Effective Regulation of Morphologies and Exciton‐Generation Process Enables Quasi‐Planar All‐Polymer Organic Solar Cells Exceed 18% Efficiency

Abstract Disordered polymer chain entanglements within all‐polymer blends limit the formation of optimal donor–acceptor phase separation, and thus the performance of all‐polymer organic solar cells (all‐PSCs). Considering the challenge and importance of morphology regulation in all‐PSCs, a diluted layer‐by‐layer (N‐LBL) strategy is thereby adopted to fine‐tuning the properties of all‐polymer blends. When comparing the traditional PM6:PY‐IT based bulk‐heterojunction (BHJ) film and PM6/PY‐IT layer‐by‐layer (LBL) film, the N‐LBL film, which is prepared from diluted PM6 (with 3% PY‐IT) bottom layer and diluted PY‐IT (with 6% PM6) top layer, displayed a clearer bi‐continuous fibrillar network and a higher exciton generation process. Benefiting from these unique characters, the all‐PSC consisting the N‐LBL active layer exhibited a short‐circuit current density over 26 mA cm −2 and a power conversion efficiency (PCE) of 18.33%, which are both higher than those of BHJ (16.88%) and LBL (17.13%) devices. Moreover, the universality of the dilution strategy in other all‐polymer blends (PM6 and PY‐DT, PM6 and PY‐FT‐ o ) is also demonstrated with unanimously improved device performance. This work underscores the effectiveness of the diluted layer‐by‐layer method in tuning the morphologies and charge dynamics for high‐performance all‐PSCs.