1. Rationale: Describe the need or problem addressed by this activity.

(Indicate the customer, what benefits they will receive, and if possible, quantify the impact on the return on investment [ROI] if the Document is implemented.)

Metal-Wrap-Through (MWT) technology is one of the most effective solutions for reaching higher cellefficiency and higher module power output (Figure 1). Not only the cell efficiency is improved by reducing the front side metallization, but also the ohmic losses of the module interconnection can be potentially decreased. Laser drilling of vias is one of the unique processes for MWT solar cells. Via metallization canthen be done.

Figure 1: MWT cell structure

MWT cells may be designed differently at both front (Figure 2) and back (Figure 3) sides.

Figure 2: different front design of MWT cells

Figure 3: different back design of MWT cells

Both front and back sides of MWT cells can be designed differently as shown above. However, the metalized vias are common to all MWT cells, which are shown in Figure 1.

The metallization within vias plays an important role for the performance of MWT solar cells because the generated current collected by the front fingers will be transferred through the vias to the rear side of the cells. If vias metallization is not fully optimized, there will be poor contact between the front finger and rearpad. This kind of contacts increases series resistance which results in the decreasing of the fill factor andfinally bad cell performance. In addition to higher Rs, the shunting occurs easily at the vias sidewall and rear pad due to very thin or even no silicon nitride on it. Methods to reduce high series resistance have been widely discussed in practice, including via paste modification, screen printing process, additional vacuum step during printing. Figure 4 shows the status of via hole at the optimized and non-optimized conditions. When the cell was fabricated at non-optimized condition, fill factor dramatically dropped due to the high series resistance.

For both MWT cell manufacturers and MWT module makers, they need test method to qualify the quality of the metalized vias of MWT cells.

It will be helpful if there is test method standard for quality of metalized vias of MWT cells in the industry.

Figure 4: Cross section image of a via-hole after the metallization process (left: optimized condition, right:

non-optimized condition)