Development of Pulsed Laser Deposited TiO2, ZnO and AZO Thin UV-Protection Films for Enhanced Perovskite Photostability
Master of Engineering Science
Mechanical and Materials Engineering
Perovskite solar cells are an emerging sustainable energy conversion technology with the potential to provide relief from the global energy crisis. However, the UV-induced degradation of perovskites has been a barrier to commercialization. Thin film encapsulation represents a promising solution for extending device lifetimes. Three materials with suitable bandgaps for blocking UV light are identified: TiO2, ZnO and AZO. Herein, the optical properties of TiO2, ZnO and AZO thin films grown by room-temperature pulsed laser deposition are optimized by varying the oxygen partial pressure during deposition. UV-Vis spectroscopy reveals facile bandgap tuning via the concentration of O2 vacancies. Accelerated UV-aging experiments find that the films which screen the most UV light are also most effective in delaying perovskite degradation. A comparison of TiO2, ZnO and AZO photoprotective coatings concludes that ZnO is most suitable for perovskite solar cell encapsulation since it provides a ∼50% reduction in UV-degradation without significantly compromising visible light transmittance.
Summary for Lay Audience
In the face of increasing energy demands and growing concerns over global warming, there is a heightened need for a sustainable source of energy. Among renewable energy sources, solar is one of the most promising due to its inherent abundance. Currently, crystalline silicon solar cells dominate the photovoltaics market. Alternatively, solar cells can be made with low-cost materials called perovskites, which contribute to fewer greenhouse gas emissions due to less energy-intensive manufacturing. Given their competitive power conversion efficiencies and the promise of low-cost manufacturing, perovskite solar cells (PSCs) have the potential to disrupt the incumbent silicon technology. However, issues associated with the stability of perovskites in water, oxygen and UV light persist, preventing widespread adoption. As a result, the success of PSCs relies now on the improvement of their long-term stabilities. Significant efforts to-date have been placed on preventing water- and oxygen-induced perovskite degradation, however, this thesis focuses on the less studied issue of UV light-induced degradation. It looks to extend the lifetime of PSCs by encapsulating devices with transparent thin films of titanium dioxide (TiO2), zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO), optimized to block UV-light. The suitability of each material for the encapsulation application is assessed by subjecting TiO2-, ZnO-, and AZO-protected perovskites to harsh UV radiation and monitoring the degree to which each sample is degraded. While all thin films delayed the onset of UV-induced degradation, ZnO provided the most substantial protection and is therefore considered most promising for extending PSC lifetimes. Overall, this work will help to advance the commercialization of perovskite solar technologies, providing a more a reliable source of renewable energy, and relief from the global energy crisis.
Lochhead, Kate, "Development of Pulsed Laser Deposited TiO2, ZnO and AZO Thin UV-Protection Films for Enhanced Perovskite Photostability" (2023). Electronic Thesis and Dissertation Repository. 9150.
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Available for download on Monday, April 01, 2024