Mechanistic Insight into the Attachment of Fullerene Derivatives on Crystal Faces of Methylammonium Lead Iodide Based Perovskites

Recent studies suggest that electron transport layers (ETLs) comprising [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), employed in planar perovskite solar cells, reduce hysteresis by passivating the deep trap states, thereby underscoring the importance of interfacial structures. To gain physical insights into the PCBM–perovskite interfaces during solution processing, we performed molecular dynamics simulations of PCBMs solvated in chlorobenzene near (110) and (100) perovskite surfaces. Our results indicate strong orientational preferences of deposited PCBMs with the strongest associations between the carbonyl oxygen atom of PCBM and the terminating Pb and H atoms of (110) and (100) faces of perovskite, respectively. The phenyl moiety shows weak associations with the (100) perovskite surface enabling two-pronged anchoring that might facilitate charge transfer. In-plane ordering of PCBMs on perovskite surfaces indicates that a more densely packed monolayer is formed on the (110) surface compared to that on the (100) surface and might lead to more efficient electron transport.