Utilization of electron-donating linkers in M-series dimerized acceptors to achieve high-voltage and efficient organic solar cells

Abstract

Dimerized small-molecule acceptors (DSMAs) have emerged as an effective strategy to resolve the stability–efficiency paradox in organic solar cells (OSCs). Linkers play a pivotal role in modulating the molecular conformation of DSMAs, which is crucial for simultaneously optimizing both the efficiency and stability of OSCs. However, conventional linkers used in M-series DSMAs are typically electron-deficient, limiting improvements in the open-circuit voltage (V_oc) of the resulting devices. In this work, two linkers, namely 3,4-dimethoxythiophene and 3,4-ethylenedioxythiophene, were incorporated into M-series acceptors, yielding two novel DSMAs, denoted DM-DMOT and DM-EDOT, respectively. Benefiting from the introduction of strong electron-donating groups, both DM-EDOT and DM-DMOT exhibit upshifted lowest unoccupied molecular orbital (LUMO) energy levels, which enhance the V_oc of the corresponding OSCs. The best-performing DM-EDOT-based OSC shows a synergistic improvement in both V_oc and short-circuit current density (J_sc), ultimately achieving a high power conversion efficiency (PCE) of 17.31%. Notably, the DM-EDOT-based OSC also exhibits superior stability, with an extrapolated T₈₀ lifetime of 915 hours under continuous illumination and retention of 96% of its initial PCE after 2500 hours of thermal annealing at 65 °C. These results demonstrate that 3,4-ethylenedioxythiophene is an excellent linker for designing high-efficiency and stable DSMAs.