Isomeric phenyl side chain based small molecule for optimizing morphology of ternary organic solar cells

Abstract

Optimizing morphology is essential to enhancing the performance of ternary organic solar cells (TOSCs). Incorporating a third component with suitable crystallinity and aggregation to regulate TOSC morphology proves to be an efficient method for improving device efficiency. In this work, two multifunctional donor small molecules with phenyl isomeric side chains, L1 (C4-Ph) and L2 (Ph-C4), are employed as guest components in the PM6:Y6-based ternary system. The impact of the phenyl positions in their molecular structures on molecular crystallinity, aggregation, and morphology of the TOSC is systematically investigated. The results indicate that the incorporation of 10 wt% L1 significantly improves the morphology of the blend film. Specifically, L1 disrupts the excessive aggregation of PM6 long-chain molecules, improves donor-acceptor compatibility, and reduces phase separation size in the active layer film. Exciton dissociation and charge transport in the active layer are promoted, and the final power conversion efficiency (PCE) increases from 15.97 % to 17.23 %. It is shown that the crystallinity and aggregation of the small molecule donor can be precisely regulated by the side-chain structure, which promotes its synergistic effect with the polymer donor. This approach provides an innovative idea for controlling the morphology of the active layer and improving the device performance.