Laser-based metallization of full-size solar cells by LIFT

The laser-induced forward transfer (LIFT) process is a technique to transfer locally different materials and in different sizes onto a number of different substrates. The laser beam is focused in the donor substrate/ribbon interface. During the pulse duration, the laser energy is deposited within the laser spot size into the interface, evaporating a little amount of the material and generating the expansion of the remaining material, accelerating the non-evaporated part of the metal film towards the acceptor substrate. Main objective of WP7 was to design and develop reliable schemes for direct writing of flex electronics and photovoltaics in planar geometry using laser sources. In this third year of APPOLO project, the main results accomplished in the Work Package 7 are summarized. It has been proved that laser curing and sintering of silver paste lines printed using LIFT can be achieved at different laser powers and scanning speeds, but there is a small parametric window for obtaining the desired properties (increased electrical conductivity and good mechanical adhesion), making it a very sensitive process. It has been proved that the selective laser curing and sintering can be combined with other laser direct writing printing techniques and be implemented in future photovoltaic industrial applications for developing an all-laser based metallization process. And it has been shown that can be used as a low temperature process due to its capability to produce local heat suitable for the process but leaving the rest of the cell almost at room temperature. As a proof of concept, the full metallization of a CIGS solar cell on steel flex substrate with fingers and busses deposited by the proposed LIFT technology has been performed and a working solar cell has been obtained. The method used for LIFT printing of silver lines has overcome one of its main problems for industrialization, as is the printing of long lines. As a result of the work done in WP7 Mondragon Assembly has developed a flexible industrial machine tool for adhesives/pastes dispensing, as well as for curing/sintering processes.