AbstractAlthough there is extensive attention to the eminent perovskite solar cells, the deep‐level defects such as Pb‐Pb dimers in the solution‐processed polycrystalline perovskites inevitably result in photovoltaic output losses and subsequent degradation. Recently, it is reported that an electron‐donating group can passivate Pb dimer defects efficiently. However, the mechanism for the causation of metallic lead (Pb⁰) from the iodide vacancy (V_I) is unclear. Herein, a chain reaction mechanism is proposed for the possible transformation process from V_I to Pb⁰ with the Pb dimer intermediates. In this regard, a host‐guest strategy is adopted by using 4‐tert‐Butyl‐1‐(ethoxycarbonyl‐ methoxy) thiacalix[4]arene (tBuTCA) to complex with the cations and out‐of‐cage (Lead(II) iodide) PbI₂. Moreover, a host‐guest complexation can be formed due to the Pb²⁺‐π interactions. Continuously, the negative charge compensation for iodine vacancy can hinder the formation of Pb‐Pb dimer, thus significantly suppressing non‐radiative recombination. Consequently, the resulting solar cells show more than 24% power conversion efficiencies and maintain over 96% of their initial performance without encapsulation for 486 h under an ambient environment. This work highlights the significance of supramolecular engineering in constructing a high‐quality perovskite for efficient and stable perovskite solar cells.