Defect Modulation via SnX<sub>2</sub> Additives in FASnI<sub>3</sub> Perovskite Solar Cells
Syed Joy, Tareq Hossain, Adam Tichy, Stephen L. Johnson, Kenneth R. Graham
Abstract
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.