Investigation of Laser Ablation Induced Defects in Crystalline Silicon Solar Cells

In this paper, the laser induced defects that result from a picosecond laser ablation (wavelength 355 mm) of passivating SiO2 and SiNx layers on textured silicon surface are investigated for various laser fluence ranging from 0.48J/cm2 to 1.43 J/cm2. In the first part of this paper, we employ the Wright etching technique to identify and quantify thermally propagated dislocations as one of the resulting defects as a function of the laser fluence. Dislocations densities in the order of 4 - 13 x 106 cm-2 are measured. The second part of the paper takes a closer look at the impact of laser induced defects on the effective lifetime and surface recombination current. By comparing both parameters on structures with laser ablation and photo-lithography to pattern the dielectric, it is observed that dislocations formed during the laser ablation process do indeed enhance minority carrier recombination within the silicon wafers. The recombination current at the laser ablated area, for a moderate laser power, is shown to be four times larger than in the case of using lithography.