Solvent spray produces black perovskite for solar cells

"Pure formamidinium perovskite could produce perovskite solar cells that are more efficient and stable than those made with other commonly used hybrid perovskites based on methylammonium. This could be really important for commercializing this technology, particularly as the process can easily be scaled up."Joe Briscoe, Queen Mary University of London

An international team of researchers, including some from Queen Mary University of London in the UK, has developed a new process for producing stable perovskite materials to create more efficient solar cells. The researchers report this new process in a paper in Advanced Materials.

Crystalline silicon is the most widely used material for solar cells. However, over the past decade, solar cells made from metal halide perovskite materials have shown potential for being cheaper and more efficient than solar cells made from silicon.

But whilst perovskite solar cells can now compete in terms of efficiency with more established silicon-based solar cells, their chemical instability remains a key challenge. Perovskite materials are very sensitive to moisture, oxygen and even light, meaning they can degrade rapidly in air.

One perovskite material, formamidinium perovskite (FAPbI₃), could help to solve this issue, as its pure, black-colored crystal structure is more chemically stable than many other perovskites. Its optical properties are also much better suited for absorbing light and producing electricity efficiently in a solar cell than existing perovskite materials. However, creating this black, stable form of the material is difficult, and it can often instead form a yellow phase that isn’t suitable for solar cells.

One of the challenges with making FAPbI₃ is that the required high temperature (150°C) can cause the crystals within the material to ‘stretch’, making them strained, which favours the yellow phase. Some previous reports have used small amounts of additional chemicals, or ‘additives’, to help form FAPbI₃ under these conditions. But it can be very hard to control the uniformity and amounts of these additives when making solar cells at a very large scale, and the long-term impact of including them is not yet known.

The fabrication process developed by the international team instead exposes films of FAPbI₃ to an aerosol containing a mixture of solvents at a lower temperature (100°C). The researchers found this could induce the formation of very stable black-phase FAPbI₃ after just one minute, in comparison to other approaches that can take around 20 minutes. They also showed that the lower temperatures help to ‘relax’ the crystals within the material.

“Pure formamidinium perovskite could produce perovskite solar cells that are more efficient and stable than those made with other commonly used hybrid perovskites based on methylammonium," said Joe Briscoe, reader in energy materials and devices at Queen Mary. "This could be really important for commercializing this technology, particularly as the process can easily be scaled up.

“In this study, we’ve demonstrated a novel, more efficient approach to create pure and stable black formamidinium perovskite FAPbI₃. As our process uses an ‘inverted’ perovskite solar cell structure and lower annealing temperature, this also makes it very suitable for making flexible solar cells on plastic, which could have a lot of applications for example in clothing and vehicles.”

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