Controlled Crystallization Kinetics via Conjugated Organic Spacers Enables Ordered Epitaxial Growth of Two‐Step Deposited Tin‐based Perovskite Solar Cells

Abstract Tin‐based perovskite films typically exhibit random crystal orientations, with significant accumulation of defects acting as charge recombination centers, which severely limit device performance. Furthermore, the disordered two‐dimensional (2D) perovskite significantly impacts the subsequent crystal growth of three‐dimensional (3D) perovskite through epitaxial growth mechanism, while the insulating properties of bulky spacer cations impede out‐of‐plane charge transport. Herein, we have innovatively developed a facile quasi‐epitaxial growth strategy by introducing 2‐(naphthalen‐2‐yl)ethanamine hydroiodide (NEAI) with reinforced π‐conjugation interaction to construct orientationally aligned 2D perovskite, which acts as a template for 3D perovskite with (100)‐dominant facet orientation. NEAI reacts with SnI 2 to pre‐form NEA 2 SnI 4 , which subsequently converts to NEA 2 FASn 2 I 7 and ultimately FASnI 3 through an energetically unfavorable pathway to delay crystallization kinetics. Moreover, this innovative approach optimizes carrier transport dynamics while conferring device robust thermal degradation resistance and enhanced long‐term stability. Consequently, the NEAI‐based solar cells exhibit the impressive efficiencies of 14.03% (0.04 cm 2 ) and 12.44% (1 cm 2 ), representing the record performance for two‐step deposited tin‐based perovskite photovoltaics. This study offers new insights into the preparation of highly ordered tin‐based perovskite films, paving the way for high‐performance lead‐free perovskite photovoltaics.