Design, Optimization and Characterization of Colloidal Photonic Crystals for Environmental Application

Abstract

The use of solar energy is generally considered as one of the most beneficial solutions against non-renewable resources such as coal and oil. Substantial efforts have been made to design, test and synthesize new materials that can transform light energy into thermal, chemical, and electrical energy. Semiconductor materials are widely examined because of their ability to produce photo-generated electrons which can, therefore, be used to produce energy or generate chemical reactions. Therefore, regardless of how solar energy is utilized, the main issue is the light-harvesting capability of the materials, which essentially determines the number of photoinduced carriers. This thesis offers insights into the use of spherical colloidal photonic crystals or otherwise known as photonic beads as light harvesters for environmental applications involving sensors, photocatalysis and photoelectrochemical cells (PEC). The spherical photonic crystal structure can possibly be the cutting-edge material for next-generation light-harvesting devices. The present work offers the development of robust, easy, stable photonic beads generation along with the technical challenges of building the structure under different methods. For the first time, we have demonstrated that the spherical photonic crystal structure offers extra leverage for light trapping as opposed to planar photonic crystals, particularly for fluorescent signal enhancement. Subsequently, the fabrication of inverse spherical photonic crystal structure was demonstrated in order to study the electron-hole pair separation in photocatalysis by effectively trapping light at the photonic band edges. The use of photoelectrochemical systems (PECs) is an attractive option for solar-driven water splitting, which can provide continuous, viable, carbon-free energy by converting direct sunlight into more useable energy. We have also designed and developed PEC cells to collect a full spectrum of solar energy and increase the efficiency of the PEC device by incorporating the photonic crystals, which can effectively enhance light-harvesting capabilities and thereby improving the stability of the device. The objective of this thesis is to analyze the interaction of light-matter in spherical colloidal photonic crystals experimentally and to optimize the structures for use with optical sensors, photocatalysis and wireless photoelectrochemical cells. The finding of this research not only enhance our knowledge for light manipulation in spherical colloidal photonic crystals but also contribute to the development of a new effective platform.