The Thermal And Mechanical Effects During Pulsed Laser Interaction With Semiconductor Materials And The Application Of Laser Scribing On The CIGS Thin Film Solar Cell

The melting threshold and surface morphology of semiconductor materials, thermal stress distribution, the initiation mechanism of the surface crack of silicon induced by laser and the application of laser scribing CIGS thin film solar cell are studied with the theoretical analysis, finite element method as well as experimental method.The melting threshold of silicon induced by millisecond laser, nanosecond laser and picoseconds laser are obtained to study the relation between the melting threshold and the laser pulse duration. The results indicate that the damage thresholds increase with the increasing laser pulse duration. The damage morphologies of silicon induced by millisecond laser, nanosecond laser and picoseconds laser are compared. The heat cumulative effect is obvious for the millisecond laser. The damage morphology is deep melting crater. The damage morphologies induced by nanosecond laser and picoseconds laser are surface damage.Based on the thermo elastic-plastic theory, two-dimensional spatial axisymmetric finite element model of silicon irradiated by laser is establised. IR pyrometer is used to measure the tempertuare to verify the numerical simulation result. Then the transient thermal stress field of silicon irradiated by millisecond laser is obtained.The shape of the dominant cracks on silicon induced by millisecond laser with different energy densities is different. Finite element method is used to calaulate the thermal stress before the crack initiation. The initiation mechanism of the different cracks is explained qualitavely combined with the experimental result. The moment of the crack initiation is predicted.The results show that the cleavage crack is located within the laser spot. The radial crack and the circumferential crack are located outside the laser spot. The cleavage cracks are generated after laser irradiation. The radial crack and the circumferential crack occur during laser irradiation. The radial crack is influenced by hoop stress. The circumferential crack is generated under the action of the radial stress and shear stress together.The laser front side direct ablation scribing and backside ablation for front side patterning are performed to finish laser scribing the CIGS thin film solar cell. The laser scribing quality is stable but the opportunity of local shunt generation is higher for the front side direct ablation. Nested circular laser scribing technique is proposed to optimize the laser scribing parameter simply and fast. The current-voltage curve is measured in process after laser scribing without demounting sample. The equivalent circuit model of solar cell is improved to study the influence of the laser scribing quality on the electrical character.Results of this thesis may provide theoretical and experimental basis for the thermal and mechanical effect on semiconductor induced by laser, and may accelerate the development and application of laser scribing the CIGS thin film solar cell.