Impact of benzothiadiazole position on the photovoltaic properties of solution-processable organic molecule materials

Organic molecule materials (BDT-HTH-BT and BDT-BT-HTH) applied for solution-processable organic solar cells (OSCs) have been synthesized to investigate the impact of the location of acceptor unit on the photovoltaic properties. Benzothiadiazole (BT) group was introduced as an acceptor unit, which was linked to bithienyl-substituted benzodithiophene (BDT) unit directly in BDT-BT-HTH or with hexyl-thiophene unit in BDT-HTH-BT, respectively. The molecular weight of BDT-BT-HTH and BDT-HTH-BT are the same. However, due to the different position of the BT unit, BDT-HTH-BT and BDT-BT-HTH exhibit apparently different optical and electro-chemistry properties, corresponding to the photovoltaic properties. The OSCs device based on a blend of BDT-BT-HTH and PC71BM (1:0.8, w/w, 0.5% DIO) reached a PCE (power conversion efficiency) of 3.45%, with a short-circuit current density of 6.85 mA cm(-2), an open-circuit voltage of 0.815 V and an fill factor of 61.8%. In comparison, the PCE of the OSCs device based on BDT-HTH-BT as donor material is recorded only 0.32% under the same experimental conditions.