A Bidirectional Molecular Barrier for Efficient and Stable Inverted Perovskite Solar Cells

The inward diffusion of Ag electrodes and outward migration of perovskite constituents trigger a vicious degradation cycle in inverted perovskite solar cells (PSCs), severely limiting device longevity. Herein, 2,5‐dimercapto‐1,3,4‐thiadiazole (DMTD) is introduced as a bidirectional ionic barrier layer to simultaneously stabilize the Ag electrode and the perovskite lattice. The ‐SH groups strongly coordinate with Ag + to establish a molecular barrier against Ag migration, while the ‐N‐N‐ groups bind Pb 2+ to passivate defects and reinforce the crystal structure. This synergistic bidirectional inhibition effectively prevents interfacial reactions between perovskite species and Ag + , thereby breaking the chain of mutually reinforced degradation. As a result, DMTD‐modified devices achieve a power conversion efficiency of 26.13% and exhibit outstanding stability, retaining 87.68% of their initial PCE after 3000 h of storage at 25°C (15% ± 5% RH), and 80.87% after 1000 h under continuous heating at 85°C.