Molecular Engineering of Azahomofullerene-based Electron Transporting Materials for Efficient and Stable Perovskite Solar Cells

The rational molecular design of fullerene-based molecules with exceptional physical and electrical properties is in high demand to ensure efficient charge transport at the perovskite/electron transport layer interface. In this work, novel azahomofullerene (AHF) is designed, synthesized, and introduced as the interlayer between the SnO2/perovskite interface in planar n-i-p heterojunction perovskite solar cells (PSCs). The AHF molecule (denoted as AHF-4) is proven to enhance charge transfer capability compared to the commonly used fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) due to its superior coordination interaction and electronic coupling with the SnO2 surface. In addition, the AHF-4 interlayer concurrently improves the quality of the perovskite film and reduces charge recombination in PSCs. The resultant AHF-4-based device exhibits a maximum efficiency of 21.43% with lower hysteresis compared to the PCBM device (18.56%). Benefiting from the enhanced stability of the AHF-4 film toward light soaking and elevated temperature, the AHF-4-based devices show improved stability under continuous 1 sun illumination at the maximum power point and 45 ?. Our work opens a new direction to the design of AHF derivatives with favorable physical and electrical properties as an interlayer material to improve both the performance and stability of PSCs.