π-Extended Spiro Core-Based Nonfullerene Electron-Transporting Material for High-Performance Perovskite Solar Cells

Electron transport materials (ETMs) play a significant role in perovskite solar cells (PSCs). However, conventional solution processable organic ETMs are mainly restricted to fullerene derivatives and it is challenging to obtain nonfullerene ETMs with satisfactory properties. In this work, a new organic semiconductor SPS-4F is synthesized by utilizing the classical spiro[fluorine-9′9-thioxanthene] unit to construct a π-extended core. Although spiro is normally used in hole transport materials, the new spiro derivative SPS-4F is successfully used as an ETM in inverted PSCs with power conversion efficiency over 20%. In addition, SPS-4F can strongly coordinate with MAPbI₃ perovskite and lead to efficient surface trap passivation. The resultant PSCs exhibit excellent stability in air because of the hydrophobic property of SPS-4F. This work opens up opportunities to obtain a new family of ETMs based on spiro and paves a way to the fabrication of high-performance PSCs with low cost.