There have been many new exciting advancements in Perovskite solar cell technology with research teams across the globe establishing new efficiency records. These discoveries could have the potential to see a surge in the use of solar panels. Perovskites have been identified as inexpensive materials for high-efficiency commercial photovoltaics. They are a family of semiconducting materials that can be used as the light absorbing material that converts solar energy into electrical energy.
In Dr Dunbar's study, Perovskite crystallization dynamics during spin casting: an in situ wide angle X-ray scattering study, published in American Chemical Society - Applied Energy Materials, in situ wide angle X-ray scattering (WAXS) has been measured during the spin coating process used to make the precursor films required for the formation of thin films of perovskite.
The findings of Dr Dunbar and his colleagues indicate that there are significant differences between the crystallization pathways for two of the most commonly studied perovskite materials.
Why is this paper important?
Perovskite based solar cells have had phenomenal success in recent years and are now poised to challenge silicon as the solar cell material of choice. They are attractive because they can be processed from a solution which is relatively inexpensive. This occurs in a few stages, first a thin film of precursor materials is formed, usually by spin coating for small lab samples but this can be done by industrially scale-able processes like spray coating or slot dye casting. The films of precursor materials are then heated to convert them into the final perovskite. Several studies have used in situ characterization techniques to understand the processes occurring during the second heating stage of the process, but very few have looked at the first precursor film formation stage in detail.
Several studies have used in situ characterization techniques to understand the processes occurring during the second heating stage of the process, but very few have looked at the first precursor film formation stage in detail. We are the first research group to do so using in situ WAXS in transmission geometry.
Dr Alan Dunbar
Department of Chemical and Biological Engineering.
How did you do this?
The WAXS experiments or wide angle x-ray scattering were conducted at the Diamond Light Source and permitted us to follow the crystallization processes at molecular length scales as they happened. To do this we had to build a unique hollow axis spin coater so we could do the x-ray measurements during the spin casting process used to make the thin films from the precursor inks. We used our unique x-ray scattering experiments to watch films of two of the most commonly studied inks used to make perovskite solar cells (methylammonium lead iodide chloride and formamidinium lead iodide chloride) drying in order to better understand the differences between them.
What is the potential impact of the study?
We found that there are significant differences in the crystallization processes for these two popular perovskite materials. The crystallization rates and dimensionality of the precursor crystalites are very different. This insight opens up the exciting possibility of being able to better control the structure of the films formed and therefore more reliably produce the structures desired for high performance solar cells.