Laser ablation of SiO2 for locally contacted si solar cells with ultra-short pulses

We apply ultra-short pulse laser ablation to create local contact openings in thermally grown passivating SiO2 layers. This technique can be used for locally contacting oxide passivated Si solar cells. We use an industrially feasible laser with a pulse duration of tau(pulse) similar to 10ps. The specific contact resistance that we reach with evaporated aluminium on a 100 Omega/sq and P-diffused emitter is in the range of 0.3-1 m Omega cm(2). Ultra-short pulse laser ablation is sufficiently damage free to abandon wet chemical etching after ablation. We measure an emitter saturation current density of J(0e) = (6-2 +/- 1-6) X 10(-13) A/cm(2) on the laser-treated areas after a selective emitter diffusion with R-sheet similar to 20 Omega/sq into the ablated area; a value that is as low as that of reference samples that have the SiO2 layer removed by HF-etching. Thus, laser ablation of dielectrics with pulse durations of about 10ps is well suited to fabricate high-efficiency Si solar cells. Copyright (c) 2007 John Wiley & Sons, Ltd.