Fullerene derivative anchored SnO₂ for high-performance perovskite solar cells

A fullerene derivative, 9-(1-(6-(3,5-bis(hydroxymethyl)phenoxy)-1-hexyl)-1H-1,2,3-triazol-4-yl)-1-nonyl [60]fullerenoacetate (C9), is employed to anchor the surface of a SnO₂ electron transport layer (ETL) in planar heterojunction perovskite solar cells (PSCs). C9 suppresses charge recombination due to efficient passivation of oxygen-vacancy-related defects on the surface of the SnO₂ ETL through the formation of a Lewis adduct between the under-coordinated Sn in SnO₂ and hydroxyl terminal groups in C9. The C9 modifying layer enhances the extraction of photogenerated charge carriers due to the negligible injection barrier and strong electron affinity. C9 can also improve the quality of the perovskite film with enlarged grain size, reduced grain boundary and improved crystallinity. The PSCs based on C9-modified SnO₂ exhibit improved photovoltaic performance with efficiency up to 21.3% with negligible hysteresis, which is superior to the control devices based on bare SnO₂ (20.0%). Moreover, the ambient, photo and electric-field stability of the modified devices is also enhanced.