Nanoantennas for solar energy harvesting

Abstract

Recent years have witnessed an enormous interest in developing solar cells by utilising different materials to increase their efficiency. This interest was motivated by the rapid world demand on cheap and clean energy sources, where the main source of world’s power is the fossil fuels. The current photovoltaics technology can not meet the solar power market due to the very low efficiency provided. The philosophy of this thesis is to find an efficient alternative by designing an efficient nanoantenna for receiving the solar radiation and coupling it to an integrated rectifier for AC to DC conversion. This thesis presents the design and optimisation of different types of nanoantennas with a performance comparison to find the optimum solution for this application. The figure of merit in choosing the best design was the captured electric field in the feed gap of the nanoantenna and the area under curve, which is essential in calculating the harvested energy. In addition, this thesis investigates the use of nanoarray instead of single elements. The aims is to increase the captured electric field at the gap of the array where all the elements will contribute in increasing the field in one common gap. Feeding lines will be employed to drive the captured fields from the centre of each single element towards the common gap. Another reason behind using nanoarrays is to reduce the number of rectifiers by using one rectifier per array instead of one rectifier per single element, and hence increase the total efficiency. Futhermore, a simple analysis on dipole nanoantenna using method of moments (MoM) is presented in this thesis. The results obtained from this method is compared with those found from finite element method (FEM) simulations and an acceptable agreement is achieved. To calculate the total conversion efficiency of solar rectennas, it is important to compute the rectification efficiency of the metal/insulator/metal (MIM) diode along with the coupling efficiency between the antenna and the diode. To this end, quantum mechanics was used to calculate the characteristics of the MIM diode. The results show that bowtie nanoantennas are the best candidate for this application in either the single and array form since they have wider bandwidth and larger area under curve. Additionally, the analysis using MoM gives the designer better understanding on how the system works and exhibits lower complexity and reduced computational requirements.