Opto-electronic Properties of a Few Dimensionally Controlled Hybrid Halides and Related Systems

Abstract

To mitigate the adverse environmental effects of burning fossil fuels, it became necessary to explore alternative ‘clean’ renewable energy sources to meet the ever-increasing energy demands. While silicon-based solar cell devices have been at the forefront for decades, recently organic-inorganic hybrid halide perovskites APbX3 [A = methylammonium (MA+), formamidinium (FA+); X = halides] have transpired as a new family of materials as the alternatives, owing to their exceptional optoelectronic properties such as tuneable bandgap, low exciton binding energy, high carrier mobility, high defect tolerance etc. Remarkably, the efficiency of these solar cells with hybrid perovskites as the active layer has shot up from 3.8% in 2009 to exceed 25% at present. However, the environmental stability of the given materials remains elusive, placing a considerable hurdle on the way to its commercialization. Compositional engineering by partially substituting ‘A-site’ (MA+ with FA+) and/or ‘X-site’ (I- with Br-) ions of the perovskite have proven to be one of the successful approaches to enhance the stability of these materials. More recently, reasonable success in increasing environmental stability is achieved by incorporating bulkier and hydrophobic organic cations at the ‘A-site’, resulting in 2D layered counterparts with enhanced bandgap and exciton binding energy. In this thesis work, we have explored the opto-electronic and thermal properties of dimensionally controlled 2D as well as compositionally engineered 3D hybrid halide systems. In addition to the solar energy, hydrogen evolution reaction (HER) has a great significance in promoting electrochemical energy conversion in fuel cells. Being one of the most efficient catalysts for HER, MoS2 – the flagship member of the 2D layered transition metal dichalcogenides family, has gained much attention recently. We have also discussed the electronic structure of MoS2, responsible for such novel applications.