Highly Efficient Nonfullerene Acceptor with Sulfonyl-Based Ending Groups.

Ending groups play a vital role in regulating the band gap and energy level of low-band gap nonfullerene acceptors (NFAs). In this work, a novel NFA, BTP-IS, is synthesized by adopting sulfonyl-based ending groups. Compared to the ketone counterpart BTP-IC, BTP-IS exhibits a red-shift in absorption spectra with lower lowest unoccupied molecular orbital level. More importantly, the BTP-IS-based organic solar cells with PM6 as donor present a high power conversion efficiency (PCE) of 12.79%, which is much higher than that of the BTP-IC device (PCE of 7.54%). The efficient charge transfer between the polymer donor and NFA acceptor, the balance charge transport, and the fine photoactive morphology bear on the effective exciton dissociation and charge collection in the BTP-IS device, which induces high short circuit current (JSC) and fill factor (FF) values. This research has shed light on designing novel NFAs from the perspective of ending groups.