Molecularly Confined Domains Enable Halide-Stable Wide-Bandgap Perovskites

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 T₉₆ lifetime of 1000 h under continuous operation.