This study presents an effective surface treatment strategy using iso-butylammonium iodide (iso-BAI) to improve the surface quality and performance of tin-based perovskite solar cells (PSCs). Tin-based PSCs are promising alternatives to lead-based ones due to their lower toxicity, but they currently have lower power conversion efficiencies (PCEs) due to challenges like uncontrollable crystallization, poor film coverage, and oxidation. The iso-BAI treatment, unlike traditional passivation methods, promotes surface recrystallization by leveraging the higher solubility of tin-based perovskites in common solvents. A mixed solvent of 5% 2-methyl-2-butanol (MB) and 95% chlorobenzene (CB) was used to dissolve the defective surface while preserving the bulk. The treatment enhanced surface crystallinity, reduced strain and defects, and improved charge transport, leading to a PCE increase from 11.8% to 14.2%. The iso-BAI treatment did not form 2D perovskite structures but instead guided recrystallization, resulting in a smoother surface and better optoelectronic properties. Surface characterization techniques like SEM, AFM, and KPFM confirmed the treatment's effectiveness in reducing surface defects and oxidation. GIWAXS analysis showed improved crystallinity and reduced microstrain in the treated films. NMR studies indicated interactions between iso-BAI and tin-based perovskites, facilitating recrystallization. The treatment also reduced trap density and recombination, enhancing device performance. The study highlights the distinct mechanisms of surface treatments in tin-based perovskites compared to lead-based ones, emphasizing the need for tailored strategies to improve tin-based PSCs. The results demonstrate that iso-BAI treatment significantly enhances the performance and stability of tin-based PSCs, bringing their PCE closer to the current record.This study presents an effective surface treatment strategy using iso-butylammonium iodide (iso-BAI) to improve the surface quality and performance of tin-based perovskite solar cells (PSCs). Tin-based PSCs are promising alternatives to lead-based ones due to their lower toxicity, but they currently have lower power conversion efficiencies (PCEs) due to challenges like uncontrollable crystallization, poor film coverage, and oxidation. The iso-BAI treatment, unlike traditional passivation methods, promotes surface recrystallization by leveraging the higher solubility of tin-based perovskites in common solvents. A mixed solvent of 5% 2-methyl-2-butanol (MB) and 95% chlorobenzene (CB) was used to dissolve the defective surface while preserving the bulk. The treatment enhanced surface crystallinity, reduced strain and defects, and improved charge transport, leading to a PCE increase from 11.8% to 14.2%. The iso-BAI treatment did not form 2D perovskite structures but instead guided recrystallization, resulting in a smoother surface and better optoelectronic properties. Surface characterization techniques like SEM, AFM, and KPFM confirmed the treatment's effectiveness in reducing surface defects and oxidation. GIWAXS analysis showed improved crystallinity and reduced microstrain in the treated films. NMR studies indicated interactions between iso-BAI and tin-based perovskites, facilitating recrystallization. The treatment also reduced trap density and recombination, enhancing device performance. The study highlights the distinct mechanisms of surface treatments in tin-based perovskites compared to lead-based ones, emphasizing the need for tailored strategies to improve tin-based PSCs. The results demonstrate that iso-BAI treatment significantly enhances the performance and stability of tin-based PSCs, bringing their PCE closer to the current record.