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Optimization of picosecond laser structuring for the monolithic serial interconnection of CIS solar cells

Authors


  • This article was published online on [23 January 2012]. Error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected [10 September 2012].

Correspondence: Gerhard Heise, Laser Center, Munich University of Applied Sciences, Lothstrasse 34, 80335 Munich, Germany.

E-mail: gerhard.heise@hm.edu

ABSTRACT

We report on the optimization of selective picosecond laser structuring for the monolithic serial interconnection of (Cu(In,Ga)(S,Se)2) CIS thin film solar cells. We introduce a quantitative value to compare the energy efficiency of the different investigated laser processes, the specific ablation energy, which indicates the required energy to remove a certain volume of the specific material. We have examined the structuring efficiencies for induced laser ablation processes for a modification of the beam profile (elliptical and flat-top beam shaping) and for the application of different laser wavelengths (1064 and 532 nm). Application of induced laser processes (often referred as “lift-off”) decreases the specific ablation energy dramatically by nearly one order of magnitude. Modifications of the beam profile such as elliptical and flat-top beam shaping are nearly halving the energy per ablated volume relative to a circular beam. The application of a laser wavelength 532 nm decreases the specific ablation energy compared with 1064 nm significantly for processes involving the CIS layer. We finally demonstrate that with a picosecond laser power of only 2 W, the molybdenum back contact (P1, glass side) and the ZnO front contact (P3, ZnO on CIS) can be structured with a process speed of up to 4 m/s. About 2 µm thick CIS layer (P2) is structured by standard direct laser ablation at higher energy densities with 200 mm/s. Copyright © 2012 John Wiley & Sons, Ltd.

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