Device simulation of 17.3% efficient lead-free all-perovskite tandem solar cell

Present research paper brings forth the results of simulation-based studies carried out on all-perovskite tandem (both top and bottom subcells made up of perovskites) multijunction devices. The all-perovskite tandem structure presented in this work employs a wide bandgap perovskite, i.e., Cs2AgBi0.75Sb0.25Br6 (1.8 eV) and a narrow bandgap perovskite, i.e., FACsPb0.5Sn0.5I3 (1.2 eV) as top and bottom cell respectively. An additional merit of the reported work is projection of lead (Pb)-free perovskite, Cs2AgBi0.75Sb0.25Br6 and low Pb content-based perovskite, FACsPb0.5Sn0.5I3 based tandem solar cell. The viability of proposed tandem design is performed in two steps firstly, 1.8 eV perovskite-based top cell is simulated and calibrated to fit the state-of-the-art conversion efficiency of 10.1%, and then, 1.2 eV perovskite-based bottom cell is simulated to have a calibrated efficiency of 14.2%. After calibrating the standalone (top and bottom) subcells, both the devices are evaluated for tandem configuration. The current matching conditions between the top and bottom cell is obtained at different thicknesses of the absorber layer in both top and bottom subcell. The optimized thickness for perovskite, 380 nm for top cell and 400 nm for bottom cell are obtained for tandem configuration. Top and bottom cells (fed with the filtered spectrum) reflect the conversion efficiency of 10.01% and 7.36%, respectively. Overall, tandem design showed a conversion efficiency of 17.3% owing to an enhancement in open-circuit voltage (VOC), which is 1.83 V.