Laser-silicon interaction for selective emitter formation in photovoltaics. II. Model applications

Laser doping is an attractive way to manufacture a selective emitter in high efficiency solar cells, but the underlying phenomena, which determine performance, are not well understood. The mathematical model developed in Part I solves the equations of conservation of mass, momentum, and energy and is used here to investigate the effects of processing parameters on molten zone geometry, average phosphorus dopant concentration, dopant profile shape, and sheet resistance. The empirically calculated sheet resistance values are in good agreement with independently measured sheet resistance values reported in the literature. Process maps for output power and travel speed show that molten zone geometry and sheet resistance are more sensitive to output power than travel speed. The highest molten zone depth-to-width aspect ratios and lowest sheet resistances for 532nm laser beams are obtained at higher laser powers (>13W) and lower travel speeds (<2m/s). Once the power level is set, the travel speed can be varied for further optimization of dopant concentration and geometry.