EXPERIMENTAL INVESTIGATION OF FRICTIONAL PROPERTIES OF TWO-DIMENSIONAL HYBRID ORGANIC-INORGANIC PEROVSKITES

Abstract

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) have attracted remarkable attention over the years because of their outstanding physical properties for application in optoelectronic devices. 2D HOIPs have been proposed as the next generation materials for solar-collecting applications as well as light-emitting diodes, due to the higher moisture and illumination stability. Recently, extensive efforts have been made to understand the properties of 2D HOIPs. As a result, it was found that 2D HOIPs may provide improved electronic properties and environmental stability by using pentylamine as organic spacer molecules between inorganic materials without significantly affecting the optical properties. It was also shown that 2D HOIPs encapsulated hexagonal boron nitride exhibited higher environmental stability. In addition, the photoluminescence of 2D HOIPs was found to be promoted by mixing with polymers. It was further shown that the optical bandgap of the polymer-mixed 2D HOIPs gradually increased with increasing concentration of polymers and that the photoluminescence lifetime increased due to the improved crystalline quality and reduced trapping states. Given that mechanical properties of 2D HOIPs may significantly affect the manufacturing process as well as the durability of devices, mechanical properties such as elasticity and hardness were investigated. Especially, recent studies showed that replacing the organic parts with stiff and multifunctional components may improve the stability of perovskite solar cell absorption and using a specially engineered structure of a thin organic layer can increase elastic modulus and hardness. However, the fundamental frictional properties of 2D HOIPs have not been explored. In this study, the effects of topography, thickness, and organic molecule chain length in HOIPs on friction were experimentally investigated using atomic force microscopy (AFM). The results showed that the effect of topography on nanoscale friction has been observed according to local slope variation, but the intrinsic friction is low. Also, the thickness-dependent friction behavior and the effect of chain length on the friction characteristics at the nanoscale are significantly smaller than that of the silicon oxide substrate and most clearly observed in single-layer, bi-layer, and bulk films. The findings of this work may be helpful for the performance of 2D HOIPs in various device applications.