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The production of CIS thin film solar cells is still employing some mechanical steps of structuring, where thin layers have to be selectively separated in three patterns (P1 to P3) for the monolithic serial interconnection. We report on the high speed structuring of these patterns by picosecond laser ablation at 1064 nm. We demonstrate on 100x100 mm2 samples, that the molybdenum back electrode can be structured with a process speed of up to 15 m/s. The ZnO front electrode film can be line separated with up to 15 m/s, the CIS absorber layer is structured with up to 4 m/s. Furthermore we extended our laser processes to 300 x 300 mm2 pilot line samples which were displaying efficiencies of 13.4%.
A femtosecond laser is used for selective structuring of biocompatible sensorchips consisting of a Ta2O5/Pt layer system on glass substrate. It was observed, that for low fluences the Ta2O5 can be selectively lifted-off from the Pt, while high fluences enable a removal of both layers. The underlying physical effects are investigated by pump-probe microscopy allowing the observation of the whole ablation process ranging temporally from femtoseconds to microseconds. Results show the formation of a gas-liquid mixture at 3 ps, causing the Ta2O5 to bulge after some ns. The Ta2O5 is disrupted in small particles after 50 ns.
For the monolithic serial interconnection of CIS thin film solar cells, 470 nm molybdenum films on glass substrates must be separated galvanically. The single pulse ablation with a 660 fs laser at a wavelength of 1053 nm is investigated in a fluence regime from 0.5 to 5.0 J/cm². At fluences above 2.0 J/cm² bump and jet formation can be observed that could be used for creating microstructures. For the investigation of the underlying mechanisms of the laser ablation process itself as well as of the bump or jet formation, pump probe microscopy is utilized to resolve the transient ablation behavior.
A picosecond laser lift-off process of an about 0.5 μm thick Mo layer on a glass substrate can be induced by irradiating the layer from the glass side. A pump-probe setup for time- and space resolved microscopy is used to investigate the ablation process in a time domain from a few picoseconds up to 3.6 ns. The results display a bulging of Mo within 1 ns followed by a lift-off at times past 3.6 ns. Furthermore, the setup is used for in situ investigations of a multi pulse ablation through the whole layer stack (ZnO/CIS/Mo/Glass) of a CIS thin film solar cell.