Electro-conductive paste comprising Ag nano-particles and spherical Ag micro-particles in the preparation of electrodes
View Patent ↗The invention relates to an electro-conductive paste comprising Ag nano-particles and spherical Ag micro-particles in the preparation of electrodes, particularly in electrical devices, particularly in temperature sensitive electrical devices or solar cells, particularly in HIT (Heterojunction with Intrinsic Thin-layer) solar cells. In particular, the invention relates to a paste, a process for preparing a paste, a precursor, a process for preparing an electrical device and a module comprising electrical devices. The invention relates to a paste comprising the following paste constituents: a. Ag particles, b. a polymer system; wherein the Ag particles have a multi-modal distribution of particle diameter with at least a first maximum in the range from about 1 nm to about less than 1 μm and at least a further maximum in the range from about 1 μm to about less than 1 mm; wherein the difference between the first and the further maximum is at least about 0.3 μm; wherein at least 50 wt. % of the Ag particles with a diameter in the range from 1 μm to 1 mm are spherical.
1. A precursor comprising the following precursor parts:
i) a paste comprising the following paste constituents:
a. Ag particles, and
b. a polymer system;
wherein the Ag particles have a multi-modal distribution of particle diameter with at least a first maximum in the range from about 1 nm to about less than 1 μm and at least a further maximum in the range from about 1 μm to about less than 1 mm;
wherein the difference between the first and the further maximum is at least about 0.3 μm;
wherein at least 50 wt. % of the Ag particles with a diameter in the range from 1 μm to 1 mm are spherical; and
wherein the ratio of the total weight of Ag particles with a diameter in the range from 1 nm to less than 1 μm to the total weight of Ag particles with a diameter in the range from 1 μm to less than 1 mm is about 1:1 to about 10:1; and
ii) a semiconductor substrate.
2. A precursor according to claim 1 , wherein the semiconductor substrate is temperature sensitive.
3. A process for the preparation of a device comprising the following steps:
i) providing a precursor according to claim 1 ; and
ii) heating the precursor to obtain the device.
4. A device obtained by the process according to claim 3 .
5. A device at least comprising as device parts:
i) a semiconductor substrate; and
ii) an electrode comprising Ag particles and a polymer system;
wherein the Ag particles present in the electrode have a multi-modal diameter distribution with at least a first maximum in the range from about 1 nm to about less than 1 μm and at least a further maximum in the range from about 1 μm to about less than 1 mm;
wherein the first maximum and the further maximum are separated by at least about 0.3 μm; and
wherein at least 50 wt. % of the Ag particles with a diameter in the range from 1 μm to less than 1 mm are spherical; and
wherein the ratio of the total weight of Ag particles with a diameter in the range from 1 nm to less than 1 μm to the total weight of Ag particles with a diameter in the range from 1 μm to less than 1 mm is about 1:1 to about 10:1.
6. A module comprising at least one device according to claim 4 and at least a further device.
7. The precursor according to claim 1 , wherein the paste contains not more than about 0.1 wt. % glass based on the total weight of the paste.
8. The precursor according to claim 1 , wherein the ratio of the total weight of Ag particles with a diameter in the range from 1 nm to less than 1 μm to the total weight of Ag particles with a diameter in the range from 1 μm to less than 1 mm is about 2:1 to about 8:1.
9. The precursor according to claim 1 , wherein the ratio of the total weight of Ag particles with a diameter in the range from 1 nm to less than 1 μm to the total weight of Ag particles with a diameter in the range from 1 μm to less, wherein the ratio of the total weight of Ag particles with a diameter in the range from 1 nm to less than 1 μm to the total weight of Ag particles with a diameter in the range from 1 μm to less than 1 mm is about 3:1 to about 6:1.
10. The process according to claim 3 , wherein the heating is conducted at a temperature between about 70° C. and about 250° C.
11. The precursor according to claim 1 , wherein the Ag particles have a bimodal diameter distribution.
12. The precursor according to claim 1 , wherein the Ag diameter distribution has at least one maximum in the range from about 100 to about 800 nm.
13. The precursor according to claim 1 , wherein the Ag diameter distribution has at least one maximum in the range from about 1 to about 10 μm.
14. The precursor according to claim 1 , wherein the polymer system is a thermosetting system.
15. The precursor according to claim 14 , wherein the thermosetting system comprises a crosslinking compound having at least two unsaturated groups.
16. The precursor according to claim 14 , wherein the thermosetting system comprises a radical generator.
17. The precursor according to claim 1 , wherein the polymer system is a thermoplastic polymer system, wherein the thermoplastic polymer system comprises a thermoplastic polymer.
18. The precursor according to claim 17 , wherein the thermoplastic polymer system comprises a solvent and the solvent is present in the thermoplastic polymer system in an amount of at least 50 wt. %, based on the total weight of the thermoplastic polymer system.
19. The precursor according to claim 1 , wherein the ratio of the total weight of Ag particles with a diameter in the range from 1 nm to less than 1 μm to the total weight of Ag particles with a diameter in the range from 1 μm to less than 1 mm is in the range from about 1 to about 9.
20. The precursor according to claim 1 , wherein the total weight of Ag particles is in the range from about 60 to about 95 wt. % based on the total weight of the paste.
21. The precursor according to claim 1 , wherein the paste contains not more than about 1 wt. % glass based on the total weight of the paste.