Effect of spherical silver powders with different sizes in back electrode paste on the conversion efficiency of silicon solar cells

Abstract

In the present paper, spherical silver powders of three different sizes (0.5–2.0 µm) and high dispersity were synthesized by a chemical reduction method using ascorbic acid as reducing agent and silver nitrate as oxidant. Then the properties of three back-side silver pastes made of spherical silver powders with three different sizes (D90 < 1.0, 1.5 and 2.0 µm) were investigated when these back-side silver pastes were printed and further formed to back-side electrodes on solar cells. The results showed that the surface consistency, weldability and welding tension of the back-side silver electrodes, as well as the photoelectric conversion efficiency of the solar cells increased with the decreasing of silver particle size. A series of comparative experiments confirmed that the spherical silver powder (a) with the size of D90 < 1.0 µm was optimal for making back-side silver paste. The average welding tension of formed back-side silver electrode and the photoelectric conversion efficiency of the solar cells have reached 7.6 N and 17.60 %, respectively, which meet the requirements of current commercialization for back-side silver pastes. In addition, the electrical performance of back-side silver pastes with different silver contents was also investigated. In order to reach the demands of the highest photoelectric conversion efficiency and the lowest cost for back-side silver pastes, the back-side silver pastes prepared by silver powder (D90 < 1.0 µm) with the content of 54.72 wt% was found to be optimal.