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

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 T₉₀ lifetime (882 h vs. 99 h) compared to control devices.