Fully Lead-Free All Perovskite Tandem Solar Cell with Improved Efficiency: Device Simulation Using SCAPS-1D

This paper proposes a fully lead-free all-perovskite multi-junction solar cell that has 24.86% efficiency of the power conversion. Cs2AgBi0.75Sb0.25Br6 has been used for the upper layer and CH3NH3SnI3 for the lower layer as the perovskite absorber layer in the multi-junction structure. Both of the absorber materials are completely free of Pb while absorbing more light from the solar spectrum being of different bandgaps. In order to ensure the same output current for both the cells, the tandem design was calibrated for an extensive range of thickness changes for both layers. The thickness for the lower layer was taken as 426nm and for the upper layer as 400nm in the current matching condition. Overall, open-circuit voltage (Voc) of 1.944V and PCE of 24.86% were found with an improved fill-factor of 68.48% was demonstrated by the device.