Fused-Ring Electron Acceptors as a Versatile Additive Platform for Efficient Perovskite Photovoltaics

Various additives with rich chemical properties have been used to control crystal growth and passivate defects to boost the efficiency of perovskite solar cells (PSCs). However, the poor reproducibility between different research groups deteriorates the reliability of high-performance PSCs due to the "super" diversity of reported additives and lack of a reliable molecular design platform for versatile additives. Here, we present a general and rational additive design based on fused-ring electron acceptors (FREAs) to construct reproducible and efficient PSCs. The FREAs that we pioneered are a well-established molecular design platform with advantages in facile structural tailoring and property modulation, while the wide applicability and reproducibility of the FREAs have been confirmed worldwide in the organic photovoltaics community. Through building block design of the FREAs we reveal that the energy level alignment can be modulated by tailoring the FREA main chain to facilitate charge transport in perovskite films, while the wrinkled morphology with proper lattice strain can be induced by designing the FREA side chain to suppress ion migration for improved device stability. With optimized design, a champion efficiency of 26.66% (26.35% certified) was achieved by a new FREA additive, with dramatically improved stability of less than 8% efficiency loss after 2150 h of continuous operation under 1 sun illumination.