Device Optimization of a Pb-Free All Perovskite Tandem Solar Cell with 29.59% Power Conversion Efficiency

Abstract

This study has focused on simulating a highly efficient lead-free all-perovskite tandem solar cell using the SCAPS 1D device simulation tool. In the tandem structure, the top cell used Cs2AgBi0.75Sb0.25Br6 (Eg = 1.80 eV), and the bottom cell used FAMASnGeI3 (Eg = 1.40 eV) as the absorber material. Also, ZnO and NiOx were used as the electron transport layer (ETL) and the hole transport layer (HTL), respectively. Primarily the individual top cell and bottom cell have been optimized. The highest efficiency of the top cell was found to be 17.13% with performance parameters VOC = 1.23V, JSC = 15.57 mA/cm2 and FF = 89.39%, whereas the optimized efficiency of the bottom cell was found to be 17.58% with performance parameters VOC = 0.85V, JSC= 27.38 mA/cm2 and FF = 75.34%. The thickness of the absorber of the top cell and bottom cell shows a significant impact on the device performance and the optimum thickness for the Cs2AgBi0.75Sb0.25Br6 absorber layer was found to be 400 nm, whereas for the FAMASnGeI3 layer was found to be 200 nm. Careful optimization of the tandem device has resulted in an improvement of the performance and obtained an efficiency of 29.59 %, with JSC of 17.50 mA/cm2, VOC of 2.09 V, and FF of 80.87%. The final simulated device sums up tremendous potential for the fabrication of a highly efficient PSC device using lead-free perovskite materials towards excelling commercialization.