High‐Efficiency All‐Polymer Solar Cells: Toward Sustainable Smart Windows With Flexibility, Semitransparency, and Thermal Insulation

ABSTRACT Layer‐by‐layer (LBL) all‐polymer solar cells (all‐PSCs) feature flexible modulation of donor/acceptor morphology and crystallinity, a unique merit for unlocking maximum material potential toward high efficiency, while rational selection of donor/acceptor regulators is crucial for advanced device fabrication. In this study, 1‐methoxynaphthalene (1‐MeON) is identified as an additive capable of inducing ordered stacking of classic polymer donors (D18, PM6 and PBQx‐TF). Building on this, we employed distinct additives to independently optimize the ordered stacking/aggregation of polymer donor and acceptor in LBL all‐PSCs, as well as the vertical phase distribution, which well match the excellent charge management and deliver an outstanding efficiency of 20.03% (certified 19.60%) for rigid and 18.76% for flexible binary devices. Importantly, this combined strategy further enables thickness‐tunable donor layers to balance efficiency and transmittance, facilitating high‐performance semitransparent devices. The rigid semitransparent all‐PSC achieves an efficiency of 16.07% with transmittance of 20.1%, while the flexible counterpart reaches an efficiency of 15.17% and retains over 96% of its initial efficiency after 1000 bending cycles. Moreover, these semitransparent devices also demonstrate excellent thermal insulation (reducing temperature over 10 degrees celsius). This achievement establishes a pivotal paradigm for high‐efficiency all‐PSCs and verifies their immense practical application in sustainable smart windows.