Assessment of the scribing technology for CIGS solar cell with ps-lasers

Due to the modification of the WP3 objectives the work was concentrated on perovskite photovoltaic that is currently a hot topic in the PV community. Perovskite-based devices do not only allow potential low-cost and simple manufacturing of solar modules but the technology can also be added to already existing PV concepts like c-Si and CIGS in tandem configuration to increase the efficiency without substantially increasing the production complexity. In order to allow fast implementation of the technology a reliable and fast monolithic interconnecti

on concept needs to be developed. In a first step the consortium in WP3 concentrated on understanding the mechanisms of the laser-scribing processes of the various layers in the particular perovskite device architecture; studies of the performance of the laser scribing with standard and ultrashort laser sources were performed. The studies of the surface morphology of the laser scribes in dependence on the laser scribing parameters result in the discovery of the material removal mechanism that can be laser ablation or a laser delamination process. The fundamental parameters for ultrashort laser pulses with ps length are the irradiation direction, film or rear side, and the laser wavelength that determine the mechanism.
Within this task a protocol for sample handling and shipping was developed that ensures minimized degradation of the samples to guarantee reproducible results. Making use of this protocol, the electrical properties of laser scribes have been studied also considering the final functionality of the scribes. For the separation scribe lines P1 and P3 the insulation resistance in dependence on the laser scribing parameters has been studied and optimized. In both cases specific procedures have been developed to achieve reproducible results. For the connecting scribe P2 the contact resistance in dependence on the laser-scribing process and design parameters, e.g. the scribe width, was studied to enabling further optimization.

As first proof of concept perovskite mini-modules on glass substrate were fabricated and tested by using specific device architecture and large-area deposition methods developed at EMPA and applying the adapted laser scribing techniques.
The perovskite mini-modules were fully characterized including the morphology of the scribes, the characteristics of the interconnection area and the photovoltaic properties of the mini-modules. Further results have been obtained by additionally defining single reference solar cells both by laser and mechanical scribing. The currently achieved module efficiencies that are exceeding 10% and are almost comparable to their small-sized reference cells confirm the high quality of the ps-laser-scribing processes. The obtained results are the basis for minimizing serial resistance and dead area losses of the interconnection area for further module efficiency improvements.