Perovskites: A solar scientist’s bread and butter

Universities and research institutes the world over claim to have developed solutions that could be applied to the mass production of perovskite solar cells, and to have solved the stability and durability issues that plagued the material’s development in earlier years.

But perovskites have still not seen any significant commercial application to date (though this could now be around the corner). And it remains to be seen which materials from the perovskite family, and industrially scalable processes developed by scientists to produce them, could be picked up by the companies looking to manufacture perovskite solar products, or if these can be successfully commercialized at all.

Scientists at the Netherlands’ University of Groningen have now developed another technique, which they say can produce stable perovskite solar cells at high volume. The technique is described in the paper Scalable fabrication of high-quality crystalline and stable FAPbI thin films by combining doctor-blade coating and the cation exchange reaction, published in the Royal Society of Chemistry’s journal Nanoscale.

The first stage in their technique involves “spreading” material onto a substrate using a blade, known as a “doctor blade” technique – which the researchers compare to buttering bread. They had calculated that the compound formamidinium lead iodide could be a good candidate for a stable solar cell, but difficult to produce as a thin film using existing techniques.

“This formamidinium lead iodide material has very good characteristics, but the A position formamidinium ion causes instability in the structure,” explains Professor of Photophysics and Optoelectronics Maria Antonietta Loi. “Three-dimensional films made from this material most often turn out to be a mixture of a photoactive and a photoinactive phase, the latter being detrimental to the final application.”

To get around this problem, the team started working with a different perovskite, phenylethlyammonium lead iodide. A 500-nanometer layer of this material is deposited on a substrate using the “doctor blade” technique.

This layer was then used as a “template” to grow a perovskite layer from the formamidinium lead iodide material. The film was dipped in a solution containing formamidinium iodide, and through “cation exchange” formamidinium took the place of 2 phenylethylammonium.

“These films show much higher photoluminescence compared to reference 3-D formamidinium lead iodide films and show increased stability when exposed to light or moisture,” says Loi. “This means that we now have a method for the production of high-quality films for perovskite solar cells using an industrially scalable technique.”

…but they won’t work in space

Another group of scientists from Skolkovo Institute of Science and Technology in Moscow have also looked into the potential for perovskites to be used to power spacecraft. The team exposed a lead-based perovskite, known as a triple cation perovskite, to 5000 Gray Units.

Their results, published in the paper γ-Ray Induced Degradation in the Triple-Cation Perovskite Solar Cells, in the Journal of Physical Chemistry Letters, found that the cells quickly degraded under such doses of radiation, and are therefore not suitable for use in space applications. “Higher doses resulted in a rapid decay of short circuit current density (J_sc) and power conversion efficiency of the devices,” explains Skoltech Ph.D. student Aleksandra Boldyreva. “Solar cells in space should withstand not only a severe solar radiation, but also must be tolerant to high doses of gamma rays to achieve stable operation for years.

The team now plans to focus on identifying new materials that exhibit the enhanced stability required for such applications.