TWI596073B - Conductive paste for solar cell manufacturing - Google Patents

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 bonding a p-type semiconductor and an n-type semiconductor to form a solar cell substrate, and a pn 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 addition, a conventional solar cell contains a lead component, such as the solar cell structure disclosed in US Pat. No. 2011/0120548, which includes: a substrate having a front surface, a back surface, and a hole penetrating the substrate; a first electrode, at least filling the hole from the back surface of the substrate; and a second electrode disposed on the front surface of the substrate and located on the first electrode, wherein the lead oxide of the silver paste of the first electrode is formed The content is substantially 20% by weight or less of the vitreous material, and the silver oxide forming the second electrode has a lead oxide content of substantially more than 20% by weight of its vitreous. Or a thick film paste composition for making a solar cell, comprising: a) based on the total solids in the composition, 85-, as disclosed in U.S. Patent No. 8,497,420. 99.5% by weight of a conductive metal or a derivative thereof; b) 0.5 to 15% by weight, based on the solids, of lead-niobium-lithium-titanium oxide; and c) an organic medium.

However, lead is a kind of cumulative and toxic metal. It is easy to produce lead-containing waste gas and waste water in the process of manufacturing solar cells and in the process of disposing of waste solar cells. If it is not treated with care, it will be discharged, in addition to polluting the environment and directly poisoning natural organisms. In addition, the human body may also ingest lead by air pollution or eat contaminated food (such as fish contaminated with lead-containing wastewater). Lead is not easily metabolized and degraded, it can damage the child's nervous system and cause diseases in the blood circulation system and brain. Long-term exposure to lead and its salts (especially soluble and strongly oxidizing PbO ₂ ) can cause kidney disease and abdominal pain similar to colic and increase the risk of carcinogenesis and mutation. Moreover, it is difficult to automatically remove lead after it is accumulated in the human body. It can only be removed by certain drugs, and it will cause considerable harm to the human body after long-term accumulation. Therefore, the manufacturing materials used in conventional solar cells need to be improved and adjusted to avoid environmental pollution and direct or indirect harm to the human body.

The main object of the present invention is to solve the problem that the material used in the manufacture of solar cells contains lead, which causes environmental pollution and harm to the human body.

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 20 wt.%, cerium oxide in a weight percentage between 20 wt.% and 80 wt.%, and a weight percentage between 5 wt.% and 40 Lithium oxide between wt.%, lithium oxide in a weight percentage between 0.1 wt.% and 5 wt.%, and zinc oxide in a weight percentage between 0.1 wt.% and 20 wt.%.

It can be seen from the above that the conductive paste for the solar cell process of the present invention replaces the conventional lead-containing material by zinc oxide, and changes the composition and proportion of the glass medium, so that the conductive paste can be free of lead. Maintaining the efficiency of the solar cell when using the conductive paste to form a conductive electrode, and further avoiding environmental pollution.

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 is selected from the group consisting of ethyl cellulose (Ethyl cellulose), polyacrylic acid (Polyvinylic acid), polyvinyl butyral (Polyvinyl butyral), polyvinyl alcohol (Polyvinyl alcohol), polyolefin (Polyolefin), and poly 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 and its derivatives And the weight percentage of the organic carrier is between 4.9 wt.% and 19.9 wt.%.

In the present invention, the weight percentage of the glass medium in the conductive paste is between 0.1 wt.% and 10 wt.%, and includes two parts by weight between 0.1 wt.% and 20 wt.%. Cerium oxide, cerium oxide having a weight percentage between 20 wt.% and 80 wt.%, antimony trioxide having a weight percentage between 5 wt.% and 40 wt.%, and a weight percentage of 0.1 wt. Lithium oxide between % and 5 wt.% and zinc oxide between 0.1 wt.% and 20 wt.% by weight. Cerium dioxide is a typical glass former (Glass former), often used as the main body of glass networks. While cerium oxide, antimony trioxide and zinc oxide are glass intermediates, a glass network can be formed under certain conditions, such as the presence of a glass former or a high self-content. In the silver paste application on the front side of the solar cell, zinc oxide in the glass is used as an anti-reflection coating etchant, but under high temperature sintering conditions, excessive zinc oxide tends to cause an increase in ohmic contact resistance, and zinc oxide etching Excessive can even cause a short circuit in the battery. Therefore, in the present invention, the glass softening point and viscosity are controlled by using the content ratio of cerium oxide, cerium oxide and zinc oxide to optimize the contact resistance and line width of the final product to achieve the purpose of improving the efficiency of the battery. The addition of cerium oxide can also greatly improve the dissolution and re-precipitation behavior of the silver powder on the contact interface, thereby reducing the contact 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 front conductive electrode 31 is formed by bonding to each other; and the rear conductive paste layer 40 is formed into 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 0.1 wt.% and 20 wt.%, the front conductive electrode 31 and the n-type semiconductor layer are formed. The contact resistance between 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. The 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, the zinc oxide is replaced by a zinc oxide having a weight percentage of between 0.1 wt.% and 20 wt.% (for example, two Lead oxide) and regulating the weight percentage of cerium oxide between 0.1 wt.% and 20 wt.%, so that the pattern of the front conductive electrode can be stably non-diffused, and the front conductive electrode is compared with the solar cell substrate The low contact resistance, in turn, maintains the process yield and photoelectric conversion efficiency of the solar cell without lead. Therefore, the present invention is highly advanced and meets the requirements for applying for a patent for invention, and is submitted according to law, and the praying office is an early one. Granting a patent, it is really sensible.

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

FIG. 1 is a schematic view showing the structure of a solar cell according to the present invention. 2A-2D are schematic views showing the manufacturing steps of the present invention applied to a 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

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 20 wt.% of cerium oxide, between 20 wt.% and 80 wt.% of cerium oxide, and between 5 wt.% and 40 wt.% by weight Antimony trioxide, lithium oxide having a weight percentage between 0.1 wt.% and 5 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. , polyamine, carboxylic acid, oleic acid, tallow diamine dioleate, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, ester alcohol, dimethyl dimethyl ester and terpineol Group. 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 4.9 wt.% and 19.9 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.%.