Highly Improved Efficiency and Stability of Planar Perovskite Solar Cells via Bifunctional Phytic Acid Dipotassium Anchored SnO2 Electron transport layer

• Phytic acid dipotassium (PAD) is selected to passivate SnO 2 /perovskite interface defects by anchoring SnO 2 NCs. • The formation of new Sn-O-P bonds between polydentate PAD and uncoordinated Sn 2+ can effectively passivate SnO 2 surface defects. • The potassium ions in PAD can promote the in-plane growth of perovskite grains and increase the average grain size of perovskite. • Optimized PSCs with PAD-SnO 2 ETLs achieved a champion PCE of 21.61%, which presents an improvement of 10.7% over than that of SnO 2 -based PSCs. The defects at the interface of SnO 2 electron transport layers (ETLs) /perovskite layer hinder extraction and transfer of charge, which restrict the further improvement of the photoelectric conversion efficiency (PCE) of SnO 2 -based perovskite solar cells (PSCs). Herein, an effective bifunctional anchoring strategy is developed to passivate SnO 2 /perovskite interface defects by adequate chelate sites in polydentate phytic acid dipotassium (PAD) to anchor SnO 2 colloids. It is confirmed that polydentate PAD anchoring can form new Sn-O-P bonds with uncoordinated Sn 2+ , which can efficiently passivate the SnO 2 surface defects and alleviate the interfacial charge recombination between SnO 2 and perovskite layer. The reduction of SnO 2 surface defects enhances the electron transport efficiency and increases the conductivity of the PAD-SnO 2 ETLs to 2.1 times that of SnO 2 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-SnO 2 -based PSCs increased sharply to 21.61%, which is 10.7% higher than that of the PSCs made with SnO 2 ETLs (19.52%). The unencapsulated PSCs deposited on PAD-SnO 2 ETLs can remain 99.5% of their initial efficiency after 60 days under 25–30% humidity.