Effects of selenophene moiety on the properties of non-fullerene acceptors for organic solar cells

Abstract

Light absorption in the near-infrared region of the non-fullerene acceptors is important for the improvement of power conversion efficiency (PCE) of organic solar cells. To utilize the near-IR region, reducing the band gap of NFAs is the basic strategy, and as a result, short-circuit current density (JSC) and PCE can be improved. Herein, we synthesized new selenophene-based acceptors, TSe-4F and TSe- 4Cl from modifying the acceptor BTP-eC9 (TS-4Cl). We substituted thieno[3,2-b]thiophene attached on the 2,1,3-benzothiadiazole unit to selenopheno[3,2-b]thiophene, and the band gap reduced from 1.36 eV to 1.33 and 1.32 eV for TSe-4F and TSe-4Cl, respectively. Furthermore, we studied the impact of end-group by comparing TSe-4F and TSe-4Cl, which has fluorine and chlorine atoms, respectively. By substituting the end-group to fluorine atoms, D18:TSe-4F showed an improvement of fill factor (FF) of 78.38%, and as a result, the PCE of D18:TSe-4F was 16.64%. The reason of improved FF was because of better charge extraction and collection processes.