Two-dimensional metal halide perovskites (2D MHPs) are promising candidates for transistor channel materials because of their high mobility in the lateral direction; however, Sn-based 2D MHPs exhibit poor film quality and oxidation stability. Here, we report a simple method to improve the performance and stability of 2D MHP transistors by incorporating sodium iodide (NaI) additives. By adding 1 vol % NaI (Na1), the transistors with phenethylammonium tin iodide (PEA2SnI4) exhibited reduced dual-sweep hysteresis, robust bias stability, and larger hole mobility (2.13 cm2 V-1 s-1) than that of a pristine device (0.39 cm2 V-1 s-1). Improvements in the film quality, such as increased grain size, crystallinity, and better film coverage, were observed in the PEA2SnI4:NaI film. In addition, NaI effectively passivated the iodine vacancies at the grain boundaries, thereby suppressing the defects.
Keywords: alkali metal cation; defect passivation; phenethylammonium tin iodide; thin-film transistors; two-dimensional metal halide perovskite.