Unveiling Mechanisms of Nano- and Picosecond Laser Scribing of Bilayer Molybdenum Thin Films on Flexible Polyimide for CuInxGa(1-x)Se2 Solar Photovoltaic Module Fabrication

Abstract

Flexible CuInxGa(1-x)Se2 (CIGS) thin-film solar cells are promising for future applications in buildings, mobility, and aerospace due to their high efficiency, lightweight, and flexible nature. To achieve large-area monolithic-integrated modules, a scribing process, dividing into multiple cells for series connection, is indispensable. Despite numerous merits laser scribing can offer, further improvement is required for high-quality solar module. Picosecond laser, generally accepted as an efficient tool to suppress thermal impact, often causes problems in achieving a shunt-free P1 scribing process that isolates the back contact, typically bi- or multilayered Mo thin films, due to edge deformation as a source of shunt. In this study, we experimentally compare the performance of picosecond and nanosecond lasers in scribing bilayered Mo films of different microstructures on flexible polyimide through morphological analysis and shunt evaluation for selected scribing conditions. Thermal analysis and time-resolved measurement of laser-induced emission further elucidate relevant scribing mechanisms. It will be shown that nanosecond lasers, usually not a preferred solution for temperature-sensitive architectures, have significant merits in scribing complex multilayered structures of relatively large thickness, preferentially launching indirect interfacial heating mechanism for optically nontransparent film-substrate combinations.