Face-to-face type giant dimeric donors synergistically improve the stability and efficiency of organic solar cells†

With the development of organic solar cells (OSCs), maintaining the batch stability of photovoltaic donor materials and improving device stability have become new challenges. Given the successful application of giant oligomeric acceptors, increasing the molecular size while maintaining a precise molecular structure has proven to be an effective method. However, the efficiency of giant oligomeric donors remains limited owing to a lack of design principles. Herein, we innovatively designed and developed “face-to-face” type giant dimeric donors (GDDs), DZ-1 and DZ-2, by covalently tethering the BTR-Cl monomer. Using different rhodanine-based terminals significantly tuned their molecular interaction and thermally driven assembly capabilities. DZ-2 exhibited moderate molecular stacking and compatible miscibility in the blend film, achieving a higher PCE of 13.27%, which was comparable to that of OSCs based on BTR-Cl:Y6 (13.83%), indicating that face-to-face type dimeric donors could maintain the excellent performance of small molecule donors. Importantly, GDDs with increasing molecular size improved the T_g and suppressed molecular diffusion in the blend films. Furthermore, ternary OSCs based on PM6:DZ-2:L8-BO achieved an improved PCE of 19.07% and higher device stability owing to the establishment of a 3D charge transport channel and suppression of molecular diffusion. This study provides a new design strategy for giant molecule donors to develop high-performance and stable OSCs.