Rational design and modification of the buried interface toward high performance perovskite solar cells (PSCs) are highly desired and challenging. Here, we demonstrate a series of guanidinium passivators with multiamine substitutions to shed light on the effective passivation geometry at the SnO2/perovskite heterojunction interface. Comparative theoretical and experimental studies reveal that the binding geometry of the highly polarized imine moiety in guanidinium passivators dominates its energeti-cally favorable passivation on the SnO2 surface, which decreases the trap density to 1.11 x 1016 cm-3 with reduced interior/interface nonradiative recombination in the unsymmetrical aminoguanidine hydrochloride (Agu) platform. Consequently, the PSCs with buried Agu passivator deliver a champion power conversion efficiency (PCE) of 24.4% with an advanced open-circuit voltage (VOC) of 1.197 V and prolonged lifetime over 90% of the initial PCE after 900 h in ambient conditions.