Highly improved efficiency and stability of planar perovskite solar cells via bifunctional phytic acid dipotassium anchored SnO₂ electron transport layer

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.