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Comprehensive simulation and acceleration of the foil-metallization laser process

: Graf, M.; Nekarda, J.; Lazzarotto Togny, F.; Streek, A.; Böhme, R.; Preu, R.

Postprint urn:nbn:de:0011-n-3668481 (646 KByte PDF)
MD5 Fingerprint: a2d88ed2d3609d4e920f76f3f4be4bfd
Created on: 24.11.2015

Energy Procedia 77 (2015), pp.694-700
ISSN: 1876-6102
International Conference on Crystalline Silicon Photovoltaics (SiliconPV) <5, 2015, Constance>
Journal Article, Conference Paper, Electronic Publication
Fraunhofer ISE ()
PV Produktionstechnologie und Qualitätssicherung; Silicium-Photovoltaik; Messtechnik und Produktionskontrolle; laser processing

The upgrade of state of the art p-type silicon solar cell production lines to passivated rear side technology (PERC) will be one of the major trends in the next years and new production processes for further cost reduction will continuously gain relevance. In 2007, we have introduced the laser based foil metallization technology “FolMet”: the rear electrode of p-type PERC devices as well as the local contact is fabricated by attaching conventional aluminum foil during the so-called laser fired contact process to the silicon wafer. This process features improved internal optical properties, a huge cost saving potential and a simplified cell production process. In this publication we focus on the acceleration of the laser process, which is together with module assembly issues a remaining challenge towards industrialization. We carried out comprehensive simulations, to better understand the correlation between different laser parameters on melting- and evaporation depth of the 8 μm thin aluminum foil. We determined lower limits for crucial laser pulse parameters to successfully attach the foil onto the substrate and validated these parameters experimentally. According to these results, we set up a system based on a pulsed high power laser featuring repetition rates Frep ≤ 2 MHz with an unique ultrafast polygon scanning system, allowing for scan-speeds vscan ≤ 1000 m/s. Thereby, we demonstrate processing times tpro < 0.8 s for industrial wafer, which corresponds to a reduction in laser process time by the factor of 20 compared to state of the art laser scanning technology.