TW201638969A - Conductive paste for solar cell manufacturing process - Google Patents

Abstract

Provided is a conductive paste for solar cell manufacturing process, which includes an organic matter carrier, a conductive material and a glass medium. The conductive material and the glass medium are distributed in the organic matter carrier. The glass medium includes silicon dioxide with a weight percentage of 0.1 wt.% to 10 wt.%, lead oxide with a weight percentage of 0.1 wt.% to 23 wt.%, tellurium dioxide with a weight percentage of 20 wt.% to 80 wt.%, Bismuth(III) oxide (Bi2O3) with a weight percentage of 5 wt.% to 35 wt.%, and zinc oxide with a weight percentage of 0.1 wt.% to 20 wt.%. By increasing the weight percentage of the silicon dioxide, it is able to not only reduce the contact impedance in forming a conductive electrode, but also increase the viscosity of the conductive paste.

Description

Conductive paste for solar cell process

The invention relates to a chemical material for a solar cell, in particular to a conductive paste for a solar cell process.

A conventional solar cell basic structure is formed by a p-type semiconductor and an n-type semiconductor being bonded to each other to form a solar cell substrate, and a ppn junction is formed between the p-type semiconductor and the n-type semiconductor. When exposed to sunlight, the solar cell creates a hole-electron pair at the pn junction. Since the p-type semiconductor has a higher hole density; and the n-type semiconductor has a higher electron density, at the pn junction, electrons of the electron hole pair will go to the n-type semiconductor The hole is moved, and the hole of the pair of electron holes moves to the p-type semiconductor to generate a current, and finally the current is collected and used by the conductive electrode. The aforementioned solar cell can be referred to US Patent Publication No. US 2013/0247976, US 2014/0083489

In general, a conductive electrode used in a conventional solar cell is patterned and coated on the solar cell substrate with a conductive paste containing a glass medium, a conductive material, and an organic vehicle. In the case of current applications, silver or aluminum is mostly used as the conductive material, as disclosed in US Patent Publication No. US 2013/0026425, which discloses a conductive component and a process thereof, the conductive component comprising a conductive functional mixture, wherein the conductive functional mixture Consisting of a metal and a metal oxide, the metal is a host and the metal oxide is a filler, the metal oxide is between 0.5 wt.% and 5 wt.%, and the metal oxide comprises Alumina, copper oxide, zinc oxide, zirconium oxide, cerium oxide, and combinations thereof; or, as disclosed in US Patent No. 8,383,011, discloses a conductive ink containing a metal organic modifier containing a glass frit and a conductive material. An organic medium and one or more metal organic components which form a metal oxide after calcination, wherein the metal organic component contains a base metal organic substance and is sufficient to form at least 1 wt.% of a metal oxide after firing, the glass The material comprises cerium oxide, cerium oxide, boron oxide, cerium oxide and combinations thereof.

The glass medium in the conductive paste is mainly used to improve the adhesion of the conductive paste and provide good ohmic contact between the solar cell substrate and the metal electrode. When the sintering process is performed, the glass medium will form a liquid state, and in addition to diffusion to the solar cell substrate, a chemical reaction may occur and a product may be formed. If the composition of the glass medium is poorly selected, the solar cell substrate may occur. The adhesion to the metal electrode is poor, and a good ohmic contact resistance or contamination of the solar cell substrate between the solar cell substrate and the metal electrode is not formed. This affects the quality of the solar cell.

SUMMARY OF THE INVENTION A primary object of the present invention is to solve the problems of conventional conductive pastes for solar cells, such as adhesion and poor ohmic contact resistance.

To achieve the above object, the present invention provides a conductive paste for a solar cell process, comprising an organic carrier, a conductive material, and a glass medium, the conductive material and the glass medium being dispersed in the organic carrier, the glass medium comprising Ceria in a weight percentage between 0.1 wt.% and 10 wt.%, lead oxide in a weight percentage between 0.1 wt.% and 23 wt.%, and a weight percentage between 20 wt.% and 80 wt% Between .% of ceria, between 5 wt.% and 35 wt.% of antimony trioxide and between 0.1 wt.% and 20 wt.% of zinc oxide.

It can be seen from the above that the conductive paste for the solar cell process of the present invention changes the characteristics of the conductive paste by changing the composition and ratio of the glass medium, thereby improving the solar cell using the conductive paste to form a conductive electrode. Performance.

The detailed description and technical content of the present invention will now be described as follows:

The present invention provides a conductive paste for a solar cell process, comprising an organic carrier, a conductive material, and a glass medium, the conductive material and the glass medium being dispersed in the organic carrier, in an embodiment of the present invention, The conductive material may be silver, silver oxide, silver salt, copper, palladium, aluminum or a combination thereof, and the conductive material has a weight percentage of the conductive paste of between 80 wt.% and 95 wt.%. The material of the organic carrier may be ethyl cellulose (Ethyl cellulose), polyacrylic acid, polyvinyl butyral, polyvinyl alcohol, polyolefin, polyfluorene. Polyamide, Carboxylic acid, Oleic acid, N-Tallow-1,3-diaminopropane dioleate, Diethylene glycol Butyl Ether), 2-(2-Butoxyethoxy)ethyl Acetate, Ester alcohol, Dibasic ester, Terpineol or the aforementioned derivatives And the weight percentage of the organic carrier is between 5 wt.% and 20 wt.%.

In the present invention, the weight percentage of the glass medium is between 0.1 wt.% and 10 wt.%, and the glass medium comprises cerium oxide, weight of between 0.1 wt.% and 10 wt.% by weight. Lead oxide having a percentage between 0.1 wt.% and 23 wt.%, cerium oxide having a weight percentage between 20 wt.% and 80 wt.%, and a weight percentage ranging from 5 wt.% to 35 wt.% Between the antimony trioxide and zinc oxide in a weight percentage between 0.1 wt.% and 20 wt.%. Among them, cerium oxide is a glass former (Glass former), which is used as a glass network main body, and cerium oxide, lead oxide, cerium oxide and zinc oxide are used as glass intermediates.

When the present invention is applied to a front side silver paste of a solar cell (that is, the conductive material contains silver), lead oxide and zinc oxide in the glass medium will be used as an anti-reflection coating etchant, but sintered at a high temperature. Under the conditions, excessive levels of lead oxide and zinc oxide tend to cause an increase in ohmic contact resistance, and excessive etching of zinc oxide may even cause a short circuit in the battery. Therefore, the present invention utilizes the content of cerium oxide to control the glass softening point and viscosity of the conductive paste to optimize the contact resistance and line width of the final product to achieve the purpose of improving the efficiency of the battery.

In addition, the addition of cerium oxide can greatly improve the dissolution and re-precipitation behavior of the silver powder on the contact interface, thereby reducing the contact resistance. This is because yttrium oxide is easily co-dissolved with silver particles at high temperatures to form a stable phase such as silver telluride. Silver is precipitated in the form of nano-particles, etc. If it is deposited on the surface of the germanium wafer, it will help to form a tantalum-metal joint, that is, the tantalum will form a direct contact with the metal, and the contact resistance is better than that of the tantalum-oxide (glass). The metal junction is lower, which effectively reduces the interface resistance.

Please refer to FIG. 1 and FIG. 2A to FIG. 2D , which are schematic diagrams of the structure and process steps of the present invention applied to a solar cell. The manufacturing method of the solar cell is as follows:

S1: forming a solar cell substrate 10, preparing a p-type semiconductor substrate 11 and performing a doping process on the p-type semiconductor substrate 11 to form an n-type semiconductor layer 12, the p-type semiconductor substrate 11 and The n-type semiconductor layer 12 forms the solar cell substrate 10, and the p-type semiconductor substrate 11 may be a single crystal germanium substrate, a polycrystalline germanium substrate, a gallium arsenide substrate or a substrate coated with a germanium semiconductor film;

S2: forming an anti-reflection layer 20, the anti-reflection layer 20 is formed on a side of the n-type semiconductor layer 12 away from the p-type semiconductor substrate 11, wherein the anti-reflection layer 20 can be via sputtering, chemical vapor deposition or other A similar method is formed, and the material of the anti-reflective layer 20 may be tantalum nitride, titanium dioxide or cerium oxide;

S3: forming a front conductive paste layer 30 and a rear conductive paste layer 40, and applying the conductive paste of the present invention to the side of the anti-reflective layer 20 away from the solar cell substrate 10 to form the front conductive paste. The layer 30 is coated with a back electrode conductive paste on the side of the solar cell substrate 10 away from the anti-reflective layer 20 to form the rear conductive paste layer 40. The conductive metal of the back electrode conductive paste may be Nickel, silver, aluminum, copper, palladium, gold or tin;

S4: sintering a front conductive electrode 31 and a rear conductive electrode 41 to perform a sintering process, so that the front conductive paste layer 30 passes through the anti-reflective layer 20 and the n-type semiconductor layer 12 of the solar cell substrate 10 The bonding is performed to form the front conductive electrode 31. In addition, the post conductive paste layer 40 forms the rear conductive electrode 41 after the sintering process, which is the same as the conventional solar cell process, and thus is not described in the present invention.

Further, since the weight percentage of cerium oxide contained in the glass medium in the conductive paste is between 1 wt.% and 10 wt.%, the formed front conductive electrode 31 layer and the n-type are formed. The contact resistance between the semiconductor layers 12 is reduced, thereby improving the performance of the solar cell; secondly, the viscosity of the conductive paste can be improved, so that the line width of the front conductive paste layer 30 is not caused by the low viscosity. There is a change, that is, the conductive paste can avoid the problem of line expansion, thereby stabilizing the yield of the solar cell during the process.

In summary, since the present invention changes the composition and the relative proportion of the glass medium of the conductive paste, and adjusts the weight percentage of cerium oxide to be between 0.1 wt.% and 10 wt.%, so that the front conductive electrode The pattern can stabilize non-diffusion deformation, and the front conductive electrode and the solar cell substrate have lower contact resistance, thereby improving the process yield and photoelectric conversion efficiency of the solar cell.

10‧‧‧Solar cell substrate
11‧‧‧p-type semiconductor substrate
12‧‧‧n type semiconductor layer
20‧‧‧Anti-reflective layer
30‧‧‧Pre-conductive paste layer
31‧‧‧ Front conductive electrode
40‧‧‧After conductive paste layer
41‧‧‧After conductive electrode

1 is a schematic structural view of a solar cell according to the present invention. FIG. 2A to FIG. 2D are schematic diagrams showing a process of applying the solar cell to the present invention.

10‧‧‧Solar cell substrate

11‧‧‧p-type semiconductor substrate

12‧‧‧n type semiconductor layer

20‧‧‧Anti-reflective layer

30‧‧‧Pre-conductive paste layer

40‧‧‧After conductive paste layer

Claims (6)

An electroconductive paste for a solar cell process, comprising: an organic carrier; a conductive material dispersed in the organic carrier; and a glass medium dispersed in the organic carrier, the glass medium comprising 0.1 wt% by weight Between .% and 10 wt.% of ceria, between 0.1 wt.% and 23 wt.% of lead oxide, and between 20 wt.% and 80 wt.% Cerium oxide, cerium oxide having a weight percentage between 5 wt.% and 35 wt.%, and zinc oxide having a weight percentage between 0.1 wt.% and 20 wt.%. The conductive paste for solar cell process according to claim 1, wherein the material of the organic carrier is selected from the group consisting of ethyl cellulose, polyacrylic acid, polyvinyl butyral, polyvinyl alcohol, and polyolefin. a group consisting of carboxylic acid, oleic acid, tallow diamine dioleate, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, ester alcohol, dimethyl nylon hydride and terpineol. The conductive paste for solar cell process according to claim 1, wherein the conductive material is selected from the group consisting of silver, silver oxide, silver salt, copper, palladium and aluminum. The conductive paste for solar cell process according to claim 1, wherein the organic carrier has a weight percentage of between 5 wt.% and 20 wt.%. The conductive paste for solar cell process according to claim 1, wherein the conductive material has a weight percentage of between 80 wt.% and 95 wt.%. The conductive paste for solar cell process according to claim 1, wherein the glass medium has a weight percentage of between 0.1 wt.% and 10 wt.%.