Depth selective laser scribing of thin-film silicon solar cells on foil

Abstract

Roll-to-roll production of thin-film photovoltaic (PV) solar cells and modules is expected to decrease substantially the manufacturing costs, and thus enable a breakthrough in the price of solar electricity per kWh. The roll-to-roll concept implies that the fabrication of these PV devices on flexible substrates is significantly different from the production of the glass based devices. This is especially valid for the monolithic series interconnection of thin-film silicon solar cells into modules, where the laser scribing step of thin-films on opaque foils requires depth selectivity. As adjusting the laser wavelength to the absorption profiles of the involved layers is not sufficient, we are investigating the ablation mechanisms leading to removal of the different layers of thin-film silicon solar cells.In this paper, first results of laser scribes into working solar cells are reported using 1064 nm nanosecond pulsed lasers. Despite the apparent depth selectivity reported earlier for this type of laser, a reduced diode quality and/or shunting of the solar cells is observed. This is probably due to recast at the wall of the laser scribe either by molten material from the back contact or by re-crystallized silicon. Consequently, a broader wavelength/pulse duration matrix has been experimented to understand better the ablation processes of the individual layers, aiming at a reduction of damage of the PV devices due to the laser process.Finally, laser scribes with reduced damage on working solar cells have been achieved with a near IR picosecond laser, leading to lower losses of the solar cell efficiency than with the 1064 nm nanosecond laser.Roll-to-roll production of thin-film photovoltaic (PV) solar cells and modules is expected to decrease substantially the manufacturing costs, and thus enable a breakthrough in the price of solar electricity per kWh. The roll-to-roll concept implies that the fabrication of these PV devices on flexible substrates is significantly different from the production of the glass based devices. This is especially valid for the monolithic series interconnection of thin-film silicon solar cells into modules, where the laser scribing step of thin-films on opaque foils requires depth selectivity. As adjusting the laser wavelength to the absorption profiles of the involved layers is not sufficient, we are investigating the ablation mechanisms leading to removal of the different layers of thin-film silicon solar cells.In this paper, first results of laser scribes into working solar cells are reported using 1064 nm nanosecond pulsed lasers. Despite the apparent depth selectivity reported earlier for this type of laser, a ...