Synergistic Crystallization Control and Defect Passivation via Bifunctional Hydrogen-Bonding Networks in Methylammonium-Free Perovskite Solar Cells

Methylammonium (MA)-free Cs_XFA_1-XPbI₃ perovskite solar cells (PSCs), despite their commercial promise stemming from enhanced stability, face the dual challenge of controlling crystallization and achieving stable defect passivation. Here, we introduce 4-hydroxybenzamidine hydrochloride (4OHFACl) as a bifunctional additive to address these challenges. The amidinium and hydroxyl groups in 4OHFACl form hydrogen-bonding with I⁻ and [PbI₆]⁴⁻ in perovskite precursors, regulating the colloidal properties of the precursor solution to optimize nucleation and crystallization kinetics. This enables a synergistic process of rapid nucleation followed by slow crystal growth, yielding high-quality perovskite films with enlarged grains and low residual strain. Owing to its higher pKa, the amidinium group also provides stable defect passivation, effectively suppressing non-radiative recombination. Consequently, 4OHFACl-modified PSCs achieve a power conversion efficiency (PCE) of 26.16% along with enhanced operational stability, retaining 90% of their original efficiency after 900 h of continuous illumination. Moreover, this approach exhibits excellent scalability, enabling a 66 cm² (aperture area) perovskite solar module to attain a champion PCE of 21.15%, underscoring its potential for practical large-area fabrication. This work demonstrates a new strategy to couple precursor coordination chemistry with defect passivation, enabling concurrent control of crystallization kinetics and defect energetics for stable perovskite solar cells.