A large perovskite solar cell. Photo: Nripan Mathews, NTU Singapore.
A large perovskite solar cell. Photo: Nripan Mathews, NTU Singapore.

Perovskites are a class of materials made up of organic materials bound to a metal. Their fascinating structure and properties have propelled perovskites into the forefront of materials' research, where they are studied for use in a wide range of applications.

A type known as metal-halide perovskites are especially popular, and are being considered for use in solar cells, LED lights, lasers and photodetectors. The power-conversion efficiency of perovskite solar cells (PSCs), for example, has increased from 3.8% to 25.5% in only 10 years, surpassing other thin-film solar cells – including the market-leading polycrystalline silicon.

Perovskites are usually made by mixing and layering various materials together on a transparent conducting substrate., which produces thin, lightweight films. This process, known as 'chemical deposition', is sustainable and relatively cost-effective.

But there is a problem. Since 2014, metal halide perovskites have been made by mixing cations or halides with formamidinium (FAPbI3), because this produces perovskite solar cells with a high power-conversion efficiency. But at the same time, the most stable phase of FAPbI3 is photoinactive, meaning that it does not react to light – the opposite of what a solar power harvester ought to do. In addition, solar cells made with FAPbI3 suffer from long-term stability issues.

Now, researchers led by Michael Grätzel and Anders Hafgeldt at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed a deposition method that overcomes the formamidinium issues while maintaining the high conversion of perovskite solar cells. The researchers report the new method in a paper in Science.

In this method, the materials are first treated with a vapor of methylammonium thiocyanate (MASCN) or formamidinium thiocyanate (FASCN). This simple, innovative tweak turns the normally photoinactive FAPbI3 perovskite films into photosensitive versions.

The scientists used the new photosensitive FAPbI3 films to make perovskite solar cells, which showed more than 23% power-conversion efficiency and long-term operational and thermal stability. They also featured a low (330mV) open-circuit voltage loss and a low (0.75V) turn-on voltage of electroluminescence.

This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.