Solar Cell Metallization by Laser Transfer of Metal Micro-droplets

Laser Induced Forward Transfer (LIFT) enables a non-contact, mask-less and high-resolution/high-aspect ratio printing of various metals. However, the small gap between the donor (print head) and the acceptor (silicon wafer), which is typically <25 μm, limits its wider use in manufacturing. We demonstrate LIFT printing of metal micro-droplets from a gap larger than 100 μm to provide high quality electrical contacts to silicon. Post annealing process is not required as the contacts are formed instantaneously during the LIFT process. Printing aluminum contacts on p-type (resistivity of 10-30 Ω cm) and p+ type (0.01 Ω cm) Si substrates yields a specific contact resistance of 0.15 mΩ cm2 and 0.03 mΩ cm2 respectively. Finally, we demonstrate the use of LIFT metallization for serially connecting few vertical solar cells that are locally isolated by porous silicon.