Preparation and Characterization of Lead Halide Perovskites Towards sustainable, cost-effective and upscalable solar cell manufacture

Sveinbjörnsson, K. 2018. Preparation and Characterization of Lead Halide Perovskites. Towards sustainable, cost-effective and upscalable solar cell manufacture. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1628. 84 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-0229-4. The perovskite solar cell (PSC) is a recent contender within the photovoltaic research field. In a matter of a few years, the power conversion efficiency (PCE) of the PSC has catapulted from 4% to above 22%, which represents one of the fastest developments in the field. The PSC band-gap tunability makes them interesting for use in tandem solar cells with other established solar cell technologies. This thesis focuses on exploring the photophysics of the perovskite material as well as the development of different perovskite preparation processes and materials for potential use in large-scale manufacture and tandem solar cell applications. First, the photoconductivity of a perovskite film deposited on different metal oxide nanoparticle layers is investigated. The results show that the perovskite can generate free charge carriers without the presence of an electron acceptor. Secondly, we constructed PSCs with a conducting carbon-nanotube film, as a replacement for both the hole-selective layer and the metallic back electrode, which yielded a PCE of 15.5%. Furthermore, we explored the preparation of semitransparent PSCs for tandem solar cells by using atomic-layer deposition (ALD) for depositing a thin electron-selective metal-oxide layer. We were successful using ALD directly on a perovskite layer without damage to the perovskite. Although the PSCs did not yield high PCE, the study marks a step in further development for direct ALD deposition onto the perovskite. Finally, we developed two different methods concerning sustainable manufacture of PSCs. The first method was based on the synthesis of the mixed-ion (FAPbI3)0.87(MAPbBr3)0.17 perovskite in ambient air, which had hitherto only been possible in inert atmosphere. The best PSC was obtained by depositing the perovskite onto a 50°C warm substrate in ambient air yielding a PCE of 17.7%. In the second method, only non-hazardous solvents, water and isopropanol, were used in the synthesis of Cs0.1FA0.9Pb(I0.83Br0.17)3. It is the first publication of mixed inorganic and organic cation perovskite synthesis using a two-step preparation procedure with only non-hazardous solvents and the process yielded a PCE of 13.0%. The method allows for complete ionic control of the perovskite and further variation and improvements are therefore possible.