SOLAR ENERGY HARVESTING FOR PHOTOVOLTAIC CELLS AND PHOTOCATALYSIS

Abstract

In recent years, alternative energy resources have gathered tremendous attention due to an increase in energy demand and overcome the global effects of burning fossil fuels. Solar energy is an abundant and clean resource of energy and is one of the most promising alternatives to fossil fuels. This thesis investigates the various approaches to harvesting the solar energy and transforming it into electrical and chemical energy. The primary focus of this thesis is employing plasmonic metal nanoparticles as light harvesting elements in photovoltaic cells and photocatalytic materials. Triangular metal nanoparticles (Au, Ag) exhibit strong plasmonic effects due to the presence of sharp features, and their optical properties are tunable based on their size. By integrating Ag@SiO2 nanotriangles in dye-sensitized solar cells (DSSCs), ca. 30% enhancement in the power conversion efficiency (PCE) was achieved. However, the sharp features of Ag nanotriangles are not stable, and the Ag nanotriangles are oxidized at elevated temperatures. The changes in the morphology of these Ag@SiO2 nanoparticles at different annealing temperatures and in different environments (dry air and N2) was studied by X-ray absorption spectroscopy (XAS). Upon annealing in air, the silver nanotriangles decomposed to small (~2 nm) Ag particles, whereas in a N2 atmosphere, they formed truncated triangles. To overcome this stability issue, Ag@SiO2 nanotriangles were replaced by Au@SiO2 nanotriangles. By integrating these nanomaterials in DSSCs, panchromatic light harvesting in the device was achieved. Plasmonic light harvesting was also explored as a route to promote Pd catalysis using AuPd nanotriangles. Upon light illumination, the energy from excited plasmons in Au is transferred to Pd, and this resulted in an enhancement in the rates of the reactions. Recently, another new light harvesting material based on organic-inorganic hybrid perovskites (CH3NH3PbX3; X= Cl, I, Br) has been explored in solar cells. In perovskite solar cells, to determine the optimum conditions for efficient light harvesting and charge collection, the perovskite layer thickness and relative humidity (RH) in the atmosphere were investigated. Results showed ~ 300 nm thick perovskite layers and 40% atmospheric RH are the best conditions for achieving efficient devices.