Investigation of lead-free MASnI3-MASnIBr2 tandem solar cell: Numerical simulation

Lead-free perovskite materials have attracted noteworthy interest for photovoltaics as they are free from toxicity and instability issues encountered in lead-based perovskites. In this work, we report on a simulation study of a two-terminal monolithic all lead-free tandem solar cell. The (MASnI(3)) cell with 1.3 eV bandgap is used as a bottom cell and the top cell is (MASnIBr(2)) with a bandgap of 1.75 eV. The calibration of the standalone bottom and top cells initially gives a conversion power efficiency (PCE) of 5.42% and 5.74%, respectively. After comprising these two initial sub-cells in a two-terminal all lead-free monolithic tandem cell, a tandem efficiency of 7.66% is obtained with a matching current is 10.36 mA/cm(2) in this case. Based on parametric analysis, the values of perovskite doping, perovskite defect density and ETL/HTL affinity are optimized. The PCE of individual cells after enhancement has increased to 11.01% and 10.17% for bottom and top cells, respectively. As a result of the enhancement of the two cells, the tandem efficiency improves to 15.66% and the matching current also increases to 13.94 mA/cm(2). In addition, the current matching point is tracked while changing the band gaps of bottom and top cells in the ranges of (1.1 eV-1.4 eV) and (1.55 eV-1.85 eV), and for the thicknesses in the ranges (150 nm-400 nm) and (150 nm-500 nm), respectively. The simulations done in this paper shows the significant influence of current matching point on the tandem cell performance. All simulations are performed by using SCAPS-1D under AM1.5G illumination.