Acceptor–Donor–Acceptor Oligomers Containing Dithieno[3,2- b :2′,3′- d ]pyrrole and Thieno[2,3- c ]pyrrole-4,6-dione Units for Solution-Processed Organic Solar Cells

New acceptor-donor-acceptor (A-D-A) oligomers (1 and 2) containing a central dithieno[3,2-b:2',3'-d]pyrrole unit and end-capping thieno[2,3-c]pyrrole-4,6-dione groups have been synthesized and characterized. Bulk heterojunction solar cells were prepared together with PC61BM and PC71BM, and the best results were obtained for the latter acceptor using 1,8-diiodooctane as an additive. Photovoltaic devices containing these oligomers achieved high external quantum efficiencies up to 50%.