Small-molecular organic solar cells usually exhibited unsatisfactory device stability, which might originate from their molecular diffusion behaviors. Herein, based on the all-small-molecule system HD-1:BTP-eC9, we reported a dimerized acceptor DC9, and its corresponding monomer acceptor eOD. In comparison with eOD, the dimeric acceptor DC9 displayed higher glass transition temperature (Tg) but reduced molecular planarity and crystallinity. The all-small molecule blend utilizing HD-1:eOD demonstrated a power conversion efficiency (PCE) of 15.13%, surpassing the value of 14.10% for the HD-1:DC9 blend. While, incorporating polymer donor PM6 into the HD-1:DC9 blend improved its morphology and charge transport dynamics, resulting in a device efficiency of over 16%, representing the rare case utilizing small-molecular donor and dimeric acceptor with PCE over 16%. Morphological characterization results affirmed that the surface morphologies and molecular packing behaviors of the blend films based on HD-1 were largely retained even after prolonged annealing and aging at 85 degrees C. Consequently, the PCEs of the blend films based on HD-1:eOD, HD-1:DC9, and HD-1:PM6:DC9 consistently remained over 98% of their initial efficiency after 1000 h of thermal annealing aging at 85 degrees C. These findings highlight the potential of small-molecular based active layer in the fabrication of efficient and stable OSCs.