Synergy Effect of Both 2,2,2-Trifluoroethylamine Hydrochloride and SnF2 for Highly Stable FASnI3-xClx Perovskite Solar Cells

The environmentally friendly additive 2,2,2-trifluoroethylamine hydrochloride (TFEACl) is used in synergy with SnF2 to enhance the efficiency and stability of FASnI(3)-based solar cells. Both TFEA(+) and Cl- are present in the films, but only Cl- is incorporated into the crystal lattice of the perovskite. The addition of TFEACl suppresses the segregation of SnF2, resulting in improvements in film morphology, in addition to a more favorable energy band alignment, and improved suppression of the formation of Sn4+. Consequently, reduced charge recombination and improved charge collection result in an efficiency enhancement from 3.63 to 5.30%. The stability of the devices is also significantly enhanced, with devices with TFEACl retaining over 60% of initial PCE after 350 h of light soaking in ambient, while devices without TFEACl experience failure in 120 h under the same testing condition.