P3HT-Based Photovoltaic Cells with a High Voc of 1.22 V by Using a Benzotriazole-Containing Nonfullerene Acceptor End-Capped with Thiazolidine-2,4-dione

A novel A 2 –A 1 –D–A 1 –A 2 -type nonfullerene acceptor, using thiazolidine-2,4-dione (TD) as the terminal acceptor (A 2 ) for the first time, was designed and synthesized. The final molecule, BTA2, shows a high-lying lowest unoccupied molecular orbital (LUMO) of −3.38 eV and a wide optical band gap of 2.00 eV. Fullerene-free organic solar cells based on P3HT:BTA2 realized a high open-circuit voltage ( V oc ) of 1.22 V with a power conversion efficiency (PCE) of 4.50%. These values are significantly higher than those of the PC 61 BM-based control device ( V oc = 0.61 V, PCE = 3.67%), which indicates the feasibility of thiazolidine-2,4-dione to construct nonfullerene small-molecule acceptors with high V oc and PCE.