Dimerized small-molecule acceptors enable efficient and stable organic solar cells

The power conversion efficiencies (PCEs) of small-molecule acceptor (SMA)-based organic solar cells (OSCs) have increased remarkably, but their long-term stability is insufficient for commercialization. Here, we demonstrate that the dimerization of an SMA significantly enhances the stability of SMA-based OSCs. The dimerized SMA (DYBO) results in OSCs with high PCEs (> 18%), which allows them to outperform OSCs based on their monomer counterpart, MYBO (PCE = 17.1%). Importantly, DYBO-based OSCs exhibit excellent thermal and photo stability. For example, DYBO-based OSCs retain more than 80% of their initial PCE even after 6,000 h of thermal exposure at 100°C, whereas MYBO-based OSCs degrade to ∼80% of their initial PCE value in 36 h. The high stability of DYBO-based OSCs is mainly attributed to the high glass transition temperature (Tg) of DYBO of 179°C (Tg of MYBO = 80°C) and the improved blend miscibility, which stabilizes the blend morphology under thermal stress.