Laser parameters for silicon solar cell processing: a simulation of heat transfer and material modification

In this paper we present a simple technique for approximating laser process parameters needed for laser processing of crystalline silicon solar cells. The calculation computes the changes of silicon material properties during the time of laser-material interaction. As the laser pulse energy modifies optical and thermal properties of silicon, the chronological segmentation illustrates the temperature rise within the irradiated volume and indicates the time needed for melting or evaporation. Depending on the desired material modification, commercially available laser sources are analyzed regarding their process suitability. Simulating the laser system performance reveals its theoretical output and determines its expected efficiency. Simulations in this paper correlate well to experimental data and are done for different fields of interest: a) ablation rate during laser drilling for EWT cells, using IR wavelengths in the order of 1 μs b) depth and width of laser grooves as used for Laser Grooved Buried Contact cells (LGBC) or edge isolation, using wavelengths in the IR and VIS c) process windows during selective laser doping with 532 nm using PSG as sole phosphorous source d) laser parameters needed for Laser-Fired Contacts (LFC).