Study of Annealing Temperature for Ni/Cu/Ag Plated Front Contact Single Crystalline Solar Cells

Abstract

Ni/Cu/Ag contact formed by plating has continuously been studied as a future metallization technique of solar cells due to the lower cost of material and better electrical performance compared with the screen-printed Ag contact. For the metallization of samples, native oxide on a laser-patterned Si area was etched with a buffered oxide etch solution for uniform plating. A Ni seed layer for Cu plating was deposited by using alkaline electroless plating. Afterward, a Cu–Ag metal stack was plated by light-induced plating followed by annealing in a tube furnace with an ${{\rm{N}}_2}$ gas atmosphere. This annealing process forms NiSix, which enhances contact resistance and adhesion. However, Ni penetration through the emitter layer can produce shunting paths, which decrease cell performance. In this experiment, 2.6 N/mm was obtained as the highest adhesion result. In addition, voids that can degrade adhesion were observed at the interface of Cu–Ag due to the Kirkendall effect. According to the experiment's results, the suggestion of annealing condition was discussed to have good electrical and physical properties of plated Ni/Cu/Ag front contact.