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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.
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.
CIS (Cu(In,Ga)(S,Se)2) thin film solar cells show a high potential to achieve the efficiencies of Si wafer-based solar cells. The commonly applied patterning processes for the integrated interconnects are based on nanosecond laser ablation and mechanical scribing. Both methods introduce damages on the thin films by thermal effects and mechanical forces. By picosecond laser processing we realized all three patterning steps to the monolithic thin films CIS modules, namely the separation of the molybdenum back electrode, the absorber and the ZnO font electrode (P1, P2 and P3 respectively). We achieved an efficiency of 14.7% for 300 x 300 mm² modules.