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Carbon Nanomaterials for Dye-Sensitized Solar Cells.


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Mohammadnezhad, Mahyar (2019). Carbon Nanomaterials for Dye-Sensitized Solar Cells. Thèse. Québec, Doctorat en sciences de l'énergie et des matériaux, Université du Québec, Institut national de la recherche scientifique, 195 p.

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According to the late Nobel Laureate Richard E. Smalley, energy is one of the biggest problems to be faced by humanity over the next 50 years. At the dawn of the 21st century, with the rapid development of industrialization and globalization, worldwide energy demands have rapidly increased. Different forms of fossil fuels represent over 80% of the world’s energy use. However, the limited availability of fossil fuels, together with climate change and environmental pollution dictates a transition towards sustainable, clean and carbon-neutral energy sources, including wind power, hydroelectric and solar energy. Amongst different sources of renewable energy, solar energy is one of the cleanest energy resources to be considered as a viable alternative to fossil fuels since sunlight is the most abundant of all available carbon-free energy sources. A solar cell is an optoelectronic device that directly converts the energy of light into electricity by the photovoltaic (PV) effect. Silicon (Si) solar cells currently constitute the most widespread commercial product in this field due to their high conversion efficiency and relatively longterm stability compared to other solar cell technologies. However, their high production cost and environmental impact are restricted to the terrestrial PV market. In recent years, dye-sensitized solar cells (DSSCs) have been regarded as a promising alternative to Si solar cells. DSSCs are considered as a promising future technology due to their appealing features, including a simple fabrication process, eco-friendly materials, colour choice and transparency. DSSCs must pass three main filters for large-scale commercialization: power conversion efficiency (PCE); long-term stability; and production cost. Although the design of new and modified devices that are structured to fabricate highly efficient cells are widely investigated, thus far the long-term stability and production costs have rarely been investigated and reported in the field of DSSCs. The first part of this thesis demonstrates the effect of adding carbonaceous materials, in particular multi-wall carbon nanotubes (MWCNTs), on the stability of DSSCs under continuous simulated sunlight, indoor and ultraviolet (UV) light irradiation. After light aging, DSSCs are characterized by different techniques, to document the degradation mechanisms. The results indicate that MWCNTs can act as a strong conductive support and reinforcement of the titanium dioxide (TiO₂) matrix, which is able to significantly improve the long-term stability of DSSCs under continuous simulated one sun and indoor light by 22% and 42%, respectively. Based on UV stability measurements, MWCNTs, as an efficient absorbing and blocking agent for UV light, can successfully stabilize DSSCs for long-term operation with a 24% improvement in UV stability. The second part of this work describes an investigation into the effect of incorporating MWCNTs in the thermal stability of DSSCs. Under identical measurement conditions (aging at 80°C for 240 h in the dark), standard DSSCs present a significant loss in PCE, dropping to 59% of their initial value, while a composited device with MWCNTs attained a promising thermal stability with only a 20% reduction. This loss in cell performance in standard DSSCs is mainly associated with a dramatic reduction in short circuit current density (Jsc). The composite anode exhibited excellent microstructure stability due to the bonding between MWCNTs and TiO2 nanoparticles. Furthermore, transient photovoltage decay and electrochemical impedance spectroscopy (EIS) measurements confirm the higher electron lifetime and reduction in charge recombination in the composite network due to the excellent conductivity of MWCNTs. The final part of this work describes a simple and low-cost approach to preparing a nanocomposite film of copper sulfide-graphene (CuS-G) as a transparent conducting oxide (TCO) and platinum (Pt)-free counter electrodes (CEs) for DSSCs. Different measurements verified the structure and the composition of a nanocomposite of CuS-G with uniform distribution of graphene between the CuS particles. The results demonstrated that the addition of graphene improves the PCE of the DSSCs (~12%) compared to the DSSCs based on CEs made of pristine CuS. The prepared CuS-G nanocomposite thin films that exhibit good catalytic performance towards the reduction of the tri-iodide electrolyte exhibited an impressive PCE of 4.83%, which is comparable to that of using the Pt CE (5.14%).

Type de document: Thèse Thèse
Directeur de mémoire/thèse: Rosei, Federico
Mots-clés libres: énergie; matériaux
Centre: Centre Énergie Matériaux Télécommunications
Date de dépôt: 22 oct. 2020 17:13
Dernière modification: 22 oct. 2020 17:13
URI: http://espace.inrs.ca/id/eprint/10419

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