Simultaneous enhancement of efficiency, stability and stretchability in binary polymer solar cells with a three-dimensional aromatic-core tethered tetrameric acceptor.

Polymer solar cells (PSCs) leverage blend films from polymer donors and small-molecule acceptors (SMAs), offering promising opportunities for flexible power sources. However, the inherent rigidity and crystalline nature of SMAs often embrittle the polymer donor films in the constructed bulk heterojunction structure. To address this challenge, we improved the stretchability of the blend films by designing and synthesizing a tethered giant tetrameric acceptor (GTA) with increased molecular weight that promotes entanglement of individual SMA units. The key to this design is using tetraphenylmethane as the linking core to create a three-dimensional and high C symmetry structure, which successfully regulates their aggregation and relaxation behavior. With GTA as the acceptor, its blend films with polymer donor PM6 exhibit significantly improved stretchability, with nearly a 150% increase in crack onset strain value compared to PM6:Y6. Moreover, the PSCs achieve an increased efficiency of up to 18.71% and demonstrate outstanding photostability, maintaining >90% of their initial power conversion efficiency after operating for over 1000 hours. Our findings demonstrate that by specifically designing three-dimensional tethered SMAs and aligning their molecular weights more closely with those of polymer counterparts, we can achieve enhanced stretchability without compromising morphological stability or device efficiency.