The defects at the interface of SnO2 electron transport layers (ETLs) /perovskite layer hinder extraction and transfer of charge, which restrict the further improvement of the photoelectric conversion efficiency (PCE) of SnO2-based perovskite solar cells (PSCs). Herein, an effective bifunctional anchoring strategy is developed to passivate SnO2/perovskite interface defects by adequate chelate sites in polydentate phytic acid dipotassium (PAD) to anchor SnO2 colloids. It is confirmed that polydentate PAD anchoring can form new Sn-O-P bonds with uncoordinated Sn2+, which can efficiently passivate the SnO2 surface defects and alleviate the interfacial charge recombination between SnO2 and perovskite layer. The reduction of SnO2 surface defects enhances the electron transport efficiency and increases the conductivity of the PAD-SnO2 ETLs to 2.1 times that of SnO2 ETLs. Meanwhile, the anchoring group potassium ions (K+) in PAD can promote the in-plane growth of perovskite grains and increase the average grain size of perovskite from 560 nm to 850 nm. As a consequence, the PCE of the PAD-SnO2-based PSCs increased sharply to 21.61%, which is 10.7% higher than that of the PSCs made with SnO2 ETLs (19.52%). The unencapsulated PSCs deposited on PAD-SnO2 ETLs can remain 99.5% of their initial efficiency after 60 days under 25–30% humidity.

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