A Study of Molten Lead-Free Solder Deposited by Inkjet Printing for Interconnections of Thin-Film Solar Cell Modules

W-M Chen, C-H Wang, W-S Hwang
National Cheng-Kung University, TW

Keywords: lead-free solder, inkjet printing, thin-film solar cell

Summary:

Solar cell modules generally are bonded with photovoltaic ribbon using silver paste to increase photovoltaic conversion efficiency. However, the joint strength of silver paste between the aluminum back electrode and the ribbon may be the obstacle to the development of solar cells. A joint of lead-free solder deposited by inkjet printing on a thin-film solar cell is investigated in this study. The lead-free solder Sn3.0Ag0.5Cu is applied as the solder joint between the back electrode of a thin-film solar cell and photovoltaic ribbon. A single droplet of molten lead-free solder was ejected from the orifice for each pulse of the bipolar waveform at a suitable amplitude. An array pattern with a solder joint diameter of 46 μm was applied on the back electrode to replace silver paste. A high joint strength of 11.87N was measured for the bonding structures after a reflow process at 245 °C for 75 s. The photovoltaic conversion efficiency of this cell was 8.74%. A solder joint deposited via inkjet printing provides high strength at low cost for the energy technology applications.