Mitigating Ion Migration by Polyethylene Glycol-Modified Fullerene for Perovskite Solar Cells with Enhanced Stability

Ion migration, an intrinsic property that cannot be suppressed by device encapsulation, is of great importance to the long-term stability of perovskite solar cells. Herein, we synthesize a polyethylene glycol-modified fullerene (PCBHGE) and then incorporate it into perovskite absorber layers. It is found that PCBHGE can stabilize [PbI6](4-) octahedral frameworks by forming Lewis acid-base pairs. Decoupling the efficient defect passivation of the fullerene core, ion migration is suppressed significantly in the as-fabricated devices. As a result, our state-of-the-art device demonstrates a highest efficiency of 23.19%. Most importantly, the device with PCBHGE can retain 87% of its maximum efficiency after 206 days. Tracked at the maximum power point under a continuous bias, the device efficiency hardly decreases in the first 212 h with a UV filter and can retain 80% of its initial efficiency after the next 600 h under full spectrum illumination including UV light.