Search

Tin halide perovskites suffer from high defect densities compared with their lead counterparts. To decrease defect densities, SnF 2 is commonly used as an additive in tin halide perovskites. Herein, we investigate how SnF 2 compares to other SnX 2 additives (X = F, Cl, Br) in terms of electronic and ionic defect properties in FASnI 3 . We find that FASnI 3 films with SnF 2 show the lowest Urbach energies ( E U ) of 19 meV and a decreased p-type character, as probed with ultraviolet photoemission spectroscopy. The activation energy of ion migration, as probed with thermal admittance spectroscopy, for FASnI 3 with SnF 2 is 1.33 eV, which is higher than with SnCl 2 and SnBr 2 , which are 1.22 and 0.79 eV, respectively, resulting in less ion migration. Because of improved defect passivation, the champion power conversion efficiency of FASnI 3 with SnF 2 is 7.47% and only 1.84% and 1.20% with SnCl 2 and SnBr 2 , respectively.