Over 70% Fill Factor of All‐Polymer Solar Cells Guided by the Law of Similarity and Intermiscibility

Abstract

Poor miscibility between the polymer donor and acceptor in the active layer leads to low fill factors (FF). PCl and PCl‐Si are synthesized by polymerization of the accessible and inexpensive IDIC‐C16 with BDT‐Cl and BDT‐Cl‐Si, respectively. PCl and PCl‐Si involve a BDT skeleton that is definitely used in most highly efficient polymer donors, such as PM6. Guided by the law of similarity and intermiscibility, the similar building block acts as a bridge to improve the interfacial interaction and miscibility between the donor and acceptor, leading to a favorable morphology of the active layer. It is found that the miscibility of the active layer is sensitive to the structural similarity degree of the similar unit of the donor and acceptor. The PCl‐Si‐based device delivers a power conversion efficiency (PCE) of 9.25% with a moderate FF of 67.86%, whereas the PM6:PCl‐based device achieves a PCE of 10.02% with a higher FF of 70.25%, which is the highest FF of the device with an IDIC‐C16‐based polymer acceptor. In addition, the improved interaction between the donor and acceptor improves the device stability. These results demonstrate that regulating the structural similarity between donor and acceptor is a promising strategy to optimize and stabilize morphology for high‐performance all‐polymer solar cells.