Thermodynamically Reinforced Dual‐Interface 1D/3D Tin‐Lead Perovskite Heterostructure for Stable All‐Perovskite Tandem Solar Cells

Abstract Tin‐lead (Sn‐Pb) perovskite solar cells (PSCs) remain fundamentally constrained by the intrinsic instability of Sn ²⁺ oxidation and uncontrollable crystallization, critically limiting their operational reliability in tandem architectures. Herein, this study strategically introduces a π‐conjugated ammonium salt, 4‐aminobenzamidine dihydrochloride, which in situ directs the formation of a dual‐interface one‐dimensional/three‐dimensional (1D/3D) perovskite heterostructure, thereby re‐engineering the Sn‐Pb perovskite lattice toward enhanced thermodynamic stability. The self‐assembled 1D perovskitoid with intermolecular π‐π stacking acts as nucleation‐directing templates to relieve tensile strain and intra‐/intergranular disorder. Simultaneously, the contiguous 1D perovskitoid interphases encapsulating the 3D bulk fortify the vulnerable Sn‐I octahedral framework, effectively obstructing oxidative and ion‐migration pathways. This dual stabilization strategy endows the Sn‐Pb PSCs with unprecedented structural resilience, achieving not only a high power conversion efficiency (PCE) of 22.23% but also a T ₉₈ operational lifetime beyond 1000 hours. Building upon this enhanced structural robustness, the derived 2‐terminal (2T) all‐perovskite tandem devices deliver a PCE of 28.50% and sustain a T ₉₀ lifetime of 600 hours, underscoring the central role of lattice stabilization in advancing all‐perovskite tandem photovoltaics.