Fibrous Nanomaterials for Enhanced Light Absorption and its Applications in Photovoltaic Energy Conversion

This thesis presents a new, simple and precise nano-scale fabrication technique: by using femtosecond laser irradiation to develop novel nanofibrous structures. The well-organized web-like structure will have a high surface area that agglomerates through fusion to form interweaving fibrous structures. These structures will significantly advance microelectronic, biomedical and photonic devices. The novel optical properties in nanofibrous structures made of silicon, metal and coated material will be applicable to new solar cell technology. The synthesis, characterization, and specification of materials such as silicon, titanium, aluminum and gold-silicon are discussed in detail. Existing theories of nanoparticle formation by femtosecond ablation were used to explain some of the observed phenomena. Most of the research was devoted to the influence of laser parameters on the spectral response of web-like fibrous nanostructures. These approaches then elaborated to connect the laser parameters (pulse width, pulse frequency, laser polarization and laser dwell time) with the enhancement of optical properties of silicon nanofibre. The periodic micro-hole arrays decorated in aluminum nanofibre structure improved the light extinction of solar cells, which is fully demonstrated through this research. Instead of doping, sputtering deposition, or ball milling, the rutile (tetragonal) titanium oxide TiO2 nanospheres particles were created through irradiated bulk Ti using a femtosecond laser at an ambient condition. The growth of TiO2 nanostructure is highly recommended for the applications of dye-sensitized solar cell (DSCC) and photovoltaic applications. The number of laser pulses was also used to control the synthesis of the nanofibrous structure of a thin gold layer on a silicon wafer. The highly improved coupling efficiency between the light and the bulk quantity of gold nanoparticles may be attributed to the excitation of confined plasmon modes on structured metal surfaces. The prototype and design approach of photovoltaic (PV) based on silicon nanomaterials is presented in the application section. The illuminated and dark