Alloy aluminum paste for use on rear of PERC solar cell

1. Preparation of Lead-Free Glass Powder

Preparation of glass powder A: Based on 100 wt % of the glass powder A, 20% of ZnO, 20% of B 2 O 3 , 35% of Sb 2 O 3 , 5% of BaCl 2 , 10% of Na 2 CO 3 and 10% of Rb 2 O 2 were prepared. In this example, BaCl 2 was adopted, although metal compounds of the other halogen elements were also possible by adjusting their ratios. The materials were then well mixed using a known mixer such as a disperser or a three-roll mill, and dried for 3.5 h before being transferred into a crucible. The crucible containing the starting materials was first heated to 950° C. in a heating chamber, and then incubated for 1.5 h. The resultant liquid of the smelted materials was allowed to pass through a cooling roller to give a glass frit, which was then crushed and sieved to give the glass powder A having a median particle size D 50 of 1.36 μm and a softening temperature of 544.7° C.

Preparation of glass powder B: Based on 100 wt % of the glass powder B, 30% of V 2 O 5 , 15% of ZnO, 22% of B 2 O 3 , 10% of P 2 O 5 , 10% of WO 3 , 5% of BaCO 3 and 8% of CaO were prepared. The materials were then well mixed using a known mixer such as a disperser or a three-roll mill, and dried for 3 h before being transferred into a crucible. The crucible containing the starting materials was first heated to 1000° C. in a heating chamber, and then incubated for 1 h. The resultant liquid of the smelted materials was allowed to pass through a cooling roller to give a glass frit, which was then crushed and sieved to give the glass powder B having a median particle size D 50 of 1.33 μm and a softening temperature of 405° C.

2. Preparation of Alloy Paste

Based on 100 wt % of the alloy aluminum paste, the alloy aluminum paste of the present invention was prepared from the following components in percentages by weight:

wherein the aluminum-silicon alloy has a median particle size D 50 of 5.5 μm and an oxygen content of 0.35 wt %; the aluminum powder has a median particle size D 50 of 7.5 μm and an oxygen content of 0.4 wt %; the organic solvent ethylene glycol butyl ether has a boiling point of 227° C. The above prepared materials were mixed according to the ratios, and then ground and dispersed such that the fineness of the prepared paste did not exceed 15 μm.

1. Preparation of Lead-Free Glass Powder

Preparation of glass powder A: Based on 100 wt % of the glass powder A, 40% of ZnO, 5% of B 2 O 3 , 30% of Sb 2 O 3 , 5% of SrCl, 10% of Cs 2 CO 3 and 10% of BaO were prepared. In this example, SrCl was adopted, although metal compounds of the other halogen elements were also possible by adjusting their ratios. The materials were then well mixed using a known mixer such as a disperser or a three-roll mill, and dried for 3 h before being transferred into a crucible. The crucible containing the starting materials was first heated to 850° C. in a heating chamber, and then incubated for 2 h. The resultant liquid of the smelted materials was allowed to pass through a cooling roller to give a glass frit, which was then crushed and sieved to give the glass powder A having a median particle size D 50 of 1.89 μm and a softening temperature of 570° C.

Preparation of glass powder B: Based on 100 wt % of the glass powder B, 50% of V 2 O 5 , 5% of ZnO, 5% of B 2 O 3 , 5% of P 2 (CO 3 ) 5 , 5% of WO 3 , 15% of Sr 2 CO 3 and 15% of CaI 2 were prepared. In this example, CaI 2 was adopted, although metal compounds of the other halogen elements were also possible by adjusting their ratios. The materials were then well mixed using a known mixer such as a disperser or a three-roll mill, and dried for 3 h before being transferred into a crucible. The crucible containing the starting materials was first heated to 1000° C. in a heating chamber, and then incubated for 1 h. The resultant liquid of the smelted materials was allowed to pass through a cooling roller to give a glass frit, which was then crushed and sieved to give the glass powder B having a median particle size D 50 of 1.64 μm and a softening temperature of 426° C.

2. Preparation of Alloy Paste

Based on 100 wt % of the alloy aluminum paste, the alloy aluminum paste of the present invention was prepared from the following components in percentages by weight:

wherein the aluminum-silicon alloy has a median particle size D 50 of 6 μm and an oxygen content of 0.4 wt %; the aluminum powder has a median particle size D 50 of 8 μm and an oxygen content of 0.3 wt %; the boiling points of the organic solvents butyl carbitol and texanol are 231° C. and 255° C., respectively. The above prepared materials were mixed according to the ratios, and then ground and dispersed such that the fineness of the prepared paste did not exceed 15 μm.

1. Preparation of Lead-Free Glass Powder

Preparation of glass powder A: Based on 100 wt % of the glass powder A, 10% of ZnO, 30% of B 2 O 3 , 30% of Sb 2 O 3 , 10% of CaCl 2 , 10% of K 2 CO 3 and 10% of Cs 2 O were prepared. In this example, CaCl 2 was adopted, although metal compounds of the other halogen elements were also possible by adjusting their ratios. The materials were then well mixed using a known mixer such as a disperser or a three-roll mill, and dried for 4 h before being transferred into a crucible. The crucible containing the starting materials was heated to 1050° C. in a heating chamber, and incubated for 2 h. The resultant liquid of the smelted materials was allowed to pass through a cooling roller to give a glass frit, which was then crushed and sieved to give the glass powder A having a median particle size D 50 of 2.17 μm and a softening temperature of 530.6° C.

Preparation of glass powder B: Based on 100 wt % of the glass powder B, 10% of V 2 O 5 , 40% of ZnO, 20% of B 2 O 3 , 5% of P 2 (CO 3 ) 5 , 10% of MoO 3 , 5% of CaCO 3 and 10% of Sr 2 O were prepared. The materials were then well mixed using a known mixer such as a disperser or a three-roll mill, and dried for 3 h before being transferred into a crucible. The crucible containing the starting materials was first heated to 1000° C. in a heating chamber, and then incubated for 1 h. The resultant liquid of the smelted materials was allowed to pass through a cooling roller to give a glass frit, which was then crushed and sieved to give the glass powder B having a median particle size D 50 of 1.45 μm and a softening temperature of 435° C.

2. Preparation of Alloy Paste

Based on 100 wt % of the alloy aluminum paste, the alloy aluminum paste of the present invention was prepared from the following components in percentages by weight:

wherein the aluminum-silicon alloy has a median particle size D 50 of 5 μm and an oxygen content of 0.3 wt %; the aluminum powder has a median particle size D 50 of 7 μm and an oxygen content of 0.35 wt %; the boiling points of the organic solvents ethylene glycol butyl ether and turpentine are 227° C. and 173-175° C., respectively. The above prepared materials were mixed according to the ratios, and then ground and dispersed such that the fineness of the prepared paste did not exceed 15 μm.

Comparative Example 1

1. Preparation of Glass Powder

In part by mass, 15 parts of B 2 O 3 , 3 parts of SiO 2 , 15 parts of Bi 2 O 3 , 60 parts of PbO and 7 parts of ZnO were prepared and well mixed in a mixer before being transferred to a porcelain crucible, followed by an incubation at 900° C. for 1 h in a muffle furnace. The melted glass powder particles were quenched with ionized water, ball-milled for 2.5 h, and sieved with a 200-mesh sieve to give a glass powder having a particle size D 90 of less than 2 μm.

2. Preparation of Cell Back Surface Field Aluminum Paste

The aluminum was a commercially available aluminum powder having a purity of 99.9% and an average particle size of 1.0-2.5 μm. In part by mass, 75 parts of the aluminum powder, 7 parts of the glass powder, 15 parts of an organic binder and 3 parts of an auxiliary agent were prepared, followed by the procedures as described in the examples.

Comparative Example 2

1. Preparation of Glass Powder

In part by mass, 17 parts of B 2 O 3 , 1 parts of SiO 2 , 13 parts of Bi 2 O 3 , 65 parts of PbO and 4 parts of ZnO were prepared and well mixed in a mixer before being transferred to a porcelain crucible, followed by an incubation at 900° C. for 1 h in a muffle furnace. The melted glass powder particles were quenched with ionized water, ball-milled for 2.5 h, and sieved with a 200-mesh sieve to give a glass powder having a particle size D 90 of less than 2 μm.

2. Preparation of Cell Back Surface Field Aluminum Paste

The aluminum powder was a commercially available aluminum powder having a purity of 99.9% and an average particle size of 1.0-2.5 μm. In part by mass, 70 parts of the aluminum powder, 10 parts of the glass powder, 17 parts of an organic binder and 3 parts of an auxiliary agent were prepared, followed by the procedures as described in examples.

The performance analysis of the present invention is as follows:

The conductive pastes prepared in Examples 1 to 3 and the Comparative Examples 1 and 2 were printed by screen printing through a 250-mesh screen on a rear passivation surface of a monocrystalline silicon wafer of a PERC cell having a size of 125 mm×125 mm and a total area of passivation coating opening consisting of 0.5-1% of the area of the solar cell so as to form an electrode coating, followed by drying at 220° C. in a muffle furnace. After the drying, the aluminum electrode coating didn't not fall off. On the other side was then printed with a front silver paste, followed by sintering in a muffle furnace, with the peak temperature being 780° C. After the sintering, the electric properties were tested and the results are shown in Table 1.

As shown in the table above, the photoelectric conversion efficiency of the alloy paste for a PERC solar cell prepared according to the present invention was 22.26-22.42%, which was significantly improved compared to that in Comparative Example. The alloy paste disclosed herein is suitable for the PERC solar cell having a low opening rate, particularly a rear electrode having a total area of passivation coating opening consisting of 0.5-1% of the area of the solar cell. The alloy paste has advantages of good gap filling rate, complete and uniform BSF layer, reduced aluminum beads, and good boiling and adhesive performance.

Finally, it should be noted that the above examples are only for illustrating the technical schemes of the present invention but not for limiting the protection scope of the present invention. Although the present invention is described in detail with reference to the preferred schemes, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical schemes of the present invention without departing from the spirit and scope of the technical schemes of the present invention.