Product Code: ICA10_M1106

Depth Selective Laser Scribing of Thin-Film Silicon Solar Cells on Foil
Authors:
Laurie Wipliez, Energy Research Center of the Netherlands; Petten Netherlands
Jochen Löffler, Energy Research Center of The Netherlands; Petten Netherlands
Martijn De Keijzer, Energy Research Center of the Netherlands; Petten Netherlands
Wim Soppe, Energy Research Center of the Netherlands; Petten Netherlands
Thomas Sebastien, Energy Research Center of the Netherlands; Petten Netherlands
Aart Schoonderbeek, Laser Zentrum Hannover E.V.; Hannover Germany
Oliver Haupt, Laser Zentrum Hannover E.V.; Hannover Germany
Uwe Stute, Laser Zentrum Hannover e.V.; Hannnover Germany
Presented at ICALEO 2010

Roll-to-roll production promises to allow drastic reduction in production cost of thin-film photovoltaic (PV) solar cells and modules, and thus enable a breakthrough in the price per kWh of solar electricity. The fabrication of these PV devices in roll-to-roll mode on flexible substrates differs in many respects significantly from that for glass based devices. This holds also for the laser scribing to obtain series interconnection of thin-film silicon solar cells into monolithic modules. For thin film solar cells on opaque foil, this requires far more depth selectivity, which cannot be realized by simply adjusting the laser wavelength to the absorption profiles of the involved layers. ECN is working on the development of high-efficiency low-cost thin-film silicon solar cells on steel foil. Recently, we have presented results on depth selectivity studies with ns pulsed lasers at different wavelength on individual layers and layer stacks resembling the final devices [1], but at that time the samples used were no functional solar cells yet.
Here, first results of laser scribes into working solar cells are reported, showing some issues encountered with 1064 nm nanosecond pulsed lasers. Despite the apparent depth selectivity that was reported earlier, a reduced diode quality and/or shunting of the solar cells is observed, probably due to recast at the wall of the laser scribe either formed by molten material from the back contact or re-crystallised silicon. Consequently, a much broader wavelength/pulse length matrix has been evaluated to better understand the ablation processes of the individual layers, aiming at a reduction of damage to the PV devices due to the laser process.
Finally, improved laser scribes with reduced damage on working solar cells have been achieved in a broad process window leading to much lower solar cell efficiency losses than with the 1064 nm nanosecond laser.

[1] Löffler et al., 28th ICALEO, 2009.