Regioisomeric Engineering of Dimerized Small-Molecule Acceptors for Efficient and Stable Organic Solar Cells

The simultaneous achievement of high power conversion efficiency (PCE) and long-term stability is essential for the commercialization of organic solar cells (OSCs). However, efficient OSCs based on small-molecule acceptors (SMAs) typically show poor long-term stability, mainly because of morphological deterioration caused by the fast diffusion of SMA molecules during the thermal- and photostresses. In this study, two dimerized SMAs (DSMAs) comprising selenophene spacers with different regiopositions, DYSe-I and DYSe-O, are developed to achieve efficient and thermally stable OSCs. The different regiopositions in DSMAs have a substantial effect on various molecular properties. DYSe-I possesses a more planar backbone conformation and more continuously connected conjugation than DYSe-O. Consequently, DYSe-I exhibits a relatively higher crystallinity, electron mobility, and glass transition temperature. These favorable features of DYSe-I lead to a higher PCE (16.8%) and thermal stability (t80% lifetime = 514 h) in the resulting OSCs, surpassing those of the DYSe-O-based devices (PCE = 14.0% and t80% lifetime = 115 h). This study highlights the importance of tuning the linker structure and its regioposition in DSMAs to realize the production of high-performance and thermally stable OSCs.