Isomeric Dimer Acceptors for Stable Organic Solar Cells with over 19 % Efficiency

The strategy of isomerization is known for its simple yet effective role in optimizing molecular configuration and enhancing the power conversion efficiency (PCE) of organic solar cells (OSCs). However, the impact of isomerization on the design of dimer acceptors has been rarely investigated, and the relationship between the chemical structure and optoelectronic property remains unclear. In this study, we designed and synthesized two dimer acceptor isomers named D-TPh and D-TN, which differ in the positional arrangement of their end capping groups. Compared to D-TN, D-TPh exhibited enhanced backbone planarity, elevated lowest unoccupied molecular orbital energy level, and more ordered molecular stacking. Consequently, the OSC device based on PM6 : D-TPh achieved a PCE of 19.05 %, higher than that (PCE=18.42 %) of the device based on PM6 : D-TN. Large-area PM6 : D-TPh devices (1 cm²) yielded a PCE of 18.00 %. More importantly, the extrapolated T₈₀ lifetime of the PM6 : D-TPh device is over 2800 h with MPP tracking under continuous one-sun illumination. These results suggest that isomerization strategy is an effective way to optimize the molecular configuration of dimer acceptors for the fabrication of high-efficiency and stable OSCs.