Molecularly Confined Domains Enable Halide‐Stable Wide‐Bandgap Perovskites

ABSTRACT Stable wide‐bandgap (WBG) perovskites are essential for achieving highly efficient tandem photovoltaics. However, state‐of‐the‐art tandem solar cells typically employ mixed‐halide WBG perovskite, yet halide phase segregation remains a critical bottleneck. Here, we design a molecular confinement domain in which paired iodide‐bearing organic ligands bind adjacent FA + cations and are interconnected by a bifunctional diammonium linker, effectively suppressing halide segregation by constraining the dynamic motion of orientable FA + cations at the surface and interfaces of wide‐bandgap perovskites. The suppression of this motion effectively strengthens lead‐halide (Pb‐X) bond strength, reinforces the lattice rigidity, reduces lattice vibrational amplitude and increases halide ion migration energy barrier. As a result, I‐Br mixed‐halide segregation and defect evolution under prolonged illumination are effectively suppressed. Finally, the resulting mixed‐halide WBG films exhibit low trap densities, improved carrier transport, and enhanced light/thermal stability. Such concept is applicable to both 1.68 and 1.78 eV perovskite, yielding efficiencies of 24.21% and 21.20% in single‐junction cells, respectively. When integrated into silicon‐based tandem cells, the device delivers an efficiency of 33.59%, alongside durable long‐term stability with a T 96 lifetime of 1000 h under continuous operation.