Impact of laser pulse width on laser ablation process of high performance PERC cells

This study quantitatively compares the characteristics of ablation processes using nanosecond (ns) and picosecond (ps) pulse width green (532 nm) lasers. The laser ablation results are analyzed using Electron Probe Micro Analyzer (EPMA), quasi-steady-state photo-conductance (QSSPC) measurements and transmission electron microscopy (TEM). The ablated using the ns green laser is predominantly melted, due to the relatively longer pulse width, and laser damage is incurred to a depth of 2.5 μm. Meanwhile, the laser ablation using the ps green laser precisely removes the thin layers on the surface without severely melting the sample and the observed laser damage depth is almost negligible. However, since the maximum damage depth (∼2.5 μm) using the ns laser is much shallower than the local contact depth (10-17 μm), the passivated emitter and rear cell (PERC) efficiencies using the ns and ps pulse width lasers converge to a power conversion efficiency of 19.4%.