Reliable Contact Formation for Industrial Solar Cells by Laser Ablation and Ni/Cu Plating

Abstract

Replacing Ag paste contacts in silicon solar cells by plated Ni/Cu contacts seems a logical next step in the evolution of industrial Si solar cell manufacturing. Ag paste contacts cause a significant share of the solar cell cost today and limit the efficiency of advanced Si solar cells. However, replacing a proven technology by another requires reliability of this technology. Cost and efficiency advantages alone are a high motivation for adopting a new metallization technology in mass production. Reliability of the contacts is a must. In this contribution we show that laser ablation followed by light induced plating of Ni and Cu and plating of a thin capping layer results in good and reliable contacts on industrial solar cell precursors. After plating of the complete metal stack a thermal annealing step is used to increase mechanical adhesion and to reduce resistive losses of the plated contacts (contact resistance and grid resistance). Excellent solar cell efficiencies can be combined with reliable contacts. Adhesion data and data after 60 cell module testing (as part of IEC61215) are reported next to the most influencing factors.