LEAD-FREE HALIDE PEROVSKITE MATERIAL FOR SUPERCAPACITOR APPLICATION

Abstract

The purpose of this master's thesis is to explore lead-free halide perovskites as novel materials for energy storage devices. The objective is to create highly efficient and energy-dense smart perovskite electrodes for use in supercapacitor application. The excellent optoelectronic characteristics and mixed electronic ionic conductivity of lead-based halide perovskites have made them popular as efficient energy sources. However, one of the biggest challenges to commercialization has been lead poisoning. The research considers the development of lead-free devices and addresses the challenge of poor device performance and poor device stability in 3D and 2D material respectively. A quasi-2D or 2D/3D perovskite material is advised to achieve the ideal balance between pure 3D and layered 2D materials to improve device stability and overall device performance. Furthermore, compared to their three-dimensional (3D) counterparts, lowdimensional layered perovskite (2D) structures using bulky organic ammonium cations (PEA+) have significantly improved stability but generally worse performance. 3D perovskites with significant ion migration, one of the major concerns for structural instability, show better charge storage capacity. In contrast, strong van der Waals contacts and bulky spacer ligands in 2D perovskites inhibit the migration of halide ions. Mixed properties of 2D and 3D or quasi-2D layered perovskite demonstrate more efficient, tuneable optoelectronic properties and long-term stability. The performance and stability of the electrochemical supercapacitor may be significantly influenced by ion migration, as we have shown by fabricating porous electrodes from 3D-Cs2AgBiBr6 bulk perovskite, 2D/3D or quasi-2D PEA-Cs2AgBiBr6, and layered perovskite 2D PEA4AgBiBr8. The quasi-2D electrodes were found to have an energy density ~1.75 times higher than the 3D perovskite electrodes and ~4.5 times higher than that of pure 2D halide electrodes. Compared to 2D and 3D electrodes, quasi-2D has a maximum capacitance retention of around 93% after 2000 operation cycles. Ex-situ X-ray diffraction was conducted to examine further structural changes in the quasi-2D, 2D, and 3D perovskite electrode materials. It was determined that the ordering arrangement of Ag+/Bi3+ cation improves the crystallinity of the structure, which enhances the device performance and stability of the quasi-2D electrode. Also, Ag3+ is essential for improving the strength of quasi-2D and 2D electrodes, as evidenced by X-ray photoelectron spectroscopy (XPS). A symmetric solid-state supercapacitor was fabricated and analyzed using a two-electrode method, demonstrating that the quasi-2D configuration has the highest energy density compared to the pure 2D and 3D perovskite electrode materials.