Researchers at Huazhong University of Science and Technology, Russian Academy of Sciences, Okinawa Institute of Science and Technology Graduate University (OIST) and Shanghai Jiao Tong University have developed a design strategy that could reduce defects in FAPbI3-based solar cells, improving their power efficiency. This strategy involves the application of an additive and a coating agent to the perovskite films integrated in the solar cells.
"Power conversion efficiencies of inverted perovskite solar cells (PSCs) based on methylammonium- and bromide-free formamidinium lead triiodide (FAPbI3) perovskites still lag behind PSCs with a regular configuration," Rui Chen, Jinan Wang, and their colleagues wrote in their paper. "We improve the quality of both the bulk and surface of FA0.98Cs0.02PbI3 perovskite films to reduce the efficiency gap."
To improve the performance of such inverted PSCs, the researchers added a compound to the bulk material that could reduce the defects within it. This compound, called dibutyl sulfoxide (DBSO), has a low volatility and chemically interacts with some materials, influencing their properties or structure.
"First, we use DBSO, a Lewis base additive, to improve the crystallinity and reduce the defect density and internal residual stress of the perovskite bulk," Chen, Wang and their colleagues stated in their paper. "Then, we treat the surface of the perovskite film with trifluorocarbon-modified phenethylammonium iodide (2CF3-PEAI) to optimize the energy levels, passivate defects and protect the film against moisture."
The team applied their strategy to a FAPbI3 film, which they then used to create inverted PSCs. They evaluated these solar cells in a series of tests and found that they performed extremely well, both in terms of stability and energy efficiency.
"The inverted PSCs simultaneously achieve 25.1% efficiency (24.5% from the reverse current–voltage scan measured by a third-party institution) and improved stability," the team wrote in their paper. "The devices maintained 97.4% and 98.2% of their initial power conversion efficiencies after operating under continuous 1-sun air mass 1.5 G illumination for 1,800 h and under damp heat conditions (85°C and 85% relative humidity) for 1,000 h, respectively."
In the future, this new could be adapted and used to engineer more efficient and stable inverted PSCs. While the team specifically applied the DBSO additive and 2CF3-PEAI coating to FAPbI3 films, their approach could potentially also help to reduce defects and improve the performance of other perovskite materials.
