Supramolecular Stabilization of Wide‐Bandgap Perovskites Enables Durable Perovskite‐Organic Tandem Solar Cells

Perovskite‐organic tandem solar cells (PO‐TSCs) offer a compelling platform for flexible photovoltaics by combining wide‐bandgap (WBG) perovskite top cells with mechanically compliant organic rear cells. However, their long‐term stability is critically limited by the intrinsic instability of WBG mixed‐halide perovskites. Here, through systematic ageing and mechanistic analyses, we identify halide phase segregation in the WBG perovskite sub‐cell under photothermal stress as the dominant degradation pathway that dictates the operational stability of the PO‐TSC investigated here. To address this challenge, we develop a halogenated cyclodextrin‐based supramolecular strategy that enables precise regulation of perovskite crystallization, defect passivation and halide distribution. Synergistic host‐guest, hydrogen‐bonding, halogen‐bonding and coordination interactions simultaneously regulate crystallization and suppress ion migration to result in stabilized halide homogeneity. Consequently, 1.80‐eV WBG devices achieve 20.60% efficiency with improved operational stability. Integrated PO‐TSCs deliver an efficiency of 27.17% (certified 26.3%) together with T 80 lifetimes of 1100 h under maximum power point tracking (MPPT) operation and T 85 lifetimes of 1128 h under thermal stress of 85°C, while flexible PO‐TSCs reach an efficiency of 24.00%. This work defines a general supramolecular design paradigm for efficient, durable and flexible tandem photovoltaics.