Flexibility of perovskite as investigated by micro-tensile testing

Abstract

Exploring alternative energy sources is a highly important assignment in the world. The sun is a sustainable, reliable and almost infinite source of energy that can make significant contributions to the global demand for energy. Organic-inorganic halide perovskite solar cells have been studied as attractive candidates for highly efficient solar cells. The photovoltaic efficiency of perovskite-based solar cells has recently soared rapidly from 3.8% to above 20%. Methylammonium lead halide (CH3NH3PbX3, MAPbX3) perovskites holds promise for highly effective next-generation photovoltaic devices. Such perovskite-based devices have many advantages: remarkable optical properties, longer electron-hole diffusion lengths, high light absorption coefficients and good cost-effectiveness, and show promise not only in photovoltaic applications but also in other applications such as luminescent devices and transistors. However, these materials are still afflicted with long-term stability problems due to organic-inorganic bonding between decomposed perovskite and disturbed hydrogen because of the high polarity of water molecules. Recently, perovskite devices have attracted substantial attention for flexible/stretchable electronic devices, so that their mechanical properties are important for device reliability and durability. Some researchers have recently explored the elastic properties of perovskite-based solar cells using nanoindentation tests. Unfortunately, these nanoindentation tests can evaluate such properties only quantitatively, since such properties are strongly affected by substrates or under layers. In addition, it is difficult to determine the mechanical properties of stretchable in the pulling direction. For this reason, here we fabricate various free-standing perovskite layers and evaluated tensile mechanical properties using small-scale tensile tests. Perovskite active layers of various thicknesses were fabricated using solution processes such as spin-coating and drop casting and then were separated in different ways depending on thickness. The tensile mechanical properties related to flexible/stretchable behavior were analyzed by a nano-tensile tester in laboratory with 1 nm working resolution. This study of mechanical properties of MAPbX3 perovskites should be useful in research on solar cell durability and fundamental mechanisms.