Laser Metal Bonding (LMB) - low impact joining of thin aluminum foil to silicon and silicon nitride surfaces

We present the design, implementation and optimization of laser metal bonding (LMB), a new approach for joining thin aluminum foils and back surfaces of solar cells with a focus on low impact on the semiconductor and good adhesion. After gaining deep insights into laser-material interaction using finite difference simulations, we succeeded in establishing an expulsion free laser process that can be tuned from non-ablative bonding, which leaves the substrate largely intact, to welding, which produces highly adhesive joints. Experiments were conducted on a number of substrates, showing the correlation between damage and adhesion at different process parameters.