High volume transfer of high viscosity silver pastes using Laser Direct-Write Processing for metallization of c-Si cells

Abstract

The main objective of this work is to adapt Laser Induced Forward Transfer (LIFT), a well-known laser direct writing technique for material transfer, to define metallic contacts (fingers and busbars) onto c-Si cells. A layer of a commercial silver paste (viscosity around 30-50 kcPs), with thickness in the order of tens of microns, is applied over a glass substrate using a coater.. The glass with the silver paste is set at a controlled gap over the c-Si cell. A solid state pulsed laser (532 nm) is focused on the glass/silver interface producing a droplet of silver that it is transferred to the acceptor substra.te The process parameters (silver paste thickness, gap and laser parameters -spot size, pulse energy and overlapping of pulses) are modified and the morphology of the voxels is studied using confocal microscopy. Long lines are printed with a scanner and their uniformity, width, and height are studied. Examples of metallization of large areas (up to 10 cm x 10 cm) over c-Si cells are presented.