Passivating defects in SnO2 electron transport layer through SnF2 incorporation in perovskite solar cells

Metal halide perovskite solar cells have received a lot of attention from researchers because of their excellent performance, and their efficiency has increased rapidly over the past decade and is now comparable to that of conventional crystalline silicon solar cells. Perovskite solar cells (PSCs) are currently most commonly constructed with SnO2 as an electron transport layer (ETL). Nevertheless, its existence of bulk phase defects and surface defects pose an impediment to developing a higher level as the most favorable electron transport layer. This paper suggests an efficient technique to decrease the defects of SnO2 through incorporating a metal halide SnF2 in planar (n-i-p type) perovskite solar cells. Divalent Sn in SnF2 is easily oxidized to tetravalent Sn, leading to more conversion of divalent Sn to tetravalent Sn, which inhibits the formation of oxygen vacancies from the source. F replaces defective sites, passivates oxygen vacancy defects, and reduces the content of hydroxyl oxygen on the surface. Doping SnF2 enhances the conduction band value and conductivity of SnO2, making the energy levels of the ETL and perovskite interfaces more compatible. This eliminates energy barriers in charge transport. Consequently, the fill factor of planar PSCs that were prepared through SnO2:SnF2 ETL exhibited an increase from 80.01% to 82.12%. Furthermore, the efficiency of PCE underwent an improvement from 21.43% to 22.65%.