Low LOI tellurium-lithium-silicon-zirconium frit system and conductive paste and application thereof

Abstract

The present disclosure discloses a low LOI tellurium-lithium-silicon-zirconium frit system and a conductive paste and application thereof, and belongs to the field of conductive paste. In the low LOI tellurium-lithium-silicon-zirconium frit system, components of the frit are 24%-40% TeO.sub.2, 18%-24% Li.sub.2O, 4%-13% SiO.sub.2, 0-2% ZrO.sub.2, and a balance MO.sub.x, and M is one or a mixture of Na, K, Mg, Ca, Sr, Ti, V, Cr, Mo, W, Mn, Cu, Ag, Zn, Cd, B, Al, Ga, Tl, Ge, Pb, P, and Bi. There is no need to add additional surfactants, a viscosity change of the conductive paste prepared after standing for 30 days is less than 20%, the conductive paste has good stability, the water related weight loss of inorganic oxide of the conductive paste is less than 1.6%, and the application performance of the conductive paste is not affected after standing for 30 days.

Claims

1. A mixture comprising, in mol % 40% TeO.sub.2, 20% Li.sub.2O, 12% SiO.sub.2, 2% ZrO.sub.2, and 26% MO.sub.x, where MO.sub.x is one or a mixture of Na.sub.2O, K.sub.2O, MgO, CaO, SrO, TiO.sub.2, V.sub.2O.sub.5, Cr.sub.2O.sub.3, MoO.sub.3, WO.sub.3, MnO, CuO, Ag.sub.2O, ZnO, CdO, B.sub.2O.sub.3, Al.sub.2O.sub.3, Ga.sub.2O.sub.3, Tl.sub.2O.sub.3, GeO.sub.2, PbO, P.sub.2O.sub.5, and Bi.sub.2O.sub.3.

2. The mixture where MO.sub.x is, in mol % 15% PbO 5% Bi.sub.2O.sub.3, 2% MgO, and 4% CaO.

3. A mixture comprising, in mol %, 40% TeO.sub.2, 20% Li.sub.2O, 12% SiO.sub.2, 5% ZrO.sub.2, 14% PbO, 3% Bi.sub.2O.sub.3, 2% MgO, 4% CaO.

Description

DETAILED DESCRIPTION

(1) The present disclosure will be further described below with reference to examples, but embodiments of the present disclosure are not limited thereto.

(2) In order to improve viscosity stability of a conductive paste during storage and transportation, in the present disclosure, it has been found that viscosity of the conductive paste is unstable after the conductive paste is prepared using an inorganic oxide raw material having a large amount of hydrates, hydroxyl groups (—OH) or other forms of H.sub.2O on the surface thereof, and the viscosity of the conductive paste changes greatly with a change of storage time, ambient temperature and humidity. Therefore, it is needed to reduce the hydrates, hydroxyl groups, and other forms of water on the surface of the inorganic oxide. Specific test methods are as follows.

(3) A water vapor weight loss of the inorganic oxide is tested by using TGA-IR equipment. A sample is placed in the TGA-IR equipment and heated from room temperature to 500° C. under a nitrogen environment. TGA is used to test a weight change of the sample, IR is used to test an infrared spectrum of excluded gas, and it is determined that the weight change of the sample is due to water vapor generated by evaporation, decomposition or reaction on a surface of the sample. The water vapor weight loss needs to be controlled within 1.6%.

(4) An experimental method is as follows:

(5) (1) Inorganic oxide: metal oxides are mixed in a certain ratio, a mixed composition is melted at about 900-1300° C. and then quenched to about 25° C., and then an obtained material is pulverized using a planetary mill and dried, thereby obtaining uniform inorganic oxide powder (frit).

(6) (2) Conductive paste: an organic vehicle such as an organic binder, an organic auxiliary, and an organic solvent is mixed and stirred at 50-60° C. with a high shearing force for 1-2 hours. The inorganic oxide powder obtained in step (1) and silver powder are added into the above-mentioned mixture, sufficient stirring is performed to form a mixture, repeated rolling is carried on the paste composition with a three-roll mill, and the conductive paste is formed by milling.

(7) (3) Viscosity testing: a viscosity value of the conductive paste is measured using a Brookfield DV1 viscosity tester and a rotor SC-14 at 25° C.

(8) (4) Photoelectric conversion efficiency testing: the conductive paste is printed onto a silicon wafer substrate by a screen-printing technique. Cell sheets are dried in an infrared drying oven and then sintered at 750-850° C. in a belt type firing furnace. Cooling is performed after sintering, and cells are formed. The photoelectric conversion efficiency of the cells is tested with an IV tester.

Example 1

(9) Different metal oxides were mixed in a certain ratio according to a formula of Table 1, a mixed composition was melted at about 900-1300° C. and then quenched to about 25° C., and then an obtained material was pulverized using a planetary mill and dried to obtain uniform inorganic oxide powder. Then, ethyl cellulose and polyvinyl butyral (a mass ratio of the two was 7:3) as an organic binder in an amount of 0.6% (mass percentage, the same below), polyamide as a thixotropic agent in an amount of 0.4%, organic silicone oil in an amount of 0.5%, tallow diamine dioleate as a surfactant in an amount of 0.3%, and butyl carbitol acetate and dimethyl adipate (a mass ratio of the two was 5:5) as an organic solvent in an amount of 6.4% were mixed, and stirred at 50-60° C. under a high shearing force for 1.5 hours. The inorganic oxide powder in an amount of 2.4% and silver powder in an amount of 89.4% were added to the above mixture, and a mixture was formed after sufficient stirring. The paste composition was repeatedly milled with a three-roll mill to form a conductive paste by milling.

(10) Then the conductive paste was printed onto a silicon wafer substrate by a screen-printing technique. Cell sheets were dried in an infrared drying oven and then sintered at 750-850° C. in a belt type firing furnace. Cooling was performed after sintering, and cells were formed.

(11) A viscosity change for 30 days and photoelectric conversion efficiency of the cell were measured according to the above-mentioned methods for measuring the viscosity and testing the photoelectric conversion efficiency of the cell, and results were shown in Table 1.

(12) In comparison with a sample P1, it could be found that when a SiO.sub.2 component was added into samples P2-P5, a water weight loss of the inorganic oxide and a viscosity change rate of the paste within 30 days could be significantly reduced, and the viscosity change rate decreased with an increase of a content of SiO.sub.2, indicating that addition of SiO.sub.2 helped to effectively reduce water on the surface of the inorganic oxide. However, when the content of SiO.sub.2 was 16%, although the viscosity change rate of the conductive paste for 30 days was lower, the photoelectric conversion efficiency thereof was lowered to a certain extent compared with that obtained when the content of SiO.sub.2 was 12%. Therefore, in order to take into account the viscosity change rate and the photoelectric conversion efficiency, the content of SiO.sub.2 was preferentially 12%.

(13) TABLE-US-00001 TABLE 1 Formula (in mol %) of the samples P1-P5 and performance test data thereof Samples P1 P2 P3 P4 P5 TeO.sub.2   40%   40%   40%   40%   40% Li.sub.2O   20%   20%   20%   20%   20% SiO.sub.2    0%    4%    8%   12%   16% ZrO.sub.2 — — — — — PbO   26%   24%   20%   16%   14% Bi.sub.2O.sub.3    8%    6%    6%    6%    4% MgO    2%    2%    2%    2%    2% CaO    4%    4%    4%    4%    4% Total   100%   100%   100%   100%   100% Water related  2.23%  1.69%  1.52%  1.39%  1.35% weight loss of inorganic oxide Viscosity change of   46%   29%   23%   20%   17% paste for 30 days |Δη| Photoelectric 22.87% 22.89% 22.92% 22.93% 22.88% conversion efficiency

Example 2

(14) Different metal oxides were mixed in a certain proportion according to a formula of Table 2. Preparation methods of a conductive paste and a solar cell were the same as those in Example 1, and test results were shown in Table 2.

(15) Compared with the sample P1, the viscosity change of the finally obtained conductive paste for 30 days was significantly decreased when silicon oxide and zirconium oxide were added in samples P6-P10, and the viscosity change was reduced by 39%-74% compared with the sample P1. Meanwhile, the photoelectric conversion efficiency of the samples P6-P10 was significantly improved. In particular, the viscosity change of the sample P7 for 30 days was reduced by 73.9% and 40.0% compared with the samples P1 and P4, respectively, while the photoelectric conversion efficiency was maintained, that is, the sample P7 significantly improved the long-term storage stability of the conductive paste while maintaining the photoelectric conversion efficiency.

(16) Through a large number of experiments, it could be found that when the frit contained, in mol %, includes 24%-40% TeO.sub.2, 18%-24% Li.sub.2O, 4%-13% SiO.sub.2, 0-2% ZrO.sub.2, and a balance MO.sub.x (where MO.sub.x is one or a mixture of Na.sub.2O, K.sub.2O, MgO, CaO, SrO, TiO.sub.2, V.sub.2O.sub.5, Cr.sub.2O.sub.3, MoO.sub.3, WO.sub.3, MnO, CuO, Ag.sub.2O, ZnO, CdO, B.sub.2O.sub.3, Al.sub.2O.sub.3, Ga.sub.2O.sub.3, Tl.sub.2O.sub.3, GeO.sub.2, PbO, P.sub.2O.sub.5, and Bi.sub.2O.sub.3), the photoelectric conversion efficiency of the solar cell could be improved while significantly improving the long-term storage stability of the conductive paste. More preferentially, the frit included 28-40% TeO.sub.2, 18-20% Li.sub.2O, 12-13% SiO.sub.2, 0.2-2% ZrO.sub.2, and the balance MO.sub.x, and the viscosity change rate of the obtained conductive paste for 30 days was less than 20%, the water weight loss of the inorganic oxide was less than 1.4%, and the photoelectric conversion efficiency was greater than 22.90%. The most preferential composition was the sample P7: 40% TeO.sub.2, 20% Li.sub.2O, 12% SiO.sub.2, 2% ZrO.sub.2, and 26% MO.sub.x.

(17) TABLE-US-00002 TABLE 2 Formula (in mol %) of samples P6-P10 and performance test data thereof Samples P1 P4 P6 P7 P8 P9 P10 TeO.sub.2 40% 40% 40% 40% 28% 24%  36%  Li.sub.2O 20% 20% 20% 20% 18% 24%  20%  SiO.sub.2  0% 12% 12% 12% 13% 8% 4% ZrO.sub.2 — — 0.2%   2% 0.5%  1% 1% PbO 26% 16% 15.8%.sup.  15% 29% 31%  27%  Bi.sub.2O.sub.3  8%  6%  6%  5%  6% 6% 6% MgO  2%  2%  2%  2%  2% 2% 2% CaO  4%  4%  4%  4%  4% 4% 4% Total 100%  100%  100%  100%  100%  100%  100%  Water related 2.23%.sup.  1.39%.sup.  1.37%.sup.  1.29%.sup.  1.35%.sup.  1.48%   1.59%   weight loss of inorganic oxide Viscosity change 46% 20% 16% 12% 18% 24%  28.0%   of paste for 30 days |Δη| Photoelectric 22.87%   22.93%   22.93%   22.91%   22.91%   22.94%    22.90%    conversion efficiency

Example 3

(18) Different metal oxides were mixed in a certain proportion according to a formula of Table 3. Preparation methods of a conductive paste and a solar cell were the same as those in Example 1, and test results were shown in Table 3.

(19) It could be found that compared with the sample P7, when the content of ZrO.sub.2 in a sample P11 was too high, although the viscosity change of the conductive paste could be reduced, the photoelectric conversion efficiency thereof was significantly reduced compared with the sample P7 and lower than that in the sample P1. Compared with the sample P7, although a too low Li.sub.2O content and a too high SiO.sub.2 content in a sample P12 could reduce the viscosity change of the conductive paste, the photoelectric conversion efficiency thereof was also significantly reduced compared with the sample P7. It could be found that only when the composition was within the range of Example 2, could the effects that the viscosity change of the conductive paste within 30 days was small and the photoelectric conversion efficiency was significantly improved be achieved.

(20) TABLE-US-00003 TABLE 3 Formula (in mol %) of samples P11-P12 and performance test data thereof Samples P11 P12 TeO.sub.2   40%   32% Li.sub.2O   20%   10% SiO.sub.2   12%  20.0% ZrO.sub.2    5%  1.5% PbO   14%   25% Bi.sub.2O.sub.3    3%    6% MgO    2%    2% CaO    4%    4% Total   100%   100% Water related weight loss  1.19%  1.27% of inorganic oxide Viscosity change of paste   11%   11% for 30 days |Δη| Photoelectric conversion 22.73% 22.79% efficiency

(21) Although the present disclosure is disclosed as above in preferred examples, the examples are not intended to limit the present disclosure. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the protection scope of the present disclosure should be defined by the claims.