Interfacial Bridge Using a cis‐Fulleropyrrolidine for Efficient Planar Perovskite Solar Cells with Enhanced Stability

Fullerene derivatives, especially after purposely functionalization, have potential to efficiently passivate interfacial defects between perovskites and electron transport layers. In this work, a fullerene derivative with amine functional group, 2,5‐diphenyl C 60 fulleropyrrolidine (DPC 60 ), is synthesized and employed as an interfacial layer between a perovskite and SnO 2 in planar perovskite solar cells (PSCs). The cis ‐configuration and the specific amine group of DPC 60 effectively enhance the chemical interaction between the perovskite and DPC 60 , promoting the passivation of perovskite defects at the interface. The suitable energy level of DPC 60 and the improved conductivity of the SnO 2 /DPC 60 film facilitate the electron extraction from the perovskite layer. As a result, PSCs incorporated with DPC 60 reach a PCE of 20.4% with high reproducibility, which is much higher than that of the bare SnO 2 based devices (18.8%). Furthermore, the hydrophobic DPC 60 layer suppresses heterogeneous nucleation and improves the crystallinity of the perovskite film, resulting in better device stability, retaining 82% of its initial efficiency after 200 h of 1 sun continuous irradiation and thermal ageing (55 ± 5 °C).