INCREASING SOLAR ENERGY CONVERSION EFFICIENCY IN HYDROGENATED AMORPHOUS SILICON PHOTOVOLTAIC DEVICES WITH PLASMONIC PERFECT META – ABSORBERS

Solar photovoltaic (PV) devices are an established, technically-viable and sustainable solution to society’s energy needs, however, in order to reach mass deployment at the terawatt scale, further decreases in the levelized cost of electricity from solar are needed. This can be accomplished with thin-film PV technologies by increasing the conversion efficiency using sophisticated light management methods. This ensures absorption of the entire solar spectrum, while reducing semiconductor absorber layer thicknesses, which reduces deposition time, material use, embodied energy and greenhouse gas emissions, and economic costs. Recent advances in optics, particularly in plasmonics and nanophotonics provide new theoretical methods to improve the optical enhancement in thin-film PV. The project involved designing and fabricating a plasmonic perfect meta-absorber integrated with hydrogenated amorphous silicon (a-Si:H) solar PV device to exhibit broadband, polarization-independent absorption and wide angle response simultaneously in the solar spectrum. First, recent advances in the use of plasmonic nanostructures forming metamaterials to improve absorption of light in thin-film solar PV devices is reviewed. Both theoretical and experimental work on multiple nanoscale geometries of plasmonic absorbers and PV materials shows that metallic nanostructures have a strong interaction with light, which enables unprecedented control over the propagation and the trapping of light in the absorber layer of thin-film PV device. Based on this, the geometry with the best potential for the proposed device is identified and used for device modelling and, finally the plasmonic enhanced n-i-p a-Si:H solar cell with top surface silver (Ag) metallic structure is proposed. In order for the plasmonic enhanced PV device to be commercialized the means of nanoparticle deposition must also be economical and scalable. In addition, the method to fabricate silver nanoparticles (AgNPs) must be at lower temperatures than those used in the fabrication process for a a-Si:H PV device (less than 180 0C). The results indicate the potential of multi-disperse self-assemble nanoparticles (SANPs) to achieve broadband resonant response for a-Si:H PV devices. Finally a plasmonic enhanced a-Si:H PV using multi-disperse SANPs is realized when AgNPs are integrated to the commercially fabricated nip-a-Si:H PV devices. The devices are characterized for both quantum efficiency and light I–V to evaluate the cell parameters (Jsc, Voc, FF and η). Real–time spectroscopic ellipsometry (RTSE) data is used to model the device performance and the theoretical parameters are compared with the experimental data. Conclusions are drawn and recommendations and future work is suggested

Metamaterial Design and elaborative approach for efficient selective solar absorber

The thesis is focused on developing spectral selective coatings (SSC) composed of multilayer cermets and periodic array of resonating omega structures, turning them to behave like metamaterials, while showing high thermal stability up to1000°C. The developed SSC is intended to be used for the concentrated solar power (CSP) applications. With the aim of achieving highest possible absorbance in the visible region of the spectrum and highest reflectance in the infrared region of the spectrum. The thesis highlights the numerical design, the synthesis and optical characterization of the SSC of approximately 500 nm thickness. A bottom-up approach was adopted for the preparation of a stack with alternate layers, consisting of a distribution of Titanium Nitride (TiN) nanoparticles with a layer of Aluminum Nitride (AlN) on top. The TiN nanoparticles, laid on a Silicon substrate by wet chemical method, are coated with conforming layer of AlN, via Plasma-enhanced Atomic Layer Deposition (PE-ALD). The control of the morphology at the nanoscale is fundamental for tuning the optical behaviour of the material. For this reason, two composites were prepared. One starting with TiN dispersion made with dry TiN powder and deionized water, and the other with ready-made TiN dispersion. Nano-structured metamaterial based absorbers have many benefits over conventional absorbers, such as miniaturisation, adaptability and frequency tuning. Dealing with the current challenges of producing the new metamaterial based absorber with optimal nanostructure design along with its synthesis within current nano-technological limits, we were capable of turning the cermets into metamaterial. A periodic array of metallic omega structures was patterned on top of both the composites I and II, by using e-beam lithography technique. Parameters, such as the size of TiN nanoparticles, the thickness of AlN thin film and the dimensions of the omega structure were all revealed by the numerical simulations, performed using Wave-Optics module in COMSOL Multiphysics. The work showcased clearly compares the two kinds of composites, using scanning electron microscope, X-ray photoelectron spectroscopy(XPS) and electrical conductivity measurement. The improvement in the optical performance of the SSC after the inclusion of metallic omega structures in the uppermost layer of the two composites has been thoroughly investigated for light absorption boosting. In addition, the optical performance of the two prepared composites and the metamaterial is used as a means of validating the computational model

Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application

This book is a collection of the research articles and review article, published in special issue "Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application"

Active and Fast Tunable Plasmonic Metamaterials

Active and Fast Tunable Plasmonic Metamaterials is a research development that has contributed to studying the interaction between light and matter, specifically focusing on the interaction between the electromagnetic field and free electrons in metals. This interaction can be stimulated by the electric component of light, leading to collective oscillations. In the field of nanotechnology, these phenomena have garnered significant interest due to their ability to enable the transmission of both optical signals and electric currents through the same thin metal structure. This presents an opportunity to connect the combined advantages of photonics and electronics within a single platform. This innovation gives rise to a new subfield of photonics known as plasmonic metamaterials.Plasmonic metamaterials are artificial engineering materials whose optical properties can be engineered to generate the desired response to an incident electromagnetic wave. They consist of subwavelength-scale structures which can be understood as the atoms in conventional materials. The collective response of a randomly or periodically ordered ensemble of such meta-atoms defines the properties of the metamaterials, which can be described in terms of parameters such as permittivity, permeability, refractive index, and impedance. At the interface between noble metal particles and dielectric media, collective oscillations of the free electrons in the metal particles can be resonantly excited, known as plasmon resonances. This work considered two plasmon resonances: localised surface plasmon resonances (LSPRs) and propagating surface plasmon polaritons (SPPs).The investigated plasmonic metamaterials, designed with specific structures, were considered for use in various applications, including telecommunications, information processing, sensing, industry, lighting, photovoltaic, metrology, and healthcare. The sample structures are manufactured using metal and dielectric materials as artificial composite materials. It can be used in the electromagnetic spectrum's visible and near-infrared wavelength range. Results obtained proved that artificial composite material can produce a thermal coherent emission at the mid-infrared wavelength range and enable active and fast-tunable optoelectronic devices. Therefore, this work focused on the integrated thermal infrared light source platforms for various applications such as thermal analysis, imaging, security, biosensing, and medical diagnosis. Enabled by Kirchhoff's law of thermal radiation, this work combined the concepts of material absorption with material emission. Hence, the results obtained proved that this approach enhances the overall performance of the active and fast-tunable plasmonic metamaterial in terms of with effortless and fast tunability. This work further considers the narrow line width of the coherent thermal emission, tunable emission, and angular tunable emission at the mid-infrared, which are achieved through plasmonic stacked grating structure (PSGs) and plasmonic infrared absorber structure (PIRAs).Three-dimensional (3D) plasmonic stacked gratings (PSGs) was used to create a tunable plasmonic metamaterial at optical wavelengths ranging from 3 m to 6 m, and from 6m to 9 m. These PSGs are made of a metallic grating with corrugations caused by narrow air openings, followed by a Bragg grating (BG). Additionally, this work demonstrated a thermal radiation source customised for the mid-infrared wavelength range of 3 μm to 5 μm. This source exhibits intriguing characteristics such as high emissivity, narrowband spectra, and sharp angular response capabilities. The proposed thermal emitter consists of a two-dimensional (2D) metallic grating on top of a one-dimensional dielectric BG.Results obtained presented a plasmonic infrared absorber (PIRA) graphene nanostructure designed for a wavelength range of 3 to 14 μm. It was observed and concluded that this wavelength range offers excellent opportunities for detection, especially when targeting gas molecules in the infrared atmospheric windows. The design framework is based on active plasmon control for subwavelength-scale infrared absorbers within the mid-infrared range of the electromagnetic spectrum. Furthermore, this design is useful for applications such as infrared microbolometers, infrared photodetectors, and photovoltaic cells.Finally, the observation and conclusion drawn for the sample of nanostructure used in this work, which consists of an artificial composite arrangement with plasmonic material, can contribute to a highly efficient mid-infrared light source with low power consumption, fast response emissions, and is a cost-effective structure

Nanogenerators in Korea

Fossil fuels leaded the 21st century industrial revolution but caused some critical problems such as exhaustion of resources and global warming. Also, current power plants require too much high cost and long time for establishment and facilities to provide electricity. Thus, developing new power production systems with environmental friendliness and low-cost is critical global needs. There are some emerging energy harvesting technologies such as thermoelectric, piezoelectric, and triboelectric nanogenerators, which have great advantages on eco-friendly low-cost materials, simple fabrication, and various operating sources. Since the introduction of various energy harvesting technologies, many novel designs and applications as power suppliers and physical sensors in the world have been demonstrated based on their unique advantages. In this Special Issue, we would like to address and share basic approaches, new designs, and industrial applications related to thermoelectric, piezoelectric, and triboelectric devices which are on-going in Korea. With this Special Issue, we aim to promote fundamental understanding and to find novel ways to achieve industrial product manufacturing for energy harvesters

Investigation of Radar Signal Interaction with Crossflow Turbine for Aviation Application

The increased adoption of wind energy is an important part of the push towards a net zero-emission economy. One obstacle that stands in the way of a higher rate of wind energy adoption is the interference that wind turbines cause to nearby radar installations. Wind turbines negatively affect the performance of nearby radar sites in a variety of different ways. Almost all types of radar are affected in at least one of these ways.In order to understand the degree to which an object such as a wind turbine interacts with radar, it is important to have detailed radar cross section (RCS) data for the object. In this work, a novel, low-cost, scale model radar cross section characterization system is presented with various advantages over traditional designs. This system was used to characterize the RCS of the novel Crossflow wind turbine. Additionally, work has been carried out on the characterization of metamaterial absorber coatings that can be applied to new and existing turbines for the purposes of reducing their radar cross section and the degree to which they cause radar inter-ference. The works presented can be leveraged to reduce concerns around radar interference from wind turbines, as well as to iteratively generate ge-ometries with lower radar cross sections for the aviation and infrastructure sectors, ultimately accelerating the pace of wind energy adoption and the move towards a net zero-emission economy

Electromagnetic Energy Transduction Using Metamaterials and Antennas

The advent of rectenna systems almost half a century ago has enabled numerous applications in a number of areas, with the main goal of recycling the ambient microwave energy. In previously presented rectennas, microstrip antennas were the main energy source used to capture and convert microwaves to AC power. However, the conversion efficiency of antennas have never been examined in terms of their capability of absorbing microwave energy, and hence any enhancements to the overall efficiency of rectenna systems were mainly attributed to the rectification circuitry instead of the antenna. In the first part of this dissertation, a novel electromagnetic energy collector is presented, consisting of an array of Split Ring Resonators (SRRs), used for the first time as the main electromagnetic source of energy in a rectenna system. The SRR array is compared to an array of patch antennas to determine the radiation to AC efficiency when both arrays are placed on the same footprint. Numerical simulations and experimental tests show that the SRRs achieve higher efficiency and wider bandwidth than microstrip antennas. The idea of electromagnetic energy harvesting using metamaterials is further explored by designing a metamaterial slab based on the full absorption concept. The metasurface material parameters are tuned to achieve a surface that is matched to the free space impedance at a certain band of frequencies to minimize any reflections and ensure full absorption within the metasurface. The absorbed energy is then channeled to a resistive load placed within each element of the metasurface. Different from previous metasurface absorber designs, here the power absorbed is mostly dissipated across the load resistance instead of the substrate material. A case study is considered where the metamaterial slab is designed to operate at 3 GHz. The simulation and experimental results show radiation to AC efficiencies of 97% and 93%, respectively. A novel method is proposed in the second part of the thesis that significantly increases the conversion efficiency of electromagnetic energy harvesting systems. The method is based on utilizing the available vertical volume above a 2-D flat panel by vertically stacking panels while maintaining the same 2-D footprint. The concept is applied to SRRs and folded dipole antennas. In both cases, four vertically stacked arrays are compared to a single array panel, both occupying the same flat 2-D footprint in terms of power efficiency. The numerical and experimental results for both the SRRs and the antennas show that the stacking concept can increase the conversion efficiency by up to five times when compared to a single 2-D flat panel. The third part presents the design of a near unity electromagnetic energy harvester that uses a Tightly Coupled Antenna array. Compared to the unit cell of metamaterial surfaces, the dimension of a TCA unit cell is about five times larger, thus providing simplified channeling networks and cost-effective solutions. The TCA surface contains an array of Vivaldi shape unit cells with a diode at each cell to convert the harvested electromagnetic energy to dc power. The dc power from each unit cell is channeled to one single load via series inductors. A sample 4 X 4 TCA array, when simulated, fabricated and tested shows solid agreement between the simulated and measured results. The thesis then discusses the idea and design of a dually polarized metasurface for electromagnetic energy harvesting. A 4 X 4 super cell with alternating vias between adjacent cells is designed to allow for capturing the energy from various incident angles at an operating frequency of 2.4 GHz. The collected energy is then channeled to a feeding network that collects the AC power and feeds it to rectification circuitry. The simulation results yield a radiation to AC, and AC to DC conversion efficiencies of around 90% and 80%, respectively. As a proof of concept, an array consisting of nine super cells is fabricated and measured. The experimental results show that the proposed energy harvester is capable of capturing up to 70% of the energy from a plane wave with various incident angles and then converting it to usable DC power. As future work, the last part introduces the concept of metasurface energy harvesting in the infrared regime. The metasurface unit cells consist of an H-shaped resonator with the load placed across the gap of the resonator. Different from infrared meta-material absorber designs, the resonator is capable of not only full absorption but also maximum energy channeling across the load resistance. The numerical simulation demonstrates that 96% of the absorbed energy is dissipated across the load resistance. In addition, a cross-polarized H-resonator design is presented that is capable of harvesting infrared energy using dual polarization within three frequency bands