Numerical simulation of highly efficient lead-free all-perovskite tandem solar cell.

• All- perovskite lead –free tandem solar cell is simulated with efficiency 26.73%. • CH 3 NH 3 GeI 3 & FAMASnGeI 3 perovskite layers have been used. • Different elctron transport layers have been studied. • The impact of defect density and front electrode work function is also studied. The numerical simulation of lead-free all-perovskite tandem solar cell using solar capacitance one dimensional tool (SCAPS 1D) has been performed. The combination of methyl ammonium germanium halide (CH 3 NH 3 GeI 3) as wide band-gap (1.9 eV) perovskite layer and FA 0.75 MA 0.25 Sn 0.25 Ge 0.5 I 3 (FAMASnGeI 3) as a low band-gap (1.4 eV) perovskite layer is considered for the first time which shows the optimal device efficiency of 26.72%. The present work studies the effect of the different electron transport layer, perovskite absorber thickness and its defect density on photovoltaic performance. Further, the effect of front electrode work function on the device photovoltaic performance is also studied. It has been observed that the device open circuit voltage (Vo C) is significantly affected by the built-in voltage (V bi) across the perovskite layer. In addition, the effect of thickness of the perovskite absorber layers is also investigated. Moreover, the effect of defect density of the absorber layer is also explored, and it has been found that for better device performance the defect density needs to be as low as possible. Furthermore, it has been observed that the work function of the front contact plays a significant role and for the proposed device its value should not be more than 4.4 eV. The proposed all–perovskite tandem solar cell shows the remarkable photovoltaic parameters i.e., open circuit voltage (V OC) = 1.07 Volts, short circuit current density (J SC) = 28.36 mA/cm2, fill factor (FF) = 84.39% and efficiency (η) = 26.72%. [ABSTRACT FROM AUTHOR]