Simulation of Laser Structuring of Thin-Film Solar Cells

We present a theoretical model of the interaction of ultra-short laser pulses with semiconductorbased multilayer structures. In particular the model focuses on laser processing of thin-film solar cells. The propagation of laser light within the thin-film system is described by a finite-difference model in order to determine the distribution of absorbed power. Since light propagation in semiconductors is strongly influenced by screening due to excited carriers we include the dynamics of charge carriers which may be driven either by direct absorption of the laser radiation or by multiphoton absorption and impact ionization of highly excited carriers. Depending on the excitation wavelength and pulse energy, absorption occurs in different depths of the structure which has a large effect on the efficiency of the laser ablation process. In a second step the energy density deposited by the laser beam is transferred to a thermo-mechanical model which describes the actual ablation process. Results from this model are compared with experimental findings.