Differential Ligand–Cation Interactions Enable 2D‐Template‐Induced Ordered Assembly for Efficient Tin‐Based Perovskite Photovoltaics

ABSTRACT Environmentally friendly tin halide perovskite (THP) solar cells have recently attracted more and more research efforts as a promising alternative to toxic lead‐based perovskites. Incorporating more stable and uniformly oriented two‐dimensional (2D) phase components into the fast‐crystallizing and oxidation‐prone three‐dimensional (3D) phases as a growth template is a common strategy to enhance THP film quality. However, the simultaneous crystallization of the 2D phase with the 3D phase greatly undermines ordered crystallization for high‐performance THP devices. Herein, a fullerene derivative ligand is introduced to establish distinct ligand–cation interaction modes with the 2D and 3D components, thereby programming the A‐site cation‑mediated sequential assembly and crystallization. The 2D phase crystallizes first and serves as a template to guide the ordered epitaxial growth of the 3D phase, yielding a highly crystalline and oriented THP film with a homogeneous 2D/3D heterojunction as an efficient interface. The resulting devices achieve a significantly enhanced champion power conversion efficiency of 16.6%. Moreover, unencapsulated devices operating at maximum power point under continuous 1‐sun illumination and 50°C exhibit a nine‐fold longer T 90 lifetime (882 h vs. 99 h) compared to control devices.