Room‐Temperature‐Processed Fullerene/TiO 2 Nanocomposite Electron Transporting Layer for High‐Efficiency Rigid and Flexible Planar Perovskite Solar Cells

Room‐temperature‐processed TiO 2 (R‐Lt‐TiO 2 ) electron transporting layers (ETLs) possess low conductivity and connectivity, resulting in poor photovoltaic performance. Herein, an ethanol (EtOH)‐soluble, highly conducting fullerene derivative, C 60 RT 6 , was used as an additive for Lt‐TiO 2 ETLs. Room‐temperature processed nanocomposite ETL (R‐Fu/Lt‐TiO 2 ) is prepared simply by spin coating a C 60 RT 6 and G‐TiO 2 NPs (TiO 2 nanoparticle prepared by grinding the bulk TiO 2 powder) mixture. R‐Fu/Lt‐TiO 2 has better aligned with the frontier orbitals of the FA x MA 1−x PbI 3 , better continuity, conductivity, flatness, and higher surface hydrophilicity compared to Lt‐TiO 2 ETL. Perovskite films spin coated on R‐Fu/Lt‐TiO 2 ETLs also have slightly larger grains and thickness compared to those deposited on Lt‐TiO 2 . Perovskite solar cells (PSCs) based on a R‐Fu/Lt‐TiO 2 ETL possess higher power conversion efficiency (PCE, up to 20% on glass substrate), less (negligible) current hysteresis, and better long‐term stability compared to those using R‐Lt‐TiO 2 as an ETL. The flexible PSC (used indium tin oxide/polyethylene terephthalate (ITO/PET) as a substrate) with a R‐Fu/Lt‐TiO 2 ETL achieves a PCE of 18.06% and retains 90% of the initial PCE after 500 bending cycles with a bending radius of 6 mm. The PCE of the flexible cell with a Lt‐TiO 2 ETL is only 8.2%, and loses 60% of the initial value after 500 bending cycles.