current flows to an external circuit.

Conductive pastes (also referred to as inks) are commonly used to form conductive grids or metal contacts. The conductive paste typically comprises a glass frit, a conductive substance (e.g., silver particles), and an organic medium. To form the metal contacts, a conductive paste is printed onto the substrate in a grid line or other pattern and then fired, during which electrical contact is made between the grid lines and the semiconductor substrate.

However, crystalline silicon PV cells are typically coated with an antireflective coating such as silicon nitride, titanium oxide or silicon oxide to promote light adsorption, thereby increasing the efficiency of the cell. Such antireflective coatings also act as insulators, which impair the flow of electrons from the substrate to the metal contacts. To overcome this problem, the conductive paste should penetrate the anti-reflective coating during firing to form a metal contact that has electrical contact with the semiconductor substrate. It is also desirable to form a strong bond (i.e., adhesion) between the metal contact and the substrate as well as solderability.

The ability to penetrate the antireflective coating and form a strong bond with the substrate upon firing is highly dependent on the composition of the conductive paste and firing conditions. Efficiency, a key measure of PV cell performance, is also affected by the quality of the electrical contact made between the fired conductive paste and the substrate.

In order to provide an economical method for manufacturing PV cells with good efficiency, there is a need for thick film paste compositions that can be fired at low temperatures to penetrate the antireflective coating and provide good electrical contact with the semiconductor substrate.

Summary of The Invention

One aspect of the invention is a thick film paste composition comprising:

a) 85 to 99.5 wt% of a conductive metal or derivative thereof, based on the total solids in the composition;

b) 0.5 to 15 wt% lead-tellurium-boron-oxide, based on solids; and

c) an organic medium.

Yet another aspect of the invention is a thick film paste composition comprising:

a) 84.5 to 99 weight percent, based on total solids in the composition, of a conductive metal or derivative thereof;

b) 0.5 to 15 wt% lead-tellurium-boron-oxide, based on solids;

c) 0.5 to 15 wt.% lead-tellurium-lithium-titanium-oxide, based on solids;

and

d) an organic medium.

Another aspect of the invention is a method comprising:

(a) providing a semiconductor substrate comprising one or more insulating films deposited onto at least one surface of the semiconductor substrate;

(b) applying a thick film paste composition onto one or more insulating films to form a layered structure, wherein the thick film paste composition comprises:

i) 85 to 99.5 wt% of a conductive metal or derivative thereof, based on the total solids in the composition;

ii) 0.5 to 15 wt% lead-tellurium-boron-oxide, based on solids; and

iii) an organic medium; and

(c) firing the semiconductor substrate, the one or more insulating films, and the thick film paste to form an electrode in contact with the one or more insulating layers and in electrical contact with the semiconductor substrate.

Another aspect of the invention is a method comprising:

(a) providing a semiconductor substrate comprising one or more insulating films deposited onto at least one surface of the semiconductor substrate;

(b) applying a thick film paste composition onto one or more insulating films to form a layered structure, wherein the thick film paste composition comprises:

i) 84.5 to 99 weight percent, based on total solids in the composition, of a conductive metal or derivative thereof;

ii) 0.5 to 15 wt% lead-tellurium-boron-oxide, based on solids;

iii) 0.5 to 15% by weight, based on solids, of lead-tellurium-lithium-titanium-oxide; and

iv) an organic medium; and

(c) firing the semiconductor substrate, the one or more insulating films, and the thick film paste to form an electrode in contact with the one or more insulating layers and in electrical contact with the semiconductor substrate.

Another aspect of the invention is an article comprising:

a) a semiconductor substrate;

b) one or more insulating layers on the semiconductor substrate; and

c) an electrode in contact with one or more insulating layers and in electrical contact with the semiconductor substrate, the electrode

Comprising a conductive metal and a lead-tellurium-boron-oxide.

Brief Description of Drawings

Fig. 1 is a flowchart illustrating a process of manufacturing a semiconductor device. The reference numerals shown in fig. 1 are explained as follows.

10: p-type silicon substrate

20: n-type diffusion layer

30: insulating film

40: p + layer (Back surface field, BSF)

60: aluminum paste deposited on the back side

61: aluminum back electrode (obtained by baking aluminum paste on back side)

70: silver or silver/aluminium paste deposited on the back side

71: silver or silver/aluminum back electrode (obtained by firing back side silver paste)

500: thick film paste deposited on front side

501: front electrode (formed by firing thick film paste)

Detailed Description

Solar photovoltaic systems are considered environmentally friendly because they reduce the demand for fossil fuels.

The present invention provides compositions useful for making photovoltaic devices having improved electrical properties. The thick film paste composition comprises:

a) 85 to 99.5 wt% of a conductive metal or derivative thereof, based on the total solids in the composition;

b) 0.5 to 15 wt% lead-tellurium-boron-oxide, based on solids; and

c) an organic medium.

The thick film paste composition may further comprise: 0.5 to 15 wt.%, based on solids, of lead-tellurium-lithium-titanium-oxide.

As defined herein, the organic medium is not considered to be part of the solids in the thick film paste composition.

Conductive metal

The conductive metal is selected from silver, copper and palladium. The conductive metal may be in flake form, spherical form, granular form, crystalline form, powder or other irregular form, and mixtures thereof. The conductive metal may be provided in a colloidal suspension.

When the metal is silver, it may be in the form of silver metal, silver derivatives or mixtures thereof. Exemplary derivatives include: for example, silver alloy, silver oxide (Ag)₂O), silver salts such as AgCl, AgNO₃、AgOOCCH₃(silver acetate), AgOOCF₃(silver trifluoroacetate), silver orthophosphate (Ag)₃PO₄). Other forms of silver that are compatible with other thick film paste components may also be used.

In one embodiment, the conductive metal or derivative thereof is about 85 to about 99.5 weight percent of the solid components of the thick film paste composition. In another embodiment, the conductive metal or derivative thereof is about 90 to about 95 weight percent of the solid components of the thick film paste composition.

In one embodiment, the solid portion of the thick film paste composition comprises from about 85 to about 99.5 wt% of spherical silver particles. In one embodiment, the solid portion of the thick film paste composition comprises from about 85 to about 90 weight percent silver particles and from about 1 to about 9.5 weight percent silver flakes.

In one embodiment, the thick film paste composition comprises conductive coated silver particles. Suitable coatings comprise phosphate and surfactant. Suitable surfactants include polyoxyethylene, polyethylene glycol, benzotriazole, poly (ethylene glycol) acetic acid, lauric acid, oleic acid, capric acid, myristic acid, linoleic acid, stearic acid, palmitic acid, stearates, palmitates, and mixtures thereof. The salt counter ion can be ammonium, sodium, potassium, and mixtures thereof.

The particle size of silver is not subject to any particular limitation. In one embodiment, the average particle size is from 0.5 to 10 microns; in another embodiment, the average particle size is from 1 to 5 microns. As used herein, "particle size" or "D50" is intended to mean "average particle size"; "average particle size" means 50% volume distribution particle size. The volume distribution particle size can be determined by a laser diffraction and dispersion method using a Microtrac particle size analyzer.

Lead-tellurium-boron-oxide compositions

One aspect of the present invention relates to a lead-tellurium-boron-oxide (Pb-Te-B-O) composition. In one embodiment, these compositions may be glass compositions. In another embodiment, these compositions may be crystalline, partially crystalline, amorphous, partially amorphous, or combinations thereof. In one embodiment, the Pb-Te-B-O composition may comprise more than one glass composition. In one embodiment, the Pb-Te-B-O composition may comprise a glass composition and an additional composition, such as a crystalline composition. The term "glass" or "glass composition" will be used herein to denote any combination of the amorphous and crystalline materials described above.

In one embodiment, the glass composition described herein comprises a lead-tellurium-boron-oxide. The glass composition may also include additional components such as silicon, silver, tin, bismuth, aluminum, titanium, copper, lithium, cerium, zirconium, sodium, vanadium, zinc, fluorine, and the like.

The lead-tellurium-boron-oxide (Pb-Te-B-O) can be prepared by reacting PbO, TeO using techniques understood by those of ordinary skill in the art₂And B₂O₃(or when heated willOther materials that decompose to the desired oxide). Such preparation techniques may involve heating the mixture in air or an oxygen-containing atmosphere to form a melt, quenching the melt, and milling, and/or screening the quenched material to provide a powder having a desired particle size. The melting of the mixture of lead, tellurium and boron oxides is typically conducted to a peak temperature of 800-. The molten mixture may be quenched, for example, on a stainless steel platen or between counter-rotating stainless steel rollers to form a sheet. The resulting flakes can be ground to form a powder. Typically, the milled powder has a D of 0.1 to 3.0 microns₅₀. Alternative synthesis techniques may be used by those skilled in the art of frit manufacturing, such as, but not limited to, water quenching, sol-gel, spray pyrolysis, quenching by quenching on a metal press platen, or other suitable techniques suitable for manufacturing glass powder.

In one embodiment, the starting mixture for preparing Pb-Te-B-O may comprise (based on the weight of the total starting mixture): PbO, which may be 25 to 75 weight percent, 30 to 60 weight percent, or 30 to 50 weight percent; TeO₂It may be 10 to 70 wt%, 25 to 60 wt% or 40 to 60 wt%; b is₂O₃It may be 0.1 to 15 wt%, 0.25 to 5 wt%, or 0.4 to 2 wt%.

In one embodiment, PbO, TeO₂And B₂O₃May be 80 to 100 wt% of the Pb-Te-B-O composition. In another embodiment, PbO, TeO₂And B₂O₃May be 85 to 100 wt% or 90 to 100 wt% of the Pb-Te-B-O composition.

In another embodiment, in addition to PbO, TeO as described above₂And B₂O₃In addition, the starting mixture for preparing Pb-Te-B-O may comprise one or more of the following: PbF₂、SiO₂、BiF₃、SnO₂、Li₂O、Bi₂O₃、ZnO、V₂O₅、Na₂O、TiO₂、Al₂O₃、CuO、ZrO₂、CeO₂Or Ag₂And O. At one isIn embodiments, one or more of these components may be 0-20 wt%, 0-15 wt%, or 0-10 wt% of the Pb-Te-B-O composition. In aspects of this embodiment (based on the weight of the total starting mixture):

PbF₂may be 0 to 20 weight percent, 0 to 15 weight percent, or 5 to 10 weight percent;

SiO₂may be 0 to 11 weight percent, 0 to 5 weight percent, 0.25 to 4 weight percent, or 0 to 0.5 weight percent;

BiF₃may be 0 to 15 weight percent, 0 to 10 weight percent, or 1 to 10 weight percent;

SnO₂may be 0 to 5 wt%, 0 to 2 wt%, or 0.5 to 1.5 wt%;

the ZnO may be 0 to 5 wt%, 0 to 3 wt%, or 2 to 3 wt%;

V₂O₅may be 0 to 5 wt%, 0 to 1 wt%, or 0.5 to 1 wt%;

Na₂o may be 0 to 5 wt%, 0 to 3 wt%, or 0.1 to 1.5 wt%;

CuO may be 0 to 5 wt.%, 0 to 3 wt.%, or 2 to 3 wt.%;

ZrO₂can be 0 to 3 weight percent, 0 to 2 weight percent, or 0.1 to 1 weight percent;

CeO₂may be 0 to 5 wt%, 0 to 3 wt%, or 0.1 to 2.5 wt%;

Li₂o may be 0 to 5 wt%, 0.1 to 3 wt%, or 0.25 to 2 wt%;

Bi₂O₃may be 0 to 15 weight percent, 0 to 10 weight percent, or 5 to 8 weight percent;

TiO₂may be 0 to 5 wt%, 0.25 to 5 wt%, or 0.25 to 2.5 wt%;

Al₂O₃may be 0 to 3 wt%, 0 to 2 wt%, or 0.1 to 2 wt%; and is

Ag₂O may be 0 to 10 weight percent, 1 to 10 weight percent, or 1 to 8 weight percent.

In one embodiment, the Pb-Te-B-O may be a uniform powder. In another embodiment, the Pb-Te-B-O may be a combination of more than one powder, where each powder may be individually a uniform population. The composition of the overall combination of the plurality of powders is within the range as described above. For example, Pb-Te-B-O may comprise a combination of two or more different powders; separately, these powders may have different compositions and may or may not be within the ranges as described above; however, the combination of these powders is within the range as described above.

In one embodiment, the Pb-Te-B-O composition may comprise a powder comprising a homogeneous powder containing some but not all of the elements of the groups Pb, Te, B, and O; and a second powder comprising one or more of the elements of the groups Pb, Te, B and O. For example, a Pb-Te-B-O composition may include a first powder containing Pb, Te and O and a second powder containing B₂O₃The second powder of (1). In one aspect of this embodiment, the powders can be melted together to form a homogeneous composition. In a further aspect of this embodiment, the powder can be added separately to the thick film composition.

In one embodiment, Li₂Some or all of O may be replaced by Na₂O、K₂O、Cs₂O or Rb₂O, to yield a glass composition having properties similar to those listed above. In this embodiment, the total alkali metal oxide content may be 0 to 5 wt.%, 0.1 to 3 wt.%, or 0.25 to 3 wt.%.

In another embodiment, one or more of the Pb-Te-B-O compositions herein can comprise one or more of the components of the third group: GeO₂、Ga₂O₃、In₂O₃、NiO、CoO、ZnO、CaO、MgO、SrO、MnO、BaO、SeO₂、MoO₃、WO₃、Y₂O₃、As₂O₃、La₂O₃、Nd₂O₃、Bi₂O₃、Ta₂O₅、V₂O₅、FeO、HfO₂、Cr₂O₃、CdO、Sb₂O₃、PbF₂、ZrO₂、Mn₂O₃、P₂O₅、CuO、Pr₂O₃、Gd₂O₃、Sm₂O₃、Dy₂O₃、Eu₂O₃、Ho₂O₃、Yb₂O₃、Lu₂O₃、CeO₂、BiF₃、SnO、SiO₂、Ag₂O、Nb₂O₅、TiO₂、Rb₂O、SiO₂、Na₂O、K₂O、Cs₂O、Lu₂O₃、SnO₂And metal halides (e.g., NaCl, KBr, NaI, LiF, ZnF)₂）。

Thus, as used herein, the term "Pb-Te-B-O" may also comprise metal oxides comprising one or more oxides of elements selected from the group consisting of: si, Sn, Li, Ti, Ag, Na, K, Rb, Cs, Ge, Ga, In, Ni, Zn, Ca, Mg, Sr, Ba, Se, Mo, W, Y, As, La, Nd, Co, Pr, Gd, Sm, Dy, Eu, Ho, Yb, Lu, Bi, Ta, V, Fe, Hf, Cr, Cd, Sb, Bi, F, Zr, Mn, P, Cu, Ce and Nb.

Table 1 lists the compositions containing PbO, TeO₂、B₂O₃And other optional compounds that may be used to prepare the lead-tellurium-boron-oxide. This list is intended to be illustrative and not limiting. In table 1, the amount of the compound is shown as a weight percent based on the weight of the total glass composition.

Typically, PbO and TeO₂The mixture of powders comprises 5 to 95 mole% lead oxide and 5 to 95 mole% tellurium oxide, based on the mixed powders. In one embodiment, the molar ratio of lead to tellurium in the lead-tellurium-boron-oxide is between 5/95 and 95/5. In a fruitIn the embodiment, PbO and TeO₂The mixture of powders comprises 30 to 85 mole% lead oxide and 15 to 70 mole% tellurium oxide, based on the mixed powders.

The glass compositions described herein, also referred to as frits, contain certain components in certain percentages. Specifically, the percentages refer to the percentage of the components used within the raw materials that will subsequently be processed as described herein to form the glass composition. Such nomenclature is conventional to those skilled in the art. In other words, the composition comprises certain components and the percentages of these components are expressed in terms of the corresponding percentages of the oxide forms. As known to those of ordinary skill in the art of glass chemistry, a certain portion of the volatile species may be released during the process of making the glass. An example of a volatile substance is oxygen.

If the starting material is a fired glass, one of ordinary skill in the art can calculate the percentages of the starting components described herein using methods known to those skilled in the art, including, but not limited to: inductively coupled plasma-emission spectroscopy (ICPES), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and the like. Further, the following exemplary techniques may be used: x-ray fluorescence spectroscopy (XRF), nuclear magnetic resonance spectroscopy (NMR), electron paramagnetic resonance spectroscopy (EPR), mossbauer spectroscopy, electron microprobe Energy Dispersive Spectroscopy (EDS), electron microprobe Wavelength Dispersive Spectroscopy (WDS), Cathodoluminescence (CL).

One of ordinary skill in the art will recognize that the raw materials selected may inadvertently contain impurities that may be incorporated into the glass during processing. For example, the impurities may be present in a range of hundreds to thousands of ppm.

The presence of impurities does not alter the characteristics of the glass, thick film composition or fired device. For example, a solar cell comprising the thick film composition can have the efficiencies described herein even if the thick film composition contains impurities.

Lead-tellurium-boron-oxide and lead-tellurium-lithium-titanium-oxide compositions

One aspect of the present invention relates to lead-tellurium-boron-oxide (Pb-Te-B-O) and lead-tellurium-lithium-titanium-oxide (Pb-Te-Li-Ti-O) compositions. In one embodiment, these compositions may be glass compositions. In another embodiment, these compositions may be crystalline, partially crystalline, amorphous, partially amorphous, or combinations thereof. One embodiment relates to a mixture of Pb-Te-B-O and Pb-Te-Li-Ti-O compositions.

One embodiment of the present invention relates to a slurry comprising Pb-Te-B-O and Pb-Te-Li-Ti-O. It is contemplated that slurries including the Pb-Te-B-O slurries described herein may also comprise Pb-Te-Li-Ti-O.

In one embodiment, the Pb-Te-Li-Ti-O composition may comprise more than one glass composition. In one embodiment, the Pb-Te-Li-Ti-O composition may include a glass composition and an additional composition, such as a crystalline composition.

The Pb-Te-Li-Ti-O may also contain oxides of additional components (e.g., silicon, boron, silver, tin, etc.).

The lead-tellurium-lithium-titanium-oxide (Pb-Te-Li-Ti-O) can be prepared in a manner similar to that described above for Pb-Te-B-O.

In one embodiment, the starting mixture for preparing Pb-Te-Li-Ti-O may comprise (based on the weight of the total starting mixture): PbO, which may be 25 to 80 weight percent, 30 to 60 weight percent, or 30 to 50 weight percent; TeO₂It may be 10 to 70 wt%, 30 to 65 wt% or 50 to 65 wt%; li₂O, which may be 0.1 to 5 wt%, 0.25 to 3 wt%, or 0.5 to 2.5 wt%; TiO2₂It may be 0.1 to 5 wt%, 0.25 to 5 wt%, or 0.5 to 3 wt%.

In one embodiment, PbO, TeO2, Li2O, and TiO2 may be 80-100 wt%, 85-100 wt%, or 90-100 wt% of the Pb-Te-Li-Ti-O composition.

In anotherIn embodiments other than PbO, TeO as described above₂、Li₂O and TiO₂In addition, the starting mixture for the preparation of Pb-Te-Li-Ti-O may also comprise SiO₂、SnO₂、B₂O₃Or Ag₂One or more of O. In one embodiment, one or more of these components may be 0-20 wt%, 0-15 wt%, or 0-10 wt% of the Pb-Te-Li-Ti-O composition. In aspects of this embodiment (based on the weight of the total starting mixture):

SiO₂may be 0 to 10 wt%, 0 to 9 wt%, or 2 to 9 wt%;

SnO₂may be 0 to 5 wt%, 0 to 4 wt%, or 0.5 to 1.5 wt%;

B₂O₃may be 0 to 10 weight percent, 0 to 5 weight percent, or 1 to 5 weight percent; and is

Ag₂O may be 0 to 30 wt%, 0 to 20 wt%, or 3 to 15 wt%.

In one embodiment, the Pb-Te-Li-Ti-O may be a uniform powder. In another embodiment, the Pb-Te-Li-Ti-O may be a combination of more than one powder, where each powder may be individually a uniform population. The composition of the overall combination of two or more powders is within the ranges as described above. For example, Pb-Te-Li-Ti-O may comprise a combination of two or more different powders; separately, these powders may have different compositions and may or may not be within the ranges as described above; however, the combination of these powders is within the range as described above.

In one embodiment, the Pb-Te-Li-Ti-O composition may comprise a powder including a homogeneous powder containing some but not all of the elements of the groups Pb, Te, Li, Ti, and O; and a second powder comprising one or more of the elements of the groups Pb, Te, Li, Ti and O. For example, a Pb-Te-Li-Ti-O composition may include a first powder containing Pb, Te, Li, and O, and a first powder containing TiO₂The second powder of (1). In one aspect of this embodiment, the powders can be fused together toA homogeneous composition is formed. In a further aspect of this embodiment, the powder can be added separately to the thick film composition.

In one embodiment, Li₂Some or all of O may be replaced by Na₂O、K₂O、Cs₂O or Rb₂O instead, a glass composition having properties similar to those listed above was obtained. In this embodiment, the total alkali metal oxide content may be 0 to 5 wt.%, 0.1 to 3 wt.%, or 0.25 to 3 wt.%.

In another embodiment, one or more of the Pb-Te-Li-Ti-O compositions herein can comprise one or more of the components of the third group: GeO₂、Ga₂O₃、In₂O₃、NiO、CoO、ZnO、CaO、MgO、SrO、MnO、BaO、SeO₂、MoO₃、WO₃、Y₂O₃、As₂O₃、La₂O₃、Nd₂O₃、Bi₂O₃、Ta₂O₅、V₂O₅、FeO、HfO₂、Cr₂O₃、CdO、Sb₂O₃、PbF₂、ZrO₂、Mn₂O₃、P₂O₅、CuO、Pr₂O₃、Gd₂O₃、Sm₂O₃、Dy₂O₃、Eu₂O₃、Ho₂O₃、Yb₂O₃、Lu₂O₃、CeO₂、BiF₃、SnO、SiO₂、Ag₂O、Nb₂O₅、TiO₂、Rb₂O、SiO₂、Na₂O、K₂O、Cs₂O、Lu₂O₃、SnO₂And metal halides (e.g., NaCl, KBr, NaI, LiF, ZnF)₂）。

Thus, as used herein, the term "Pb-Te-Li-Ti-O" may also comprise one or more oxides of elements selected from: si, Sn, B, Ag, Na, K, Rb, Cs, Ge, Ga, In, Ni, Co, Zn, Ca, Mg, Sr, Ba, Se, Mo, W, Y, As, La, Nd, Bi, Ta, V, Fe, Hf, Pr, Gd, Sm, Dy, Eu, Ho, Yb, Lu, Ti, Cr, Cd, Sb, Bi, F, Zr, Mn, P, Cu, Ce and Nb.

Table 3 shows the compositions containing PbO and TeO₂、Li₂O、TiO₂And other optional compounds that may be used to prepare the lead-tellurium-lithium-titanium-oxide. This list is intended to be illustrative and not limiting. In table 3, the amount of the compound is shown as a weight percent based on the weight of the total glass composition.

In one embodiment, PbO and TeO₂The mixture of powders comprises 5 to 95 mole% lead oxide and 5 to 95 mole% tellurium oxide, based on the mixed powders. In one embodiment, the molar ratio of lead to tellurium in the lead-tellurium-lithium-titanium-oxide is between 5/95 and 95/5. In one embodiment, PbO and TeO₂The mixture of powders comprises 30 to 85 mole% lead oxide and 15 to 70 mole% tellurium oxide, based on the mixed powders.

Organic medium

The inorganic components of the thick film paste composition are mixed with an organic medium to form a viscous paste having a consistency and rheology suitable for printing. A variety of inert viscous materials can be used as the organic medium. The organic medium may be an organic medium in which the inorganic components may be dispersed with a sufficient degree of stability during manufacture, shipping, and storage of the slurry, as well as on the printing screen during the screen printing process.

Suitable organic media have rheological properties to provide stable dispersion of the solids, suitable viscosity and thixotropy for screen printing, suitable wettability of the substrate and paste solids, good drying rate, and good firing characteristics. The organic medium may comprise thickeners, stabilizers, surfactants, and/or other common additives. The organic medium may be a solution of one or more polymers in one or more solvents. Suitable polymers include ethyl cellulose, ethyl hydroxyethyl cellulose, wood rosin, mixtures of ethyl cellulose and phenolic resins, polymethacrylates of lower alcohols, and monobutyl ether of ethylene glycol monoacetate. Suitable solvents include terpenes such as alpha-or beta-terpineol or mixtures thereof with other solvents such as kerosene, dibutyl phthalate, butyl carbitol acetate, hexylene glycol and alcohols having a boiling point above 150 ℃ and alcohol esters. Other suitable organic medium components include: bis (2- (2-butoxyethoxy) ethyl adipate, dibasic esters such as DBE, DBE-2, DBE-3, DBE-4, DBE-5, DBE-6, DBE-9 and DBE1B, octyl epoxidized resinate, isodecyl alcohol and pentaerythritol esters of hydrogenated rosins the organic medium may also contain a volatile liquid to promote rapid hardening after application of the thick film paste composition on a substrate.

The optimum amount of organic medium in the thick film paste composition depends on the method of applying the paste and the particular organic medium used. Typically, the thick film paste composition comprises 70 to 95 wt% of the inorganic component and 5 to 30 wt% of the organic medium.

If the organic medium comprises a polymer, the organic composition may comprise from 8 to 15 wt% of the polymer.

Preparation of Thick film paste compositions

In one embodiment, the thick film paste composition can be prepared by mixing the conductive metal powder, the Pb-Te-B-O powder, and the organic medium in any order. In one embodiment, the thick film paste composition may further comprise Pb-Te-Li-Ti-O. In some embodiments, the inorganic material is first mixed and then added to the organic medium. The viscosity can be adjusted, if desired, by adding one or more solvents. Mixing methods that provide high shear may be useful.

Another aspect of the invention is a method comprising:

(a) providing a semiconductor substrate comprising one or more insulating films deposited onto at least one surface of the semiconductor substrate;

(b) applying a thick film paste composition onto at least a portion of one or more insulating films to form a layered structure, wherein the thick film paste composition comprises:

i) 85 to 99.5 wt% of a conductive metal or derivative thereof, based on the total solids in the composition;

ii) 0.5 to 15 wt% lead-tellurium-boron-oxide, based on solids; and

iii) an organic medium; and

(c) firing the semiconductor substrate, the one or more insulating films, and the thick film paste to form an electrode in contact with the one or more insulating layers and in electrical contact with the semiconductor substrate.

Another aspect of the invention is a method comprising:

(a) providing a semiconductor substrate comprising one or more insulating films deposited onto at least one surface of the semiconductor substrate;

(b) applying a thick film paste composition onto at least a portion of one or more insulating films to form a layered structure, wherein the thick film paste composition comprises:

i) 84.5 to 99 weight percent, based on total solids in the composition, of a conductive metal or derivative thereof;

ii) 0.5 to 15 wt% lead-tellurium-boron-oxide, based on solids;

iii) 0.5 to 15% by weight, based on solids, of lead-tellurium-lithium-titanium-oxide; and

iv) an organic medium; and

(c) firing the semiconductor substrate, one or more insulating films and the thick film paste to form

One or more insulating layers contacting and in electrical contact with the semiconductor substrate.

In one embodiment, the thick film paste may comprise lead-tellurium-boron-oxide in an amount of 0.5 to 15 wt.%, 0.5 to 7 wt.%, or 1 to 3 wt.% on a solids basis.

In one embodiment, a semiconductor device is made of an article including a semiconductor substrate bearing a junction and a silicon nitride insulating film formed on a main surface thereof. The method comprises the following steps: a thick film paste composition having the ability to penetrate an insulating layer is applied (e.g., coated or screen printed) to an insulating film in a predetermined shape and thickness and at a predetermined position, and then fired so that the thick film paste composition reacts with and penetrates the insulating film, thereby making electrical contact with a silicon substrate.

One embodiment of the process is shown in figure 1.

Fig. 1(a) shows a monocrystalline or polycrystalline silicon p-type substrate 10.

In fig. 1(b), an n-type diffusion layer 20 having an opposite polarity is formed to create a p-n junction. Phosphorus oxychloride (POCl) can be used for the n-type diffusion layer 20₃) As a phosphorus source, by thermal diffusion of phosphorus (P). Without any particular modification, the n-type diffusion layer 20 is formed on the entire surface of the silicon p-type substrate. The depth of the diffusion layer can be varied by controlling diffusion temperature and time, and is generally formed in a thickness range of about 0.3 to 0.5 μm. The n-type diffusion layer may have a film resistivity of several tens of ohms/square up to about 120 ohms/square.

As shown in fig. 1(c), after one surface of the n-type diffusion layer 20 is protected with a resist or the like, the n-type diffusion layer 20 is removed from the plurality of surfaces by etching so that it remains on only one main surface. The resist is then removed using an organic solvent or the like.

Next, in fig. 1(d), an insulating layer 30, which also serves as an antireflection coating, is formed on the n-type diffusion layer 20. The insulating layer is typically silicon nitride, but may also be SiN_xH film (i.e., the insulating film contains hydrogen for passivation during the subsequent firing treatment), titanium oxide film, silicon oxide film, carbon-doped silicon oxynitrideA film, a carbon-containing silicon nitride film, a carbon-containing silicon oxide film, or a silicon oxide/titanium oxide film. About 700 toThe silicon nitride film thickness of (a) is suitable for a refractive index of about 1.9 to 2.0. The deposition of the insulating layer 30 can be by sputtering, chemical vapor deposition, or other methods.

Then, an electrode is formed. As shown in fig. 1(e), the thick film paste composition of the present invention is screen printed on the insulating film 30, and then dried. In addition, an aluminum paste 60 and a backside silver paste 70 are screen printed onto the backside of the substrate and dried in sequence. Firing at a temperature of 750 to 850 ℃ for a time of several seconds to several tens of minutes.

Thus, as shown in fig. 1(f), during firing, aluminum diffuses from the aluminum paste into the silicon substrate on the back side, forming a p + layer 40 containing a high concentration of aluminum dopant. This layer is generally referred to as a Back Surface Field (BSF) layer and helps to improve the energy conversion efficiency of the solar cell. Firing converts the dried aluminum paste 60 into an aluminum back electrode 61. The back side silver paste 70 is simultaneously fired to become the silver or silver/aluminum back electrode 71. During firing, the boundary between the back side aluminum and the back side silver assumes an alloyed state, thereby achieving electrical connection. The aluminum electrode occupies a large area of the back electrode, in part due to the need to form the p + layer 40. At the same time, since soldering of the aluminum electrode is not possible, a silver or silver/aluminum back electrode is formed on a limited area of the back side as an electrode for interconnecting solar cells by means of copper tape or the like.

On the front side, the thick film paste composition 500 of the present invention sinters and penetrates the insulating film 30 during firing to make electrical contact with the n-type diffusion layer 20. This type of process is commonly referred to as "burn-through". The fire-through state, i.e., the extent to which the paste melts and passes through the insulating film 30, depends on the quality and thickness of the insulating film 30, the composition of the paste, and the firing conditions. When fired, the slurry 500 becomes an electrode 501, as shown in FIG. 1 (f).

In one embodiment, the insulating film is selected from titanium oxide, aluminum oxide, silicon nitride, SiN_xH, silicon oxide, carbon-doped silicon oxynitride, carbon-containing silicon nitride film, carbon-containing silicon oxide film, and silicon oxide/titanium oxide film. The silicon nitride film may be formed by sputtering, Plasma Enhanced Chemical Vapor Deposition (PECVD), or thermal chemical vapor deposition methods. In one embodiment, the silicon oxide film is formed by thermal oxidation, sputtering, or thermal chemical vapor deposition or plasma chemical vapor deposition. The titanium oxide film may be formed by coating an organic liquid material containing titanium onto a semiconductor substrate and baking, or by thermal chemical vapor deposition.

In one embodiment of the method, the semiconductor substrate may be monocrystalline or polycrystalline silicon.

Suitable insulating films comprise one or more components selected from the group consisting of: alumina, titanium oxide, silicon nitride, SiN_xH, silicon oxide and silicon oxide/titanium oxide. In one embodiment of the present invention, the insulating film is an antireflective coating (ARC). The insulating film may be applied to the semiconductor substrate, or it may be naturally formed, for example, in the case of silicon nitride.

In one embodiment, the insulating film includes a silicon nitride layer. Silicon nitride may be deposited by CVD (chemical vapor deposition), PECVD (plasma enhanced chemical vapor deposition), sputtering, or other methods.

In one embodiment, the silicon nitride of the insulating film is treated to remove at least a portion of the silicon nitride. The treatment may be a chemical treatment. Removal of at least a portion of the silicon nitride can result in improved electrical contact between the thick film paste composition conductor and the semiconductor substrate. This may result in an improved efficiency of the semiconductor device.

In one embodiment, the silicon nitride of the insulating film is part of the antireflective coating.

The thick film paste composition can be printed on the insulating film in the form of a pattern (e.g., a bus bar having a connection line). The printing may be by screen printing, electroplating, extrusion, ink-jet, molding or multi-plate printing or ribbon.

During the electrode formation process, the thick film paste composition is heated to remove the organic medium and sinter the metal powder. The heating may be carried out in air or an oxygen-containing atmosphere. This step is commonly referred to as "firing". The firing temperature profile is typically set such that the organic binder material from the dried thick film paste composition, as well as any other organic material present, is burned out. In one embodiment, the firing temperature is from 750 to 950 ℃. Sintering may be carried out in a belt furnace using high transport rates (e.g., 100 to 500 cm/min) with a final hold time of 0.05 to 5 minutes. Multiple temperature zones (e.g., 3 to 11 zones) may be used to control the desired heat distribution.

Upon firing, the conductive metal and the Pb-Te-B-O mixture penetrate the insulating film. Electrical contact between the electrode and the semiconductor substrate is made through the insulating film. After firing, an interlayer may be formed between the semiconductor substrate and the electrode, wherein the interlayer comprises one or more of tellurium, a tellurium compound, lead, a lead compound, a boron compound, and a silicon compound, wherein the silicon may be derived from a silicon substrate and/or one or more insulating layers. After firing, the electrodes comprise a sintered metal that contacts one or more insulating layers and may also contact the underlying semiconductor substrate.

Another aspect of the invention is an article formed by a method comprising:

(a) providing a semiconductor substrate comprising one or more insulating films deposited onto at least one surface of the semiconductor substrate;

(b) applying a thick film paste composition to at least a portion of one or more insulating films to form a layered structure,

wherein the thick film paste composition comprises:

i) 85 to 99.5 wt% of a conductive metal or derivative thereof, based on the total solids in the composition;

ii) 0.5 to 15 wt% lead-tellurium-boron-oxide, based on solids; and

iii) an organic medium; and

(c) firing the semiconductor substrate, the one or more insulating films, and the thick film paste to form an electrode in contact with the one or more insulating layers and in electrical contact with the semiconductor substrate.

Such articles can be used in the manufacture of photovoltaic devices. In one embodiment, the article is a semiconductor device comprising an electrode formed from a thick film paste composition. In one embodiment, the electrode is a front side electrode on a silicon solar cell. In one embodiment, the article further comprises a back electrode.

Examples

Exemplary preparation and evaluation of thick film paste compositions are described below.

Example I

Preparation of lead-tellurium-boron-oxides

Preparation of the lead-tellurium-boron-oxides of glasses 36-54 and 76 of Table 1 and of the glasses of Table 3

Lead-tellurium-boron-oxide (Pb-Te-B-O) compositions, i.e., glasses numbered 36-54 and 76 of Table 1 and glasses numbered 56-75 of Table 3, were prepared by mixing and blending the following: pb₃O₄、TeO₂And B₂O₃Powder, and optionally, Li as shown in Table 1₂O、Bi₂O₃、TiO₂、Al₂O₃PbF₂、SiO₂、BiF₃、SnO₂、ZnO、V₂O₅、Na₂O、CuO、ZrO₂、CeO₂And/or Ag₂And O. Mixing the materials togetherIs loaded into a platinum alloy crucible, which is then inserted into the crucible using air or containing O₂An atmosphere of 900-1000 ℃. The heat treatment was continued for 20 minutes after the components had reached complete dissolution. The resulting low viscosity liquid resulting from the melting of the components is then quenched with metal rollers. The quenched glass is then ground and sieved to provide a glass having a D of 0.1 to 3.0 microns₅₀The powder of (4).

Table 1: glass frit composition in weight percent

Note that: the compositions in the table are shown as weight percent based on the weight of the total glass composition.

Preparation of lead-tellurium-boron-oxides of glasses 1 to 35 and 55 of Table 1 and glasses 77 to 90 of Table 2

Adding TeO₂Powder (99 + purity%), PbO or Pb₃O₄Powder and B₂O₃Powder (ACS reagent grade, 99+ purity%) and optionally Bi₂O₃、Li₂O、Li₂CO₃、Al₂O₃、TiO₂、CuO、ZrO₂、Na₂O、Na₂CO₃、BiF₃、SiO₂And/or PbF₂The mixture of (a) is placed in a suitable container and rolled for 15 to 30 minutes to mix the starting powders. The starting powder mixture was placed in a platinum crucible, then heated to 900 ℃ in air at a heating rate of 10 ℃/minute, and then held at 900 ℃ for 1 hour to melt the mixture. The melt was quenched from 900 ℃ by removing the platinum crucible from the furnace and pouring the melt onto a stainless steel platen. Placing the resulting material in a mortar and pestleGrinding to less than 100 meshes. The milled material was then ball milled in a polyethylene container with zirconia balls and isopropanol until D₅₀Up to 0.5-0.7 micron. The ball-milled material was then separated from the milling balls, dried and passed through a 230 mesh screen to provide the powder used in the preparation of the thick film slurry.

Table 2: glass frit composition in weight percent

Note that: the compositions in the table are shown as weight percent based on the weight of the total glass composition. TeO₂The ratio of/PbO being TeO only of the composition₂And PbO.

Table 3: glass frit composition in weight percent

Frit numbering	SiO2	PbO	B2O3	Li2O	TiO2	Ag2O	SnO2	TeO2
									56	8.40	60.90		1.47	0.93		0.70	27.60
									57		46.04		0.40	4.18			49.38
58		46.78		0.83	2.22			50.17
									59		47.43		0.85	0.84			50.88
60		33.77		2.39	2.13			61.71
									61		45.35		0.48	0.43			53.74
62		36.19		1.99	1.77			60.05
									63		37.35		2.39	2.13			58.13
64		36.19		1.82	3.06			58.94
									65		40.81		2.39	2.13			54.67
66		44.28		0.16	0.42	12.29		42.84
									67		40.81		0.59	1.57	9.08		47.95
68		40.81		1.90	1.12			56.16
									69		45.77	1.09	0.80	0.71			51.64
70		41.20		0.34	2.30			56.16
									71		44.31	0.52	0.46	0.96	3.57		50.17
72		42.92	0.54	0.78	1.31			54.44
									73		4222		0.91	1.53			55.35
74		4825						51.75
									75		48.04		0.42				51.54

Note that: the compositions in the table are shown as weight percent based on the weight of the total glass composition.

Example II

Slurry preparation

Slurries preparation for tables 5, 6 and 7

Generally, slurry preparation is made using the following procedure: the appropriate amounts of solvent, medium and surfactant from table 4 were weighed and then mixed in a mixing tank for 15 minutes.

TABLE 4

Since silver is the major component in the solid, it is added incrementally to ensure better wetting. After thorough mixing, the slurry was passed repeatedly through a three-roll mill and the pressure was increased gradually from 0 to 250 psi. The gap of the rolls was set to 2 mils. The viscosity of the slurry was measured using a brookfield viscometer, and appropriate amounts of solvent and resin were added to adjust the viscosity of the slurry towards a target value between 230 and 280Pa · s. The degree of dispersion is measured by the fineness of grind (FOG). For the fourth length of continuous draw down, the typical FOG value for the slurry is less than 20 microns, and when 50% of the slurry is drawn down, the FOG value is less than 10 microns.

To prepare the final pastes used to generate the data in tables 5, 6 and 7, 2 wt% of one or more glass frits from table 1 were mixed into a portion of the silver paste and dispersed by shearing between rotating glass plates known to those skilled in the art as a mill.

The slurry examples of tables 5, 6 and 7 were prepared using the procedure described above for preparing the slurry compositions listed in the tables in accordance with the following details. The tested pastes contained 85 to 88% silver powder. Example use D₅₀Single spherical silver of =2.0 μm.

The slurry examples of table 11 were prepared by the following steps: one or two different glass frit powders as described in the table were mixed into the appropriate amount of media of table 4 and then roll milled at increasing pressures ranging from 0 to over 250psi with a 2 mil gap to produce a precursor slurry. The silver powder was then added incrementally and mixed into the precursor slurry to ensure proper wetting of the silver powder. The silver powder is 85 to 88% of the paste composition. The entire silver powder slurry was again added at increasing pressures of 0 to 75psi and a 2 mil gap roll mill. The resin and solvent are added to adjust the viscosity to between 230 and 280Pa · s. This example uses a single spherical silver powder of D50=2.0 um.

Preparation of thick film pastes for the examples in tables 8, 9 and 10

The organic components as described in table 4 (-4.6 g) were placed in a Thinky mixing jar (ThinkyUSA, Inc.) and the Thinky mixing continued at 2000RPM for 2 to 4 minutes until good blending was achieved. The inorganic components (Pb-Te-B-O powder and silver conductive powder) were tumble-mixed in a glass jar for 15 minutes. The total weight of the inorganic components is 44g, wherein 42.5-43.5g is silver powder, 0.5-1.5g is PbO, TeO₂And B₂O₃A mixture of powders. One third of the inorganic components was then added to the Thinky jar with the organic components and mixed at 2000RPM for 1 minute. This operation was repeated until all the inorganic materials were added and mixedAnd (4) preparing the components. The slurry was allowed to cool and the viscosity was adjusted to between 200 and 500Pa · s by adding solvent and then mixing at 2000RPM for 1 minute. This procedure was repeated until the desired viscosity was obtained. The slurry was then roller milled three times at 0psi and three times at 75psi with a 1 mil gap. The degree of dispersion is measured by the fineness of grind (FOG). For thick film pastes, the FOG value is typically equal to or less than 20/10. After 24 hours at room temperature, the viscosity of the slurry was adjusted to between 200 and 320Pa · s. After 3 minutes, the viscosity was measured in a viscometer at 10 RPM. The viscosity of each slurry was measured on a Brookfield viscometer (Brookfield, inc., (Middleboro, MA)) using a spindle 14 and a cup 6.

Example III

Solar cell preparation

Solar cell preparation of the examples in tables 5, 6 and 7

For the examples in tables 5, 6 and 7, the multicrystalline silicon wafer with a 65 Ω/□ phosphorus doped emitter layer was obtained from gintech energy corporation (taiwan) or deutsche cell (germany). A 6 inch (152mm) square wafer was cut to a 1.1 inch (28mm) square with a dicing saw.

The solar cell used is textured by isotropic acid etching and has SiN_XAn anti-reflective coating (ARC) of H. Efficiency and fill factor were measured for each sample. Each sample was screen printed using an ETPL555 type printer with a doctor blade speed set at 250 mm/s. The screen used had the following pattern on a 20 μm emulsion in a screen with 325 mesh and 23 μm wires: 11 finger lines with 100 μm openings and 1 busbar with 1.5mm openings. A commercially available aluminum paste (dupont pv 381) was printed on the non-light-receiving (back) side of the device.

The device with the printed pattern on both sides was then placed in a drying oven and dried at a peak temperature of 250 ℃ for 10 minutes. The substrate was then fired with the light side up, using an infrared furnace with a CF7214Despatch6 zone and using a band speed of 560cm/min, and the first five zones were set to the temperatures indicated in tables 5, 6 and 7 as well as the 650-700-550 zone and the sixth zone as well. The actual temperature of the component is measured during the process. The estimated peak temperature for each part was 770-780 ℃ and each part was above 650 ℃ for a total time of 4 seconds. The fully processed samples were then tested for PV performance using a calibrated ST-1000 tester.

Efficiency and fill factor were measured for each sample as shown in tables 5, 6 and 7. For each slurry, the mean and median values of efficiency and fill factor are shown for 6 to 10 samples.

Solar cell preparation of the examples of tables 8, 9 and 10

Solar cells for testing thick film paste performance were made from 200 micron deutsche cell poly-silicon wafers with 65 Ω/sq. phosphorus doped emitter layer having acid etched textured surface and 70nm thick PECVDSiN_xAfter the wafers were trimmed, they were screen printed using an AMI-PrescoMSP-485 screen printer to provide one busbar, eleven wires with a pitch of 0.254cm, and a screen printed aluminum back side conductor of a full ground plane, after printing and drying, the cells were placed in a BTU International Rapid thermal processing Belt furnace for firing, the firing temperatures shown in tables 8, 9, and 10 were furnace set-point temperatures in the final peak area, which were approximately 125 ℃ higher than the actual wafer temperature, the median line width of the fired wires was 120 microns, and the average line height was 15 microns, the median line resistivity was 3.0 × 10^-6Omega cm. anticipates that the performance of a 28mm × 28mm cell will be affected by edge effects to reduce the overall solar cell Fill Factor (FF) by-5%.

Solar cell preparation of the examples of Table 11

Solar cells used to test the thick film paste performance of table 11 were made from alkali textured full 6 "x 6" (152mm x 152mm) 65 Ω/□ single crystal cells supplied by gintech energy corporation (taiwan). A 65-line pattern of the paste described in table 6 was applied to the front side of the cell by screen printing using a screen with 80 μm openings in a 325 mesh screen with a 23 μm mesh diameter of 25 μm emulsion. An aluminum backside paste and a commercially available tabbing paste (dupont pv505) were applied to the back side of the cell. The average and median efficiencies and fill factors were measured using the I-V technique and are shown in table 11.

Example IV

Solar cell performance: efficiency and fill factor

Solar cell performance: efficiency and fill factor of tables 5, 6, 7 and 11

Solar cells constructed according to the methods described herein were tested for conversion efficiency. An exemplary method of testing efficiency is provided below.

In one embodiment, a solar cell constructed according to the method described herein is placed in a commercial I-V tester (TelecomSTV, model ST-1000) for measuring efficiency. The xenon arc lamp in the I-V tester simulates sunlight of known intensity AM1.5 and illuminates the front side of the cell. The tester measures the current (I) and voltage (V) at approximately 400 load resistance settings using a multi-point contact method to determine the current-voltage curve of the battery. The Fill Factor (FF) and efficiency (Eff) are both calculated from the current-voltage curves.

Solar cell performance: efficiency and fill factor of tables 8, 9 and 10

The solar cell performance of the examples of tables 8, 9 and 10 was measured at 25 ℃ ± 1.0 ℃ using a ST-1000 type IV tester from telecomstvco. The xenon arc lamp in the I-V tester simulates sunlight of known intensity and illuminates the front side of the cell. The tester measures the current (I) and voltage (V) at a load resistance set point of about 400 using a four-point contact method to determine the current-voltage curve of the cell. The efficiency (Eff), Fill Factor (FF) and series resistance (Rs) of the solar cell were calculated from the current-voltage curve (data for Rs not shown). The desirability factor was determined using the Suns-VOC technique (Suns-VOC data not shown).

The median and average values of the efficiencies and fill factors for these examples are shown in tables 8, 9, and 10.

Table 11: eff% and FF junctions of pastes containing mixtures of glass frits from tables 1 and 3 Fruit

Comparative example I: bismuth-tellurium-boron-oxide

Preparation of bismuth-tellurium-boron-oxides

Using boron oxide (B)₂O₃) Zinc oxide (ZnO), titanium oxide (TiO)₂) Bismuth oxide (Bi)₂O₃) Tellurium oxide (TeO)₂) Lithium carbonate (LiCO)₃) And lithium phosphate (LiPO)₄) And a bag was prepared by procedure l in example I aboveCompositions shown in Table 12 containing bismuth-tellurium-boron-oxide (Bi-Te-B-O). Preparation of the lead-tellurium-boron-oxides of glasses 36-54 and 76 of Table 1 and of the glasses of Table 3

Table 12: bismuth-tellurium-boron-oxide compositions in weight percent on oxide basis

Note that: the compositions in the table are shown as weight percent based on the weight of the total glass composition.

Slurry preparation

The paste using glass a was prepared by the following procedure. A paste was prepared by mixing appropriate amounts of the organic vehicle (table 4) and silver powder. The silver paste was passed through a three roll mill and the pressure was gradually increased from 0 to 75 psi. The viscosity of the silver paste was measured using a brookfield viscometer, and appropriate amounts of solvent and resin were added to adjust the viscosity of the paste towards a target value between 230 and 280Pa · s. Another slurry was prepared by mixing the appropriate amounts of organic vehicle (table 4) and glass frit a. The glass frit slurry was passed through a three roll mill and the pressure was gradually increased from 0 to 250 psi. The degree of dispersion of each slurry was measured by the fineness of grind (FOG). For the fourth length of continuous draw down, the typical FOG value for the slurry is less than 20 microns, and when 50% of the slurry is drawn down, the FOG value is less than 10 microns.

The silver and glass frit pastes were mixed together using a planetary centrifugal mixer (thinkyo corporation, Japan) to make the final paste formulations shown in table 13.

Solar cell preparation and efficiency and fill factor measurement

Slurry was applied to 1.1"× 1.1.1" dicing saw cut polycrystalline silicon solar cells with phosphorus doped emitters on p-type substrates slurry was applied to a DeutscheCell (DeutscheCell, Germany) polycrystalline silicon wafer with 62 Ω/□ emittersTexturing of the cell by isotropic acid etching and with SiN_XAn anti-reflective coating (ARC) of H. Efficiency and fill factor were measured for each sample as shown in table 13. Each sample was prepared by screen printing using an ETPL555 type printer with a doctor blade speed set at 200 mm/s. The screen used had the following pattern on a 20 μm emulsion in a screen with 325 mesh and 23 μm wires: 11 finger lines with 100 μm openings and 1 busbar with 1.5mm openings. A commercially available aluminum paste (dupont pv 381) was printed on the non-light-receiving (back) side of the device.

The device with the printed pattern on both sides was then placed in a drying oven and dried at a peak temperature of 250 ℃ for 10 minutes. The substrate was then fired with the light side up in a CF7214Despatch6 zone infrared furnace using a band speed of 560cm/min and temperature set points of 500-. The actual temperature of the component is measured during the process. The estimated peak temperature for each part was 745 ℃ 775 ℃, and each part was above 650 ℃ for a total time of 4 seconds. The fully processed samples were then tested for PV performance using a calibrated ST-1000 tester.

The efficiencies and fill factors shown in table 13 were measured for each sample. For each slurry, the mean and median of the efficiency and fill factor for 6 samples are shown.

Claims (15)

1. A thick film paste composition for forming an electrical connection in a photovoltaic device, said photovoltaic device comprising a semiconductor substrate having at least one insulating layer on one major surface thereof, said thick film paste composition comprising:

a) 85 to 99.5 wt% of a conductive metal or derivative thereof, based on total solids in the composition;

b) 0.5 to 15 wt.% on solids basis of a lead-tellurium-boron-oxide comprising 0.25 to 15 wt.% of B₂O₃25-75 weight portionsPbO in an amount of 10 to 70 wt%, TeO in an amount of 10 to 70 wt%₂(ii) a And

c) an organic medium;

upon firing, the thick film paste is permeable to the at least one insulating layer.

2. The thick film paste composition of claim 1, wherein said conductive metal comprises silver.

3. The thick-film paste composition of claim 1, wherein the molar ratio of lead to tellurium in the lead-tellurium-boron-oxide is between 5/95 and 95/5.

4. The thick-film paste composition of claim 1, wherein the lead-tellurium-boron-oxide further comprises: 0-20.0 wt% of a component selected from the group consisting of: PbF₂、SiO₂、Bi₂O₃、BiF₃、LiO₂、SnO₂、AgO₂、ZnO、V₂O₅、Al₂O₃、Na₂O、TiO₂、CuO、ZrO₂And CeO₂。

5. The thick-film paste composition of claim 4, wherein the lead-tellurium-boron-oxide further comprises: 0.1-5 wt% TiO₂。

6. The thick-film paste composition of claim 5, wherein said organic medium further comprises one or more additives selected from the group consisting of solvents, stabilizers, surfactants, and thickeners.

7. The thick film paste composition of claim 1, wherein said conductive metal is 90-95 wt% of said solids.

8. The thick-film paste composition of claim 1, wherein said lead-tellurium-boron-oxide is at least partially crystalline.

9. The thick film paste composition of claim 4, further comprising an additive selected from the group consisting of: PbF₂、SiO₂、Na₂O、K₂O、Rb₂O、Cs₂O、Al₂O₃、MgO、CaO、SrO、BaO、V₂O₅、ZrO₂、MoO₃、Mn₂O₃、Ag₂O、ZnO、Ga₂O₃、GeO₂、In₂O₃、SnO₂、Sb₂O₃、Bi₂O₃、BiF₃、P₂O₅、CuO、NiO、Cr₂O₃、Fe₂O₃、CoO、Co₂O₃And CeO₂。

10. The thick-film paste composition of claim 1, wherein said lead-tellurium-boron-oxide further comprises an oxide of one or more elements selected from the group consisting of Si, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, V, Zr, Mo, Mn, Zn, B, P, Se, Sn, Ga, Ge, In, Sb, Bi, Ce, Cu, F, Ni, Cr, Fe, Co and Ag.

11. The thick film paste composition of claim 1, further comprising:

0.5 to 15 wt.%, based on solids, of lead-tellurium-lithium-titanium-oxide.

12. The thick-film paste composition of claim 11, wherein the lead-tellurium-lithium-titanium-oxygen

The compound comprises:

25-80 wt% of PbO,

10-70 wt.% of TeO₂、

0.1-5 wt% of Li₂O, and

0.1-5 wt% TiO₂。

13. A method of forming a photovoltaic device, comprising:

(a) providing a semiconductor substrate comprising one or more insulating films deposited onto at least one surface of the semiconductor substrate;

(b) applying a thick film paste composition onto at least a portion of the insulating film to form a layered structure, wherein the thick film paste composition comprises:

i) 85 to 99.5 wt% of a conductive metal or derivative thereof, based on total solids in the composition;

ii) 0.5 to 15 wt.%, based on solids, of a lead-tellurium-boron-oxide comprising 0.25 to 15 wt.% of B₂O₃25-75 wt% of PbO, 10-70 wt% of TeO₂(ii) a And

iii) an organic medium; and

(c) firing the semiconductor substrate, insulating film and thick film paste to form an electrode in contact with the insulating layer and in electrical contact with the semiconductor substrate.

14. A photovoltaic device, comprising:

(a) a semiconductor substrate;

(b) an insulating layer on the semiconductor substrate; and

(c) an electrode in contact with said insulating layer and in electrical contact with said semiconductor substrate, said electrode being made from a thick film paste composition according to any one of claims 1-12.

15. The photovoltaic device of claim 14, wherein the photovoltaic device is a solar cell.