Novel Rear Contact Architectures in CIGS Solar Cells: Modelling and Experimental Fabrication

Abstract

Cu(In,Ga)Se2 (CIGS) solar cells are amongst the best performing thin-film technologies mainly due to post-deposition treatment (PDT) improvement of the last years. However, the electrical simulation baseline models did not quite follow the experimental results. Moreover, there is no baseline model for recent CIGS solar cells until the time of writing of this thesis, whereas a scientific paper is already being written to be submitted, to provide with an updated model. This study provided with an updated experimentally-based baseline model for electrical simulations in SCAPS-1D with the incorporation of the PDT effects and high-efficient device characteristics. This baseline model produces comparable results with high-efficient 22.6 % record cell from ZSW. In order to be even more cost and environmental competitive with the widely used silicon photovoltaic technology, it is important the implementation of ultra-thin devices. However, electrical and optical limitations prevent the widespread of these devices, such as rear recombination and insufficient light absorption. The baseline model is applied to ultra-thin absorbers, whereas an increased bulk CIGS defect density is necessary to model the experimental data. Furthermore, simulations results reveal that by addressing these limitations would be possible to achieve an ultra-thin solar cell with at least 19.0 % power conversion efficiency, with open circuit voltage values even higher compared to the ZSW record cell. On the other hand, it is shown the feasibility of the fabrication of a metal/dielectric structure at the rear contact with industrial-friendly processes. The innovative rear contact has the potential to tackle the rear recombination with the passivating dielectric and improving light absorption with the high reflecting metal layer in ultra-thin devices. Such structure effectively with both benefits has not been reported yet.