This thesis is concerned with measuring ultrafast electron dynamics taking place in dye-sensitized mesoporous semiconductor films employed as working electrodes in dye-sensitized solar cells (DSCs). An understanding of these ultrafast charge transfer mechanisms is essential for designing efficient photovoltaic (PV) devices with high photon-to-current conversion efficiency. Optical-pump terahertz-probe (OPTP) spectroscopy is a sub-picosecond resolution, non-contact, photoconductivity measurement technique which can be used to directly measure charge carrier dynamics within nanostructured materials without the need for invoking complex modelling schemes. A combination of OPTP and photovoltaic measurements on mesoporous TiO2 films show an early-time intra-particle electron mobility of 0.1 cm2/(Vs). This value is an order of magnitude lower than that measured in bulk TiO2 and can be partly explained by the restricted electron movement because of geometrical constraints and increased trap sites in the nanostructured material. In addition, the mesoporous film behaves like a nanostructured composite material, with the TiO2 nanoparticles embedded in a low dielectric medium (air or vacuum), leading to lower apparent electron mobility. THz mobility measured in similar mesoporous ZnO and SnO2 films sensitized with the same dye is calculated to be 0.17 cm2/(Vs) for ZnO and 1.01 cm2/(Vs) for SnO2. Possible reasons for the deviation from mobilities reported in literature for the respective bulk materials have been discussed. The conclusion of this study is that while electron mobility values for nanoporous TiO2 films are approaching theoretical maximum values, both intra- and inter-particle electron mobility in mesoporous ZnO and SnO2 films offer considerable scope for improvement. OPTP has also been used to measure electron injection rates in dye-sensitized TiO2, ZnO and SnO2 nanostructured films. They are seen to proceed in the order TiO2 >SnO2 >ZnO. While the process is complete within a few picoseconds in TiO2/Z907, it is seen to extend beyond a nanosecond in case of ZnO. These measurements correlate well with injection efficiencies determined from DSCs fabricated from identical mesoporous films, suggesting that the slow injection components limit the overall solar cell photocurrent. The reasons for this observed difference in charge injection rates have been explored within. It is now fairly common practice in the photovoltaic community to apply a coating of a wide band-gap material over the metal-oxide nanoparticles in DSCs to improve device performance. However, the underlying reasons for the improvement are not fully understood. With this motivation, OPTP spectroscopy has been used to study how the conformal coating affects early-time mechanisms, such as electron injection, trapping or diffusion length. The electron injection process is unaffected in case of TiCl4-treated TiO2 and MgO-treated ZnO, while it becomes much slower in case of MgO-treated SnO2. Finally, a light-soaking effect observed in SnO2-based solid-state DSCs has been examined in detail using THz spectroscopy and transient PV measurement techniques. It is concluded that continued exposure to light results in a rearrangement of charged species at the metal-oxide surface. This leads to an increase in the density of acceptor states or a lowering of the SnO2 conduction band edge with respect to the dye excited state energy level, ultimately leading to faster electron transport and higher device photocurrents.

Light stabilisation of photochromic dyes is seen as the most challenging part in the development of photochromic dyes. The aim of this research is to compare stabilisation methods and their effect on the lifetime of a photochromic print on textile. The vision is to create a textile UV-sensor that detects current UV light exposure in the surroundings and alarms the wearer by showing colour. The developed inks have been formulated for ink-jet printing as a novel production method with resource saving properties. UV-LED light curable ink formulations were prepared for two dye classes; a non-commercial spirooxazine, a commercial spirooxazine (Oxford Blue) and a commercial naphthopyran (Ruby Red). Two different stabilisation methods were applied; chemically by incorporation of hindered amine light stabilisers and physically by polyurethane coating. Fatigue tests were performed to evaluate and compare the stabilisation methods. The tests included were household washing, multiple activations and intensive sun-lamp exposure. As a result it was found that Oxford Blue and spirooxazine had an initial better resistance to photodegradation than Ruby Red. The coating reduced the ability of colour development in higher extend for Oxford Blue and spirooxazine compared to Ruby Red. Moreover, the photocolouration increased with the number of activations for Oxford Blue and spirooxazine in particular. In general, the physically stabilised samples showed a better or similar fatigue resistance compared to chemically stabilised samples. On the other hand the results are weak in significance. It is concluded that the developed coating method in combination with further optimising has potential.

published_or_final_version / Urban Planning / Master / Master of Science in Urban Planning

<p>För att undersöka skillnad i prestationsförmåga mellan celler sensiterade med växtextraktsbaserad färg, och celler sensiterademed ruteniumkomplex-baserad färg, samt huruvida presskraften påverkar en cells prestationsförmåga, tillverkades icke-slutna fotoelektrokemiska färg-sensiterade solceller med tunnfilmsfotoelektroder av pressad, nanoporös titandioxid.</p><p>Cellerna pressades med tre olika presskrafter och sensiterades med växtextraktsfärg från rödkål, rödbeta, viol och henna, samt en ruteniumkomplex-baserad färg som fick utgöra kontrollbetingelse. För varje cell uppmättes IPCE- och iV-värde och motsvarande fyllnadsgrad (fill factor) och dessa jämfördes.</p><p>Ingen signifikant skillnad kunde fastställas mellan celler pressade med olika presstryck. Bland cellerna sensiterade med växtextraktbaserad färg presterade rödbeta bäst. Cellen med högst effektivitet hade fyllnadsgraden 70%. Emellertid uppvisade de växtfärgade cellerna genomgående sämre effektivitet än de rutenium-sensiterade och fotoströmmarna var mycket låga. IPCE-värdena var allmännt låga: den bäst presterande cellen hade ett IPCE-värde på något över 0,06 i våglängdsintervallet 440-470 nm. En förklaring till detta är de övriga ämnen som förutom pigment återfinns i de växtbaserade färgerna. Dessa hindrar pigmentmättnad och förhindrar att växtfärgen når ruteniumfärgens intensitet. En annan anledning består i svårigheten att passa ihop energinivåerna i cellens elektrolyt-halvledarsystem med energinivåerna hos pigmentet i växtfärgen.</p> / <p>Non-sealed photoelectrochemical dye sensitised solar cells (DSSC) with pressed nanoporous TiO2 thin film photoelectrodes were manufactured for the purposes of finding out whether plant extractbased dye sensitised cells can perform as well as ruthenium complex-based dye sensitised cells and whether the pressing force affects the cell performance.</p><p>The cells were pressed with three different pressing forces and sensitised with plant extracts from red cabbage, beetroot, violet and henna, as well as with a ruthenium complex-based dye for comparison. The IPCE and iV values and the corresponding fill factors of the cells were evaluated and compared.</p><p>No significant difference between the cells pressed with different pressing forces could be established. Among the plant extract-based dye sensitised cells the ones sensitised with beetroot extract performed best. The cell that achieved the highest efficiency had a fill factor of 70%. Compared to the ruthenium-sensitised cells the overall performance of the plant dye sensitised cells were very poor and the produced photocurrents very low. The IPCE values were generally low: one of the best-performing cells had an IPCE value of slightly over 0.06 in the 440-470 nm wavelength ranges. One reason for this is that it is difficult to obtain a plant extract dye as intense and deep in colour as ruthenium complex-based dyes, since pigment saturation is obstructed by the presence of other chemical compounds in the plant extracts. Another is that it is a delicate and difficult matter to match the energy levels in the electrolyte-semiconductor system with the energy levels of the pigments in the plant extract dye.</p>

<p>Currently, fossil fuels and nuclear power are our primary energy sources. However, both have critical disadvantages due to the limited supply and the hazard issues. Renewable energy research becomes one of most important research topics in the 21st century. Nanostructured materials show unique electrochemical properties in various energy conversion or storage devices. This dissertation starts with fundamental optical studies of nanomaterials (carbon nanotubes), followed by synthesizing novel nanomaterials for energy conversion (solar cells) and storage (lithium ion batteries) devices. </p><p> (1) There is an on-going debate concerning the ability of double walled carbon nanotubes (DWNTs) to exhibit photoluminescence (PL). We aim to clearly resolve this debate through the study of carefully separated DWNTs using density gradient ultra-centrifugation (DGU). Here, we clearly show that light is emitted from the inner wall of DWNTs. Interestingly, it was found that a very narrow range of diameters of the inner walls of DWNTs is required for photoluminescence (PL) to be observable. All other diameters led to complete PL quenching in DWNTs. (2) Inexpensive dye sensitized solar cells (DSSCs) on flexible plastic substrates have a bright future, but they require low temperature annealing (< 200°C). The method to fabricate low temperature DSSCs should resolve poor electron transfer between titanium dioxide (TiO2) nanoparticles (NPs) due to their incomplete contiguity and insulating layer of organic residues from binders in the photoactive film. Here, we have developed uniform CNTs/TiO2 composites for low temperature DSSCs by using modified sol gel method. DSSCs were fabricated to study incorporating functionalized few walled carbon nanotubes (f-FWNTs) effect on TiO2 NPs. Incorporating f-FWNTs can be beneficial for the low temperature annealing process of DSSCs to overcome extremely poor electron transport through TiO2 photoactive film. Incorporating f-FWNTs with TiO2 active layer improves electrons transport in some degree, but this advantage is limited. (3) Conductive fillers, such as amorphous carbon, carbon nanotube and graphene, have been mixed with nanostructured metal oxide materials to improve the performance of electrode materials in energy storage devices. However, ineffective junctions between conductive fillers are limiting the overall conductivity of the electrode. Therefore, we developed a convenient, inexpensive and scalable method for synthesizing hybrid carbon and titanium dioxide (C/TiO2) co-gels and co-aerogels to improve their electrochemical capacity in lithium ions batteries (LIBs). The monolith of the hybrid C/TiO2 co-aerogel can be directly used as active electrodes without the addition of binders. As a result, the capacitance of LIB anodes using the hybrid co-aerogel is significantly improved over current LIBs based on carbon/titanium oxide composite. Other metal oxides could also form co-gels with carbon to improve their potentials in numerous electrochemical, photocatalytic, and photoelectronic devices.</p> / Dissertation

Recent studies suggest that the performance of dye-sensitised solar cells (DSC) has appeared to have reached a limit, therefore solar cells based on semiconductor materials, such as extremely thin absorber (ETA) solar cells and tandem solar cells are currently the subject of intense research in the framework of low-cost photovoltaic devices as sources of harvesting sunlight to generate electricity. Generally, semiconductor solar cells have been divided into two different types, namely anodic and cathodic type solar cells. Extensive research and development work has been focused on anodic semiconductor sensitised solar cells to date. In contrast, the cathodic semiconductor sensitised solar cells have received no attention which is very surprising. Developing the cathodic semiconductor sensitised solar cell concept is very important in the development of tandem solar cells as well as other new solar cell configurations. The main reason for the lack of research in this area was due to the rarity of p-type semiconductor materials, which made it difficult to find suitable materials to match the energy band edges for cathodic semiconductor sensitised solar cells (CSSC) as well as solid-state cathodic semiconductor solar cells (SS-CSSC). The primary aim of this thesis was to construct cathodic semiconductor sensitised solar cells as well as their solid-state analogues (SS-CSSC). The work conducted within this doctoral study presents state-of-art materials and thin film processing/preparation methods, their characterisation and developing CSSCs and SS-CSSCs employing such films in cascade configurations. No reports have been published in the literature on SS-CSSC to date. The first stage of this thesis is focused on optimising the morphology and the texture (porosity) of the CuI and NiO semiconductor photocathode, by the introduction of new deposition methods namely, pulsed-electrodeposition (PED) and Aerosol-Assisted Deposition (AAD) and Aerosol-Assisted Chemical Vapour Deposition (AACVD). The electrodes prepared by employing the methods mentioned above and controlling the deposition parameters systematically, we have achieved significant improvement in the film morphology and the texture of the deposited films. The resulting electrodes showed excellent improvement in the photoelectrochemical performance which made it suitable for application in construction of both CSSC and SS-CSSC. The photoelectrochemical performance of the electrodes can be seen clearly through the photocurrent density data. For the case of bare CuI, the PEC performance of electrode prepared by the AAD and PED compared against that of continuous-electrodeposition (ED) electrodes. The photocurrent density achieved for the electrodes prepared by AAD and PED was reported around 175 and 75 µAcm-2 respectively which are way higher than the ED case. At the second stage of this study, the work focused on fabrication and characterisation of the CSSCs. Cathodic sensitised PEC solar cells (CuI/Cu2S/(Eu2+/Eu3+) and NiO/Cu2S/(I3-/I-)) were fabricated by deposition of p-Cu2S on the texture controlled CuI and NiO photocathodes. The morphological properties of the photocathode, in particular layer thickness, particle size and film porosity, play an important role in the PEC performance of CSSCs. Optimisation of these parameters led to increased adsorption of the Cu2S light harvester on the photocathode s surface. As a result, the charge injection from Cu2S to the wide band gap photocathode material (CuI and NiO) was significantly improved. Due to this, the CSSC performance showed significant improvement as semiconductor sensitised cathodic solar cells (CSSC). The IPCE and photocurrent density of the CSSC achieved in this study was around (19 and 7 %) and (1 and 0.5 mAcm-2) for the CuI/Cu2S and NiO/Cu2S electrodes respectively. Finally, the SS-CSSC has been fabricated by employing n-Fe2O3 electron transport layer. The construction of SS-CSSC for the first time using the n-Fe2O3 electron transport layer (CuI/Cu2S/Fe2O3 and NiO/Cu2S/Fe2O3) allowed us to study the materials, optical and photoelectrochemical properties of this device. Under AM 1.5 illumination, the SS-CSSC shows a photocurrent density of 6 and 9 µAcm-2 for CuI/Cu2S/Fe2O3 and NiO/Cu2S/Fe2O3 solar cells, respectively. The results of this work indicated low performance for both SS-CSSC compared to CSSC results, due to the lack of adsorption between the absorber and Fe2O3 electrode. However, this study proved the concept of SS-CSSC based on semiconductor material, which is valuable for the future work of cathodic semiconductor sensitised solar cells as well as solid-state tandem solar cells.

Near-level Prairie landscapes have received limited attention in hydrological research. For this thesis, hydrometric measurements and four tracing experiments were completed at three “riparian-to-stream” sites in the Catfish Creek Watershed (southeastern Manitoba) to enhance Prairie hydrology understanding. First, hydrologic state variables were examined to infer vertical and lateral water movement. Second, tracer data were analyzed to evaluate the relative importance of surface versus subsurface water movement. Results show that hydrologic state variables can be useful for inferring riparian-to-stream water movement. Tracer data also revealed that subsurface water movement can contribute significantly to streamflow during snowmelt- and rainfall-triggered events in the study watershed. This thesis demonstrated that subsurface flow is a significant runoff generation mechanism in Prairie landscapes, thus challenging surface water-focused conceptualizations and management strategies that are traditionally used. The findings summarized in this thesis will be critical to improve the performance of hydrological models when applied to the Prairies. / February 2017

No description available.

This thesis improves our understanding of the charge-transfer dynamics in organic materials employed in dye-sensitized and nanotube-thiophene solar cells. For the purpose of this work, a femtosecond transient absorption spectroscopy setup was built. Additionally, microsecond transient absorption spectroscopy was utilised to explore dynamics on a longer time-scale. In the first study, the dependence of dye regeneration and charge collection on the pore- filling fraction (PFF) in solid-state dye-sensitized solar cells (DSSCs) is investigated. It is shown that while complete hole transfer with PFFs as low as ~30% can be achieved, improvements beyond this PFF are assigned to a stepwise increase in the charge-collection efficiency in agreement with percolation theory. It is further predicted that the chargecollection efficiency saturates at a PFF of ~82%. The study is followed by an investigation of three novel hole-transporting materials for DSSCs with slightly varying HOMO levels to systematically explore the possibility of reducing the loss-in-potential and thus improving the device efficiency. It is shown that despite one new HTM showing a 100% hole-transfer yield, all devices based on the new HTMs performed worse than those incorporating spiro-OMeTAD. Furthermore, it is demonstrated that the design of the HTM has an additional impact on the electronic density of states present at the TiO₂ electrode surface, and hence influences not only hole- but also electron-transfer from the sensitizer. Finally, a study on a polymer-single-walled carbon nanotube (SWNT) molecular junction is presented. Results from femtosecond spectroscopic techniques show that the polymer poly(3-hexylthiophene) (P3HT) is able to transfer charges to the SWNT within 430 fs. Addition of excess P3HT polymer leads to long-lived free charges making these materials a viable option for solar cells.

This research explored a Digital Laser Dye (DLD) patterning process as an alternative coloration method within a textile design practice context. An interdisciplinary framework employed to carry out the study involved Optical Engineering, Dyeing Chemistry, Textile Design and Industry Interaction through collaboration with the Society of Dyers and Colourists. In doing so, combined creative, scientific and technical methods facilitated design innovation. Standardized polyester (PET) knitted jersey and plain, woven fabrics were modified with CO2 laser technology in order to engineer dye onto the fabric with high-resolution graphics. The work considered the aesthetic possibilities, production opportunities and environmental potential of the process compared to traditional and existing surface design techniques. Laser-dyed patterns were generated by a digital dyeing technique involving CAD, laser technology and dye practices to enable textile coloration and patterning. An understanding of energy density was used to define the tone of a dye in terms of colour depth in relation to the textile. In doing so, a system for calibrating levels of colour against laser energy in order to build a tonal image was found. Central to the investigation was the consideration of the laser beam spot as a dots-per-inch tool, drawing on the principles used in digital printing processes. It was therefore possible to utilise the beam as an image making instrument for modifying textile fibres with controlled laser energy. Qualitative approaches employed enabled data gathering to incorporate verbal and written dialogue based on first-hand interactions. Documented notes encompassed individual thought and expression which facilitated the ability to reflect when engaged in practical activity. As such, tacit knowledge and designerly intuition, which is implicit by nature, informed extended design experiments and the thematic documentation of samples towards a textile design collection. Quantitative measurement and analysis of the outcomes alongside creative exploration aided both a tacit understanding of, and ability to control processing parameters. This enabled repeatability of results parallel to design development and has established the potential to commercially apply the technique. Sportswear and intimate apparel prototypes produced in the study suggest suitable markets for processing polyester garments in this way.