Anion-competition regulation of PbI2 frameworks for two-step fabricated perovskite solar cells

Abstract

Achieving high-efficiency and stable large-area perovskite solar cells (PSCs) via scalable fabrication remains a significant challenge, largely due to difficulties in controlling lead iodide (PbI₂) film morphology and crystallization kinetics. Herein, we develop a multifunctional ionic liquid, 4-fluoro-phenethylammonium formate (4F-PEAFa), to regulate the Pb²⁺ coordination environment via an anion competition strategy. The strong interaction between formate anions and Pb²⁺ suppresses the formation of undesired methylammonium lead iodide (MAPbI₃) intermediates, facilitating the growth of phase-pure, porous, and highly oriented PbI₂ films. This optimized scaffold ensures thorough precursor infiltration and uniform perovskite conversion. When integrated into a screen-printing process, this strategy yields exceptionally uniform films with reduced defect density and accelerated carrier transport. Consequently, the resulting devices deliver a peak power conversion efficiency (PCE) of 25.01% (0.05 cm²) and a remarkable 22.16% for large-area modules (12.6 cm²). Notably, unencapsulated devices retain 87% of their initial PCE after 1150 h under ISOS-L-1 testing, demonstrating a robust pathway toward stable and scalable perovskite photovoltaics.