School of Chemistry - Theses
Permanent URI for this collection
Search Results
1 - 3 of 3
-
ItemSolid-state thin films solar cells on polymer substrates( 2015)To meet the world’s ever-growing energy needs while facing current environmental challenges, solid-state thin film solar cells offer a low-cost renewable alternative for generating electricity. Polymer substrates give thin films lightweight and flexibility, broadening their potential applications to consumer electronics and power-generating textiles. The use of solution processable materials on flexible substrates paves the way towards roll-to-roll printing of photovoltaics, taking advantage of available, low-cost manufacturing technologies. However, constructing efficient solar devices on plastic substrates remains difficult due to the substrate’s intrinsic low-temperature limitation. Furthermore, the stability of thin films needs to be addressed in order for them to become viable candidates for commercial applications. In the first research Chapter, volatile liquid electrolytes were replaced with composite polymer electrolytes to improve the stability of dye-sensitized solar cells (DSCs). On one hand, the infiltration of viscous electrolytes through the TiO2 working electrode was suspected to constitute a major limitation to producing efficient flexible devices. On the other hand, the temperature restriction of polymer substrates prevented the sintering of mesoporous TiO2 directly onto these substrates. Therefore, submicrometer-sized mesoporous TiO2 beads, that can be treated prior to the device fabrication, were investigated as a potential route to overcome the aforementioned issues. Efficient quasi-solid-state DSCs were successfully fabricated on plastic substrates, and studies on the infiltration of the electrolyte through the electrode were conducted. Then, efforts were focused on photovoltaics utilizing inorganic-organic perovskites, an emerging technology with reported efficiencies rivalling existing commercial solar cell technologies. Solution processed, these hybrid materials can be prepared at low temperature, thus becoming a potential candidate for application to polymer substrates. Nevertheless, the majority of these solid-state devices constructed on glass employ a high temperature processed inorganic hole blocking layer (≥450 °C), non-compatible with flexible applications. In this regard, efforts were directed towards the development of methods to fabricate efficient flexible solid-state perovskite devices on polymer substrates with a range of low-temperature processed hole blocking layers. As a result of the moisture and temperature sensitivity of these hybrid perovskites, a perovskite deposition method was developed and optimized, in order to improve the reproducibility of these devices. In Chapter 4, power conversion efficiencies (PCEs) over 13 % were attained for TiO2-based flexible planar perovskite devices, with an average efficiency of 11.8 ± 1.8 %. In Chapter 5, ZnO was chosen as an electron selective material given its advantages for printing, and PCEs over 10 % were achieved for spin-coated ZnO-based perovskite solar cells on polymer substrates. Exacerbated degradation of CH3NH3PbI3 was observed when deposited on ZnO, therefore the correlation between the annealing conditions and the decomposition of the perovskite film was examined. In Chapter 6, practical industrial concerns such as the stability and the manufacturing processability of these devices were considered. PCEs over 10 % were obtained for flexible perovskite devices with a printed TiO2 layer, but the device reproducibility was affected by the fabrication protocol. Finally, the stability of TiO2-based perovskite devices on polymer substrates was assessed, and encapsulation of flexible devices was performed to extend the device lifetime. To understand the origins of the degradation of CH3NH3PbI3-based solar devices, a range of storage conditions was used, and their impacts on the perovskite film were investigated. The following research questions will be addressed throughout the thesis: -Is the infiltration of the electrolyte through the TiO2 film critical? -Can the low temperature processing restriction on polymer substrates be overcome by developing a low temperature inorganic blocking layer synthesis? -Can solid-state solar cells on polymer substrates be made commercially viable? -What are the parameters that affect the degradation of CH3NH3PbI3-based perovskite solar cells?
-
ItemExcitation energy transfer in nanocrystal systems( 2014)The development of sensing platforms capable of accurately and sensitively detecting toxins, small molecules and DNA, has been an area of intense interest by researchers in defence, medicine and public safety. The photophysical phenomenon of Förster Resonance Energy Transfer (FRET) provides a route to achieving a high quality transduction signal for analyte detection, and the creation of next-generation sensing platforms. However, whether this model is valid to describe energy transfer in nanoparticle-dye systems has yet to be satisfactorily proven. A detailed background to FRET in general, and its application to nanoparticle fluorophores specifically, will be provided in Chapter 1. A detailed description of experimental protocols for both the synthesis of semi-conducting nanocrystal fluorophores, so called ‘Quantum Dots’, and a number of rigid, dye labelled polyproline peptides will be detailed in Chapter 2. Back- ground information about specific experimental techniques, including peptide synthesis and single particle spectroscopy, is also provided. In Chapter 3 energy transfer between Quantum Dots (QDs) and molecular dye molecules, is detailed. Using rigid polyproline spacers to controllably vary the separation it is found that, in contrast to simple dye-dye systems, the ratio of dye adsorbed to each QD must be explicitly accounted for by the Poisson distribution. Moreover, it is found that dye fluorescence quantum efficiency is also distance dependent, which obscures enhancements to the dye fluorophore due to energy transfer. However, accounting for both of these effects, it is found that the efficiency of energy transfer from QDs to adsorbed dye molecules obeys an R−n dependence with n = 6, as predicted from Förster Resonance Energy Transfer (FRET). In Chapter 4 energy transfer between ZnO nanoparticles to adsorbed dye molecules, is detailed. Remarkably, energy transfer in this system is found to occur from an intraband electronic state. It is found that the entire broad emission from radiative decay of this state, is uniformly reduced upon dye adsorption with a concomitant enhancement in the dye emission. These observations demonstrate that energy transfer from ZnO involves a single electronic state coupled to the phonon modes of the crystal lattice. It is also found that this energy transfer to the adsorbed dye molecules is very efficient, regardless of the orientation of the dipole moment of the dye molecule and the distance to the defect state. Finally in Chapter 5, a novel parameter for quantifying fluorescence intermittency, ‘blinking’, in QDs is presented. As energy transfer at the single particle level is often confounded by this phenomenon, additional insight that leads to its suppression is desirable. The parameter is essentially a measure of the total fractional correlation of single QD time-trajectories, which is found is related to the ensemble photoluminescence quantum yield and effectively independent of the manner in which the time-trajectory is binned.
-
ItemCubic phase lipids as novel biosensing surfaces( 2011)Sub-micron particles, called cubosomes, formed from the fragmentation and steric stabilization of inverse bicontinuous cubic phases (QII) of lipids have a microenvironment reminiscent of biological lipid bilayers, making them promising class of material for a number of applications. The phase behaviour of the amphiphile phytantriol (3,7,11,15-tetramethyl-1,2,3-hexadecanetriol) is well characterised and we describe studies of cubosomes formed from the QII phase of phytantriol/water systems. Cubosomes tailored for specific applications require additional components, which can alter the structure and phase behaviour of the system, for example the incorporation of ligands such as a receptor lipid or protein for biomedical applications. Hence, a study of the effect of additives on the phase behaviour of cubosomes was undertaken. Data obtained using the small-angle X-ray scattering (SAXS) beam line at the Australian Synchrotron showed that addition of non-functional amphiphiles to the matrix of phytantriol/water cubosomes affected the lattice parameter of the cubosomes and, hence, the cubosome microstructure. Oleic acid and monoolein stabilized the Pn3m cubic phase of the cubosomes, whilst CTAB and SDS caused a loss of structure at lower temperatures/molar concentrations of additive. Synchrotron SAXS was also used to investigate the effect of functional additives, the ganglioside receptor, GM1, and the biotinylated phospholipid, bDSPE, on the matrix of the phytantriol/water cubosomes. The results of these studies indicated that both systems would yield stable double diamond Pn3m cubosomes at low – medium molar concentrations of additive. To further investigate the viability of these systems for biomedical and biosensing applications we screened their binding capacity against their natural ligands. Using a combination of enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR), and quartz crystal microbalance (QCM) techniques, we showed that GM1 containing cubosomes specifically bind to cholera toxin (CT) with an IC50 of 1.6 nM, which is more potent than any currently available inhibitor. Specific targeting of bDSPE containing cubosomes to avidin-modified surfaces was visualised using cryogenic transmission electron microscopy (cryo-TEM), as was the ability of surface-bound bDSPE cubosomes to specifically bind ligands from solution. Further QCM results demonstrated how bi-functionalised cubosomes, containing GM1 and bDSPE, could be targeted to a surface via one functionality, then sense a secondary ligand via a separate functionality. The results presented in this thesis provide insight into the effect of additives on the phase behaviour of cubosome systems and factors, which affect their potential biomedical and biosensor applications.