Date of Award
31-8-2024
Document Type
Thesis
School
School of Electrical & Electroncis Engineering
Programme
Ph.D.-Doctoral of Philosophy
First Advisor
Dr.K.Sangeetha
Keywords
Lead Free Hybrid Halide Perovskite, 2D Perovskites, White Light Emission Optical Limiting, Structure Related Properties
Abstract
Two-dimensional (2D) hybrid halide perovskites have become a versatile material in diverse applications like optoelectronics, lighting and display, magnetism, etc. These materials are often termed as layered hybrid halide perovskites (LHHPs) due to their unique structure with alternate organic and inorganic layers. The presence of insulating organic layers separates the inorganic perovskite slabs, creating a quantum-confined architectural configuration. This unique configuration endows these materials with a spectrum of distinctive functionalities, encompassing photovoltaics, lighting and displays, second harmonic generation, optical limiting, ferroelectricity, and ferromagnetism. The exceptional attribute is that a single LHHP can respond autonomously to external stimuli, such as changes in pressure or temperature, by transforming their structure into another stable form and this behaviour underscores their intelligence, sustainability, and multifunctionality. Therefore, the realization of such functionalities relies on carefully deciding their compositions that in turn precisely control symmetry, alignment, and orientation of the molecular moieties.
The general form of LHHP is A2BX4 (A – Organic cation, B – Metal cation, X – Halide). Some organic-lead halide perovskites like (N-MEDA)PbBr4, (EDBE)PbBr4, 2,3,4(MBA)2PbBr4 were all luminescent giving a broad visible spectrum (white light) irrespective of different organic (A) cations. Similarly, (BEA)2CuCl4 and (CEA)2CuCl4 were reported to exhibit reversible thermochromism. On the other hand, in (EDBE)PbX4 the change in X halide anion (X = Cl, Br, I), has altered the absorption edges and triggered white light emission. Therefore, a change in an A-site cation or a halide anion directs the perovskite to alter slightly the existing properties of the LHHP.
But a B-site metal cation, when changed, the LHHP show multifunctionality and fascinating switching behaviours in response to external stimuli. For instance, (PEA)2CuCl4, demonstrated concurrent ferroelectric and ferromagnetic characteristics. Conversely, (PEA)2ZnCl4 exhibited a switching behaviour between luminescence and dielectric properties in response to temperature variations. Therefore, changing B-site metal cation introduces a novel spectrum of multifunctionalities marked by exotic coupling and switching behaviours within the perovskite.
Our investigation aims in bringing the multifunction to LHHP by altering the B-site cation and therefore unravelling the underlying intricacies of structure-property relationship of LHHP.
4MBACl, 4MBA2CdCl4, 4MBA2CuCl4 and 4MBA2PbCl4 are the four distinct materials (4MBA: 4-methoxybenzylamine) that were synthesized and crystallized using a simple and cost-effective slow solvent evaporation method for the investigation. 4MBACl is a simple organic halide without a metal cation and the other three were LHHPs, each with different B-site metal cations (B = Cd, Cu and Pb). The thesis reports luminescence, nonlinear optical limiting, thermochromic property, nonlinear harmonic frequency generations and ferromagnetic property of these different hybrid materials.
In general, 3D HHPs, in addition to their intriguing research possibilities, poses unsettling challenges related to their stability. They are sensitive to external forces including oxygen, moisture, light, temperature, mechanical pressure, etc. All these factors have raised significant concerns regarding the long-term operational stability of the material. Efforts are still being made for improving their intrinsic stability by developing encapsulation techniques, incorporation of hydrophobic components, chemical passivation, designing functional additives and finding many more innovative solutions. In this line, the present investigation has enhanced the stability by reducing the dimension to 2D (LHHPs), purposely choosing bulky organic cation 4MBA as A-site, that can sterically hinder the interactions between the inorganic layers.
Recommended Citation
E, Anu Ranjani Ms, "Investigations on Structure-Related Properties of Organic Inorganic Hybrid Materials for Multifunction" (2024). Theses and Dissertations. 203.
https://knowledgeconnect.sastra.edu/theses/203