N‑Type Doping of Fullerenes for Planar Perovskite Solar Cells

Modification of TiO2 by using fullerenes is an efficient strategy to further improve the device efficiency and enhance the cell stability of perovskite solar cells (PSCs). However, the intrinsic issues of low electron mobility and electrical conductivity of fullerene materials may restrict their potential application in PSCs. Here, we demonstrated an n-doped electron-transporting layer by doping bis­(1-[3-(methoxycarbonyl)­propyl]-1-phenyl)-[6,6]­C62 (bis-PCBM) with decamethylcobaltocene (DMC) to fabricate n–i–p structure PSCs. We successfully realized an n-type doping of bis-PCBM via a solution-processed doping process. DMC doping played a series of roles in adjusting the energy levels, improving the electron mobility and enhancing the film conductivity of bis-PCBM. A bis-PCBM:DMC composite film could act as an underlay for the deposition and growth of a subsequent perovskite layer owing to its smooth morphology. In addition, the bis-PCBM:DMC composite film also presented good solvent resistance, which could slow down the degradation process of the perovskite layer. Consequently, a champion device with a maximum PCE of 20.14% was approached.