Doping PCBM with fullerene phosphinate derivatives enhances the interface energy alignment and synergistic passivation capability

Phenyl-C₆₁-butyric acid methyl ester (PCBM) serves as a common electron transport layer (ETL) in inverted p-i-n structure perovskite solar cells (IPSCs), yet energy barriers and insufficient passivation at the PCBM-perovskite interface hinder device effectiveness and durability. In this study, we present a series of novel Fullerene Phenylacid Ester Derivatives (FPEDs: FPP, FTPP, FDPP) incorporated into PCBM. Our investigations illustrate that FPEDs effectively act to passivate the perovskite surface by forming robust interactions with uncoordinated Pb²⁺ ions via the phosphine oxide groups present in their molecular structures, thereby enhancing the stability of the devices. Moreover, these additives elevate the energy level of the lowest unoccupied molecular orbital (LUMO) of ETL, diminish the electron injection barrier, and enhance the efficiency of interlayer electron transport. Incorporating FPEDs enhances ETL coverage on the perovskite layer, reducing leakage current significantly. Notably, Devices with PCBM/FTPP achieved a peak PCE of 23.62% and showed superior stability, maintaining 96.8% of the initial PCE after 500 h, while control devices retained merely 80.7% over the same period.