A Facile Anti‐Solvent Method to Simultaneously Improve Efficiency and Reproducibility of Layer‐by‐Layer Organic Solar Cells

Layer‐by‐layer (LBL) spin‐coating is a widely recognized method for developing high‐efficiency organic solar cells (OSCs). However, in the LBL device with a conventional architecture, the residual solvents trapped in the underlying donor film will affect the interface between donor and acceptor materials as well as the morphology of upper acceptor materials, thus leading to poor reproducibility and efficiency. This study provides a facile strategy that spin‐coats a mixed solvent of methanol and acetic acid, facilitating the removal of residual solvents from the donor material. The introduction of the mixed anti‐solvent can also optimize the roughness, facilitate the crystallization of the donor material, and improve interfacial properties. The devices without any further treatment exhibit a power conversion efficiency (PCE) of 17.8%, while devices treated with pristine methanol achieve an efficiency up to 18.4%. Notably, devices treated with mixed methanol and acetic acid further boost efficiency to 19.3%. Furthermore, this approach is also applicable to flexible OSCs, yielding an efficiency of 18.0%.