CIGS P3 scribing using ultrashort laser pulses and thermal annealing

In general, laser structuring of CIGS solar modules causes material modifications in the vicinity of the processed area. The irradiated region often reveals high densities of defect states or melt that affect the electrical properties dramatically. In particular, this is a problem for laser P3 scribing where trenches should isolate the front from the back electrode. In this paper, we demonstrate optimized P3 scribes using ultrashort-pulse laser processing in combination with thermal annealing yielding permanently increased solar cell performance. We further investigate this behavior with the help of a two-diode equivalent circuit model. The simulations correlate very well to our obtained experimental results. We show that basically two main effects are responsible for the performance increase after thermal annealing. Firstly, the recombination current within the p-n junction decreases over orders of magnitudes, and secondly, the overall shunt resistance rises significantly.