Consolidating a Pb–X framework via multifunctional passivation with fluorinated zwitterions for efficient and stable perovskite solar cells

Abstract

Ionic defects in perovskite films decrease both the power conversion efficiency (PCE) and stability of a perovskite solar cell (PSC). Herein, fluorinated D-pentafluoro-phenylalanine (D-PFPAA) zwitterions are introduced into a perovskite to passivate the ionic defects and effectively consolidate the Pb–X framework to suppress ion migration. The results demonstrate that the amino, carboxyl, and fluorine groups in D-PFPAA can support the multifunctional passivation of both positive and negative ionic defects, including uncoordinated Pb²⁺ ions and halogen (X⁻) defects in the perovskites, thereby effectively suppressing charge recombination. Consequently, a D-PFPAA-modified device shows a highest PCE of 21.56% with an increased open circuit voltage of 1.15 V. Apart from the consolidated Pb–X framework, resulting from multifunctional passivation, the fluorine groups in D-PFPAA can also form an effective hydrophobic barrier to protect the perovskite film from moisture-related erosion. As a consequence, the D-PFPAA-modified device retains more than 85% of its original PCE after undergoing 500 h of aging at 45% relative humidity under ambient conditions. This work provides a promising strategy for the realization of efficient and stable PSCs via the selection of fluorinated zwitterions to passivate the ionic defects, inhibit ion migration, and protect against moisture damage.