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

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.