Linker engineering of dimerized small molecule acceptors for efficient and stable organic solar cells

Abstract

The simultaneous achievement of a high-power conversion efficiency (PCE) and long-term stability is essential for the commercialization of organic solar cells (OSCs). Conventionally, polymer donor and small molecule acceptor (SMA) are key components in active layer for achieving high power conversion efficiency (PCE) in OSCs. However, efficient OSCs based on SMAs typically show poor stability mainly because of morphological deterioration caused by the fast diffusion of SMA molecules during the thermal- and photo-stresses. To address this issue effectively, it is crucial to conduct a comprehensive investigation in dimerized SMA (DSMA), which is an efficient structure to attain both enhanced stability and efficiency. In this study, two DSMAs comprising selenophene spacers with different regio-positions, DYSe-I and DYSe-O, are developed to achieve efficient and thermally stable OSCs. The different regio-positions 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).