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

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 SnI₂ to pre-form NEA₂SnI₄, which subsequently converts to NEA₂FASn₂I₇ and ultimately FASnI₃ 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 cm²) and 12.44% (1 cm²), 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.