Fluorinated Lead-Chelating Molecules Boost Performance, Stability, and Safety of Hole Transport Layer-Free...

Hole transport layer-free carbon-based perovskite solar cells (HTL-free C-PSCs) hold promise for low-cost, stable photovoltaics but suffer from poor interfacial charge extraction, inferior defect passivation, and unresolved environmental risk. Here, we reported a multifunctional interfacial engineering strategy using fluorinated lead-chelating (FLC) molecules containing sulfonate groups, fluoride atoms, and metal ions. Sulfonate groups coordinated with undercoordinated Pb²⁺ ions, fluoride atoms formed hydrogen bonds with organic cations, and K⁺ ions stabilized halide anions, synergistically passivating deep-level defects and enhancing thermal stability. FLC modification also reduced the perovskite work function (from -4.14 to -4.39 eV), improving energy level alignment and facilitating hole extraction at the perovskite/carbon interface. As a result, the optimized devices achieved a champion power conversion efficiency of 20.7%, among the highest for fully solution-processed planar HTL-free C-PSCs. Unencapsulated devices retained over 93% of initial efficiency after 2000 h in ambient air or after 500 h at 60 °C. Importantly, strong FLC-Pb²⁺ chelation significantly reduced lead leakage from severely damaged devices under acidic aqueous environment (334.7 to 53.7 mg m^-2 h^-1), achieving ∼84% sequestration efficiency. This work presents a unified strategy to enhance efficiency, stability, and environmental safety of simplified perovskite photovoltaics.