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

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.