Decoupling Bidirectional Photochemical Degradation via Radical Scavenging for Stable Inverted Perovskite Solar Cells

ABSTRACT

Interfacial instability between perovskite absorbers and fullerene‐based electron transport layers critically limits the operational stability of inverted perovskite solar cells (PSCs). Here, we discover a bidirectional coupling degradation mechanism at the perovskite/fullerene interface: photo‐oxidation of formamidinium iodide (FAI) generates iodine radicals that catalyze PCBM dimerization via [2+2] cycloaddition, while PCBM concurrently accelerates FAI deprotonation and iodine‐species formation, creating a self‐reinforcing degradation cycle. To disrupt this cascade, we introduce the nitroxide radical scavenger 4‐oxo‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy radical (O‐TEMPO) at the interface, which selectively quenches iodine and carbon‐centered radicals, suppressing both perovskite decomposition and PCBM dimerization while maintaining optimal charge extraction. O‐TEMPO‐modified devices achieve a champion efficiency of 26.99% and retain 95.1% of initial performance after 1000 h of maximum power point tracking under ISOS‐L‐2 conditions (65°C), significantly outperforming control and conventionally 3‐(methylthio)propylammonium iodide (3MTPAI)‐passivated devices. This work elucidates the molecular origins of interfacial degradation and establishes radical‐scavenging interfacial engineering as a universal strategy to decouple synergistic degradation pathways, providing a robust framework for developing highly stable perovskite photovoltaic technologies.