Formation of electrical conductors by wet chemical metallization is well-known in the electronics industry, with decades of implementation in the fabrication of printed circuit boards and microelectronics. However, its usage in the photovoltaic industry is still in its early stages. As the solar cell fabrication process matures, wet chemical copper metallization will move from acceptable, to preferred, to required. Relative to screen printed silver paste, copper allows higher aspect ratio, self-aligned conductors, and compatibility with increasingly complex materials and processes. Many of the highest efficiency cell architectures already require, or benefit from, wet chemical metallization. Future commodity cells are predicted to require copper conductors, due to the need to continually improve efficiency while simultaneously driving costs lower. This paper is a review of the current status of wet chemical metallization in the photovoltaic space, and a prospectus for where the technology trends are leading. Also included is a brief history of plating in PV, as well as its advantages, challenges, application to specific cell types, and path to mass adoption.

The aim of this work was to demonstrate the advantages of the Ni/Cu/Ag plating process when the number of busbars on the solar cell is increased. Cells with four and five busbars were processed and compared to those with three in respect of efficiency, finger and solder adhesion. It is shown that the efficiency can be increased by 0.15%, while the finger adhesion remains the same or improves and the solder adhesion remains mostly greater than 1 N/mm2, if the number of busbars is increased from 3 to 4 or 5. The mass of metal deposited can be reduced by up to 30% for 5 busbars compared to that required for 3 busbars. Furthermore, it is estimated that the cost of metallisation can be reduced from 9 €ct/wafer for three busbars to 8.6 €ct/wafer for five busbars.

As silicon solar cell technology featuring screen printed silver paste continues to mature, the cost of the front side conductor continues to grow as a percentage of the overall manufacturing cost. A cell concept based on electroplated nickel and copper contacts offers a significant cost savings, as well as a benefit to cell efficiency through reduced shading and lower contact and line resistance. This work details a new, simplified metallization process featuring pico-second laser ablation of the ARC combined with single-sided plating from a novel, high-speed copper formulation. More importantly, we present the details of a low cost scale-up of the metallization process on high volume mass production tools, plus fabrication of industrial modules and reliability testing according to IEC specifications. Electrical and adhesion data is presented on a statistically comprehensive sample set, proving the benefits of the new contact structure. These data offer the combined benefit of improved efficiency, a sizeable reduction in cell materials cost, and a clear pathway for the implementation of the process on a mass production scale.

This paper describes a viable path for the mass production of Si solar cells that lead to lower cost for PV electrical energy. Systems and modules having solar cells with plated metal contacts benefit from both, a higher solar cell performance as well as significantly reduced consumable cost. As most advances in industrial solar cell production over the past decades the introduction of plating technology benefits from significant equipment and material improvements. In parallel this road offers to shift the limits with respect to achievable solar cell efficiency by inherent advantages such as the possibility to form narrower metal contacts of excellent conductivity at low cost and the possibility to contact moderately doped Si areas. Efficiency improvements depend on the degree that other processing steps are adapted to the new degree of freedom in optimization offered by plated contact formation. Efficiency improvement is experimentally demonstrated. Equipment solutions and cost aspects are addressed. Besides good reliability and adhesion of the plated contacts we show efficiency potential exceeding 21% for PERC-type Si solar cells.

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.

In an effort to increase solar cell efficiencies while simultaneously reducing materials costs, a two-step metallization process for the production of silicon solar cells is presented. A novel, cyanide-free electroless silver plating solution (LIEP – light induced electroless plating) was developed, which has the benefits of higher conductivity than printed paste, simple equipment requirements and a wide process window. LIEP silver plating was demonstrated to increase efficiency of poorly conducting production cells by reducing series resistance. Additionally, printing of fine line patterns and thickening the contacts with LIEP silver combines the benefits of better electrical performance while reducing silver usage and associated costs. The LIEP silver deposit is denser than sintered paste, providing a platform for improved soldering, increased ribbon peel strength, and improved module reliability.