TWI541833B - Conductive aluminum adhesives for use in local backlash solar cells and solar cells using the conductive aluminum - Google Patents

Description

Conductive aluminum glue for partial back field solar cell and solar cell using the same

The present invention relates to a conductive aluminum paste, and more particularly to a conductive aluminum paste containing vanadium oxide. The invention also relates to a solar cell using the conductive aluminum paste.

Solar cells are a kind of device that converts sunlight into DC power output. Among them, silicon-based solar cells are the mainstream of solar power generation (accounting for more than 80% of the industry). Most of the existing products in the industry use P-type germanium substrates as the base. The light-receiving surface forms a n ⁺ emitter by a high-temperature phosphorus diffusion to form a PN junction diode; then a 60-80 nm anti-reflection layer is formed on the n ⁺ surface; and then the anti-reflection layer is printed on the screen 30~ 90μm elongated grid-shaped silver electrode and front busbar (busbar); the other side (p-face) is also printed with a backside bus electrode, followed by aluminum glue as an aluminum source, the purpose of which is to form aluminum with bismuth base in high temperature environment The tantalum alloy and the back surface field (BSF) layer avoid the chance of a few carriers recombining on the back side.

In order to improve the efficiency of the solar cell, the technology of local back surface field (LBSF) has been gradually introduced since 2013. Another name of this technology is the emitter passivation and the back electrode (Passivated Emitter and Rear Contact (PERC) is a method of coating at least two or more oxide layers (one bottom oxide layer/one top oxide layer) by using a plating method, wherein the bottom oxide layer is used to repair defects on the surface of the germanium wafer; The cap layer protects the bottom oxide layer from being destroyed by the aluminum paste. Increase optical reflection. After the two layers of oxide coating are completed, it is common to use laser or acid etching to form openings (30~40μm parallel line openings or 200μm diameter dot openings), and printed with aluminum glue into a rapid high temperature sintering furnace for co-firing. In this way, the aluminum glue only forms a partial back surface field at the opening, so it is called the partial back surface field (LBSF) technology.

One of the main technical problems faced by LBSF technology is that the conventional aluminum glue is too corrosive to the two oxide layers on the bottom layer, resulting in a weakening or disappearing ability of the bottom oxide layer to repair defects. If the corrosion of the aluminum glue is to be alleviated, the adhesion of the aluminum glue to the top oxide layer is also reduced.

In order to solve this problem, the general aluminum glue industry is to design a low-corrosion aluminum glue. For example, the patent document CN 103545013, US 2011120535 A1, US 2013183795 A1 uses high lead content glass powder, and utilizes lead oxide (PbO). ) It is easy to melt and react easily, and strengthens the adhesion between aluminum glue and top oxide layer.

However, the conventional aluminum glue is already a lead-free system, and the above-mentioned aluminum glue for LBSF uses a high-lead glass powder, which is contrary to the current environmental protection trend and safety standards. Therefore, how to develop a conductive aluminum paste that can be used for LBSF can maintain the same photoelectric conversion efficiency and pulling force while reducing the amount of lead oxide, which is the technical focus of all LBSF researchers.

In order to solve the above-mentioned shortcomings of the prior art, the present invention provides a conductive aluminum paste for a partial back surface field (LBSF) solar cell and a solar cell using the same. In order to improve the conductive aluminum paste which is conventionally used for the partial back field solar cell, it is necessary to use a high lead content glass powder to improve the photoelectric conversion efficiency and the pulling force of the solar cell.

To achieve the above and other objects, the present invention provides a conductive aluminum paste for a partial back surface field solar cell comprising: aluminum powder; an organic vehicle comprising a resin and a solvent; and vanadium oxide.

The conductive aluminum paste described above may be directly added with vanadium oxide, and the vanadium oxide is added in an amount not higher than 1.5% of the total weight of the conductive aluminum paste.

The above conductive aluminum paste, wherein the conductive aluminum paste comprises vanadium oxide by adding a vanadium oxide-containing glass powder.

The conductive aluminum paste described above, wherein the content of vanadium oxide in the glass frit is not more than 75%.

The conductive aluminum paste described above, wherein the content of the glass powder is not more than 10% of the total weight of the conductive aluminum paste.

The conductive aluminum paste described above, wherein the content of the glass powder is not more than 3% of the total weight of the conductive aluminum paste.

The conductive aluminum paste mentioned above, wherein the content of the aluminum powder is preferably 65 to 75% of the total weight of the conductive aluminum adhesive.

The conductive aluminum paste, wherein the aluminum powder preferably comprises: a small aluminum powder having a particle size of less than 3 μm; and a large aluminum powder having a particle size of 3 to 8 μm, wherein the content of the small aluminum powder It is not higher than 30% of the total weight of the conductive aluminum paste.

The conductive aluminum paste mentioned above, wherein the content of the small aluminum powder is preferably 5 to 25% of the total weight of the conductive aluminum adhesive.

The above conductive aluminum paste, wherein the organic carrier preferably accounts for 10 to 30% of the total weight of the conductive aluminum paste.

The conductive aluminum paste described above, wherein the organic carrier preferably accounts for 20-28% of the total weight of the conductive aluminum paste.

The above conductive aluminum paste, wherein the organic vehicle comprises: a resin selected from the group consisting of ethyl cellulose, wood rosin and polyacrylonitrile; and a solvent.

The conductive aluminum paste described above may further comprise: an additive selected from the group consisting of a dispersant, a leveling agent, a defoaming agent, an anti-settling agent, a thixotropic agent, and a coupling agent.

To achieve the above and other objects, the present invention also provides a solar cell comprising the above-described conductive aluminum paste.

The conductive aluminum glue for the partial back surface field solar cell and the solar cell using the conductive aluminum glue can improve the photoelectric conversion efficiency and the tensile force of the partial back surface field solar cell under the condition that the lead content is completely eliminated or reduced.

In order to fully understand the object, features and effects of the present invention, the present invention will be described in detail by the following specific embodiments, which are illustrated as follows: The conductive aluminum paste provided by the present invention generally comprises aluminum powder and organic carrier. And vanadium oxide, and may further comprise glass powder and various additives.

The aluminum powder may account for 65 to 80%, preferably 70 to 76%, of the total weight of the conductive aluminum rubber.

The aluminum powder is preferably composed of two or more kinds of particles, and can be roughly divided into two types: small aluminum powder and large aluminum powder. If the small aluminum powder has a particle size of less than 3 μm, the large aluminum powder has a particle size of 3 to 8 μm. The aluminum powder accounts for no more than 30% by weight of the conductive aluminum rubber, and preferably 5 to 25 wt%.

Vanadium oxide (V ₂ O ₅ ) is used to improve the adhesion of the conductive aluminum paste of the present invention to the substrate and to control the reaction characteristics of the conductive aluminum paste. Vanadium oxide can be directly added to the conductive aluminum paste of the present invention in the form of an oxide, used in combination with other lead-free glass powder, or with leaded glass powder to reduce the amount of lead-containing glass powder. The conductive aluminum paste of the present invention may further comprise vanadium oxide by adding a vanadium oxide-containing glass powder, and the glass frit may be obtained by melting a plurality of elements or compounds at a high temperature, the glass powder containing at least vanadium oxide, and the glass The content of vanadium oxide in the powder is preferably not more than 75 wt%. For example, vanadium oxide, zinc oxide, phosphorus oxide and cerium oxide can be melted at a high temperature to obtain a V ₂ O ₅ -ZnO-P ₂ O ₅ -Sb ₂ O ₃ glass powder containing vanadium oxide. The average particle diameter of the glass frit is less than 6.0 μm, and the content is 0 to 10% by weight based on the total weight of the conductive paste, and is preferably not more than 3% by weight.

Organic carriers are used to provide screen printing and drying strength. It is prepared by mixing at least one kind of resin with at least one organic solvent, and the resin may be ethyl cellulose, wood rosin or polyacrylonitrile, but not limited thereto; the solvent may be an ester alcohol film forming agent (TEXANOL®, EASTMAN CHEMICAL COMPANY), terpineol or diethylene glycol butyl ether, etc., but not limited thereto; the organic carrier accounts for 10 to 30% by weight of the total weight of the conductive aluminum rubber, preferably 20 to 28% by weight.

Additives are used to enhance the stability, printability, flatness, reactivity and powder adhesion of aluminum adhesives. Dispersants, leveling agents, defoamers, anti-settling agents, thixotropic agents, coupling agents can be selected. Etc., but not limited thereto, the additive totals 0 to 5 wt% of the total weight of the conductive aluminum paste, preferably 0 to 1.3 wt%.

The conductive aluminum adhesives of Examples 1 to 4 and Comparative Examples 1 to 4 of the present invention are prepared according to the formulations and percentages shown in Tables 1 and 2 below, wherein the group of Table 1 is not directly added with vanadium oxide, and the embodiment 1 is The conductive aluminum paste contains vanadium oxide by adding vanadium oxide-containing glass powder, and the vanadium oxide is directly added to the conductive aluminum rubber in the group of the second group:

Example 1

The conductive aluminum paste of Example 1 was prepared by the following steps:

Step 1 (manufacturing of organic carrier): Ethyl cellulose (ETHOCEL Std 20) / terpineol / diethylene glycol butyl ether was added to the reaction tank at a ratio of 15:20:65, and the oil bath at 110 ° C was 300 rpm. Stir for more than 3 hours until completely dissolved.

Step 2: According to the formula and percentage shown in Table 1, the vanadium oxide-containing glass powder, aluminum powder and other formulations are added to the organic carrier prepared in the first step to prepare 300 g of mixed aluminum rubber.

Step 3: Mix the aluminum rubber prepared in the second step with a high-speed mixer for 3 minutes, mix it thoroughly, and grind it three times with a three-roll mill (factory model: Exakt 80E) to obtain a viscosity of 30 to 50 Pa. s, a conductive aluminum paste having an average particle diameter of 6 μm.

Examples 2 to 4 and Comparative Examples 1 to 4

The conductive aluminum pastes of Examples 2 to 4 and Comparative Examples 1 to 4 were prepared by the same procedures as in Example 1, but in the second step, the formulations and percentages were changed according to Table 1 or Table 2, respectively.

Test case

Using the conductive aluminum paste prepared in the above Examples 1 to 4 and Comparative Examples 1 to 4, a solar cell was prepared in accordance with the following procedure:

Step 1 (printing): The backside silver paste and the front silver paste are separately printed on the LBSF semi-finished product (front side SiN _x , back side 6 nm Al ₂ O ₃ bottom oxide layer + 80 nm SiN _x top oxide layer) by screen printing. After drying in an oven at 200 ° C with the front side, the conductive aluminum paste prepared in Examples 1 to 4 and Comparative Examples 1 to 4, the conductive aluminum paste and the back silver paste were printed on the back side of the back surface of the tantalum substrate. There must be some overlap. The printing parameters and the screen mesh number were adjusted to control the printing weight to 1.1 g, and the oven was dried in a 200 ° C oven for 3 minutes to obtain a printed enamel substrate to be sintered.

Step 2 (Sintering): After the drying step is completed, the printing ruthenium substrate prepared in the first step is placed in a Despatch CF furnace for sintering to obtain a solar cell. In the sintering step, the relevant parameters are set to Z1/Z2/Z3/Z4/Z5/Z6/speed=500°C/550°C/600°C/680°C/830°C/930°C/230ipm, and the infrared rapid sintering furnace is used The conveyor belt conveys the printing enamel substrate to be sintered, and the printing enamel substrate to be sintered passes through different temperature zones such as Z1 to Z6, and the conveying speed of the conveyor belt is 230 ipm (inch/min).

According to the above steps, solar cells were fabricated using the conductive aluminum pastes of Examples 1 to 4 and Comparative Examples 1 to 4, respectively, and tested under the following properties:

Photoelectric conversion efficiency measurement: Using solar cell simulation test system, testing solar cell photoelectric conversion efficiency (%), open circuit voltage (Voc (mv)) and fill factor (FF (%)), test machine model is Finland Endeas The company produces the QuickSun 120CA.

Pulling force: The EVA film is cut into 1×10cm strips, and the EVA film is placed on the back side of the solar cell, and hot pressed three times through a laminator at 150° C., so that the EVA film is hot pressed on the back surface of the solar cell, and the tensile force is measured. The maximum tensile force between the EVA film and the solar cell is measured, and below 10N (Newton) is NG.

Water resistance: After adding 500 cc of deionized water to the beaker, it was placed on a hot plate and heated to a water temperature of 75 ° C. The solar cell was placed flat on the bottom, and continuous foaming was NG within 10 minutes.

Warpage: After cooling, the solar cell was cooled for 1 hour, and the thickness was measured using a thickness gauge. When it was over 1.8 mm, it was NG.

Aluminum convex: The surface of the solar cell after sintering has a orange peel-like convex surface, that is, NG.

The test results of the above properties are summarized in Tables 3 and 4 below, and the test results are poorly marked in bold:

From the test results of Table 3, it can be understood that Example 1 and Comparative Example 3 using the vanadium oxide-containing glass frit have photoelectric conversion efficiency (%), open circuit voltage (Voc (mv)), and filling factor (FF (%)). In terms of characteristics, it is comparable to or slightly better than Comparative Example 1 and Comparative Example 2 using lead-containing glass frit; Comparative Example 1 and Comparative Example 2 are superior to Comparative Example 1 in tensile properties. And Comparative Example 2 shows that the use of the vanadium oxide-containing glass frit can provide the solar cell with better tensile properties. Further, in comparison with the formulation ratios and test results of Example 1 and Comparative Example 3, it can be understood that Comparative Example 3 uses a glass powder containing 80% of vanadium oxide, resulting in warpage and aluminum protrusion. In contrast, Example 1 is Use 55% vanadium oxide glass Powder, no warping and aluminum convex phenomenon. Therefore, in the case where the conductive aluminum paste of the present invention contains vanadium oxide by adding a vanadium oxide-containing glass frit, the content of vanadium oxide in the glass frit is preferably not more than 75 wt%.

Furthermore, it can be understood from the test results in Table 4 that in the case where 0.9 to 1.5% of vanadium oxide is directly added (Examples 2 to 4), cerium oxide-containing (Example 2) and vanadium oxide are further added (Examples) 3) Or the glass powder containing lead oxide (Example 4), the solar cell obtained can have good photoelectric properties, tensile strength and water resistance, and no warpage and aluminum convexity appear. Further comparing the formulation ratios and test results of Example 2 and Comparative Example 4, it can be understood that Comparative Example 4 directly added 2.0% of vanadium oxide, resulting in warpage and aluminum protrusion. In contrast, Example 2 was directly added. 0.9% of vanadium oxide, no warping and aluminum convex phenomenon. Therefore, in the case of directly adding vanadium oxide, the amount of vanadium oxide added is preferably not more than 1.5% of the total weight of the conductive aluminum paste.

The invention has been described above in terms of the preferred embodiments, and it should be understood by those skilled in the art that the present invention is not intended to limit the scope of the invention. It should be noted that variations and permutations equivalent to those of the embodiments are intended to be included within the scope of the present invention. Therefore, the scope of protection of the present invention is defined by the scope of the patent application.

Claims (2)

A conductive aluminum adhesive for a partial back surface field solar cell, comprising: aluminum powder, which accounts for 65 to 75 wt% of the total weight of the conductive aluminum rubber, wherein the aluminum powder comprises: small aluminum powder, the particle size thereof Less than 3 μm; and a large aluminum powder having a particle size of 3 to 8 μm; and an organic carrier, which accounts for 10 to 30% by weight of the total weight of the conductive aluminum rubber, wherein the organic carrier is in a ratio of 15:20:65 Ethyl cellulose / terpineol / diethylene glycol butyl ether; containing vanadium oxide glass powder, which accounts for 2.40% by weight of the total weight of the conductive aluminum rubber, wherein the content of vanadium oxide in the vanadium oxide containing glass powder is It is 55 wt%; and an auxiliary agent which accounts for 0.20 wt% of the total weight of the conductive aluminum paste. The conductive aluminum paste according to claim 1, wherein the small aluminum powder is not more than 30% by weight based on the total weight of the conductive aluminum paste.