Julolidine functionalized benzimidazoline-doped fullerene derivatives for efficient and stable perovskite solar cells

Fullerene derivatives are highly attractive materials in solar cells, organic thermoelectrics, and other devices. However, the intrinsic low electron mobility and electrical conductivity restrict their potential device performance, such as perovskite solar cells (PSCs). Herein, we successfully enhanced the electric properties and morphology of phenyl-C₆₁-butyric acid methyl ester (PCBM) by n-doping it with a benzimidazoline derivative, 9-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)-julolidine (JLBI-H) via a solution process. We found the n-doping can not only improve the conductivity and optimize the band alignment but also enable the PCBM to have a constantly strong charge extraction ability in a wide temperature from 173 to 373 K, which guarantees a stable photovoltaic performance of the corresponding PSCs under a wide range of operating temperatures. With the JLBI-H-doped PCBM, we improved the efficiency from 17.9% to 19.8%, along with enhanced stability of the nonencapsulated devices following the aging protocol of ISOS-D-1.