High‐Efficiency Sequential‐Cast Organic Solar Cells Enabled by Dual Solvent‐Controlled Polymer Aggregation

The precise tuning of the active layer morphology to improve organic solar cells (OSCs) efficiency remains a key issue in the field of organic photovoltaics. Herein, a new solution to the above problem is provided by using the dual‐solvent modulated polymer‐assisted sequential spin‐coating method. Herein, the sequential spin‐coated OSCs based on the D18‐Cl/Y6 system are prepared for the first time and an efficiency of 16.38% is obtained, similar to that of bulk heterojunction OSCs. On this basis, the performance is further improved by using a dual solvent to balance the dissolution and crystallization of D18‐Cl, separately optimizing the morphology of the donor layer and allowing the subsequent spin‐coated Y6 solution to penetrate uniformly into the D18‐Cl framework. After the dual‐solvent treatment, the D18‐Cl (CF + CB)/Y6‐based device obtains a power conversion efficiency (PCE) of 17.33% and the D18‐Cl (THF + CB)/Y6‐based device achieves an even better PCE of 17.73%. It is worth noting that no post‐treatment is adopted here and after 2500 h of placement, the efficiency of the aforementioned devices is still 90% of the original. Thus, this work provides a simple method for tuning the film morphology to prepare efficient and stable devices, which is beneficial for future commercial production of OSCs.