Production of CIGS solar modules – What's new in basic research?

The Munich University of Applied Sciences has conducted in-depth investigations into the ablation mechanism for molybdenum during the CIGS production. Up to now, it had been assumed that a rapidly expanding gas is responsible for removing material from the rear. The research findings refute this model.

In order to manufacture CIGS solar modules, a thin molybdenum film is deposited on the glass substrate. This film is subdivided into a large number of thin, electrically insulated strips in order to increase the voltage of the module. This structure is created using a laser process known as laser ablation. This technique is significantly more efficient when an ultra-short-pulse laser hits the molybdenum film from the back through the glass. In contrast to the long-established method of firing the laser from the front, this approach results in far fewer microcracks and melting.

The team working with Dr. Matthias Domke at Munich University of Applied Sciences has conducted in-depth investigations into the ablation mechanism for molybdenum. Plansee supported the project and provided molybdenum-coated glass samples which had been manufactured in their in-house PVD coating lab.

Up to now, it had been assumed that a rapidly expanding gas is responsible for removing material from the rear. According to this theory, the gas is formed as a result of vaporization under the high energy of the laser pulse at the glass/molybdenum interface. The research findings refute this model: It is only the thermal expansion caused by the heating and melting of the molybdenum that generates the pressure wave which causes material to be removed. Abrupt vaporization is only of minor significance in this context.

You can find more details in the paper Evidence of Pressure Waves in Confined Laser Ablation.