Solder Joint Analysis on Coated Aluminum for Silicon Solar Cell Interconnection

Foil metallized solar cells combine the high-efficiency passivated emitter and rear cell technology with a cost-efficient rear side metallization based on a thin aluminum foil. The cell interconnection with the soldering processes usually used in photovoltaics, is hampered by the native oxide film Al 2 O 3 . This work evaluates solder joints on Al substrates, modified with either physical vapor deposition (PVD), roll cladding or zincate treatment. Our analysis reveals low contact resistivities of ~0. 02 m Ωcm 2 , temperature-stable for 1000 hours aged at 85°C in ambient air. Additional tests under damp heat conditions (85°C, 85 % relative humidity) with encapsulated samples yield as well no electrical degradation for the PVD coated samples within 1000 hours aging. The mechanical characterization by a 90° peel test shows initial adhesion of 6 N/mm (PVD), 4 N/mm (roll cladding) and 0.8 N/mm (zincate). Degradation of the roll cladded samples is observed and analyzed further by EDX spectroscopy.