Abstract
Titanium -dioxide (TiO2) has garnered immense interest as a potential photon absorber after the discovery of its photocatalytic properties. However, its absorption is limited to the ultraviolet region of the solar spectrum. Despite numerous efforts being made, the challenge to extend its absorption capability to the entire visible and near infrared region (vis-NIR) still exists, which together constitute about 90 % of the solar spectrum. In this dissertation, a multiphase nano TiOx network, rich in defects and oxygen vacancies, has been presented which can absorb photons over a broader range of the solar spectrum. Experimental studies were initially conducted to phase functionalise titanium towards enhanced photon absorption via a single step, ultrashort laser pulse material interaction process. This phase functionalised titanium, characterised to be uniquely composed of multiple oxide phases of titanium, can effectively absorb photons in the vis-NIR region. Using the above study as a template, a complex three-dimensional self-assembled nano network composed of similar multiphase titanium oxides, was then synthesised. Free of any external dopants, it exhibits a remarkable absorption of photons ranging from 300-1000 nm. To further improve the absorptive properties of this ‘multiphase nano TiOx network’, particularly in the lower visible range, the phenomenon of Surface Plasmon Resonance was utilised via its hybridisation with gold and gold/palladium alloy. This successfully resulted in further optimisation of its absorption. The final study of the multiphase nano TiOx was done to understand the fundamental physics behind its broadened photon absorptive behaviour. The condition of synthesis was varied by introducing various contrasting plasma environments. Pronounced disorders and oxygen defects of varying degrees within the crystalline structure were observed. The enhanced and broadened absorption spectrum achieved was attributed to such defects and disorders. The research done in this thesis demonstrates a unique nanomaterial based on multiple oxides phases of titanium that is capable of absorbing photons both in the visible and NIR regions. The contribution made towards the synthesis, investigation and subsequent manipulation of the self-assembled multiphase nano TiOx network can thus be exploited in various photon harvesting applications like photovoltaics and photo catalysis, where such a broadband photon absorption is desirable.
Highlights
Absorption of photons is desirable in diverse applications
This chapter deals with the experimental setup of the laser fabrication system, materials and methodology employed for the experiments and the various characterisation methods used for the studies in this dissertation
This chapter describes the experimental set up used for synthesis of the nanomaterials for this study, followed by the various methods used for its material characterisation and absorption studies
Summary
Absorption of photons is desirable in diverse applications This involves the transfer of energy from photons to electrons of the absorbing material. Solar cells and various solar energy harvesting devices on the other hand, desire materials that have a steady photon absorption over a broader range of wavelengths, and can harvest as many photons as possible. Surface texturing and destructive interference coatings have been utilised to reduce reflection and to trap more photons They attempt to enhance absorption by coupling and trapping of light through total internal reflection [1]–[5]. The process of up-conversion was first implemented for infrared detectors, [6] It was explored for photovoltaic applications where typical up-convertors consisting of active ions set in a host material were integrated into solar devices [7]. With the advent of nanoscience and nanotechnology, attempting to harvest photons over a broader wavelength using nanomaterials has become promising
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