Pyridine-Functionalized Fullerene Electron Transport Layer for Efficient Planar Perovskite Solar Cells

In
regular perovskite solar cells (PSCs), the commonly used electron
transport layer (ETL) is titanium oxide (TiO2). Nevertheless,
the preparation of a high-quality TiO2 ETL demands an elevated-temperature
sintering procedure, unfavorable for fabrication of PSCs on flexible
substrates. Besides, TiO2-based devices often suffer from
notorious photocurrent hysteresis and serious light soaking instability,
limiting their potential commercialization. Herein, a novel pyridine-functionalized
fullerene derivative [6,6]-(4-pyridinyl)-C61-ethyl acid
ethyl ester (PyCEE) was synthesized and applied as an ETL to replace
TiO2 in n–i–p PSCs. PyCEE-based devices achieved
a champion power conversion efficiency (PCE) of 18.27% with significantly
suppressed hysteresis, superior to that of TiO2-based devices.
PyCEE has suitable energy levels and high electron mobility, which
facilitate electron extraction/transport. Besides, the pyridine moiety
within PyCEE affords coordination interactions with the Pb2+ ion within CH3NH3PbI3, passivating
the trap states of CH3NH3PbI3 and
thus improving the device performance and suppressing hysteresis greatly.
Moreover, PyCEE ETLs were applied in flexible PSCs, achieving a PCE
of 15.25%. Our results demonstrated the applicability of PyCEE ETLs
in flexible devices and provided new opportunity for the commercialization
of PSCs.