Material Joint Analysis of Lead-Free Interconnection Technologies for Silicon Photovoltaics

Due to the negative environmental impact, efforts are being made to eliminate lead from electronic components, also in the photovoltaic industry. The development of a “green” solar module is of high relevance. For the series interconnection of solar cells, currently lead-containing solder alloys are used. The aim of this work is to evaluate the microstructure and impact on solar module performance of two industrially feasible interconnection materials with high potential for the interconnection of high-efficiency silicon heterojunction solar cells: lead-free solder and lead-free electrically conductive adhesives. Isothermal aging shows that the microstructure of soldered joints is submitted to significant changes such as intermetallic compounds growth (Ag3 Sn, Cu3 Sn, Cu6 Sn5) and, compared to glued joints, seem to influence the electrical performances of PV modules. The long-term stability is analyzed by thermal cycling of small-scale PV modules. Modular integration has been shown to be possible for both alternatives, about 80 % of the modules tested have successfully passed the thermal cycling test (power loss less than 5%).