F. Fink

Controlling the thermal impact of ns laser pulses for the preparation of the P2 interconnect by local phase transformation in CIGSe

The thermal impact of nanosecond laser pulses was beneficially employed and well-controlled for the preparation of the P2 interconnect by local phase transformation (i.e., by drawing conductive lines rather than removing the material) in CIGSe mini-modules, which were demonstrated to outperform their conventionally needle-patterned counterparts. Conductivity and elemental composition of the scribed lines as well as the extent of the heat-affected area were analyzed, quantified and taken into account for achieving optimal CIGSe solar module performances. This approach opens new prospects for significant simplification of the serial interconnection, since the P2 und the P3 can be scribed simultaneously after deposition of both the CIGSe and the TCO layer.

Electrical and structural functionality of CIGSe solar cells patterned with picosecond laser pulses of different wavelengths

Electrical and structural functionality of monolithic interconnection of CIGSe solar cells by P1-P3 picosecond laser ablation has been successfully established and evaluated as being competitive to conventional needle scribing. In all three patterning steps the material is selectively and completely removed yielding structurally well-defined trenches at high scribing speeds up to 1 m/s. P1 and P2 ps laser scribing clearly improves the solar cell efficiencies whereas P3 scribing is still challenging due to shunts resulting from laser-induced alteration of the absorber material.

Direct pulsed laser interference texturing for light trapping in a-Si:H/μc-Si:H tandem solar cells

We present results on direct pulsed laser interference texturing for the fabrication of diffraction gratings in ZnO:Al layers. Micro gratings of 20 micron diameter with a groove period of 860 nm have been written using single pulses of a 355 nm picosecond laser using a home-built two-beam interference setup. The groove depth depends on the local laser intensity, and reaches up to 120 nm. At too high pulse energies, the grooves vanish due to surface melting of the ZnO. The fast scanning stage and the high repetition rate laser of a laser scribe system have been used to write grating textures of several cm2 in ZnO:Al films with a surface coverage of about 80%. A typical laser written grating texture in a ZnO:Al film showed a haze value of about 9% at 700nm. The total transmission of the film was not lowered compared to the film before texturing, while the sheet resistance increased moderately by 15%. A-Si:H/μc-Si:H solar cells with laser textured ZnO:Al front contact layers so far reach an efficiency of 10% and current densities of 11.0 mA/cm2, and 11.2 mA/cm2 for top and bottom cell, respectively. This is an increase of 16% for the bottom cell current as compared to reference cells on planar ZnO:Al. The voltage of the laser textured cells is not reduced compared to the reference cell when slightly overlapping laser pulses of reduced pulse energy are applied. This method allows to write textures in ZnO:Al films that e.g. have been deposited with strongly varying deposition conditions, or cannot be texture etched in HCl. The method can be improved further by using 2D periodic patterns and optimizing the groove pitch, and may be applicable also to other solar cell technologies.