<p>Defect-rich buried interfaces remain a critical bottleneck limiting the efficiency and stability of perovskite solar cells (PSCs). Notably, oxygen vacancies at the SnO₂/perovskite interface act as dominant nonradiative recombination centers, severely inhibiting device performance. While conventional interfacial passivation strategies have primarily focused on localized coordination by anionic anchoring groups, the role of π-conjugated anions in interfacial modifiers remains insufficiently understood. Here, a conjugated anion modulation is established by comparing potassium acetate (KAc) and potassium sorbate (KSb), which share identical K⁺–carboxylate frameworks but differ in anion conjugation, elucidating the contribution of the π-conjugation effect in interfacial defect suppression. Unlike the localized interaction of KAc, the π-conjugated framework of KSb enables more delocalized electronic interactions, contributing to spatially extended passivation from the buried interface into the perovskite region. These extended interactions enable favorable energy-level alignment and effective passivation of oxygen vacancies in SnO₂, while also improving perovskite crystallinity and suppressing interfacial recombination. As a result, KSb-modified devices achieve an efficiency of 22.16% with an open-circuit voltage of 1.183&#xa0;V and a fill factor of 84.30%, surpassing KAc and control devices. Unencapsulated KSb devices retain 97% of their initial efficiency after 1000&#xa0;h under dark ambient storage and demonstrate improved film-level thermal stability. Our findings highlight π-conjugated anion engineering as an effective strategy for achieving spatially extended defect passivation at buried interfaces, offering potential for molecular design for improving perovskite optoelectronic devices.</p> Graphical abstract <p></p>