Simultaneously improving efficiency and stability of organic solar cells by enhancing molecular crystallinity and intermolecular interactions

Precisely controlling bulk heterojunction (BHJ) morphology through molecular design is one of the main longstanding challenges in developing high-performance organic solar cells (OSCs). Herein, three small molecule acceptors (SMAs) with different side chains (methyl, 2-ethylhexyl, and 2-decyl tetradecyl on benzotriazole unit), namely R-M, R-EH, R-DTD, were designed and synthesized. Such side-chain engineering can effectively modulate the intermolecular interactions between acceptor/acceptor (A/A) and donor/A (D/A) molecules, thereby fine-tuning the bulk microstructures of BHJ active layer systems. Compared with R-M and R-DTD, R-EH shows stronger A/A and D/A interactions with donor PM6, which delivers improved BHJ networks with better molecular ordering, enhancing charge transport and extraction properties. Consequently, PM6:R-EH not only performs a competitive device efficiency of over 18% but also exhibits excellent operation stability without obvious degradation behaviors among the three systems. This study deepens the synergistic effects of A/A and D/A interactions on BHJ morphology to achieve industrially viable OSCs with high device efficiency and stability.