Electrically conductive paste for front electrode of solar cell and preparation method thereof

Abstract

The present invention provides an electrically conductive paste for a front electrode of a solar cell and a preparation method thereof. The electrically conductive paste is composed of a corrosion binder, a metallic powder and an organic carrier. The corrosion binder is one or more glass-free Pb—Te based crystalline compounds having a fixed melting temperature in a range of 440° C. to 760° C. During a sintering process of the electrically conductive paste for forming an electrode, the corrosion binder is converted into a liquid for easily corroding and penetrating an antireflective insulating layer on a front side of the solar cell, so that a good ohmic contact is formed. At the same time, the electrically conductive metallic powder is wetted, and the combination of the metallic powder is promoted. As a result, a high-conductivity front electrode of a crystalline silicon solar cell is formed.

What is claimed is: 
     
         1 . An electrically conductive paste for a front electrode of a solar cell, the electrically conductive paste comprising:
 a metallic powder having a weight ratio of 70 wt % to 95 wt % based on a given total weight;   a corrosion binder having a weight ratio of 0.5 wt % to 12 wt % based on the given total weight; and   an organic carrier having a weight ratio of 5 wt % to 25 wt % based on the given total weight;   wherein the corrosion binder is a glass-free Pb—Te—O crystal compound having a fixed melting temperature between 440° C. and 760° C.; and the metallic powder and the corrosion binder are randomly dispersed in the organic carrier.   
     
     
         2 . The electrically conductive paste of  claim 1  wherein the corrosion binder comprises one compound selected from PbTe 4 O 9 , PbTeO 3 .0.33H 2 O, PbTeO 3 , PbTeO 4 , PbTe 3 O 7 , PbTe 5 O 11 , Pb 2 TeO 4 , Pb 2 Te 3 O 7 , Pb 2 Te 3 O 8 , Pb 3 TeO 5 , Pb 3 TeO 6 , Pb 3 Te 2 O 8 .H 2 O, Pb 4 Te 1.5 O 7 , Pb 5 TeO 7 , Pb 5 TeO 7 , Pb 6 Te 5 O 18 .5H 2 O, PbTe 2 O 5 , PbH 4 TeO 6 , PbTeCO 5  and Pb 3 TeN 2 O 8  crystal compounds or any combination of above compounds. 
     
     
         3 . The electrically conductive paste of  claim 1  wherein the corrosion binder is a glass-free crystalline compound having a fixed melting point between 460° C. and 650° C., which is converted from a solid state into a liquid state when temperature reaches or exceeds the melting point substantially without any glass-softening transition. 
     
     
         4 . The electrically conductive paste of  claim 1  wherein the corrosion binder comprises a plurality of dispersed glass-free crystal particles having shapes selected from sphere, droplet, aciculate, dendritic-shape, massive, spherical-shape, flake, granular-shape, and colloidal-particle-shape and sizes ranging from 0.1 μm to 15.0 μm. 
     
     
         5 . The electrically conductive paste of  claim 1  wherein the metallic powder comprises one or more metal materials selected from silver, gold, platinum, copper, iron, nickel, zinc, titanium, cobalt, chromium, manganese, palladium, and rhodium. 
     
     
         6 . The electrically conductive paste of  claim 1  wherein the metallic powder comprises a plurality of particles made from one or more metals selected from copper, iron, nickel, zinc, titanium, cobalt, chromium, aluminum and manganese, each particle being associated with a thickness of silver coating ranging from 10 nm to 2,000 nm. 
     
     
         7 . The electrically conductive paste of  claim 1  wherein the metallic powder is a mixture of a first powder without silver coating and a second powder with silver coating; wherein the first powder without silver coating comprises a first plurality of particles made from one or more metals selected from silver, gold, platinum, copper, iron, nickel, zinc, titanium, cobalt, chromium, manganese, palladium and rhodium, and the second powder with silver coating comprises a second plurality of particles made from one or more metals selected from copper, iron, nickel, zinc, titanium, cobalt, chromium, aluminum and manganese with each particle being coated with a silver layer ranging from 10 nm to 2,000 nm; wherein a weight ratio of the first powder without silver coating to the second powder with silver coating is in a range of 5:95 to 95:5. 
     
     
         8 . The electrically conductive paste of  claim 1  wherein the metallic powder comprises a plurality of particles having sizes ranging from 0.1 μm to 5.0 μm. 
     
     
         9 . A method for forming a conductive paste comprising:
 providing a plurality of metal particles with a weight composition ranging from 70 wt % to 95 wt % based on a predetermined total weight;   providing an organic carrier with a weight composition ranging from 5 wt % to 25 wt % based on the predetermined total weight;   providing a corrosion binder made from a plurality of glass-free Pb—Te—O-based crystalline particles with a weight composition ranging from 0.5 to 12 wt % based on the predetermined total weight;   mixing the plurality of metal particles, the corrosion binder, and the organic carrier to form a mixture material; and   grinding the mixture materials to obtain a conductive paste.   
     
     
         10 . The method of  claim 9  wherein the corrosion binder comprises one or a combination of two or more selected from the following glass-free Pb—Te—O based crystalline compounds: PbTe 4 O 9 , PbTeO 3 .0.33H 2 O, PbTeO 3 , PbTeO 4 , PbTe 3 O 7 , PbTe 5 O 11 , Pb 2 TeO 4 , Pb 2 Te 3 O 7 , Pb 2 Te 3 O 8 , Pb 3 TeO 5 , Pb 3 TeO 6 , Pb 3 Te 2 O 8 .H 2 O, Pb 4 Te 1.5 O 7 , Pb 5 TeO 7 , Pb 5 TeO 7 , Pb 6 Te 5 O 18 .5H 2 O, PbTe 2 O 5 , PbH 4 TeO 6 , PbTeCO 5  and Pb 3 TeN 2 O 8 , characterized by a fixed melting point between 440° C. and 760° C. 
     
     
         11 . The method of  claim 9  wherein providing a corrosion binder comprises:
 mixing a telluric acid solution and a lead acetate solution to form a mixed solution, wherein the molar ratio of Te to Pb in the mixed solution is in a range of 0.1:10 to 10:0.1; 
 stirring the mixed solution at temperature between 80° C. and 120° C. using a stirring speed ranging from 1,000 to 1,500 r/min for 2 to 5 hours, to generate a precipitate; 
 collecting the precipitate as a solid material through solid-liquid separation; 
 washing the solid material using filtered water, till that a pH value of the filtrated water is in a range of 5 to 7; 
 drying the solid material at about 150° C. for 2 to 3 hours, to obtain the Pb—Te based crystalline compound; and 
 pulverizing the Pb—Te based crystalline compound to obtain the plurality of glass-free Pb—Te—O-based crystalline particles. 
 
     
     
         12 . The method of  claim 9  wherein providing a corrosion binder comprises:
 introducing Pb x Te y  alloy vapor into a reaction chamber filled with oxygen atmosphere; 
 reacting the Pb x Te y  alloy vapor with oxygen at a temperature ranging from 1,000° C. to 1,400° C. for 1 to 4 hours to form a reaction product; 
 cooling the reaction product naturally to 25° C. to obtain a glass-free Pb—Te—O based crystalline compound; and 
 pulverizing the glass-free Pb—Te based crystalline compound to obtain the plurality of glass-free Pb—Te—O-based crystalline particles. 
 
     
     
         13 . The method of  claim 9 , wherein providing a corrosion binder comprises:
 heating a tellurium oxide and a lead oxide in a non-reducing atmosphere comprising oxygen, air, nitrogen, and argon gas, to a temperature between 700° C. and 1,000° C. to form a reaction product;   cooling the reaction product naturally in air to 25° C. to obtain glass-free Pb—Te—O-based crystal compounds;   pulverizing the glass-free Pb—Te—O-based crystal compounds to small chunks; and   grinding the small chunks to obtain the plurality of glass-free Pb—Te—O-based crystalline particles.   
     
     
         14 . The method of  claim 9 , wherein providing a corrosion binder comprises:
 melting a tellurium oxide and a lead oxide in a vacuum atmosphere, at a temperature between 700° C. and 1,000° C. to from a product material;   cooling the product material naturally to 25° C.; and   pulverizing and grinding the product material to obtain the plurality of glass-free Pb—Te—O based crystalline particles.   
     
     
         15 . The method of  claim 9  wherein the plurality of glass-free Pb—Te—O based crystalline particles has particle sizes ranging from 0.1 μm to 15.0 μm. 
     
     
         16 . The method of  claim 9  wherein the plurality of metal particles comprises one or more metals selected from silver, gold, platinum, copper, iron, nickel, zinc, titanium, cobalt, chromium, aluminum, manganese, palladium and rhodium. 
     
     
         17 . The method of  claim 9  wherein the plurality of metal particles comprises one or more metals selected from copper, iron, nickel, zinc, titanium, cobalt, chromium, aluminum and manganese and respectively coated with a thickness of silver ranging from 10 nm to 2,000 nm. 
     
     
         18 . The method of  claim 9  wherein the plurality of metal particles is a mixture of a first powder without silver coating and a second powder with silver coating; wherein the first powder without silver coating comprises a first plurality of particles made from one or more metals selected from silver, gold, platinum, copper, iron, nickel, zinc, titanium, cobalt, chromium, manganese, palladium and rhodium, and the second powder with silver coating comprises a second plurality of particles made from one or more metals selected from copper, iron, nickel, zinc, titanium, cobalt, chromium, aluminum and manganese with each particle being coated with a silver layer ranging from 10 nm to 2,000 nm; wherein a weight ratio of the first powder without silver coating to the second powder with silver coating is in a range of 5:95 to 95:5. 
     
     
         19 . The method of  claim 9  wherein the plurality of metal particles has particle sizes ranging from 0.1 μm to 5.0 μm. 
     
     
         20 . A method for manufacturing a front electrode of a semiconductor device, the method comprising:
 providing a semiconductor device including an insulation surface coating;   printing an electrically conductive paste overlying a patterned contact region of the insulation surface coating, the electrically conductive paste comprising:
 a metallic powder with a weight composition ranging from 70 to 95 wt % based on a given total weight of the electrically conductive paste; 
 a corrosion binder made from a plurality of glass-free Pb—Te—O-based crystalline particles with a weight composition ranging from 0.5 to 12 wt % based on the given total weight; 
 an organic carrier with a weight composition ranging from 4.5 to 25 wt % based on the given total weight; 
 wherein the corrosion binder is one or a combination of two or more glass-free Pb—Te—O based crystalline compounds, having a fixed melting temperature in a range of 440° C. to 760° C.; 
   sintering the electrically conductive paste overlying the patterned contact region of the insulation surface coating, wherein the sintering comprises:
 drying the electrically conductive paste at a first temperature range from 180° C. to 260° C. for 30 s up to 70 s; 
 heating up to a second temperature range from 720° C. to 950° C. for 20 s up to 50 s; and 
 cooling back to 25° C. to form an electrode; 
 wherein the drying and heating from the first temperature range to the second temperature range are associated with releasing of the organic carrier, melting of the corrosion binder at the fixed melting temperature after the releasing of the organic carrier, and forming of a metallic bulk from the metallic powder wet by molten corrosion binder; 
 wherein the molten corrosion binder induces etch-removing of the insulation surface coating at the patterned contact region to form an ohmic contact between the metallic bulk and the crystalline silicon solar cell. 
   
     
     
         21 . The method of  claim 20  wherein the corrosion binder comprises one or a combination of two or more selected from the following glass-free Pb—Te—O based crystalline compounds: PbTe 4 O 9 , PbTeO 3 .0.33H 2 O, PbTeO 3 , PbTeO 4 , PbTe 3 O 7 , PbTe 5 O 11 , Pb 2 TeO 4 , Pb 2 Te 3 O 7 , Pb 2 Te 3 O 8 , Pb 3 TeO 5 , Pb 3 TeO 6 , Pb 3 Te 2 O 8 .H 2 O, Pb 4 Te 1 .5O 7 , Pb 5 TeO 7 , Pb 5 TeO 7 , Pb 6 Te 5 O 18 .5H 2 O, PbTe 2 O 5 , PbH 4 TeO 6 , PbTeCO 5  and Pb 3 TeN 2 O 8 . 
     
     
         22 . The method of  claim 20  wherein the metallic powder comprises one or more metals selected from silver, gold, platinum, copper, iron, nickel, zinc, titanium, cobalt, aluminum, chromium, manganese, palladium and rhodium. 
     
     
         23 . The method of  claim 20  wherein the metallic powder comprises a plurality of particles made from one or more metals selected from copper, iron, nickel, zinc, titanium, cobalt, chromium, aluminum and manganese and respectively coated with silver. 
     
     
         24 . The method of  claim 20  wherein the metallic powder is a mixture of a first powder without silver coating and a second powder with silver coating; wherein the first powder without silver coating comprises a first plurality of particles made from one or more metals selected from silver, gold, platinum, copper, iron, nickel, zinc, titanium, cobalt, chromium, manganese, palladium and rhodium, and the second powder with silver coating comprises a second plurality of particles made from one or more metals selected from copper, iron, nickel, zinc, titanium, cobalt, chromium, aluminum and manganese with each particle being coated with a silver layer ranging from 10 nm to 2,000 nm; wherein a weight ratio of the first powder without silver coating to the second powder with silver coating is in a range of 5:95 to 95:5. 
     
     
         25 . The method of  claim 20  wherein the metallic powder comprises a plurality of particles having particle ranging from 0.1 μm to 5.0 μm.