|Author:||Wong, Chiu Po|
|Title:||Fabrication of flexible electrodes for photovoltaic applications|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Physics|
|Pages:||112, xviii leaves : ill. (some col.) ; 30 cm.|
|Abstract:||Traditional solar cells are usually bulky in size, heavy in weight and expensive in production cost. Because of these constraints, they are impossible for fashion clothing applications. Metalized polymers are new hybrid materials which have already generated a steady research interest because of their high conductivity, high flexibility, light weight and cheap production cost in the application of electronic components. Metalized polyester fibres enhance applicability of these metalized polymers because of their advantageous flexibility and wearability. They provide chances for photovoltaic applications on textile and clothing industry. In the future, solar cell will be fabricated on these plastic fibres so as to develop "wearable solar cell". The polyester fibres to be metallized in this project were PET fibres whose diameter was around 125 microns. In the first part of this project, the bottom electrodes, the metal coatings on PET fibres which acted as the flexible substrates, were required to have good conductivity. Metallization methods based on wet chemical techniques were used to coat the required metal layers on the plastic fibres. In this project, two different metals (nickel and copper) had been employed. The Ni-coated polyester fibres were fabricated by electroless plating method. The thickness of the Ni-layer was about 200 nanometres. Cu layers with thicknesses varied from 1.5 to 20 microns were further deposited on the Ni-coated polyester fibres using electro-plating method. The effects of various processing parameters such as sodium hydroxide etching time, concentration of NaOH, deposition time and temperature for the Ni-electroless plating process on the surface roughness of the metal coatings were conducted. The transport properties of the coated metal layers coated were investigated by measuring the current-voltage curve (I-V Curve) using a four-point probe. Based on these measurements, the resistivity as well as conductivity of the metal layers had been worked out. For the structural characterization, surface and cross-sectional morphologies of Ni- and Cu-coated polyester fibres were observed by optical microscope (OM) and scanning electron microscope (SEM). The structural phases of the metal coatings on the polyester fibres were studied by X-ray diffraction (XRD).|
In the second part, vertical-aligned ZnO nanorod arrays were grown on Ni-coated polyester fibres by wet chemical methods. ZnO nanorods with length about 2 microns and diameter about 0.5 micron (aspect ratio in between three and four) were deposited onto these Ni-coated polyester fibres using a chemical solution deposition (CBD) technique. Besides direct growth of ZnO nanorods on Ni-coated PET fibres using CBD method, a ZnO seed layer was first deposited on the Ni-coated PET fibres before using the CBD method to coat ZnO nanorod. This ZnO seed layer improved the vertical alignment of the ZnO nanorods on the metal-coated polyester fibres. This ZnO seed layer was deposited by pulsed laser deposition (PLD). The phases of the grown ZnO nanorods were studied by XRD and Raman spectroscopy. The surface and cross-section morphologies of the ZnO nanorods were examined using field-emission scanning electron microscope (FE-SEM). The optical properties of the ZnO nanorods grown on PET sheet using CBD with same conditions as those on the Ni-coated fibres were also characterized. Room-temperature transmittance measurement and photoluminescence measurement were performed using UV-Visible spectrophotometer and Nd:YAG laser operated with wavelength of 266 nanometre respectively. On the basis of our results, high-quality ZnO nanorods were shown to be successfully fabricated on Ni-coated polyester fibres.
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