Thermal processing of thin films using ultra-short laser pulses: applied to photovoltaic materials

In this thesis a novel approach to raise the thermal selectivity of superficial heat treatments, exploiting ultra-short laser pulses, is proposed and studied. That is, the effective applicability of ultrafast lasers for selective heat treatments is proven by increasing the performance of different films of materials adopted for manufacturing thin film photovoltaic devices - i.e. SnO2, ZnO and Mo. At the same time, the scalability of surface processing with ultrafast lasers for future possible industrial applications is evaluated and shown to be in practice only limited by the available laser power. First, a finite-element model was developed for ZnO and Mo thin films. It is analytically demonstrated that ultra-short pulses can be exploited to increase the selectivity during thermal processes, via numerical comparison of the induced temperature-cycles induced by ns- and ps-pulses. It is also numerically demonstrated that the heat selectivity is preserved when the beam is expanded, hence showing the scalability of the process. Next, the effect of selective thermal processing of SnO2, ZnO and Mo thin films is studied experimentally. The conclusion of this thesis is positive regarding the beneficial effects of ultra-short laser pulses exploited for highly selective thermal processing of thin films.