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

Abstract

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 (MASnI3) cell with 1.3 eV bandgap is used as a bottom cell and the top cell is (MASnIBr2) 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/cm2 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/cm2. 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.