Simulation study of single solar cell structures based on the compositionally variable perovskite material CsSn(I1−xBrx)3 for tandem configured solar cells

This work involves simulating the performance of a single solar cell configured TiO₂/CsSn(I_1−xBr_x)₃/Cu₂O, based on the lead-free, metallic CsSn(I_1−xBr_x)₃ perovskite absorber, whose bandgap energy is tunable as a function of its bromine content. The simulation model used takes into account the variation of the physical parameters of the absorber as a function of its composition, represented by the ratio x, and also makes it possible to obtain the photovoltaic performance of the device studied as a function of x. The state of the front interface between the ETL electron-transport layer and the perovskite absorber was evaluated as a function of (x), by calculating the conduction bandgap offset and the misfit strain. Different electron transport layers were considered. The simulation results showed that the absorber composition influences all photovoltaic parameters, and that the choice of electron transport layer is important to achieve a compromise between device performance and the correct state of the front interface. The results indicate that CdZnS and CdS ETL materials correspond to bromine absorption ratios of x = 0 and x = 0.35 for which the conduction band offset values are − 0.03 eV and 0 eV respectively and the misfit strain 0.09 and 0.057, while ZnSe and ZnS correspond to ratios of x = 0.75 and x = 1 for which the conduction band offsets are 0 eV and 0.38 eV respectively and the strain 0.056 and 0.08. Based on these results, we determined the following optimal structures: CdZnS/CsSnI₃/Cu₂O and CdS/CsSn(I_0.65Br_0.35)₃/Cu2O, which achieved yields of 18.1% and 18.5% respectively, as suitable for lower subcells with narrow bandgap energies, while the structures: ZnSe/CsSn(I_0.25Br_0.75)₃/Cu₂O and ZnS/CsSnBr₃/Cu₂O, which achieved efficiencies of 17.5% and 18% respectively, as top sub-cells with wide bandgap energies, in a tandem solar cell device. The aim is to develop highly efficient, non-toxic and stable single and tandem perovskite cells.