Setting the baseline for the modelling of Kesterite solar cells: The case study of tandem application

The Kesterite solar cells research landscape is at a crossroad and despite a much improved understanding of the limitations of this class of materials, the current performance deficit contrasts with the several other thin film technologies reaching conversion efficiency values well above 20%. It is more important than ever for the Kesterite community to collaborate directly or indirectly and data sharing is an essential building block in that regard. This work proposes a detailed set of modelling baselines and parameters, based on a consistent set of properties obtained with experimental devices made by our group. These parameters permit to accurately reproduce all photovoltaic figures of merits of reference experimental Kesterite cells with a relative accuracy of 1% or less. As a case study, and using optical modelling based on the transfer matrix method in complement, the potential of Kesterite materials in tandem devices with either a Perovskite or a Crystalline Silicon partner is evaluated. It is found that a moderate improvement of pure selenium CZTSe, feasible in the short to middle term, would realistically permit to use this material as bottom subcell in tandem with a Perovskite top cell and obtain efficiencies reaching the 30% threshold. On the other hand, using a Kesterite absorber in a top subcell with a silicon bottom subcell appears as particularly ambitious even when considering several important optimizations to the material, and it is believed that only an important breakthrough would render this material viable for such application. The complete set of material parameters, optical indices and modelling files are shared for the Kesterite community to use and build improve upon.