Property Modulation of Two-Dimensional Lead-Free Perovskite Thin Films by Aromatic Polymer Additives for Performance Enhancement of Field-Effect Transistors.

The inevitable oxidation of Sn2+ and p-type self-doping has plagued the development of two-dimensional (2D) Sn-based perovskite field effect transistors. In this work, we demonstrate the modulation of the properties of phenethylammonium tin iodide ((PEA)2SnI4) perovskite thin films by introducing the aromatic polymer additives of poly(4-vinylphenol) (PVP) and poly(vinyl pyrrolidone) (PVPD) during the crystallization processes, keeping the 2D layered structure of (PEA)2SnI4 unchanged. The proposed formation mechanisms of the polymer-assisted (PEA)2SnI4:PVP and (PEA)2SnI4:PVPD films disclose that the interactions between the polymers and (PEA)2SnI4, such as hydrogen bonds, π-π interactions, and coordination bonds, lead to the improvement of the morphology and crystallization as well as the inhibition of Sn2+ oxidation of the films. However, the field-effect transistors based on the two polymer-assisted (PEA)2SnI4 thin films constructed on the dielectric of poly(vinyl alcohol) (PVA) modified by crosslinking PVP (CL-PVP) exhibit quite a different performance. Compared with the (PEA)2SnI4 transistor, without sacrificing the hole mobility, the on-off current ratio of the (PEA)2SnI4:PVP device increases by one order of magnitude, and the subthreshold slope declines slightly due to the reduced leakage current, which results from the reduction of p-type self-doping of the perovskite film and the improved quality of the perovskite/dielectric interface because of the strong π-π interactions between the benzene rings in CL-PVP and (PEA)2SnI4:PVP. In contrast, the (PEA)2SnI4:PVPD transistor exhibits relatively poor overall performance because of the N-vinylpyrrolidone of PVPD. More importantly, employing PVP and PVPD as additives can effectively enhance the chemical stability of (PEA)2SnI4 as well as the operational stabilities of the corresponding transistors. Our work provides an effective strategy for selecting chemical additives to improve 2D perovskite properties and suppress the oxidation of Sn-based perovskites, and paves a way toward the future applications of Sn-based perovskite optoelectronic devices with high performance and stability.