Fluorination effects of A-D-A small molecule donors based benzotriazole for organic solar cells

To explore the effect of fluorine atom on photophysical properties, in this work, we synthesized three new small molecules (SMs) with acceptor-donor-acceptor (A-D-A) configuration, SM-0F , SM-2F and SM-4F , where 4,8-bis(octyloxy)benzo[1,2-b:4,5-b']dithiophene ( BDT ) as the electron-donating and benzo[d][1,2,3]triazole ( BTA ) or fluorinated BTA as electron-withdrawing. The three small molecules exhibit good solubility and thermal stability as well as strong absorption. The fluorination of BTA unit made SM-2F and SM-4F possess a relatively lower the highest occupied molecular orbital (HOMO) and higher electron mobility in comparison with SM-0 F. We treated the three small molecules as donor and PC 71 BM as the acceptor to manufacture small molecule organic solar cells. After introduction of F, the power conversion efficiency (PCE) is improved. Among them, device based on SM-2F gave the best device performance with a PCE of 3.94% with J sc of 11. 37 mA/cm 2 , V oc of 0.76 V, fill factor ( FF ) of 0.45. These studies show that the incorporation of fluorine atom is an effective method to increase the efficiency of organic solar cells.