Effects of the number of methoxy groups in the thiophene π-bridges on the photovoltaic performance of the A-π-A type quasi-macromolecular acceptors

Abstract

A-π-A type quasi-macromolecular (QM) acceptors have garnered significant research attention owing to their well-defined structural characteristics and excellent long-term stability. The π-bridge, serving as the core structural motif, plays a critical role in determining both the optoelectronic properties of the acceptor and the overall performance of the device. This work proposes a strategy of introducing methoxy groups into thiophene π-bridges to improve molecular planarity through non-covalent interactions, while leveraging its electron-donating capacity to enhance the open-circuit voltage (VOC) and minimize voltage losses in devices, ultimately achieving excellent photovoltaic performance. Three A-π-A-type QM acceptors, QM-T, QM-OT and QM-DOT were constructed by varying the number of methoxy groups in the thiophene π-bridge. Theoretical calculations and experimental revealed distinct geometry and structural features among the three molecules. Notably, QM-OT, featuring a 3-methoxythiophene π-bridge, showed optimal molecular planarity, which facilitated favorable π-π stacking and demonstrated superior compatibility with the polymer donor PM6. Therefore, the PM6:QM-OT-based active layer formed a nanoscale morphology with optimal phase separation, effectively mitigating voltage and charge recombination losses while promoting efficient exciton dissociation and charge transport. As a result, the PM6:QM-OT-based device achieved an impressive PCE of 18.15% with the highest VOC of 0.956 V, a JSC of 25.15 mA cm−2, and an FF of 75.5%. This work provides some guidance for further improving the performance of organic solar cells.