Conductive Polymer Bridges Mediate High‐Performance Flexible Perovskite–Organic Tandem Solar Cells

ABSTRACT In flexible perovskite–organic tandem solar cells (TSCs), the numerous grain boundaries (GBs) in Br‐rich perovskite films are critical in determining their efficiency and mechanical durability. Exacerbated carrier recombination, photon‐induced lattice expansion, and phase segregation originating from GBs substantially reduce the photovoltaic performance and reliability. In this work, we developed a conductive polymer composite by incorporating an ionic liquid into polyurethane (PU), which passivates Pb‐ and FA‐related defects and suppresses halide segregation while mitigating residual stress. Critically, it establishes efficient lateral conductive polymer bridges (CPB) across GBs. The CPB significantly increased carrier diffusion length and suppressed nonradiative recombination. As a result, the rigid wide‐bandgap (WBG) perovskite solar cells (PSCs) achieved a champion efficiency of 20.85% along with outstanding operational stability ( T 90 > 1000 h). In flexible configurations, CPB‐mediated devices attained a high efficiency of 19.03% and exhibited excellent mechanical robustness, retaining 92% of their initial PCE after 10 000 bending cycles. Furthermore, the perovskite–organic TSCs reached notable power conversion efficiencies of 25.92% for rigid versions and 24.02% for flexible ones. Remarkably, the rigid tandem cells maintained 87% of their initial PCE after 1000 h of continuous light exposure, while the flexible counterparts retained 81% of their original PCE after 10 000 bending cycles.