The laser is an extremely suitable non-contact tool for automated processes needed in order to improve the efficiency of solar cells. One of the most common laser processes in the production of crystalline silicon solar cells is laser edge isolation. Ultra–short pulse laser sources with sufficient power to meet 1 s cycle time promise to improve the process. Due to the short interaction time they ablate material nearly without melting and hence reduce losses in the cells due to thermal damage which would occur during ablation caused by nanosecond laser pulses. The necessary ablation depths for successful pn-junction isolation can achieved either by using high pulse energy at a certain repetition rate or by using much higher repetition rates with a lower pulse energy such that more pulses are released per area in the same period of time. These two approaches lead to different thermal impacts, morphology and shunt resistances. Furthermore, it is shown that the complete ablation of the n+-doped layer, with a thickness of approx. 0.5 μm, is not sufficient for edge isolation even if an ultra-short pulse laser is used. This is visualized by a logistic model used to describe shunt resistance as a function of depth.