Researchers from Queen Mary University of London, in collaboration with an international team of scientists, developed a new process for creating FAPbI3.

One of the challenges with making FAPbI3 is that the high temperatures (150°C) used can cause the crystals within the material to ‘stretch’, making them strained, which favors the yellow phase that isn’t suitable for solar cells. While previous reports have used small amounts of additional chemicals/additives to help form FAPbI3 under these conditions, 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 novel approach described in the study instead exposes films of FAPbI3 to an aerosol containing a mixture of solvents at a lower temperature (100°C). The researchers found that they could form very stable black-phase FAPbI3 after just one minute, in comparison to other approaches that can take around 20 minutes. They also show that the lower temperatures used help to ‘relax’ the crystals within the material.

Dr. Joe Briscoe, Reader in Energy Materials and Devices at Queen Mary, said: “Pure formamidinium perovskite could produce perovskite solar cells that are more efficient and stable that 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.”

“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.”

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