Researchers at EPFL in Switzerland have reported on the use of Flash Infrared Annealing (FIRA) to rapidly produce efficient, stable perovskite solar cells.
FIRA shares many characteristics with thermal annealing techniques already used to grow pure crystal phases for the semiconductor industry. It works by using a short IR pulse to rapidly nucleate a perovskite film from a precursor solution, without the need for a high-temperature scaffold. The high speed and relatively low processing temperatures mean that FIRA is compatible with large-area deposition techniques, like roll-to-roll processing. For PSCs, it could offer a practical route to scaling-up production.
The researchers first annealed a layer of TiO2 using multiple FIRA cycles over a period of 10 minutes, and then spin-coated a novel perovskite compound onto the substrate. The perovskite layer was composed of formamidinium lead iodide, combined with small amounts of cesium. They also added guanidinium, which decreased the surface energy by providing enhanced hydrogen bonding. This led to a more uniform, compact perovskite film. A low-temperature post-treatment with tetrabutylammonium iodide (TBAI) further improved the film’s long-term stability. Synthesis of the perovskite film took just 1.6 seconds, and was shown to retain its performance for at least one month.
Devices made in this manner displayed power conversion efficiencies of over 20%, which the authors say demonstrates “that FIRA can be used as a standard method for fast production, high performance and highly reproducibly manufactured devices”. The shorter annealing time reduces the energy requirements for the process, while also speeding it up. In a separate work, the same authors report that their FIRA method has “only 8% of the environmental impact and 2% of the fabrication cost of the perovskite active layer” compared to the antisolvent method currently used to produce thin films for lab-scale cells. Although this second study looked at a different perovskite composition, taken together, these results suggest that FIRA has huge potential as a practical fabrication route for PSCs.