Browsing by Author "Kumalo, Sandile"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Efficiency Enhancement in Photovoltaic Devices Using Light Management and Morphology
    (University of the Witwatersrand, Johannesburg, 2024-04) Kumalo, Sandile; Quandt, Alexander; Wamwangi, Daniel
    Meeting the ever-increasing global demand for energy is society’s principal challenge for attaining economic growth and dynamic technological progress. Novel materials and technologies to extend photoabsorption and harness the solar emission spectrum are critical for producing solar-based electricity on a large scale. Current techniques and nanostructure-based approaches can revolutionise the production of solar electricity. In this work, experimental light management strategies through plasmonic nanostructures in silicon-based thin film solar cells were explored to augment power conversion efficiency (PCE). These devices incorporated plasmonic, magnetoplasmonic, and coreshell nanostructures coated with SiO2. It was demonstrated that magnetoplasmonic nanoparticles enhance interactions with both the charge of electrons and the unpaired spin with the B-field component of the electromagnetic spectrum. Furthermore, core-shell structures passivate the surface of the nanoparticles, significantly enhancing PCE. The highest PCE (10.7%) was observed for Au@SiO2 nanoparticles, attributed to a bonding plasmon mode at the interface between the nanoparticles and the surrounding bulk material. Additionally, F e3O4@SiO2 nanoparticles primarily enhanced the short-circuit current (Jsc), due to magnetic interactions with superparamagnetic nanoparticles. A detailed investigation into the Curie temperature (Tc) of various magnetic nanoparticles revealed that 4 nm F e3O4 nanoparticles possess the highest Tc of 906.1 K, indicating strong magnetic stability under operational conditions. For Ni@Fe core-shell nanoparticles, a decrease in Tc with increasing Ni content was observed, highlighting the critical role of composition in tuning magnetic properties. Morphological analysis through TEM imaging revealed uniform dispersion and spherical morphology for Au nanoparticles, crucial for consistent plasmonic properties. The addition of SiO2 shells to both Au and Ag nanoparticles significantly improved their optical absorption characteristics due to the modification of the local dielectric environment. Furthermore, a study on the bulk heterojunction of organic solar cells demonstrated that processing solvents play a pivotal role in optimising active layer performance. It was found that solvent mixtures, particularly 2-MEA and toluene in a 7:3 ratio, significantly enhance device efficiency by promoting better phase separation and charge transport, achieving a PCE of 5.77%. These findings showcase the significant potential of nanostructures and solvent processing in improving the efficiency of photovoltaic devices. The enhanced PCE and stability of devices incorporating plasmonic and magnetoplasmonic nanoparticles, along with optimised solvent processing techniques, provide valuable insights for future research and development in solar energy technologies.
  • No Thumbnail Available
    Item
    Fabrication of plasmon enhanced amorphous silicon solar cells using RF magnetron sputtering
    (2019) Kumalo, Sandile
    Renewable energy continues to attract intensive interest as a possible alternative to fossil fuel based energy sources due to its merits which are abundance, clean and geographically unlimited natural resources. The increased concerns of the harmful effects to the environment by fossil fuels has prompted a massive drive for photovoltaic based energy solutions. The current available solar technologies,thin film solar cells,have the potential of reducing production costs. However,the low photo conversion efficiency slows the irrapid integration into the energy mix. In this work,we explore sophisticated light management strategiesofsiliconbasedthinfilmsolarcellstoenhancetheirphotoconversioneciency. These strategies ensure the enhancement of absorption of the complete solar spectrum, also reduced materials costs and a strongly reduced emission of greenhouse gases. The work involved fabricating and designing three significant layers of a hydrogenated amorphous silicon (a-Si:H) solar cell device, and integrating plasmonic nanoparticles in the commercial a-Si device to enhance optical absorption through Surface Plasmon Resonance (SPR). The project also involved several strategies to increase the conversion effciency of a commercial a-Si standard device for comparative studies. Recent approaches in the improvement of light absorption in solar cells were due to the use of plasmonic nanoparticles. It is well known theoretically as well as experimentally that metallic nanostructures have a strong interaction with light. This interaction allows remarkable control of the trapping and propagation of the photons in the intrinsic layer of thin film devices. For such a plasmon enhanced device to be economically viable and commercialised, the nanoparticles must be silver (Ag) and gold (Au), and the method used for the deposition must be carried out at temperatures lower than the ones used for the fabrication of a-Si:H layers. Thus the RF magnetron sputtering technique in combination with ion implantation of each a-Si layers to form n and p-type a-Si was used to fabricate the three layers of an a-Si:H device. The architecture of the device is in a n-i-p or p-i-n sequence of doped semiconductor layers and each layer is fabricated using sputtering. Then Ag and Au nanoparticles were integrated into the commercial a-Si reference device. The devices are characterized for power conversion efficiency and I-V characteristics.