Effects of d0 and s2 cations on optical properties of silicate glasses

There is a growing requirement worldwide for low-cost, reliable, and green electricity. From 2000 to 2015, the total installed capacity worldwide of solar photovoltaics (PV) increased from 4 GW to 227 GW, and is worth more than £75 billion annually. Solar photovoltaics are available in a multitude of technologies such as various morphologies of silicon, perovskite, organics, and other semiconducting technologies. However, a common issue regardless of technology is a spectral mismatch, where the incident solar irradiance does not equally match the range in which the semiconductor efficiently absorbs photons, and a second issue is degradation of polymeric components from UV photons. Ultimately critical failure of a solar module can occur due to the degradation of polymeric glues in the module, which allows for the ingress of water which rapidly leads to failure. Even before the critical failure, transmission of light is reduced due to the polymeric components becoming discoloured under UV irradiation to a yellow and brown colour due to the formation of organic radicals and short chain alkenes. Glass front sheets are used for the transmission of light to the active semiconducting material in a PV module whilst providing environmental, chemical and physical protection. Spectral mismatch and polymeric damage can be ameliorated through absorption of ultraviolet (UV) photons in the glass layer of the PV module. Incorporation of particular cations, in specific oxidation states into a glass matrix can afford strong UV absorption, and no visible or infrared (IR) absorption allowing for the protection of the polymeric species within the module with no reduction in transmission of lower-energy photons required by the PV cell for conversion to electric current. Furthermore, broadband visible emission can be induced from the absorption of UV photons with careful selection and preparation of the cations in the glass matrix, which allows a better spectral matching 8 from the incident (and re-emitted) radiation and the absorption profile of the semiconductor. This thesis describes the effects of certain cations with d0, d10 and s2 electron configurations in silicate glasses. Investigations into the optical, structural and chemical properties of doping silicate (soda lime silica and borosilicate) glasses with cations of titanium, zirconium, hafnium, niobium, tantalum, molybdenum, and tungsten (d0), zinc (d10), bismuth, lead and tin (s2) ions. Shifts in the absorbance profiles of doped and base glasses were measured by UV Visible IR absorption spectroscopy. These measurements were conducted in conjunction with UV Visible IR fluorescence emission and excitation spectroscopy measurements, by which the oxidation state(s) and fluorescence profiles of the dopants can be elucidated. X-Ray diffraction (XRD) was undertaken to confirm the amorphous nature of the materials prepared. Raman spectroscopy was used to investigate the structure of the glasses and to determine whether changes occurred upon addition of the dopants studied. Electron paramagnetic resonance spectroscopy (EPR) and X-Ray Absorption Near Edge Structure (XANES) measurements were performed to elucidate the oxidation state/s of the dopants within the glasses. X-Ray fluorescence (XRF) spectroscopy was carried out to measure the proportions of oxides within the glasses and confirm that the melt-quench regime did not result in excessive volatilisation of materials or other contamination. Differential scanning calorimetry (DSC) was used to determine the glass transition temperature (Tg) of the prepared glasses.