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Metallization is one of the key and most expensive step in the typical solar cell fabrication. Amongst the metallization techniques of photovoltaic solar cell, the screen printing technique has achieved a great success. It is the most widely employed and robust method for finger printing in the present photovoltaic industry. However, due to the limitation of the technique, it can hardly print silver paste line with height more than 30 μm. Therefore, the line aspect ratio is limited to less than 0.4. In the last few years, researchers have been focused on the development of innovative and cost-effective metallization techniques for printing high-resolution patterns. During the last few decades, laser-based manufacturing technology has become an essential tool in the photovoltaic industrial. Among these techniques, laser cutting and edge isolation have already been widely used in the crystalline solar cell industrial manufacturing. And the laser scribing is also applied in the thin film technology. With the development in new laser technologies and system, public groups are bridging the gap between these laser techniques and high efficiency solar cells. In this thesis work, a new concept of two-step front metallization of the solar cell is proposed aiming at adapting the Laser-induced forward transfer techniques (LIFT), a wellknown laser direct writing technique for material transfer towards 3D printing, to define the front metallic contacts onto flexible photovoltaic devices (specially in planar geometry) as the pre-metallization process. Combining another laser-based post-metallization technique, which is the selective laser curing/sintering, the deposited silver paste line can be functionalized in the direct write way by means of laser irradiation. In the context, this Thesis proposes a completely original method, demonstrating the possibility of the formation of silver paste front contact lines with height more than 60 μm and an aspect ratio more than 0.6 by means of laser-induced forward transfer. This result obtained for the first time at international level in this work, breaking thought the limitation of the screen printing technique. The easy set-up and free-style pattern printing ability has revealed the feasibility for the industrial development of this technique in the future. In this work LIFT for front contact formation process, investigated from voxel to line printing, has been developed and optimized for different acceptor substrates, demonstrating the advantages and limitations of the technique using both ns and pspulsed laser sources. Good results have been obtained in both crystalline silicon wafer and flexible CIGS thin film substrate. The lines deposited by LIFT and post-metallized by SLS in CIGS substrates has shown good mechanical adhesion under bending test and electrical properties under TLM test. In particular, four transfer regimes of micro-sized silver paste are defined in the LIFT process. And among them a new transfer mechanism, which is totally different from those previously studies using Newtonian fluid or nanopastes, is observed and studied for the first time. This founding is highly remarkable for that the formation of silver paste bridge between donor and acceptor substrate leads to the concrete-dot voxel. By using computer controlled translation stages or galvanometric scanning mirrors, silver paste line with high aspect ratio can be formed by the overlapping of the voxel as the front contact on the photovoltaic substrate. Moreover, in the line printing section it is found that the pitch distance for overlapping the voxels in line scanning condition exists a threshold value above which the transfer will be ceased due to the escaped pressure through the laser-induced tunnel. Apart from the influences of the LIFT process parameters, the interaction of silver paste and acceptor substrate through wetting and adhesion also play an important role in forming highresolution metal lines. From this point of view, an approach of increasing surface roughness by texturing is proposed in the thesis for the first time for preventing the spreading of the paste and keeping the line with high aspect ratio in the LIFT process. In addition, the work performed in the systematic study of LIFT process, which shows the high flexibility in material and acceptor substrate choosing and the ability for free-style pattern printing, is not only adapted to the scope of photovoltaic devices, but also is of highly relevance in the optoelectronics device toward 3D printing. In the end, it is appreciated for a collaboration between Centro Laser of UPM, where the author made his work, and the department of mechanical and aerospace engineering of Princeton University, where most works of the time-resolved imaging experiment were made. This work was supported in the context of several projects with public funding, such as EUROPEAN COMISSION APPOLO FP7-2013-NMP-ICT-FOF.609355 and Spanish MINECO projects SIMLASPV-MET (ENE2014-58454-R) and HELLO (ENE2013-48629C4-3R) and support from the NSF MRSEC program through the Princeton Center for Complex Materials (grant DMR-0819860) and the Rutgers-Princeton NSF IGERT on Nanotechnology for Clean Energy. Chapter

Desarrollo de procesos para formación de contactos con láser para módulos thin film CIGS para aplicaciones fotovoltaicas