Depth selective laser scribing of thin films for roll-to-roll production of silicon solar cells

Abstract

Significant cost reductions for thin-film silicon solar cells are expected from a transition to roll-to-roll production. However, in contrast to state-of-the-art batch-type fabrication of glass based products, for thin-film photovoltaic modules on foil substrates no standard processes for one essential production step – the monolithic series interconnection-are presently available. Laser scribing is the preferred technology here as it allows fast, non-contact, local and precise removal of the thin films. ECN is currently developing the technology and setting up a pilot line for the production of tandem solar cells based on microcrystalline and amorphous silicon on steel foil substrates [1]. To allow monolithic series interconnection on these electrically conducting substrates, an insulating layer is required. In the presented module concept, first all layers of the solar cell are deposited, and after that series interconnection can be realized in one process step by three depth selective laser scribes which are then filled by insulating and electrically conductive inks. In this contribution, we present the latest status of our process development on nanosecond pulsed lasers with three different wavelengths to achieve depth selective scribing of these flexible thin-film silicon solar cells. To gain more insight into the selectivity of the process, the ablation thresholds of the different layers have been determined. Then, continuous lines were scribed by systematically varying the pulse energy and spot overlap. The required depth selective scribes could be obtained with all employed lasers (wavelengths of 355 nm, 532 nm, and 1064 nm).Significant cost reductions for thin-film silicon solar cells are expected from a transition to roll-to-roll production. However, in contrast to state-of-the-art batch-type fabrication of glass based products, for thin-film photovoltaic modules on foil substrates no standard processes for one essential production step – the monolithic series interconnection-are presently available. Laser scribing is the preferred technology here as it allows fast, non-contact, local and precise removal of the thin films. ECN is currently developing the technology and setting up a pilot line for the production of tandem solar cells based on microcrystalline and amorphous silicon on steel foil substrates [1]. To allow monolithic series interconnection on these electrically conducting substrates, an insulating layer is required. In the presented module concept, first all layers of the solar cell are deposited, and after that series interconnection can be realized in one process step by three depth selective laser scribes whi...