CONDUCTIVE PASTE COMPRISING A SILICONE OIL

Abstract

The invention relates to a conductive paste comprising from 30 to 97% by weight of electrically conductive particles, from 0 to 20% by weight of a glass fit, from 3 to 70% by weight of an organic medium and from 0.1 to 67% by weight of a silicone oil, each based on the total mass of the paste, wherein the silicone oil hasa boiling pointor a boiling rangein the range between 180 C. and 350 C. The invention further relates to a use of the conductive paste and a process for producing electrodes on a semiconductor substrate using the paste.

Claims

1-12. (canceled)

13. A conductive paste comprising: from 30 to 97% by weight of electrically conductive particles; from 1 to 20% by weight of a glass frit; from 3 to 70% by weight of an organic medium; and from 0.1 to 67% by weight of a silicone oil; wherein each % by weight is based on a total mass of the conductive paste; and wherein the silicone oil has a boiling point or a boiling range in a range between 180 C. and 350 C.

14. The conductive paste according to claim 13, wherein the silicone oil comprises at least one selected from the group consisting of a linear silicone oil molecule, a branched silicone oil molecule, and a cyclic silicone oil molecule.

15. The conductive paste according to claim 13, wherein the silicone oil comprises polydimethylsiloxane.

16. The conductive paste according to claim 14, comprising the linear silicone oil molecule, wherein the linear silicone oil molecule is at least one selected from the group consisting of decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane, and hexadecamethylheptasiloxane.

17. The conductive paste according to claim 14, comprising the cyclic silicone oil molecule, wherein the cyclic silicone oil molecule is at least one selected from the group consisting of decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, and tetradecamethylcycloheptasiloxane.

18. The conductive paste according to claim 13, wherein the electrically conductive particles comprise carbon, silver, gold, aluminum, platinum, palladium, tin, nickel, cadmium, gallium, indium, copper, zinc, iron, bismuth, cobalt, manganese, molybdenum, chromium, vanadium, titanium, tungsten, mixtures thereof, alloys thereof, or core-shell structures thereof.

19. The conductive paste according to claim 13, wherein the electrically conductive particles are coated with an organic additive.

20. A printed electrode on a semiconductor substrate, the printed electrode comprising the conductive paste according to claim 13.

21. A process for producing an electrode on a semiconductor substrate, the process comprising: (a) screen printing the conductive paste according to claim 13 on a semiconductor substrate in a predetermined pattern to form a printed semiconductor substrate; (b) drying the printed semiconductor substrate at a temperature in a range from 100 to 300 C. to obtain a dried printed semiconductor substrate; (c) heating the dried printed semiconductor substrate to a sintering temperature in a range from 650 to 900 C. to sinter the electrically conductive particles.

22. The process according to claim 21, wherein the drying (b) is carried out for a duration in a range from 10 to 50 sec.

23. The process according to claim 21, wherein the heating (c) comprises: heating the dried printed semiconductor substrate from room temperature to the sintering temperature within 5 to 50 sec; holding the sintering temperature for 1 to 5 sec; and cooling the dried printed semiconductor substrate down to room temperature within 3 to 60 sec.

24. The process according to claim 21, wherein the semiconductor substrate is a semiconductor substrate for a solar cell.

Description

EXAMPLES

[0053] Conductive pastes according to the compositions in table 1 have been screen printed with the screen parameters as shown in table 3.

TABLE-US-00001 TABLE 1 Paste composition sample E1 E2 component mass % mass % silver powder 88.50 88.50 glass frit 3.00 3.00 organic additive blend A 1.25 1.25 organic solvent blend A 7.25 6.45 silicone oil 0.00 0.80 sum 100.00 100.00

[0054] In formulation E2 solvent blend A partially has been substituted by silicone oil. Organic additive blend A contains a mixture of a dispersants, polymers and thixotropes. Organic solvent blend A contains a mixture of texanol and dimethyl adipate.

[0055] Screen prints have been conducted with the following screen parameters:

TABLE-US-00002 TABLE 2 screen parameters mesh count [wires/inch] 360 wire thickness [m] 16 emulsion thickness [m] 15 fabric thickness [m] 22 line opening [m] 36 number of lines 100 busbar type 2 segmented

TABLE-US-00003 TABLE 3 Slip measurement sample E1 E2 average rotation speed at 1000 Pa [rpm] 1.89 2.12 standard deviation of rotation speed at 1000 Pa [rpm] 0.014 0.034

[0056] Formulation E2 shows less adhesion on the stainless steel surfaces of a rheometer with plate-plate geometry. Therefore in case of formulation E2 the upper plate shows faster rotation speed at constant shear stress.

[0057] Results of the printing process are shown in FIGS. 1 and 2.

[0058] FIGS. 1 and 2 show microscope pictures of printed lines of the paste compositions E1 and E2 after drying at 250 C. and subsequent sintering at 800 C. By comparison of the lines shown in FIGS. 1 and 2 it can be seen that the line printed with the inventive formulation E2 shows less seepage.

TABLE-US-00004 TABLE 4 characteristics of the printed lines sample E1 E2 median shaded line width [m] 86.1 66.4 median line height [m] 13.4 16.4

[0059] 8 multi crystalline wafers have been screen printed with each of pastes E1 and E2. Results of cell efficiency measurements are shown in FIG. 3. Results of thermal gravimetric analysis are shown in FIG. 4.

[0060] From FIG. 3 it can be clearly seen, that the paste composition according to the invention which comprises a silicone oil has a higher cell efficiency than a paste composition which does not contain a silicone oil.

[0061] FIG. 4 shows that the mass reduction during the heating step for both pastes nearly is the same, which shows that during the heating step no silica is formed from the silicone oil which would lead to a reduction of cell efficiency.