Perovskites are a class of materials made up of organic materials attached to a metal. Their fascinating structure and properties have brought perovskites to the forefront of materials research, where they are being studied for use in a wide variety of applications. Metal halide perovskites are particularly popular and are being considered for use in solar cells, LED lights, lasers, and photo detectors.
For example, the energy conversion efficiency of perovskite solar cells (PSCs) has increased from 3.8% to 25.5% in just ten years, outperforming other thin-film solar cells – including the market-leading polycrystalline silicon.
Perovskites are typically made by mixing and layering different materials on a transparent conductive substrate, creating thin, lightweight films. The process known as “chemical deposition” is sustainable and relatively inexpensive.
But there is a problem. Since 2014, metal halide perovskites have been produced by mixing cations or halides with formamidinium (FAPbI3). The reason for this is that this recipe results in high energy conversion efficiency in perovskite solar cells. At the same time, the most stable phase of FAPbI3 is photoinactive, which means it doesn’t respond to light – the opposite of what a solar harvester should do. In addition, solar cells made with FAPbI3 have long-term stability problems.
Now, researchers under the direction of Michael Graetzel and Anders Hafgeldt from EPFL have developed a deposition method that overcomes the formamidinium problems while maintaining the high conversion of perovskite solar cells. The work was published in Science.
In the new method, the materials are first treated with a steam made from methylammonium thiocyanate (MASCN) or formamidinium thiocyanate FASCN. This innovative optimization transforms the photoinactive FAPbI3 perovskite films into the desired light-sensitive ones.
With the new FAPbI3 films, the scientists produced perovskite solar cells. The cells showed an efficiency of more than 23% in energy conversion and a long-term operational and thermal stability. They also exhibited a low (330 mV) open circuit voltage drop and a low (0.75 V) turn-on voltage for electroluminescence.
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Materials provided by Swiss Federal Institute of Technology in Lausanne. Originally written by Nik Papageorgiou. Note: the content can be edited by style and length.