HK1180672B

HK1180672B - Thick-film pastes containing lead-tellurium-lithium-titanium-oxides, and their use in the manufacture of semiconductor devices

Info

Publication number: HK1180672B
Application number: HK13107991.9A
Authority: HK
Inventors: A．F．卡罗尔; K．W．杭; B．J．劳克林; K．R．米克斯卡; C．托拉迪; P．D．韦尔努伊
Original assignee: 索特电子材料香港有限公司
Priority date: 2010-05-04
Filing date: 2011-05-04
Publication date: 2017-01-27

Description

Thick film pastes comprising lead-tellurium-lithium-titanium-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 source of a conductive metal or derivative thereof, and a lead-tellurium-lithium-titanium-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 a suitable wavelength incident on the p-n junction of the semiconductor serves as an external energy source for the generation of electron-void pair charge carriers. 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 typically 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 antireflective coatings such as silicon nitride, titanium oxide or silicon oxide to promote light absorption, 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. Strong adhesion (i.e., adhesion) and solderability formed between the metal contact and the substrate are also desirable.

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, an important measure of PV cell performance, is also affected by the quality of the electrical contact formed 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.

Disclosure of Invention

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

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

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

c) 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) 85-99.5 wt.% based on solids of a source of a conductive metal;

ii) 0.5 to 15% by weight, based on solids, of lead-tellurium-lithium-titanium-oxide; 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 an article comprising:

a) a semiconductor substrate;

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

c) an electrode in contact with the one or more insulating layers and in electrical contact with the semiconductor substrate, the electrode comprising a conductive metal and a lead-tellurium-lithium-titanium-oxide.

Drawings

Fig. 1 is a process flow diagram illustrating the manufacture of 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 the back side)

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

71: silver or silver/aluminum back electrode (obtained by baking 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. A thick film paste composition comprising:

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

c) an organic medium.

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

Conductive metal

The conductive metal is selected from the group consisting of 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 can be provided in the form of 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: 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 source of the conductive metal or derivative thereof is from 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 include phosphates and surfactants. 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 laser diffraction and dispersion methods with a Microtrac particle size analyzer (Largo, FL).

Lead-tellurium-lithium-titanium-oxide compositions

One aspect of the present invention relates to a lead-tellurium-lithium-titanium-oxide (Pb-Te-Li-Ti-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-Li-Ti-O composition may include 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 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-lithium-titanium-oxide. The glass composition may also include additional components such as silicon, boron, silver, tin, zinc, niobium, cerium, vanadium, aluminum, and the like.

The lead-tellurium-lithium-titanium-oxide (Pb-Te-Li-Ti-O) can be prepared by reacting PbO, TeO using techniques understood by those of ordinary skill in the art₂、Li₂O and TiO₂(or other materials that decompose to the desired oxide upon heating). 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, lithium and titanium 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 platen, or other techniques suitable for manufacturing glass powder.

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 25-65 wt%, 30-60 wt%, or 30-50 wt%; TeO₂It can be 25-70 wt%, 30-65 wt%, or 50-65 wt%; li₂O, which may be 0.1-5 wt%, 0.25-3 wt%, or 0.5-2.5 wt%; TiO2₂It may be 0.1-5 wt%, 0.25-5 wt%, or 0.5-3 wt%.

In one embodiment, PbO, TeO₂、Li₂O₃And TiO₂May be 80-100 wt% of the Pb-Te-Li-Ti-O composition. In another embodiment, PbO, TeO₂、Li₂O₃And TiO₂May be 85-100 wt% or 90-100 wt% of the Pb-Te-Li-Ti-O composition.

In another embodiment, in addition to 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、B₂O₃、ZnO、Nb₂O₅、CeO₂、V₂O₅、Al₂O₃Or Ag₂One or more of O. In aspects of this embodiment (based on the weight of the total starting mixture):

SiO₂can be 0-10 wt%, 0-9 wt%, or 2-9 wt%;

SnO₂can be 0-5 wt%, 0-4 wt%, or 0.5-1.5 wt%;

B₂O₃can be 0-10 wt%, 0-5 wt%, or 1-5 wt%; and is

Ag₂O can be 0-30 wt%, 0-20 wt%, or 3-15 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 combination of the overall compositions of the two 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, a Pb-Te-Li-Ti-O composition may include a first powder including a homogeneous powder containing some, but not all, of the Pb, Te, Li, Ti, and O group elements, and a second powder including one or more of the Pb, Te, Li, Ti, and O group elements. 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 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 glass frit compositions herein may comprise one or more of a third set of components: GeO₂、Ga₂O₃、In₂O₃、NiO、ZnO、CaO、MgO、SrO、BaO、SeO₂、MoO₃、WO₃、Y₂O₃、As₂O₃、La₂O₃、Nd₂O₃、Bi₂O₃、Ta₂O₅、V₂O₅、FeO、HfO₂、Cr₂O₃、CdO、Sb₂O₃、PbF₂、ZrO₂、Mn₂O₃、P₂O₅、CuO、CeO₂、Nb₂O₅、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 metal oxides comprising oxides of one or more elements selected from: si, Sn, B, Ag, Na, K, Rb, Cs, Ge, Ga, In, Ni, Zn, Ca, Mg, Sr, Ba, Se, Mo, W, Y, As, La, Nd, Bi, Ta, V, Fe, Hf, Cr, Cd, Sb, Bi, F, Zr, Mn, P, Cu, Ce and Nb.

Tables 1, 2 and 3 list the compositions comprising PbO, 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 tables 1, 2 and 3, the amounts of the compounds are shown as weight percent based on the weight of the total glass composition. In table 1a, the amount of compound is shown as mole% based on the total glass composition.

Typically, PbO and TeO₂The mixture of powders comprises 5-95 mole% lead oxide and 5-95 mole% tellurium oxide, based on the mixed powders. In one embodiment, PbO and TeO₂The mixture of powders comprises 30-85 mole% lead oxide and 15-70 mole% tellurium oxide, based on the mixed powders.

In one embodiment, a Pb-Te-Li-Ti-O composition may include a first powder including a homogeneous powder containing some, but not all, of the Pb, Te, Li, Ti, and O group elements, and a second powder including one or more of the Pb, Te, Li, Ti, and O group elements. For example, a Pb-Te-Li-Ti-O composition may include a first powder including Pb, Te, Li, and O and TiO₂The 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.

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 into a glass composition as described herein. 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 (ICP-ES), 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, impurities may be present in the 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.

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, shipment and storage of the paste, and may be dispersed on the printing screen during the screen printing process.

Suitable organic media have rheological properties that provide stable dispersion of the solids, appropriate viscosity and thixotropy for screen printing, appropriate wettability of the substrate and paste solids, good drying rates, 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-terpineol or beta-terpineol or mixtures thereof with other solvents such as kerosene, dibutyl phthalate, butyl carbitol acetate, hexylene glycol and alcohols and alcohol esters having a boiling point above 150 ℃. 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 70-95 wt% inorganic components and 5-30 wt% 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 may be prepared by mixing the conductive metal powder, the Pb-Te-Li-Ti-O powder, and the organic medium in any order. In some embodiments, the inorganic materials are first mixed and then added to the organic medium. If desired, the viscosity can be adjusted by adding a solvent. Mixing methods that provide high shear may be useful.

Another aspect of the invention is a method comprising:

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

iii) an organic medium; and

In one embodiment, the thick film paste may comprise lead-tellurium-lithium-titanium-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 capable of penetrating the insulating layer is applied (e.g., coated or screen printed) in a predetermined shape and thickness to predetermined locations on the insulating film, and then fired so that the thick film paste composition reacts with and penetrates the insulating film to make electrical contact with the 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 the diffusion temperature and time, and is typically formed in a thickness range of about 0.3-0.5 microns. 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_xAn H film (i.e., an insulating film containing hydrogen for passivation during a subsequent firing treatment), a titanium oxide film, a silicon oxide film, a carbon-doped silicon oxynitride film, a carbon-containing silicon nitride film, a carbon-containing silicon oxide film, or a silicon oxide/titanium oxide film. AboutThe silicon nitride film thickness of (a) is suitable for a refractive index of about 1.9-2.0. The deposition of the insulating layer 30 may 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 750-850 ℃ for 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 p containing a high concentration of aluminum dopant⁺Layer 40. 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, due in part 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 penetrates 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, and a 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 nitride film is formed by thermal oxidation, sputtering, or thermal chemical vapor deposition or plasma chemical vapor deposition. The titanium oxide film can be formed by applying an organic liquid material containing titanium to the semiconductor substrateThe bottom and fired 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 oxide.

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 layer is treated to remove at least a portion of the silicon nitride. The treatment may be a chemical treatment. Removing at least a portion of the silicon nitride can improve electrical contact between the conductor of the thick film paste composition and the semiconductor substrate. This improves the 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 performed by screen printing, electroplating, extrusion, ink-jet, molding or multi-plate printing or ribbons.

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 750-. The firing may be carried out in a belt furnace using a high transport rate (e.g., 100-500 cm/min) with a final hold time of 0.05-5 minutes. Multiple temperature zones (e.g., 3-11 zones) may be used to control the desired thermal profile.

Upon firing, the conductive metal and the Pb-Te-Li-Ti-O mixture penetrate the insulating film. Penetrating the insulating film results in electrical contact being made between the electrode and the semiconductor substrate. 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, where silicon may be derived from the silicon substrate and/or the insulating layer. After firing, the electrodes comprise sintered metal, which contact 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:

iii) an organic medium, and

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-lithium-titanium-oxides

Preparation of Pb-Te-Li-Ti-O glasses in tables 1 and 2

By mixing and blending Pb₃O₄、TeO₂、Li₂CO₃And TiO₂Powder, and optionally, SiO as shown in Table 1₂、B₂O₃、Ag₂O and/or SnO₂To prepare the lead-tellurium-lithium-titanium-oxide (Pb-Te-Li-Ti-O) compositions of table 1. Table 1b shows the same composition as table 1, but in mole%. By mixing and blending Pb₃O₄、TeO₂、Li₂CO₃And TiO₂Powder, and optionally, B as shown in Table 2₂O₃、ZnO、Nb₂O₅、Ag₂O、CeO₂And/or V₂O₅To prepare the lead-tellurium-lithium-titanium-oxide (Pb-Te-Li-Ti-O) compositions of table 2. The blended powder batch was charged into a platinum alloy crucible and then inserted into a furnace at 900-₂Of the atmosphere (c). The duration of the heat treatment was 20 minutes, after which a solution formed by all the components was obtained. The low viscosity liquid resulting from the component fusion is then quenched with a metal roller. The quenched glass is then ground and sieved to provide D₅₀Is 0.1-3.0 μm powder.

Table 1: glass frit composition (% by weight)

Frit numbering	SiO2	PbO	B2O3	Li2O	TiO2	Ag2O	SnO2	TeO2
									1	8.40	60.90		1.47	0.93		0.70	27.60
2		46.04		0.40	4.18			49.38
									3		46.78		0.83	2.22			50.17
4		47.43		0.85	0.84			50.88
									5		33.77		2.39	2.13			61.71
6		45.35		0.48	0.43			53.74
									7		36.19		1.99	1.77			60.05
8		37.35		2.39	2.13			58.13
									9		36.19		1.82	3.06			58.94
10		40.81		2.39	2.13			54.67
									11		44.28		0.16	0.42	12.29		42.84
12		40.81		0.59	1.57	9.08		47.95
									13		40.81		1.90	1.12			56.16
14		45.77	1.09	0.80	0.71			51.64
									15		41.20		0.34	2.30			56.16
16		44.31	0.52	0.46	0.96	3.57		50.17
									17		42.92	0.54	0.78	1.31			54.44
18		42.22		0.91	1.53			55.35
									19		48.25						51.75
20		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.

Table 1 a: glass frit composition (mol%)

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

Table 2: glass frit composition (% by weight)

Preparation of Pb-Te-Li-Ti-O glasses in Table 3

Lead-tellurium-lithium-titanium of Table 3The oxide (Pb-Te-Li-Ti-O) composition was prepared in the following manner: adding TeO₂(purity 99 +%), PbO, Li₂CO₃(ACS reagent grade, purity 99 +%), Al₂O₃And TiO₂The mixture of (a) is placed in a suitable container and rolled for 15-30 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 ℃/min, 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. The resulting material was placed in a mortar and ground to less than 100 mesh with a pestle. 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 extended through a 230 mesh screen to provide a glass frit powder for preparing a thick film paste.

Table 3: glass frit composition (% by weight)

Note that: the compositions in the table are shown as weight percent based on the weight of the total glass composition. The TeO2/PbO ratio is the molar ratio between TeO2 alone and PbO in the composition.

Example II

Preparation of the slurry

Slurry preparation for the examples in tables 5-12

Generally, the slurry formulation was prepared using the following procedure: the appropriate amounts of solvent, binder, resin and surfactant in table 4 were weighed and mixed in a mixing tank for 15 minutes to form an organic medium.

TABLE 4

Components	By weight%
		2,2, 4-trimethyl-1, 3-pentanediol monoisobutyrate	5.57
Ethyl cellulose (50-52% hydroxyethyl)	0.14
		Ethyl cellulose (48-50% hydroxyethyl)	0.04
N-tallow-1, 3-diaminopropane dioleate	1.00
		Hydrogenated castor oil	0.50
Pentaerythritol tetraesters of perhydroabietic acid	1.25
		Adipic acid dimethyl ester	315
Glutaric acid dimethyl ester	0.35

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

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

Table 6 shows the mixed frit compositions of the examples of table 7. The mixed frit compositions shown in table 6 were calculated with the frit compositions of table 1 at the blending ratios of table 7.

The slurry examples of tables 5, 7, 8, 9, 11 and 12 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 85-88% silver powder. By usingThe examples shown (examples 2 and 8 of Table 5 and examples 9, 10 and 11 of Table 7) comprise D₅₀First spherical silver and D of =2.0 mu m₅₀50/50 blend of a second spherical silver of =1.8 μm; all other examples use D₅₀Single spherical silver of =2.0 μm.

Slurry examples 31 of tables 11 and 12 were prepared using the procedure described above for preparing the slurry compositions listed in the tables in accordance with the following details. Two glass frit compositions described in table 2 were mixed with silver powder and medium in the ratios described in tables 11 and 12. Slurries example 32 of tables 11 and 12 were prepared using the procedure described above for preparing the symbols listed in the tablesThe slurry composition is described in detail below. Mixing a glass frit composition described in Table 2 with TiO₂Powder additive (100% anatase TiO)₂Having a surface area of 9.3m²/g) and mixed with silver powder and medium in the proportions described in tables 11 and 12.

Table 10 shows the mixed frit compositions of the examples of tables 11 and 12. The mixed glass frit compositions shown in table 10 were calculated with the glass frit compositions of table 2 at the blending ratios described in tables 11 and 12.

Slurry preparation for the examples in tables 13 and 14

The organic components as described in table 4 (about 4.6g total) were placed in a Thinky mixing jar (ThinkyUSA, Inc.) and the Thinky mixing continued at 2000RPM for 2-4 minutes until good blending was achieved. Inorganic component (Al having Table 3)₂O₃Powdered Pb-Te-Li-Ti-O and silver conductive powder) were placed in a glass jar for 15 minutes of tumble mixing. The total weight of the inorganic components is 44g, wherein 42.5-43.5g is D₅₀2 μm spherical silver powder, 2.5g PbO, TeO described in Table 3₂、Li₂O、TiO₂And Al₂O₃A 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 components had been added and mixed. 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 is repeated until the desired viscosity is obtained. The slurry was then roll milled at a 1 mil gap 3 times at 0psi and 3 times at 75 psi. 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 the viscosity of the slurry was adjusted to between 200 and 320pa.s at room temperature. After 3 minutes the viscosity was measured with a viscometer at 10 RPM. The viscosity of each slurry was measured using a Brookfield viscometer (Brookfield, inc., Middleboro, MA) using a 14-spindle and a 6-cup.

Example III

Preparation of solar cells

Preparation of solar cells of the examples in tables 5 to 12

A polysilicon wafer with a 65 Ω/sq phosphorus doped emitter layer was obtained from gintech energy corporation (taiwan). A156 mm (6.14 ") wafer was cut to 28mm (1.1") with a dicing saw. The solar cell used is textured by isotropic acid etching and has SiN_xH an anti-reflective coating (ARC). The efficiency and fill factor of each sample were measured. 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. Commercially available aluminum paste dupont pv381 is printed on the non-light-receiving side (back side) of the device.

The device with the printed pattern on both sides was then dried in a drying oven at a peak temperature of 250 ℃ for 10 minutes. The substrate was then fired with the light side up in an infrared furnace in the CF7214Despatch6 zone using a band speed of 560cm/min and temperature set points of 550-. 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.

Preparation of solar cells of the examples in tables 13 and 14

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_xAnd (4) antireflection coating. Use of diamond particlesThe blade saw cuts the wafer into 28mm x 28mm wafers. After the wafer was trimmed, it was screen printed using an AMI-PrescoMSP-485 screen printer to provide bus bars, 11 wires at 0.254cm pitch, and a screen printed aluminum back side conductor to the full ground plane. After printing and drying, the cells were fired in a btuinaterial rapid thermal processing belt furnace. The firing temperature shown in table 4 is the furnace set point temperature in the final peak region, which is about 125 ℃ higher than the actual wafer temperature. The fired wire had a median wire width of 120 microns and an average wire height of 15 microns. Median line resistivity of 3.0X 10^-6Omega cm. It is expected that the performance of a 28mm x 28mm cell will be affected by edge effects to reduce the overall solar cell Fill Factor (FF) by about 5%.

Example IV

Solar cell performance: efficiency and fill factor

Test procedures for the examples in tables 5-12

Solar cells constructed according to the methods described herein were tested for conversion efficiency. Exemplary efficiency testing methods are 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 utilizes a multi-point contact method to measure current (I) and voltage (V) at approximately 400 load resistance settings to determine the current-voltage curve of the battery. Both Fill Factor (FF) and efficiency (Eff%) are calculated from the current-voltage curves.

The efficiency and fill factor of each sample were measured as shown in tables 5-12. For each slurry, the mean and median values of the efficiency and fill factor for 5-12 samples at each temperature are shown.

Test procedure for the examples in tables 13 and 14

The solar cell performance of the examples of tables 8, 9 and 10 was measured using an ST-1000(TelecomSTVCo.) IV tester at 25 ℃ ± 1.0 ℃. The xenon arc lamp in the IV 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 solar cell efficiency (Eff), Fill Factor (FF), and series resistance (Rs) were calculated from the current-voltage curves (data of Rs not shown).

The median and mean values of the efficiencies and fill factors for these examples are shown in tables 13 and 14.

Table 5: eff% and FF results for pastes using selected glass frits of table 2

Representing a paste containing two different types of silver (all other examples containing only one type of silver).

Table 6: mixed glass frit compositions obtained from the blended glass frit experiments of Table 7

Table 7: eff% and FF results for a paste using a blend of two different frits (mixed frit composition given in table 4)

Table 8: eff% data from single frit experiments

Table 9: FF data from single frit experiments

Table 10: blended glass compositions (wt%) of the dual frit paste experiments in tables 11 and 12

Composition "I" uses glass 25 and TiO₂50/50 blend of additive powders wherein the additive is of 9.3m²100% anatase/g surface area.

Comparative example I: bismuth (III)Tellurium-lithium-titanium-oxide

Preparation of bismuth-tellurium-lithium-titanium-oxides

Boron oxide (B2O3), zinc oxide (ZnO), titanium oxide (TiO2), bismuth oxide (Bi2O3), tellurium oxide (TeO2), lithium carbonate (LiCO3) and lithium phosphate (LiPO4) were used and prepared by the above example I: procedures in the preparation of the Pb-Te-Li-Ti-O glasses of tables 1 and 2 compositions as shown in table 15 were prepared containing bismuth-tellurium-lithium-titanium-oxide (Bi-Te-Li-Ti-O).

Table 15: bismuth-tellurium-lithium-titanium-oxide compositions (in% by weight based on the oxide)

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

Preparation of the slurry

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 rolled with 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 to a target value between 230 and 280 Pa-s. Another slurry was prepared by mixing the appropriate amounts of organic vehicle (table 4) and glass frit a. The glass frit paste was rolled with 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 grind fineness value for the slurry is less than 20 microns, and when 50% of the slurry is drawn down, the grind fineness value is less than 10 microns.

The silver paste and glass frit slurry were mixed together using a planetary centrifugal mixer (thinky corporation, Tokyo, Japan) to make the final slurry formulations shown in table 16.

Preparation of solar cells and measurement of efficiency and fill factor

The slurry was applied to a 1.1 "x 1.1" dicing saw cut polycrystalline silicon solar cell with a phosphorus doped emitter on the p-type substrate of the solar cell. The slurry was applied to a DeutscheCell (DeutscheCell, Germany) polysilicon chip with a 62 Ω/□ emitter. The solar cell used was textured by isotropic acid etching and had a SiNX: H antireflective coating (ARC). The efficiency and fill factor of each sample were measured as shown in table 16. Each sample was screen printed using an ETPL555 type printer with a doctor blade speed set at 200 mm/s. The screen used had the following pattern on a 20mm emulsion in a screen with 325 mesh and 23mm wires: 11 finger lines with 100mm openings and 1 busbar with 1.5mm openings. Commercially available aluminum paste dupont pv381 is printed on the non-light-receiving side (back side) of the device.

The device with the printed pattern on both sides was then dried in a drying oven at a peak temperature of 250 ℃ for 10 minutes. The firing was then carried out in an infrared furnace in the CF7214Despatch6 zone, with the light side of the substrate facing upward, 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-. The fully processed samples were then tested for PV performance using a calibrated ST-1000 tester.

The efficiency and fill factor for each sample were measured as shown in table 16. For each slurry, the mean and median of the efficiency and fill factor for 6 samples are shown.

Claims

1. A thick film paste composition comprising:

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

c) an organic medium.

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-lithium-titanium-oxide is between 5/95 and 95/5.

4. The thick-film paste composition of claim 1, wherein the lead-tellurium-lithium-titanium-oxide comprises:

25 to 65 wt% of PbO,

25-70 wt.% of TeO₂，

0.1-5 wt% of Li₂O, and

0.1-5 wt% TiO₂。

5. The thick-film paste composition of claim 1, wherein said organic medium comprises a polymer.

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-lithium-titanium-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、MgO、CaO、SrO、BaO、V₂O₅、Al₂O₃、ZrO₂、BiF₃、MoO₃、Mn₂O₃、Ag₂O、ZnO、Ga₂O₃、GeO₂、In₂O₃、SnO₂、Sb₂O₃、Bi₂O₃、P₂O₅、CuO、NiO、Cr₂O₃、Fe₂O₃、CoO、Co₂O₃And CeO₂。

10. The thick-film paste composition of claim 1, wherein said lead-tellurium-lithium-titanium-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, Al, Sb, Bi, Ce, Cu, Ni, Cr, Fe, Co and Ag.

11. A method of manufacturing a semiconductor device, comprising:

(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:

iii) an organic medium; and

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

12. The method of claim 11, wherein the thick film paste composition is applied onto the insulating film in a pattern.

13. The method of claim 11, wherein the firing is performed in air or an oxygen-containing atmosphere.

14. A semiconductor article comprising:

(a) a semiconductor substrate;

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

(c) an electrode in contact with the one or more insulating layers and in electrical contact with the semiconductor substrate, the electrode comprising a conductive metal and a lead-tellurium-lithium-titanium-oxide.

15. The semiconductor article of claim 14, wherein the semiconductor article is a solar cell.