Performance of low series-resistance interconnections on the polycrystalline solar cells

The performance of four ribbons of lead SnAgPb (SAP) and lead-free SnAgCu (SAC) photovoltaic (PV) ribbons in patterned (pat-) and high-conductivity (con-) types soldered on silicon solar cells are investigated by electron characteristics and microstructure analyses. The electrical performances of the solar strings were characterized before and after the soldering process by a solar flasher, and strings with commercial ribbons of lead and lead-free are compared. In general, lead ribbon solar strings show lower power loss value than lead-free counterparts. And the commercial lead and lead-free ribbon strings show highest power loss around 6.66%–10.65% of all the solar strings. Furthermore, the power losses for patterned lead (pat-SAP) and lead-free (pat-SAC) solar string are 3.93% and 5.51%, respectively, implying that a patterned structure should improve the soldering process and result in lower power loss. Yet, significant low output power loss values are detected in the solar strings which are soldered with high-conductivity ribbons. It is estimated that the power loss for high-conductivity lead (con-SAP) and lead-free (con-SAC) solar strings are 3.89% and 4.43%, respectively. And a similar condition was revealed when the solder materials were practically interconnected the solar cells in PV modules. According to the microstructure analyses, the low power loss of con-SAP solar string should be due to the good electrical performance in low series resistance (Rs) and high shunt resistance (Rsh), thus resulting in a high fill factor of the solar device.