A–D–C–D–A type non-fullerene acceptors based on the benzotriazole (BTA) unfused core for organic solar cells

Abstract

It was well known that the “face-on” molecular orientation of acceptors is crucial for efficient charge transport in devices, but less is known about the role of the halogen atoms in controlling the molecular packing. In this article, a set of three acceptor materials with a benzotriazole-based unfused core, coded as BTC6-XF respectively with zero, two and four F atoms on the end groups, were designed and synthesized. Moreover, the effect of halogen atoms on the molecular alignment control was investigated. GIWAXS profiles show that BTC6-0F prefers the edge-on stacking, BTC6-2F adopts the mixed edge-on and face-on packing, and BTC6-4F tends to form the face-on molecular orientation. Additionally, it was found that BTC6-4F possessed more effective carrier transport and less charge recombination than BTC6-0F or BTC6-2F. As a result, the BTC6-4F-based OSC achieved the champion PCE of 11.23% when paired with the polymer donor PBDB-T, while the corresponding BTC6-2F and BTC6-0F based devices respectively gave 10.10% and 8.49% PCEs. This work sheds some light upon the design of small-molecule non-fullerene acceptors for efficient organic solar cells.