Molecular Riveting Stabilizes Wide‐Bandgap Perovskites by Reinforcing Cation‐Octahedron Coupling

ABSTRACT High‐quality wide‐bandgap (WBG) perovskites are essential top‐cell absorbers for perovskite/silicon tandem cells, yet their stability is limited by light‐induced halide phase segregation and defect evolution. Here, we report a molecular riveting strategy that reinforces surface/interface cation‐octahedron coupling in mixed‐halide WBG perovskites. 6‐propyl‐2‐thiouracil (PTU) preferentially resides at structurally vulnerable surface and grain‐boundary regions, where its nitrogen‐ and sulfur‐containing groups simultaneously form hydrogen bonds with FA + cations and coordinate undercoordinated Pb 2+ sites in incomplete [PbX 6 ] 4− octahedra. This dual binding bridges the organic cations and inorganic octahedra, stabilizing the surface organic‐inorganic framework and suppressing photoinduced lattice fluctuation, defect formation, and halide demixing. Consequently, WBG single‐junction devices increases from 22.05% to 23.63%, with 95% of the initial efficiency retained after 1000 h of continuous tests. When integrated with a silicon bottom cell, the optimized perovskite top cell enables a tandem device with an efficiency of 32.22%, which maintains 95% of its initial performance after 1160 h of maximum‐power‐point tracking. This work establishes molecular riveting as an effective design principle for durable WBG perovskites and tandem photovoltaics.