Engineering of Electron Extraction and Defect Passivation via Anion-Doped Conductive Fullerene Derivatives as Interlayers for Efficient Invert Perovskite Solar Cells.

The major limitation of organic-inorganic perovskite solar cell performance is the existence of numerous charged defects at the absorption layer surface, which caused the charge carrier to recombine depravation. These defects have a remarkable influence on charge extraction, which further caused the instability of the device and induced severe hysteresis. Here, three low-cost anion-doped conductive fullerene derivatives, fullerene bis(phenethyl alcohol) malonate (FMPE-I), fullerene bis(ethylenediamine) malonamide (FEDA-I), and fullerene bis(propanediamine) malonamide (FPDA-I), are developed for the first time as interfacial layers between perovskite and phenyl-C-butyric acid methyl ester (PCBM) in planar invert perovskite solar cells by mild solution fabrication. The constituent Lewis basic halides and the specific amide groups of conductive fullerene derivatives efficaciously heighten the chemical interaction between perovskite and conductive fullerene derivatives since the iodide can combine with undercoordinated Pb by electrostatic interaction and the amide group can facilely be combined with I by hydrogen bonding, improving the dual passivation of perovskite defects. Moreover, due to the well-matched energy level of conductive fullerene derivatives and the high conductivity of the perovskite/interlayer film, the electron extraction capacity can be effectively enhanced. Consequently, superior optoelectronic properties are achieved with an improved power conversion efficiency of 17.63%, which is considerably higher than that of the bare PCBM-based devices (14.96%), for the perovskite device with conductive interlayer treatment along with negligible hysteresis. Moreover, hydrophobic conductive fullerene derivatives improve the resistance of the device to moisture. The conductive fullerene derivative-based devices without encapsulation are maintained at 85% of the pristine power conversion efficiency value after storage under ambient conditions (25 °C temperature, 60% humidity) for 500 h.