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Transparent conductive oxide (TCO) thin films were removed from glass substrates using femtosecond laser pulses. Irradiating through the glass, the threshold for complete TCO ablation was much lower than for front-side irradiation. Additionally, the former method created almost rectangular crosssectional groove profiles despite the Gaussian laser beam. This indicates a non-thermal ultrafast ablation mechanism via critical carrier concentration achieved by the femtosecond pulse in the TCO at the interface. Very narrow scribes of only 5 µm width provided very good electrical separation, making this technique very attractive for micro-structuring applications like scribing of thin-film solar cells.

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Laser ablation for the preparation of isolating trenches in transparent conductive oxide films on glass has been studied comparing the use of nano- and femtosecond pulses at approximately 1 mu m wavelength. By a detailed analysis of the obtained ablation craters and grooves, it can be shown that this processing, which is called P1 scribing in the field of thin film photovoltaics, can be considerably optimized with so-called "cold" ablation: Using femtosecond pulses, the P1 scribe can be done with almost rectangular cross section profiles, achieving the required electrical separation already at widths well below 10 mu m, without thermal and mechanical stresses in the substrate or adjacent material. Analogous preliminary results for P2 scribes indicate that this technique allows reducing the total scribe region (optically inactive zone) to widths below 50 mu m

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