Humidity Effects on Pure and Doped All-Inorganic Perovskite Thin Films Analyzed by Scanning Probe Microscopy

We doped the perovskite (PVSK) surface with tin or germanium to replace a portion of the lead. This substitution not only reduced the lead toxicity but also stabilized the overall structure due to the size-matching relationship between the substituted ions and the internal ions of the PVSK. A scanning Kelvin probe microscope was used to analyze the trend of surface potentials of PVSK thin films stored under different humidity conditions (RH: 25–75%). Results showed that the overall change in surface potential due to increased humidity for Sn-doped and Ge-doped PVSK was lower than that of undoped PVSK. Additionally, force curves were acquired under controlled ambient humidity conditions to measure the adhesion forces between the probe and the pure PVSK and Sn-doped PVSK surfaces. An overall trend of increasing adhesion was observed going from low to high humidity for all surfaces. Between surfaces, in particular for the Sn-doped versus the pure PVSK sample at RH 75%, the adhesion was much lower at 15.66 versus 19.21 nN, respectively. This indicates that the Sn-doped PVSK surface exhibits higher resistance to water adsorption. The force curve method is useful for investigating the hydrophilic and hydrophobic properties of the PVSK surface.