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 Al2O3. 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·cm2, 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.