Laser Based Metallization using Silver Pastes

In this work we present a laser-based metallization process, using commercial silver pastes, of potential application in photovoltaics (PV) and flexible electronics. The process comprises two steps to achieve the final conductive structures: the first one is intended to transfer the material in the appropriate geometries and the second one produces the curing/sintering of the material avoiding the standard furnace step for firing. For the first step, a particular adaption of the Laser Induced Forward Transfer Technique (LIFT) is used, and in this work we discuss the physical principles of the proposed technique. For the second, depending on the device characteristics, a standard furnace firing process can be used or, as an alternative, we use local irradiation using CW lasers for sintering and electrical functionalization of the predeposited lines. This later approach makes the technique fully compatible with a number of low temperature device concepts of increasing importance in high efficiency PV. Our group has developed this technique as an alternative to standard screen-printing metallization processes as part of FP7 Appolo project activity (www.appolo-fp7.eu). We have shown that it is possible to use this technique to define metallic contacts using commercial silver pastes of high viscosity with improved aspect ratios in the deposited structures and to obtain resistivity values similar to those specified by commercial screen-printed cells and. In addition processing speeds can be very high, what makes this technology to some extent a potential competitor at industrial level of standard screen printing techniques