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 τ_pulse ∼ 10ps. The specific contact resistance that we reach with evaporated aluminium on a 100Ω/sq and P-dijfused emitter is in the range of 0-3-1 mΩ cm². 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) × 10^-13 A/cm² on the laser-treated areas after a selective emitter diffusion with R_sheet ∼ 20 Ω/sq into the ablated area; a value that is as low as that of reference samples that have the SiO ₂ 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.