Unlocking photovoltaic potential: leveraging unique diazo multimembered ring acceptors†

Innovations in active layer materials with unique structures and superior performances have made organic solar cells more attractive to the organic photovoltaic community. Herein, three unique non-fullerene acceptors, 6C-2F, 7C-2F and 8C-2F, with diverse diazo multi-membered rings, were constructed through the unconventional strategy of ring expansion. The effects of these building blocks on their properties were then systematically investigated, including molecular configuration, absorption, aggregation, and photovoltaic performance. Compared with planar 6C-2F and flexible 8C-2F, 7C-2F with its 1,4-diazepine moiety afforded a wavy shape, medium crystallinity and optimal miscibility with PM6, which was conducive to a preferred morphology. Consequently, a 7C-2F based binary device delivered a decent PCE of 18.83%, which was far superior to that of 6C-2F and 8C-2F based devices. In particular, a greatly suppressed energy loss and enhanced stability were achievable in the PM6:7C-2F system. This work provides insights for a new design of stable and efficient photovoltaic material and devices.