School of Chemistry - Theses

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    Solid-state thin films solar cells on polymer substrates
    DKHISSI, YASMINA DELPHINE ( 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?