Device Engineering of Highly-Efficient Eco-Friendly Novel FASnI 3 Based Tandem Photovoltaic Cells

Power Conversion Efficiency (PCE) of Silicon-based Solar Cells (SiSC) has nearly stagnated, which has led to extensive research in area of the Perovskite Solar Cell (PSC) as well as their tandem configuration with SiSC to achieve high PCE Perovskite-Silicon Tandem Solar Cell (TSC). However, existence of lead together with instability of perovskite is a key challenge which requires exploring non-toxic perovskite material. This work focuses on investigating and optimizing a novel lead-free absorber material Formamidinium Tin Iodide (FASnI 3 ) and a lead-based MAPbI 3 for PSCs, analyzing their performance by considering the optimization of absorber thickness, interface defects and electrical properties in standalone configurations; and further, it is followed by realizing tandem configuration of FASnI 3 and MAPbI 3 based PSC as top cells with SiSC as bottom cell. Two terminal (2-T) monolithic TSC has been designed by calculating transmitted filtered spectrum of top cell through transfer matrix approach & current matching techniques. Through altering the perovskite layer thickness, the present investigation has focused on examining current (J SC ) matching conditions in between top PSC & bottom SiSC. The optimized thickness values for FASnI 3 and MAPbI 3 has been observed to be, respectively, 175 nm and 260 nm. Optimized Standalone PSCs based on FASnI 3 and MAPbI 3 exhibit PCE of 27.63 % and 30.90 %, respectively. A lead-free TSC with FASnI 3 on Si exhibits PCE of 31.99 % (V OC : 2.29 V; J SC : 18.62 mA/cm 2 ) in contrast to a lead-based TSC of MAPbI 3 on Si delivering PCE of 40.60 % (V OC : 2.32 V; J SC : 19.30 mA/cm 2 ). This work can be an useful contribution to understand comparative differences between lead-based and lead-free TSC, and to realize lead-free, highly-efficient eco-friendly perovskite-silicon TSC.