Dimerized small-molecule acceptors with enhanced crystallinity afford efficient and stable polymer solar cells

Abstract

High power conversion efficiency (PCE) and long-term stability are essential for the commercialization of polymer solar cells (PSCs). In this work, we develop a series of dimerized small-molecule acceptors (DSMAs) with enhanced crystallinity and electron mobility, achieved through systematic linker engineering using three different benzodithiophene (BDT) derivatives: 1) Dimerized Y-type SMA (DY)-BDT featuring a BDT linker, 2) DY-DTBDT containing a conjugation-extended BDT derivative (dithieno[2,3-d:2 ',3 '-d"]benzo[1,2-b:4,5-b']dithiophene, DTBDT), and 3) DY-DTBDT-Cl featuring chlorinated thiophene side-chains on DTBDT. Among them, DY-DTBDT-Cl shows a higher crystallinity and superior electron mobility compared to other DSMAs. Additionally, DY-DTBDT-Cl shows improved molecular compatibility with PM6 donor compared to Y6-BO SMA and other DSMAs due to the chlorinated BDT linker. Consequently, incorporation of DY-DTBDT-Cl into the binary PM6:Y6-BO blend significantly enhances both the PCE and photostability. The resulting ternary PSCs exhibit a higher PCE (18.65%) compared to that of PM6:Y6-BO (17.81%). Notably, the DY-DTBDT-Cl-containing PSCs retain >80% of initial PCE after 500 h under continuous 1-sun illumination, whereas the PCE of PM6:Y6-BO control decreases below 80% within 20 h. Furthermore, the DY-DTBDT-Cl ternary blend demonstrates enhanced mechanical stability in intrinsically stretchable PSCs, retaining >80% of the initial PCE after 20% strain, whereas PM6:Y6-BO exhibits lower than 80% of initial PCE after 10% strain. This study highlights the importance of linker engineering in optimizing DSMAs, offering a promising strategy for enhancing the performance and long-term stability of PSCs.